Astronomers Find Hyperactive Galaxies in the Early Universe

Looking almost 11 billion years into the past, astronomers have measured the motions of stars for the first time in a very distant galaxy and clocked speeds upwards of one million miles per hour, about twice the speed of our Sun through the Milky Way.

The fast-moving stars shed new light on how these distant galaxies, which are a fraction the size of our Milky Way, may have evolved into the full-grown galaxies seen around us today. The results will be published in the August 6, 2009 issue of the journal Nature, with a companion paper in the Astrophysical Journal.

"This galaxy is very small, but the stars are whizzing around as if they were in a giant galaxy that we would find closer to us and not so far back in time," says Pieter van Dokkum, professor of astronomy and physics at Yale University in New Haven, Conn., who led the study. It is still not understood how galaxies like these, with so much mass in such a small volume, can form in the early universe and then evolve into the galaxies we see in the more contemporary, nearby universe, which is about 13.7 billion years old.

The work by the international team combined data collected using NASA's Hubble Space Telescope with observations taken by the 8-meter Gemini South telescope in Chile. According to van Dokkum, "The Hubble data, taken in 2007, confirmed that this galaxy was a fraction the size of most galaxies we see today in the more evolved, older universe. The giant, 8-meter mirror of the Gemini telescope then allowed us to collect enough light to determine the overall motions of the stars using a technique not very different from the way police use laser light to catch speeding cars." The Gemini near-infrared spectroscopic observations required an extensive 29 hours on the sky to collect the extremely faint light from the distant galaxy, which goes by the designation 1255-0.

"By looking at this galaxy we are able to look back in time and see what galaxies looked like in the distant past when the universe was very young," says team member Mariska Kriek of Princeton University in Princeton, N.J. 1255-0 is so far away that the universe was only about 3 billion years old when its light was emitted.

Astronomers confess that it is a difficult riddle to explain how such compact, massive galaxies form, and why they are not seen in the current, local universe. "One possibility is that we are looking at what will eventually be the dense central region of a very large galaxy," explains team member Marijn Franx of Leiden University in the Netherlands. "The centers of big galaxies may have formed first, presumably together with the giant black holes that we know exist in today's large galaxies that we see nearby."

To witness the formation of these extreme galaxies astronomers plan to observe galaxies even farther back in time in great detail. By using the Wide Field Camera 3, which was recently installed on the Hubble Space Telescope, such objects should be detectable. "The ancestors of these extreme galaxies should have quite spectacular properties as they probably formed a huge amount of stars, in addition to a massive black hole, in a relatively short amount of time," says van Dokkum.

This research follows recent studies revealing that the oldest, most luminous galaxies in the early universe are very compact yet surprisingly have stellar masses similar to those of present-day elliptical galaxies. The most massive galaxies we see in the local universe (where we don't look back in time significantly) that have a mass similar to 1255-0 are typically five times larger than the young compact galaxy. How galaxies grew so much in the past 10 billion years is an active area of research, and understanding the dynamics in these young compact galaxies is a key piece of evidence in eventually solving this puzzle.

The Hubble Space Telescope observations were made with the Near Infrared Camera and Multi-Object Spectrometer (NICMOS).

The Gemini observations were made using the Gemini Near Infrared Spectrograph (GNIRS), which is currently undergoing upgrades and will be reinstalled on the Gemini North telescope on Mauna Kea in 2010.

August 5, 2009

Curiosities: How many galaxies have humans discovered?

Credit: NASA, ESA, S. Beckwith (STScI) and HUDF Team

“We don’t know,” says Ed Churchwell, professor of astronomy. “We know it’s a very large number.”

It’s in the hundreds of billions, Churchwell says. In contrast, there are but 4 billion stars in our own galaxy, the Milky Way — and the number will keep growing for some time before we run out of galaxies to count.

“To count them all, you have to be able to look far enough back in time or deep enough in space to see when galaxies were formed,” Churchwell says. “We haven’t reached that point yet. It’s not a well-determined number, but at some point we’re going to reach it.”

For the time being, those hundreds of billions in the tally are extrapolated from a picture taken by the Hubble Space Telescope in 2003 and 2004. Pointed at a single piece of space for several months — a spot covering less than one-tenth of one-millionth of the sky — Hubble returned an image of galaxies 13 billion light years away.

“You look at that and say, ‘How many galaxies can I see?’” Churchwell explains. “And that turns out to be a very large number.”

In fact, there are about 10,000 galaxies in the picture, called the Hubble Ultra Deep Field.

“Then you take that number of galaxies from that postage-stamp-sized piece of the sky and multiply it by the number of postage-stamp-sized pieces of sky,” Churchwell says. “And that turns out to be a much larger number.”

Monday, August 03, 2009

Trio of Galaxies Mix It Up

Compass and Scale Illustration of HCG 90
Illustration Credit: NASA, ESA, and Z. Levay (STScI)
Credit: NASA, ESA, and R. Sharples (University of Durham)

Monday, March 02, 2009

Though they are the largest and most widely scattered objects in the universe, galaxies do go bump in the night. The Hubble Space Telescope has photographed many pairs of galaxies colliding. Like snowflakes, no two examples look exactly alike. This is one of the most arresting galaxy smash-up images to date.

At first glance, it looks as if a smaller galaxy has been caught in a tug-of-war between a Sumo-wrestler pair of elliptical galaxies. The hapless, mangled galaxy may have once looked more like our Milky Way, a pinwheel-shaped galaxy. But now that it's caught in a cosmic Cuisinart, its dust lanes are being stretched and warped by the tug of gravity.

Unlike the elliptical galaxies, the spiral is rich in dust and gas for the formation of new stars. It is the fate of the spiral galaxy to be pulled like taffy and then swallowed by the pair of elliptical galaxies. This will trigger a firestorm of new stellar creation. If there are astronomers on any planets in this galaxy group, they will have a ringside seat to seeing a flurry of starbirth unfolding over many millions of years to come.

Eventually the ellipticals should merge too, creating one single super-galaxy many times larger than our Milky Way. This trio is part of a tight cluster of 16 galaxies, many of them being dwarf galaxies. The galaxy cluster is called the Hickson Compact Group 90 and lies about 100 million light-years away in the direction of the constellation Piscis Austrinus, the Southern Fish.

Galactic Dust Bunnies Found to Contain Carbon After All

The image is a composite of data from Spitzer's infrared array camera. Light with a wavelength of 3.6 microns is rendered as blue, 5.8 microns is displayed as green and 8.0 microns is represented in red. The brightness of the central area has been greatly reduced to make it possible to maintain its visibility while enhancing the brightness of the much fainter outer features. Overall colors have been enhanced to better show slight variations in hue.

Cat's Eye Nebula (NGC 6543)
NASA/JPL-Caltech/J. Hora (Harvard-Smithsonian CfA)

Thursday, March 12, 2009

Using NASA's Spitzer Space Telescope, researchers have found evidence suggesting that stars rich in carbon complex molecules may form at the center of our Milky Way galaxy.

This discovery is significant because it adds to our knowledge of how stars form heavy elements — like oxygen, carbon, and iron — and then blow them out across the universe, making it possible for life to develop.

Astronomers have long been baffled by a strange phenomenon: Why have their telescopes never detected carbon-rich stars at the center of our galaxy even though they have found these stars in other places? Now, by using Spitzer's powerful infrared detectors, a research team has found the elusive carbon stars in the galactic center.

"The dust surrounding the stars emits very strongly at infrared wavelengths," says Pedro García-Lario, a research team member who is on the faculty of the European Space Astronomy Center, the European Space Agency's center for space science. He co-authored a paper on this subject in the February 2009 issue of the journal Astronomy & Astrophysics.

"With the help of Spitzer spectra, we can easily determine whether the material returned by the stars to the interstellar medium is oxygen-rich or carbon-rich."

The team of scientists analyzed the light emitted from 40 planetary nebulae — blobs of dust and gas surrounding stars — using Spitzer's infrared spectrograph. They analyzed 26 nebulae toward the center of the Milky Way — a region called the "Galactic Bulge" — and 14 nebulae in other parts of the galaxy. The scientists found a large amount of crystalline silicates and polycyclic aromatic hydrocarbons, two substances that indicate the presence of oxygen and carbon.

This combination is unusual. In the Milky Way, dust that combines both oxygen and carbon is rare and is usually only found surrounding a binary system of stars. The research team, however, found that the presence of the carbon-oxygen dust in the Galactic Bulge seems to be suggestive of a recent change of chemistry experienced by the star.

The scientists hypothesize that as the central star of a planetary nebula ages and dies, its heavier elements do not make their way to the star's outer layers, as they do in other stars. Only in the last moments of the central star's life, when it expands and then violently expels almost all of its remaining outer gasses, does the carbon become detectable. That's when astronomers see it in the nebula surrounding the star.

"The carbon produced through these recurrent 'thermal pulses' is very inefficiently dredged up to the surface of the star, contrary to what is observed in low-metallicity, galactic disk stars," said García-Lario. "It only becomes visible when the star is about to die."

This study supports a hypothesis about why the carbon in some stars does not make its way to the stars' surfaces. Scientists believe that small stars — those with masses up to one-and-a-half times the mass of our sun — that contain lots of metal do not bring carbon to their surfaces as they age. Stars in the Galactic Bulge tend to have more metals than other stars, so the Spitzer data support this commonly held hypothesis. Before the Spitzer study, this hypothesis had never been supported by observation.

This aging and expelling process is typical of all stars. As stars age and die, they burn progressively heavier and heavier elements, beginning with hydrogen and ending with iron. Towards the end of their lives, some stars become what are called "red giants." These dying stars swell so large that if one of them were placed in our solar system, where the sun is now, its outermost border would touch Earth's orbit. As these stars pulsate — losing mass in the process — and then contract, they spew out almost all of their heavier elements. These elements are the building blocks of all planets, including our own Earth (as well as of human beings and any other life forms that may exist in the universe).

The paper is co-authored by José Vicente Perea-Calderón of the European Space Astronomy Center in Villanueva de la Cañada, Spain; Domingo Anibal García-Lario-Hernández of the Instituto de Astrofísica de Canarias, on Spain's Tenerife island; Ryszard Szczerba of the Nicolaus Copernicus Astronomical Center in Torun, Poland; and Matt Bobrowsky of the University of Maryland, College Park.

About the Object

* Object name: Cat's Eye, NGC 6543

* Object type: Nebula

* Position (J2000): RA: 17h 58m 33.42s Dec: 66° 37' 59.52"

* Distance: 3300 Light Years

* Constellation: Draco

About the Data - Spitzer Data

* Image Credit: NASA/JPL-Caltech/J. Hora (Harvard-Smithsonian CfA)

* Instrument: IRAC

* Wavelength: 3.6 Micron (Blue), 5.8 Micron (Green), 8.0 Micron (Red)

* Release Date: 2009/03/12

Astronomers have found new evidence of an "inconvenient" galaxy.

In this color image of NGC4622, note the strong inner counter-clockwise outward winding single arm and the strong outer clockwise outward winding pair of arms. NASA/Hubble/STScI/AURA

January 14, 2008

Provided by the University of Alabama

Discovery of two new components within a puzzling spiral galaxy confirm it must have a pair of arms winding in the opposite direction from most galaxies, according to results presented last Tuesday to the American Astronomical Society meeting in Austin, Texas.

"While the existence of a galaxy with a pair of 'backward' arms may seem like an inconvenient truth to many, our latest analysis indicates it is, nonetheless, a reality," says Gene Byrd, professor of astronomy at the University of Alabama.

The galaxy, known as NGC4622, lies 200 million light-years away in the constellation Centaurus.

Spiral arm pairs seen in galaxies are thought to trail, meaning they wind outward, opposite the direction of rotation of the disk material. Leading arms, such as the pair reported by the astronomers for NGC4622, do the opposite, opening outward in the same direction as the rotation of the galaxy's disk.Using a Fourier component image method to further analyze a 2001 Hubble Space Telescope image, the team discovered a previously hidden inner counterclockwise pair of spiral arms.

"Contrary to conventional wisdom, with both an inner counterclockwise pair and an outer clockwise pair of spiral arms, NGC4622 must have a pair of leading arms," Byrd says. "With two pairs of arms winding in opposite directions, one pair must lead and one pair must trail. Which way is which depends on the disk's rotation. The outer clockwise pair must be the leading pair if the disk turns clockwise. Alternatively, the inner counterclockwise pair must be the leading pair if the disk turns counterclockwise."

In this Fourier component image of NGC4622’s arm pairs, one of the previously known strong pair of outer clockwise arms is marked with white dots. Interior to this, one of the newly discovered pair of counter-clockwise arms is marked with black dots. NASA/Hubble/STScI/AURA

The team also discovered an outer clockwise single arm, previously hidden by the stronger outer clockwise arm pair. The galaxy also has a previously identified inner single counterclockwise arm. This confirms the galaxy must have a single leading arm. The outer clockwise arm must be the leading arm if the disk turns clockwise. The inner counterclockwise arm must be the leading single arm if the disk turns counterclockwise.The researchers also performed a more complicated analysis of different color Fourier image components. This revealed the stronger outer clockwise pair of arms as the leading pair.

In 2002, team members first published, to great skepticism, results from a previous method that indicated the galaxy had a leading pair of spiral arms.

Other astronomers were skeptical of the 2002 announcement, in part, because the galaxy disk is only tilted about 19 degrees from face-on and because clumpy dust clouds might be concentrated on one side of the disk, creating misleading results. In response, the team's new Fourier component method is actually assisted by the small tilt, and the effects of dust are not used in the latest analysis.

"Two independent methods now indicate that NGC4622's arms do indeed behave in a very unusual fashion, with the outer arms winding outward in the same direction the galaxy turns," says Byrd.

Further studies of the origin of this behavior are needed, the researchers said. The Hubble Space Telescope image reveals a dark dust lane in the center which suggests the galaxy may have consumed a smaller companion galaxy, the researchers said.

New information on galaxies

This THINGS image shows dwarf galaxy IC2574. Walter et al., NRAO/AUI/NSF

January 16, 2008

Provided by NRAO

Astronomers have produced a scientific gold mine of detailed, high-quality images of nearby galaxies that is yielding important new insights into many aspects of galaxies, including their complex structures, how they form stars, the motions of gas in the galaxies, the relationship of "normal" matter to unseen "dark matter," and many others.

An international team of scientists used more than 500 hours of observations with the National Science Foundation's Very Large Array (VLA) radio telescope to produce detailed sets of images of 34 galaxies at distances from 6 to 50 million light-years from Earth. Their project, called The HI Nearby Galaxy Survey, or THINGS, required 2 years to produce nearly one TeraByte of data. HI ("H-one") is an astronomical term for atomic hydrogen gas. The astronomers presented their initial findings to the American Astronomical Society's meeting in Austin, Texas.

"Studying the radio waves emitted by atomic hydrogen gas in galaxies is an extremely powerful way to learn what's going on in nearby galaxies. The THINGS survey uses that tool to provide sets of images of the highest quality and sensitivity for a substantial sample of galaxies of different types," says Fabian Walter, of the Max-Planck Institute for Astronomy in Heidelberg, Germany.

Most of the galaxies studied in the THINGS survey also have been observed at other wavelengths, including Spitzer space telescope infrared images and GALEX ultraviolet images. This combination provides an unprecedented resource for unraveling the mystery of how a galaxy's gaseous material influences its overall evolution.Analysis of THINGS data already has yielded numerous scientific payoffs. For example, one study has shed new light on astronomers' understanding of the gas-density threshold required to start the process of star formation. "Using the data from THINGS in combination with observations from NASA's space telescopes has allowed us to investigate how the processes leading to star formation differ in big spiral galaxies like our own and much smaller, dwarf galaxies," says Adam Leroy and Frank Bigiel of the Max-Planck Insitute for Astronomy at the Austin AAS meeting.

Because atomic hydrogen emits radio waves at a specific frequency, astronomers can measure motions of the gas by noting the Doppler shift in frequency caused by those motions. "Because the THINGS images are highly detailed, we have been able to measure both the rotational motion of the galaxies and non-circular random motions within the galaxies," notes Erwin de Blok of the University of Cape Town, South Africa.

The motion measurements are providing new information about the mysterious, unseen dark matter in the galaxies. "The non-circular motions revealed by the THINGS observations, turn out to be too small to solve a long-standing problem in cosmology, namely the inability of state-of-the-art computer simulations to describe the distribution of dark matter in disk galaxies. It was thought that random motions could explain that inability, but our data show otherwise," de Blok explains.

The THINGS images revealed what Elias Brinks of the University of Hertfordshire, UK, calls a "stunning complexity of structures in the tenuous interstellar medium of the galaxies." These structures include large shells and "bubbles," presumably caused by multiple supernovae explosions of massive stars. Analyzing the detail of these complex structures will help astronomers better understand the differences in star formation processes in the varied types of galaxies.

Even such a simple question such as how big are the disks of gas in spiral galaxies had largely eluded astronomers previously. "The quality and sensitivity of the THINGS images has allowed us to see the actual edges of these disks in a large sample of galaxies," says Brinks.

The new survey also showed a fundamental difference between the nearby galaxies: part of the "current" universe, and far more distant galaxies, seen as they were when the universe was much younger. "It appears that the gas in the galaxies in the early universe is much more 'stirred up,' possibly because galaxies were colliding more frequently then and there was more intense star formation causing material outflows and stellar winds," explains Martin Zwaan of the European Southern Observatory. The information about gas in the more distant galaxies came through non-imaging analysis.

These discoveries, the scientists predict, are only the tip of the iceberg. "This survey produced a huge amount of data, and we've only analyzed a small part of it so far. Further work is sure to tell us much more about galaxies and how they evolve. We expect to be surprised," Walter says.

Astronomers uncover ancestors of Milky Way-type galaxies

Galaxy M74 is representative of spiral galaxies that evolved from recently discovered galaxies in the early universe. odd Boroson/NOAO/AURA/NSF

January 25, 2008

Provided by Rutgers University

Astronomers at Rutgers and Penn State universities have discovered galaxies in the distant universe that are ancestors of spiral galaxies like our Milky Way.

These ancient objects, some of the first galaxies ever to form, are being observed as they looked when the universe was a mere 2 billion years old. Today, scientists peg the universe's age at 13.7 billion years, so light from these galaxies traveled almost 12 billion years to reach Earth.

The newly discovered galaxies are quite small, one-tenth the size and one-twentieth the mass of our Milky Way. They also have fewer stars, only one-fortieth as many as are in the Milky Way. From ground-based telescopes, they look like individual stars in size. Recent images made by the Hubble Space Telescope, however, reveal them as regions of active star formation.

"Finding these objects and discovering that they are a step in the evolution of our galaxy is akin to finding a key fossil in the path of human evolution," says Eric Gawiser, assistant professor in the Department of Physics and Astronomy in the Rutgers School of Arts and Sciences.The researchers determined that these galaxies were fertile breeding grounds for new stars, which burned hot and bright. These stars ionized the hydrogen atoms around them, stripping them of their electrons and causing them to emit a tell-tale sharp band of ultraviolet light known as Lyman alpha.


This image shows an extended, chain-like Lyman alpha emitter. NASA/ESA/C. Gronwall/Penn State

The researchers also noted that several of these galaxies, sometimes 10 or more, pulled together over the ensuing few billion years to form a single spiral galaxy.

"The Hubble Space Telescope has delivered striking images of these early galaxies, with 10 times the resolution of ground-based telescopes," says Caryl Gronwall, senior research associate in Penn State's Department of Astronomy & Astrophysics. "They come in a variety of shapes, round, oblong, and even somewhat linear, and we are starting to make precise measurements of their sizes."

The astronomers discovered these galaxies as part of a 5-year-old census of galaxies in the early universe, a project called MUSYC (Multi-Wavelength Survey by Yale and Chile). Gawiser, while a National Science Foundation (NSF) astronomy and astrophysics postdoctoral fellow at Yale, initiated a search for several types of galaxies that could be precursors of Milky Way-type spirals; Gronwall led an investigation into the luminosity, density and distribution of the distinctive Lyman alpha emitters. Their statistical analyses and computer simulations of how galaxies cluster led them to the conclusion they first reported in December 2007: Lyman alpha emitters are the ancestors of spiral galaxies."We knew by our understanding of cosmological theory that spiral galaxies had to evolve from low-mass galaxies such as these," Gawiser says. "The challenge was to actually find them. We'd seen other early universe galaxies, but they were bigger and destined to evolve into elliptical galaxies, not spirals."


This image shows an extended Lyman alpha emitter which shows evidence of merging. NASA/ESA/C. Gronwall/Penn State

The astronomers undertook four types of observations to find and characterize the objects they were seeking. They performed the first step, actually finding the Lyman alpha-emitting galaxies amid all the visible objects of deep space, using the Blanco 4-meter telescope at the NSF Cerro Tololo Inter-American Observatory in Chile. To measure their distance, they used the Magellan Telescope at Las Campanas Observatory, also in Chile, to measure redshift, an effect that shows how fast an object is receding from view due to a rapidly expanding universe. (The redshift at which they studied these galaxies is 3.1.) To determine how many stars are in the galaxies, they used the NASA Spitzer Space Telescope's Infrared Array Camera. And to determine how big the galaxies are, they used the NASA Hubble Space Telescope's Advanced Camera for Surveys.

"Astronomy has long used a model where big surveys are followed by detailed studies of the interesting objects they find," says Nigel Sharp, program officer in NSF's Division of Astronomical Sciences. "This work nicely couples the large area, wide-field view of our ground-based telescope with the sharp focus of the Hubble, to probe to the faintest light levels. This team has come the closest yet to finding young galaxies that resemble our own Milky Way in its infancy."

Centaurus A exposed

This image shows a composite of a radio and an optical image of Centaurus A. NASA/CXC/CfA/R. Kraft et al./ESO/VLT/ISAAC/M. Rejkuba et al.

January 10, 2008

Provided by Chandra X-Ray Center

A dramatic new Chandra image of the nearby galaxy Centaurus A provides one of the best views to date of the effects of an active supermassive black hole. Opposing jets of high-energy particles can be seen extending to the outer reaches of the galaxy, and numerous smaller black holes in binary star systems are also visible.

The image was made from an ultra-deep look at the galaxy Centaurus A, equivalent to more than 7 days of continuous observations. Centaurus A is the nearest galaxy to Earth that contains a supermassive black hole actively powering a jet.

A prominent X-ray jet extending for 13,000 light-years points to the upper left in the image, with a shorter "counterjet" aimed in the opposite direction. Astronomers think that such jets are important vehicles for transporting energy from the black hole to the much larger dimensions of a galaxy, and affecting the rate at which stars form there.High-energy electrons spiraling around magnetic field lines produce the X-ray emission from the jet and counterjet. This emission quickly saps the energy from the electrons, so they must be continually reaccelerated or the X-rays will fade out. Knot-like features in the jets detected in the Chandra image show where the acceleration of particles to high energies is currently occurring, and provides important clues to understanding the process that accelerates the electrons to near-light speeds.

The inner part of the X-ray jet close to the black hole is dominated by these knots of X-ray emission, which probably come from shock waves, akin to sonic booms, caused by the jet. Farther from the black hole there is more diffuse X-ray emission in the jet. The cause of particle acceleration in this part of the jet is unknown.

Hundreds of point-like sources are also seen in the Chandra image. Many of these are X-ray binaries that contain a stellar-mass black hole and a companion star in orbit around one another. Determining the population and properties of these black holes should help scientists better understand the evolution of massive stars and the formation of black holes.

Another surprise was the detection of two particularly bright X-ray binaries. These sources may contain stellar mass black holes that are unusually massive, and this Chandra observation might have caught them gobbling up material at a high rate.

High-energy electrons spiraling around magnetic field lines produce the X-ray emission from the jet and counterjet. This emission quickly saps the energy from the electrons, so they must be continually reaccelerated or the X-rays will fade out. Knot-like features in the jets detected in the Chandra image show where the acceleration of particles to high energies is currently occurring, and provides important clues to understanding the process that accelerates the electrons to near-light speeds.

Galaxies in the River

Credit & Copyright: Robert Gendler, Jan-Erik Ovaldsen,
Allan Hornstrup, IDA
Image data: ESO/Danish 1.5m telescope at La Silla, Chile - 2008

Thursday, November 27, 2008

Large galaxies grow by eating small ones. Even our own galaxy practices galactic cannibalism, absorbing small galaxies that get too close and are captured by the Milky Way's gravity.

In fact, the practice is common in the universe and well illustrated by this striking pair of interacting galaxies from the banks of the southern constellation Eridanus (The River).

Located over 50 million light years away, the large, distorted spiral NGC 1532 is seen locked in a gravitational struggle with dwarf galaxy NGC 1531, a struggle the smaller galaxy will eventually lose. Seen edge-on, spiral NGC 1532 spans about 100,000 light-years.

The NGC 1532/1531 pair is thought to be similar to the system of face-on spiral and small companion known as M51, the Whirlpool Galaxy.

Seeing the big cosmic picture

photo:The Sloan Digital Sky Survey is two separate surveys in one. Galaxies are identified in 2-D images (right), then have their distance determined from their spectra to create a 2- billion-light-year-deep 3-D map (left) where each galaxy is shown as a single point. The color represents the galaxy's luminosity. This 3-D map shows only 66,976 out of 205,443 galaxies that lie near the plane of Earth's equator.
Sloan Digital Sky Survey

November 9, 2003

Similar to medieval maps of Earth that included both speculations of the unknown and concrete scientific observations, cosmologists today are slowly refining our understanding of the structure and evolution of the universe as a whole. Now, a team of international astronomers has announced they have created a 2-billion-light-year-deep survey map that reveals the most precise makeup of the universe to date.

Mining data from the Sloan Digital Sky Survey (SDSS), the astronomers made precise measurements of the pattern of large-scale clustering of galaxies and associated dark matter. By plotting the three-dimensional positions of 205,443 galaxies spread over six percent of the sky, a group led by Max Tegmark of the University of Pennsylvania obtained the sharpest-ever views of gravitational-clustering patterns between galaxies. While a clumpy variation in density appears on a scale of millions of light-years, a more uniform picture of the universe emerges on larger scales.

The results are slated for publication in the Astrophysical Journal and Physical Review D as two separate papers, and the authors have pegged the overall breakdown of cosmic matter at 70 percent dark energy, 25 percent dark matter, and only 5 percent ordinary matter composed of atoms.Relieving many astronomers' angst, these latest numbers precisely match both previous theoretical predications and findings released earlier this year from the Wilkinson Microwave Anisotropy Probe (WMAP). Images taken by the WMAP team measured the cosmic microwave background radiation left behind in the aftermath of the Big Bang. By combining the WMAP measurements with those from SDSS, the newly released galaxy-mapping data have put finer constraints on cosmological parameters like the age, structure, and expansion of the universe, more than halving the uncertainties from WMAP.

"Different galaxies, different instruments, different people, and different analysis — but the results agree," explains Tegmark. "Extraordinary claims require extraordinary evidence, but we now have extraordinary evidence for dark matter and dark energy and have to take them seriously no matter how disturbing they seem."

Verifying previous inflation models, these new results also offer up critical evidence for the existence of dark energy and its critical role in the present-day expansion of the universe. But as co-investigator David Weinburg from Ohio State University points out, "The real challenge now is to figure out what these mysterious substances actually are."

Astronomers crack cosmic chicken-or-egg dilemma

photo:The Hubble Space Telescope captured this image of NGC 4603, a majestic spiral galaxy 108 million light-years away. Jeffrey Newman (UC Berkeley) / NASA

July 22, 2003

While it's well known that monster-sized black holes lurk inside the cores of most large galaxies, a great astrophysical debate has been raging over which came first. Could the pull of a black hole accumulate enough stellar matter to create a galaxy, or could a young galaxy's star-packed core give birth to one of these dark cosmic brutes?

An international team of astronomers has now discovered new evidence that points not to one of these scenarios but instead to some kind of strange, symbiotic relationship — supermassive black holes and their host galaxies apparently grow at the same rate and evolve together.

"Like the chicken and the egg, neither black hole nor galaxy can be said to come first," states Timothy Heckman, an astronomer at Johns Hopkins University and co-leader of the study. "Each is necessary for the other."

These new findings, presented last week at the International Astronomical Union's General Assembly meeting in Sydney, Australia, represent the first direct glimpse of this connection between galaxy formation and black hole formation and reveals how the two are intimately entwined.Sifting though observations of 120,000 galaxies culled from the Sloan Digital Sky Survey (SDSS), the astronomers found developing black holes and active star formation in 20,000 massive galaxies within one billion light-years of Earth.

"Since nearby galaxies can be studied much more easily than their distant and more spectacular ancestors, it is no surprise that the link between black hole growth and galaxy growth first became apparent in our own backyard," Heckman says.

photo:This 2.5-meter telescope is the main workhorse of the Sloan Digital Sky Survey. Its box-shaped structure protects it against the wind. SDSS Collaboration

By examining the telltale barcode signatures in the galaxies' spectra, the team was able to determine the growth rate of the central black holes and the amount of material being swallowed. The researchers conclude that as the rate of star formation in these massive galaxies increases, so does the rate of matter being devoured by their giant predatory tenants.

If this is indeed the case, does either the galaxy or the black hole control the growth of the other, or are the two entities feeding off each other, in a perpetual state of co-evolution? To find out, their growth process will have to be carefully studied, answers team co-leader Guinevere Kauffmann of the Max-Planck-Institute for Astrophysics in Germany.

Galactic archaeology

Space telescopes spy ancient galaxy clusters in the young universe, shedding light on the years following the Big Bang.

photo: This galaxy cluster is shown as it existed when the universe was just 5 billion years old. The cluster is as massive as 300 trillion suns and is the most massive known cluster of its epoch. This image, which was taken between May and June 2002 with Hubble's Advanced Camera for Surveys Wide Field Camera, shows just the core of the cluster. Only about 50 galaxies are shown, but the cluster likely contains thousands. Dominating the core are a pair of large, reddish, elliptical galaxies (near the center of the image). Their red color indicates they hold a population of stars that are at least a billion years old. The red galaxies surrounding the central pair are also cluster members. Many of the other galaxies, including several blue galaxies, lie in the foreground. NASA / ESA / J.Blakeslee (JHU) / M. Postman (STScI) / P. Rosati (ESO)

January 5, 2004

In piecing together the story of the universe's history, scientists are hoping to figure out exactly how and when galaxies first formed. It's a crucial question because early structure formation carries the imprint of conditions in the newborn universe, which can help us understand our cosmic beginnings. Now, two key discoveries of early galaxy clusters are helping astronomers see the foundations of the universe's galactic architecture directly.

Using a powerful combination of NASA's Chandra X-ray Observatory and the Advanced Camera for Surveys (ACS) aboard the Hubble Space Telescope, an international team of astronomers has found and studied two record-breaking ancient galaxy clusters.

The first is a cluster whose light is reaching us from 9 billion years ago, when the universe was a mere 5 billion years old. It's the most massive known cluster of that epoch, which means it must have been growing for quite some time already — a somewhat surprising result for such an early time in the universe's youth.

"We determined that the galaxies in this cluster were already about 3 billion years old," explains astronomer John Blakeslee of Johns Hopkins University, a member of the team. "Thus, these galaxies formed most of their stars about 2 billion years after the Big Bang."

The second finding is a proto-cluster of embryonic galaxies from a time when the universe was only about 1.5 billion years old. This is the most distant, and therefore earliest, proto-cluster ever found.



photo: Taken by Hubble's Advanced Camera for Surveys Wide Field Camera in July 2002, this image shows the embryonic cluster as it was when the universe was just 1.5 billion years old. This is the most distant proto-cluster known. It is dominated by a massive baby galaxy, seen as the green object near the center of this image. The galaxy is producing powerful radio emissions, and it is the brightest galaxy in the proto-cluster. The green color is indicative of glowing hydrogen gas. The galaxy's clumpy appearance suggests it is still developing. Smaller growing galaxies are scattered around the massive galaxy. The bright object in the upper part of the image is a foreground star. NASA / ESA / G. Miley and R. Overzier (Leiden Observatory)

"Given that this is a very dense region of the early universe with so many galaxies, it's quite reasonable to suggest that these galaxies are some of the oldest in the universe," Blakeslee says of this group. "More importantly, though, we are directly observing the galaxy-cluster formation epoch, and it is in clusters that the oldest galaxies tend to reside."



photo: This color composite image of the galaxy cluster RDCS 1252.9-2927 shows the X-ray (purple) light from 70-million-degree Celsius gas in the cluster, and the optical (red, yellow and green) light from the galaxies in the cluster. The X-ray data was taken by the Chandra X-ray Observatory, and the optical data is from European Southern Observatory's Very Large Telescope (VLT) in Chile.
X-ray data indicate that this cluster formed more than 8 billion years ago and has a mass at least 200 trillion times that of the Sun. It is the most massive cluster ever observed at such an early stage in the evolution of the universe. The width of the image spans 2 arcminutes. X-ray: NASA / CXC / ESO / P. Rosati et al.; Optical: ESO / VLT / P. Rosati et al.

Both findings are evidence that galaxies started forming soon after the Big Bang, as slightly denser regions in the primordial universe gravitationally coalesced. That process involved many cosmological factors: the pattern of initial density fluctuations in the universe, the nature of gravity, the expansion rate of the universe, the strength of dark energy, and the abundance of dark matter, to name a few.

Witnessing the sculpting of large-scale structure, then, allows scientists to probe these many mysteries and home in on some details of galaxy formation itself, a complicated process that is still not entirely understood. Having found such ancient clusters at various stages in the process certainly will be helpful in putting all the pieces of the puzzle together.

"It's part of the quest to understand our origins," Blakeslee says.

Big Galaxy Collisions Can Stunt Star Formation

Credit: Tomer Tal and Jeffrey Kenney/
Yale University and NOAO/AURA/NSF

Wednesday, October 08, 2008

A deep new image of the Virgo cluster has revealed monumental tendrils of ionized hydrogen gas 400,000 light-years long connecting the elliptical galaxy M86 and the disturbed spiral galaxy NGC 4438.

Taken with the wide-field Mosaic imager on the National Science Foundation’s Mayall 4-meter telescope at Kitt Peak National Observatory, this Hydrogen-alpha image and related spectroscopic measurements of the filament provide striking evidence of a previously unsuspected high-speed collision between the two galaxies.

“Our data show that this system represents the nearest recent collision between a large elliptical galaxy and a large spiral,” said Jeffrey Kenney of Yale University, lead author of a paper to be published in a November 2008 issue of Astrophysical Journal Letters. “This discovery provides some of the clearest evidence yet for high-speed collisions between large galaxies, and it suggests that the consequences of such collisions are a plausible alternative to black holes in trying to explain the mystery of what process turns off star formation in the biggest galaxies.”

The Virgo cluster is located approximately 50 million light-years from Earth. Previous studies had noticed disturbed H-alpha gas around each of the two galaxies, but no connection from the two had been inferred. Indeed, some results have suggested that NGC 4438 collided with the small lenticular galaxy NGC 4435, but NGC 4435 has a much higher line-of-sight velocity as seen from Earth and appears undisturbed.

Spectroscopy of selected regions along the filament between M86 and NGC 4438, obtained with the Sparsepak Integral Field Unit instrument on the WIYN 3.5-meter telescope on Kitt Peak, shows a fairly smooth velocity gradient between the galaxies, supporting the collision scenario. There are no obvious stars in the filaments.

“The image shows what you can find if you look deep and wide, and we needed to do both to see the M86-NGC4438 complex,” Kenney explains.

As in most elliptical galaxies, most of the gas within M86 is extremely hot, and therefore radiates X-rays. The X-ray distribution in M86 is irregular and sports a long plume, which had previously been interpreted as a tail of gas which is being stripped by ram pressure as M86 falls into the intracluster medium of the Virgo cluster. The new H-alpha image from Kitt Peak suggests that most of the disturbances to the interstellar medium in M86 are instead due to the collision with NGC 4438.

A current mystery in astronomy is what causes the biggest galaxies in the Universe—which are primarily ellipticals, like M86—to stop forming stars. “Something needs to heat up the gas so it doesn’t cool and form stars,” Kenney says. “A number of recent studies suggest that energy from active galactic nuclei associated with supermassive black holes may do this, but our new study shows that gravitational interactions may also do the trick.”

Low-velocity collisions, especially between small- to medium-sized galaxies, often cause an increase in the local star formation rate, as the collisions tend to cause gas to concentrate in the galaxy centers. But in high velocity collisions (which happen naturally between large galaxies, since their large gravity pulls mass inward much faster), the kinetic energy of the collision can cause the gas to heat up so much that it cannot easily cool and form stars.

While not many galaxies suffer such extreme collisions as M86, most galaxies experience minor mergers and gas accretion events, and these may play a significant role in heating the galaxy’s gas. These more common but modest events are very hard to study, since their observational signatures are weak.

“The same physical processes occur in both strong and weak encounters, and by studying the observable effects in extreme cases like M86 we can learn about the role of gravity in the heating of galaxy gas, which appears to be quite significant,” Kenney adds.

OSCIR Unveils Rich Dust Content in the Second Most Metal Deficient Galaxy Known

Infrared spectral energy distribution of SBS 0335-052. Symbols with error bars represent the observed broadband photometric data (OSCIR and ISOPHOT), while the solid line is the ISOCAM spectrum. Open circles represent model fluxes in the same spectral windows synthesized using the model DUSTY.

SBS 0335-052 is a gas-rich dwarf galaxy at a distance of 170 million light-years (52 Mpc). It is the second most metal-poor galaxy known, with a heavy metal content only 1/40th that of the Sun. Such a low metallicity means that this galaxy contains significantly lower quantities of the heavy elements produced by the process of nucleosynthesis in stars. This lack of metals could be because the galaxy is very young. Another possibility is that SBS 0335-052 is an old galaxy that has experienced a very low star formation rate throughout its lifetime.

Canadian Ph. D. student Stephanie Plante (Universite Laval, Quebec) and French astronomer Marc Sauvage (Service d'Astrophysique, Saclay) used OSCIR on Gemini North to image SBS 0335-052 in the mid-infrared at 10.8 and 21 microns. Their images revealed a massive supercluster of young stars with a total mass equivalent to 2 million times the mass of the Sun in the core of the galaxy. It is estimated that the age of this cluster is 5 millions years or less.

The Gemini investigators were able to infer the properties of the dust-hidden cluster by analyzing the properties of the interstellar dust surrounding these stars. This is possible since the dust 'processes' the stellar radiation produced by the stars by absorbing the ultra-violet and optical light from embedded stars and then re-radiating it in the mid-infrared. Interstellar dust particles are small solid particles made of the most common heavy elements like carbon, silicates, ices and other molecules in solid form.

Combining the Gemini observations with those made by the ISOPHOT instrument aboard the Infrared Satellite Observatory in the far infrared at 60, 65 and 100 microns, Plante and Sauvage have used the software DUSTY to model both the star cluster and its surrounding dust. The two flux points at 10.8 and 21 microns derived from the OSCIR images were crucial in constraining some of the key model parameters which allowed them to construct a detailed model of the dust properties.

These Gemini results are interesting because they indicate that the paucity of metals did not preclude SBS 0335-052 from forming 105 solar masses of dust. The unresolved N band Gemini image and calculations using the DUSTY model show that there is enough dust to hide the massive star cluster from view in the optical. Plante and Sauvage estimate the amount of extinction toward the cluster to be equivalent to 30 magnitudes in the V band, which is why the region is totally undetectable at optical wavelengths. Interestingly, this is very similar to the amount of extinction that we observe toward the center of the Milky Way galaxy. The two million solar masses of young stars are packed in a region not larger than 10 pc (~30 light-years) across.

The presence of such a high density of stars implies a high density of radiation. The ultraviolet radiation emitted by the cluster is intense enough to destroy the smallest dust molecules (PAH) and even the smallest grains (VSM) present in its near environment. Only the biggest dust grains (around 1 micron or slightly less) survive. The Q band (21 micron) observation with OSCIR allowed the researchers to ascertain that even though there are no PAH emission features seen, there is some carbonaceous dust present in SBS0335-052's massive stellar cluster.

Finally, Plante and Sauvage caution that if dust-enshrouded super-star clusters are commonly associated with a starbursting environment, the star formation rate deduced by looking at the rest-frame optical or ultraviolet portion of the spectrum should be viewed with caution.



On the left is an image of SBS 0335-052 in the I band taken by HST in the optical domain. On the right is an image of the same galaxy obtained with OSCIR on the Gemini North Telescope in the mid-infrared (10.8 micron). All the mid-infrared flux comes from a dust embedded super stellar cluster that cannot be detected at optical wavelengths.

Plante and Sauvage have published their work in The Astronomical Journal, October 2002, vol. 124, pp. 1995-2005.

*The University of Florida's OSCIR (Observatory Spectrometer and Camera for the Infrared) mid-infrared imager/spectrometer, which was built with funding from the National Science Foundation and NASA.

Gemini Observatory Captures Multi-Dimensional Movie of Active Galaxy's Core

2002 March 21

Astronomers observing with the Gemini North Telescope on Hawaii's Mauna Kea have a powerful new tool to probe mysterious cosmic caldrons like those at the cores of galaxies and stellar nurseries.Using the recently commissioned Integral Field Unit (IFU) on the Gemini Multi-Object Spectrograph (GMOS), astronomers at the observatory have recently obtained a complete multi-dimensional picture of the dynamic flow of gas and stars at the core of an active galaxy named NGC 1068 in a single snap-shot. The resulting windfall of data has been transformed into an animation that dramatically reveals the internal gyrations of the galaxy - including the interactions of a pair of galactic-scale jets that spew material for thousands of light years away from the suspected black hole at the galaxy's core."The Gemini data of NGC 1068 reveal one of the lesser know features of galaxy jets," explains Gemini North Associate Director Dr. Jean-René Roy. "For the first time we were able to clearly see the jet's expanding lobe as its hypersonic bow shock slams directly into the underlying gas disk of the galaxy. It's like a huge wave smashing onto a galactic shoreline."Dr. Gerald Cecil of the University of North Carolina, recently led an international team to study this particular galaxy using spectra taken with the Hubble Space Telescope and believes that the new Gemini spectra will clarify many patterns revealed by Hubble. "Large ground-based telescopes like Gemini are the perfect complement to Hubble because they can collect so much more light. But it's critical to use all this light cunningly, and not throw most of it away as standard slit spectrographs do. The GMOS's integral field capability now enables detailed studies of fundamental physical processes that were previously too time consuming to conduct on faint cosmic sources."By using Integral Field Spectroscopy we add dimensions to the data and can essentially make a movie with one click of the shutter," says Dr. Bryan Miller, the Gemini instrument scientist for IFUs. "When we play back our movie of the galaxy NGC1068, we see a 3-dimensional view of the core of this galaxy. It is striking how much easier it is to interpret features with this kind of data. With integral-field data we can determine the mass distributions, the true shapes, and the histories of galaxies more accurately than before." The Integral Field Spectroscopy findings by Dr. Miller et al. will appear in the Conference Series of the Astronomical Society of the Pacific.

This technology is new to the world of 8-10 meter class telescopes and is especially powerful on new generation telescopes like Gemini that use the latest optical technologies to focus starlight to razor sharpness. "We are very excited by these results and the superb capabilities that the integral field unit has given the GMOS in Hawaii", notes Dr. Jeremy Allington-Smith, the scientist from the University of Durham in the United Kingdom who managed the construction of the GMOS Integral Field Unit. "In effect we have added an extra dimension to the instrument so that it can map the motion of gas and stars at any point in the image of the object under study. The GMOS IFU will be a powerful new tool for studying the centers of active galaxies that may harbor black holes, as well as the dynamic internal motions of galaxies and star forming regions." The GMOS IFU findings by Dr. Allington-Smith et al. will appear in the Conference Series of the Astronomical Society of the Pacific.

An Integral Field Unit (IFU) like the one used in the GMOS uses hundreds of tiny optical fibers (each thinner than an human hair) with tiny micro-lenses attached to guide light from the telescope's 2-D image to a spectrograph. The spectrograph produces one individual spectrum for each fiber for a total of 1500 individual spectra that can each reveal details of the physical conditions and velocity of the gas, dust and stars it studies. This system was the first IFU to be installed on the new generation of 8 and 10m telescopes when it was commissioned on the Gemini-North telescope in 2001.

The Integral Field Spectroscopy capabilities of the Gemini Observatory are still developing. Within the next two years both telescopes will have optical and near-infrared integral field units. Some of these systems will work with adaptive optics to provide the highest spatial resolution images deliverable by the telescopes, including images in the infrared that will be sharper than can be produced by the Hubble Space Telescope at those wavelengths.

The Gemini Observatory is an international collaboration that has built two identical 8-meter telescopes. The telescopes are located at Mauna Kea, Hawaii (Gemini North) and Cerro Pachón in central Chile (Gemini South), and hence provide full coverage of both hemispheres of the sky. Both telescopes incorporate new technologies that allow large, relatively thin mirrors under active control to collect and focus both optical and infrared radiation from space. Gemini North began science operations in 2000 and Gemini South began scientific operations in late 2001.

Hubble's View of Barred Spiral Galaxy NGC 1672

April 3, 2007

This NASA Hubble Space Telescope view of the nearby barred spiral galaxy NGC 1672 unveils details in the galaxy's star-forming clouds and dark bands of interstellar dust.

One of the most striking features is the dust lanes that extend away from the nucleus and follow the inner edges of the galaxy's spiral arms. Clusters of hot young blue stars form along the spiral arms and ionize surrounding clouds of hydrogen gas that glow red. Delicate curtains of dust partially obscure and redden the light of the stars behind them by scattering blue light.

Galaxies lying behind NGC 1672 give the illusion they are embedded in the foreground galaxy, even though they are really much farther away. They also appear reddened as they shine through NGC 1672's dust. A few bright foreground stars inside our own Milky Way Galaxy appear in the image as bright and diamond-like objects.

As a prototypical barred spiral galaxy, NGC 1672 differs from normal spiral galaxies, in that the arms do not twist all the way into the center. Instead, they are attached to the two ends of a straight bar of stars enclosing the nucleus. Viewed nearly face on, NGC 1672 shows intense star formation regions especially off in the ends of its central bar.

Astronomers believe that barred spirals have a unique mechanism that channels gas from the disk inward towards the nucleus. This allows the bar portion of the galaxy to serve as an area of new star generation.

NGC 1672 is also classified as a Seyfert galaxy. Seyferts are a subset of galaxies with active nuclei. The energy output of these nuclei can sometimes outshine their host galaxies. This activity is powered by accretion onto supermassive black holes.

NGC 1672 is more than 60 million light-years away in the direction of the southern constellation Dorado. These observations of NGC 1672 were taken with Hubble's Advanced Camera for Surveys in August of 2005. The composite image was made by using filters that isolate light from the blue, green, and infrared portions of the spectrum, as well as emission from ionized hydrogen.

Hubble Finds 'Dorian Gray' Galaxy

NASA's Hubble Space Telescope quashed the possibility that what was previously believed to be a toddler galaxy in the nearby universe may actually be considered an adult. Called I Zwicky 18, this galaxy has a youthful appearance that resembles galaxies typically found only in the early universe. Hubble has now found faint, older stars within this galaxy, suggesting that the galaxy may have formed at the same time as most other galaxies.

Hubble data also allowed astronomers for the first time to identify Cepheid variable stars in I Zwicky 18, marked by the red circles. These flashing stellar mile-markers were used to determine that I Zwicky 18 is 59 million light-years from Earth, almost 10 million light-years more distant than previously believed.

I Zwicky 18 is classified as a dwarf irregular galaxy and is much smaller than our Milky Way Galaxy. The concentrated bluish-white knots embedded in the heart of the galaxy are two major starburst regions where stars are forming at a furious rate. The wispy blue filaments surrounding the central starburst regions are bubbles of gas that have been blown away by stellar winds and supernovae explosions from a previous generation of hot, young stars. This gas is now heated by intense ultraviolet radiation unleashed by a
new generation of hot, young stars.

Besides the bluish-white young stars, white-reddish stars also are visible in both I Zwicky 18 and its companion. These stars may be as old as 10 billion years. The reddish extended objects surrounding I Zwicky 18 and its companion are ancient, fully formed galaxies of different shapes that are much farther away.

The observations of I Zwicky 18 were taken in 2005 and 2006 with Hubble's Advanced Camera for Surveys. Astronomers made this image by combining observations taken with blue and red filters.

The science team consists of Alessandra Aloisi and Marco Sirianni of the Space Telescope Science Institute and the European Space Agency; Francesca Annibali, Jennifer Mack, and Roeland van der Marel of the Space Telescope Science Institute; Abhijit Saha of the National Optical Astronomy Observatories; and Gisella Clementini, Rodrigo Contreras, Giuliana Fiorentino, Marcella Marconi, Ilaria Musella, and Monica Tosi of the Italian National Astrophysics Institutes in Bologna and Naples.

October 16, 2007

NASA's Hubble Space Telescope has found a galaxy that is the equivalent of the painting of Dorian Gray, a portrait in an Oscar Wilde novel that appears mysteriously to age.

Like the fictional painting, the galaxy I Zwicky 18 appears to look older the more astronomers study it. What astronomers once thought was a toddler galaxy by galactic standards may now be considered an adult.

The galaxy's youthful appearance was identified some 40 years ago through observations at the Palomar Observatory. Those studies showed that the galaxy erupted with star formation billions of years after its galactic neighbors. Galaxies resembling I Zwicky 18's youthful appearance are typically found only in the early universe. Astronomers were thrilled that a newly forming galaxy like I Zwicky 18 could be studied nearby to learn about galactic evolution, which is normally only observable at great distances.

New Hubble data have quashed that possibility. The telescope found faint, older stars contained within the galaxy, suggesting its star formation started at least 1 billion years ago and possibly as much as 10 billion years ago. The galaxy, therefore, may have formed at the same time as most other galaxies.

"Although the galaxy is not as youthful as was once believed, it is certainly developmentally challenged and unique in the nearby universe," said astronomer Alessandra Aloisi from the Space Telescope Science Institute and the European Space Agency in Baltimore, Md., who led the new study.

Spectroscopic observations with ground-based telescopes have shown that I Zwicky 18 is almost exclusively composed of hydrogen and helium, the main ingredients created in the Big Bang. Heavier elements are forged within the cores of stars and blasted into space when the stars die. The galaxy's primordial makeup suggests that its rate of star formation has been much lower than that of other galaxies of similar age. The galaxy has been studied with most of NASA's telescopes, including the Spitzer Space Telescope, the Chandra X-ray Observatory, and the Far Ultraviolet Spectroscopic Explorer (FUSE). However, it remains a mystery why I Zwicky 18 formed so few stars in the past, and why it is forming so many new stars right now.

The Hubble data also suggest that I Zwicky 18 is 59 million light-years from Earth, almost 10 million light-years more distant than previously believed. While this is still in our own backyard, as measured by extragalactic standards, the galaxy's larger-than-expected distance may explain why astronomers have had difficulty detecting older, fainter stars within the galaxy until now. In fact, the faint, old stars in I Zwicky 18 are almost at the limit of Hubble's resolution and sensitivity.

Aloisi and her team discerned the new distance by observing flashing stellar mile-markers within I Zwicky 18. These massive stars, called Cepheid variable stars, pulse in a regular rhythm. The timing of their pulsations is directly related to their brightness. By comparing the stars' actual brightness with their observed brightness, astronomers can precisely measure their distance. The team determined the observed brightness of three Cepheids and compared it with the actual brightness predicted by theoretical models. These models were calculated specifically for I Zwicky 18's deficiency in heavy elements, indicating the galaxy's stars formed before these elements were abundant in the universe. This analysis allowed the astronomers to determine the galaxy's distance. The Cepheid distance also was validated through another distance indicator, specifically the observed brightness of the brightest red stars older than 1 billion years.

Cepheid variable stars have been studied for decades and have been instrumental in the determination of the scale of our universe. This is the first time, however, that variable stars with so few heavy elements were found. This may provide unique new insights into the properties of variable stars, which is now a topic of ongoing study.

A Midsummer Night's Dream: NGC 4618 and NGC 4625 by Martin Winder/Dietmar Hager

NGC 4625/18 - Credit: Winder / Hager

"Night's swift dragons cut the clouds full fast, And yonder shines…" Another galactic pair? Discovered by Friedrich Wilhelm Herschel in 1787, this particular galactic pairing known as Arp 23 find its home in Canes Venetici, and the duo most certainly has a colorful history. The smaller of the pair - NGC 4625 is a distorted dwarf galaxy formally classified as Sm, a structure which resembles spiral galaxies - especially the Magellanic clouds. So what does a single arm galaxy have to say for itself?

It's been theorized that asymmetrical structure could be the result of a gravitational interaction with NGC 4618 - its larger, interactive member in this picture. Yes, asymmetric structure isn't new when it comes to interacting galaxies, but the rub is only some of the neutral hydrogen gas outside the optical disc of NGC 4618. What does that mean? Quite probably that the single arm shape of the galaxy isn't a product of the interaction - but natural to the galaxy's own, unique properties.

In reading studies done by 2004 by Bush (et al) , "Asymmetry is a common trait in spiral galaxies and is particularly frequent among Magellanic spirals. To explore how morphological and kinematic asymmetry are affected by companion galaxies, we analyze neutral hydrogen observations of the interacting Magellanic spirals NGC 4618 and NGC 4625. The analysis of the H I distribution reveals that about 10% of the total H I mass of NGC 4618 resides in a looping tidal structure that appears to wrap all the way around the galaxy. Through calculations based on derived H I profiles, we show that NGC 4618 and NGC 4625 are no more asymmetric than the noninteracting Magellanic spirals analyzed recently by Wilcots & Prescott. We also derive rotation curves for the approaching and receding sides of each galaxy. By fitting the mean curves with an isothermal halo model, we calculate dynamical masses of 4.7×109 and 9.8×109 Msolar out to 6.7 kpc for NGC 4618 and NGC 4625, respectively. While the rotation curves had systematically higher velocities on the receding side of each galaxy, the effect was no more pronounced than in studies of noninteracting spirals. The degree of interaction-driven asymmetry in both galaxies is indistinguishable from the intrinsic degree of asymmetry of lopsided galaxies."

In 1985, A. V. Filippenko discovered something unusual in the spectrum of NGC 4618: "The object is almost certainly a supernova in an advanced stage, although its spectrum does not conform to published supernova spectra. Based on the present brightness and on the distance modulus of NGC 4618, it is estimated that the object reached maximum about 160 days ago and has faded by 5 to 6 mag, if it was initially a normal Type I or Type II supernova. It is noteworthy that Minkowski (1939, Ap.J. 89, 156) observed the [O I] 630.0/636.4-nm doublet to be strong after 184 days past maximum in the spectrum of the Type I supernova 1937C in IC 4182. The feature was not present in the spectrum of SN 1972E in NGC 5253 some 400 days after maximum (Kirshner and Oke 1975, Ap.J. 200, 574). Prediscovery data on the brightness of the object and future observations of the evolution of its spectrum would be of great interest."

Later that year: "Optical spectra of a bright stellar object near the nucleus of the spiral galaxy NGC 4618 reveal strong, very broad emission lines similar to those in quasars but having the wrong relative wavelengths. Although lines of hydrogen and helium are absent, the most prominent features can be attributed to neutral atoms of oxygen, sodium, and magnesium at the redshift of NGC 4618. The object is almost certainly a supernova whose highly unusual spectrum may be indicative of a fundamentally new subclass." By 1986 the studies had broadened and; "The spectrum of SN 1985f does not resemble any previously published spectra of supernovae, and it is postulated that its progenitor was a massive Wolf-Rayet star that expelled its outer atmosphere of H and He prior to supernova explosion."

However, the real beauty to this picture is what appears to be sparkling star forming regions. According to the studies done by the Elmegreens; "It is suggested that prominent star forming regions occur near the peripheries of barred Magellanic spirals and irregulars because the galaxies experience gas dynamics similar to that in the inner barred regions of massive barred spirals." But… Is the interaction between the two what's causing these exterior star forming regions? Science doesn't seem to think so. Says Zaritsky; "The stellar disks of many spiral galaxies are twice as large as generally thought (and) the phenomenon of low-level star formation well outside the apparent optical edges of disks is common and long lasting."

This is further backed up by studies done by Gil de Paz (et al). "Recent far-UV (FUV) and near-UV (NUV) observations of the nearby galaxy NGC 4625 made by the Galaxy Evolution Explorer (GALEX) show the presence of an extended UV disk reaching to 4 times the optical radius of the galaxy. The UV-to-optical colors suggest that the bulk of the stars in the disk of NGC 4625 are currently being formed, providing a unique opportunity to study today the physics of star formation under conditions similar to those when the normal disks of spiral galaxies like the Milky Way first formed. In the case of NGC 4625, the star formation in the extended disk is likely to be triggered by interaction with NGC 4618 and possibly also with the newly discovered galaxy NGC 4625A."

Yet, star formation isn't all that's going on here. NGC 4618 and NGC 4625 have also been studied for spin as well, and there's a strong possibility that tidal interaction can affect it. According to studies done by Helou. "Clues to the origin of spin in galaxies are also direct clues to the mechanism of galaxy formation. The evidence so far is clearly against a simple picture where primeval turbulence is the source of spin. But the data are consistent with, and suggestive of, the hypothesis that spins were acquired via tidal torquing; a detailed discussion is given, treating separately the possibility that the effect is primordial and the possibility that it is a result of evolution. Enough data are now becoming available that specific calculations are required to sharpen the predictions for the statistical behavior of spins, especially in binaries."

Is there still more to this pair than meets the eye? Certainly. This pair has also been studied for Seyfert nuclei - a brilliant, compact core region which can take a variety of forms, perhaps carrying clues to how the central engine is fed or triggered. Studies show that Seyfert nuclei may happen more frequently among interacting spirals - but more so those that only interact strongly, rather than with extreme tidal distortion. The fascinating work was originally done by Bill Keel and his findings backed up by later studies. It is also very possible this phenomenon simply occurs as a natural process, and the spectral features of Wolf-Rayet stars have also been detected as well. So many different factors can come into play!

No matter what happens in this unusual "inside out" forming pair - be it a detection of a black hole or just a long duration gamma ray burst - they make for fascinating study and a truly beautiful image. "If we shadows have offended, Think but this, and all is mended, That you have but slumber'd here While these visions did appear. And this weak and idle theme, No more yielding, but a dream, Gentles, do not reprehend; If you pardon, we will mend."

The light for this awesome image was gathered over a period of about 7.5 hours by AORAIA member Martin Winder and then processed by member Dr. Dietmar Hager. We thank both of them for the exclusive look at this beautiful galaxy duo.

Sombrero Galaxy

photo: The Sombrero Galaxy (M104) as observed by the Hubble Space Telescope (HST).

Credit: HST/NASA/ESA.

The Sombrero Galaxy (also known as M104 or NGC 4594) is an unbarred spiral galaxy in the constellation Virgo. It has a bright nucleus, an unusually large central bulge, and a prominent dust lane in its inclined disk. The dark dust lane and the bulge give this galaxy the appearance of a sombrero. The galaxy has an apparent magnitude of 9.0, making it a galaxy that can easily be seen with amateur telescopes. The large bulge, the central supermassive black hole, and the dust lane all attract the attention of professional astronomers.The Sombrero Galaxy was discovered in March of 1767 by Pierre Méchain, who described the object in a May 1767 letter to J. Bernoulli that was later published in the Berliner Astronomisches Jahrbuch. Charles Messier made a hand-written note about this and five other objects (now collectively recognized as M104 - M109) to his personal list of objects now known as the Messier Catalogue, but it was not "officially" included until 1921. William Herschel independently discovered the object in 1784 and additionally noted the presence of a "dark stratum" in the galaxy's disk, what is now called a dust lane. Later astronomers were able to connect Méchain's and Herschel's observations.In 1921, Camille Flammarion found Messier's personal list of the Messier objects including the hand-written notes about the Sombrero Galaxy. This was identified with object 4594 in the New General Catalogue, and Flammarion declared that it should be included in the Messier Catalogue. Since this time, the Sombrero Galaxy has been known as M104.In the 1910s, Vesto Slipher discovered that the spectra of several galaxies, including the Sombrero Galaxy, are redshifted. The average velocity calculated from these redshifts was 400 km/s. The redshift for the Sombrero Galaxy itself was calculated to be 1100 km/s. Slipher's spectra were among the first observations of the expansion of the universe, one of the key pieces of evidence for the Big Bang Theory.Slipher also detected rotation within the spectra of the Sombrero Galaxy. His observations of galaxy rotation are among the first ever performed.

Dust ring:

As noted above, this galaxy's most striking feature is the dust lane that crosses in front of the bulge of the galaxy. This dust lane is actually a symmetric ring that encloses the bulge of the galaxy. Most of the cold atomic hydrogen gas and the dust lies within this ring. The ring might also contain most of the Sombrero Galaxy's cold molecular gas, although this is an inference based on observations with low resolution and weak detections. Additional observations are needed to confirm that the Sombrero galaxy's molecular gas is constrained to the ring. Based on infrared spectroscopy, the dust ring is the primary site of star formation within this galaxy.

Nucleus:

The nucleus of the Sombrero galaxy is classified as a low ionization nuclear emission region (LINER). These are nuclear regions where ionized gas is present, but the ions are only weakly ionized (i.e. the atoms are missing relatively few electrons). The source of energy for ionizing the gas in LINERs has been debated extensively. Some LINER nuclei may be powered by hot, young stars found in star formation regions, whereas other LINER nuclei may be powered by active galactic nuclei (highly energetic regions that contain supermassive black holes). Infrared spectroscopy observations have demonstrated that the nucleus of the Sombrero Galaxy is probably devoid of any significant star formation activity. However, a supermassive black hole has been identified in the nucleus (as discussed in the subsection below), so this active galactic nucleus is probably the energy source that weakly ionizes the gas in the Sombrero Galaxy.

Central supermassive black hole:

In the 1990s, a research group led by John Kormendy demonstrated that a supermassive black hole is present within the Sombrero Galaxy.Using spectroscopy data from both the CFHT and the Hubble Space Telescope, the group showed that the speed of rotation of the stars within the center of the galaxy could not be maintained unless a mass 1 billion times the mass of the Sun, or 10⁹M☉, is present in the center. This is among the most massive black holes measured in any nearby galaxies.

Synchrotron emission:

At radio and X-ray wavelengths, the nucleus is a strong source of synchrotron emission.Synchrotron emission is produced when high velocity electrons oscillate as they pass through regions with strong magnetic fields. This emission is actually quite common for active galactic nuclei. Although radio synchrotron emission may vary over time for some active galactic nuclei, the luminosity of the radio emission from the Sombrero Galaxy only varies 10-20%.

Unidentified submillimeter emission:

In 2006, two groups published measurements of the submillimeter radiation from the nucleus of the Sombrero Galaxy at a wavelength of 850 micrometres. This submillimeter emission was found not to originate from the thermal emission from dust (which is commonly seen at infrared and submillimeter wavelengths), synchrotron emission (which is commonly seen at radio wavelengths), bremsstrahlung emission from hot gas (which is uncommonly seen at millimeter wavelengths), or molecular gas (which commonly produces submillimeter spectral lines). The source of the submillimeter emission remains unidentified.

Globular clusters:

The Sombrero Galaxy has a relatively large number of globular clusters. Observational studies of globular clusters in the Sombrero Galaxy have produced estimates of the population in the range of 1200 to 2000.The ratio of the number of globular clusters to the total luminosity of the galaxy is high compared to the Milky Way and similar galaxies with small bulges, but the ratio is comparable to other galaxies with large bulges. These results have been repeatedly used to demonstrate that the number of globular clusters in galaxies is thought to be related to the size of the galaxies' bulges. The surface density of the globular clusters generally follows the light profile of the bulge except for near the center of the galaxy.

Distance:

At least two methods have been used to measure the distance to the Sombrero Galaxy.

The first method relies on comparing the measured fluxes from planetary nebulae in the Sombrero Galaxy to the known luminosities of planetary nebulae in the Milky Way. This method gave the distance to the Sombrero Galaxy as 29.0 ± 2.0 Mly (8.9 ± 0.6 Mpc).

The other method used is the surface brightness fluctuations method. This method uses the grainy appearance of the galaxy's bulge to estimate the distance to it. Nearby galaxy bulges will appear very grainy, while more distant bulges will appear smooth. Early measurements using this technique gave distances of 30.6 ± 1.3 Mly (9.4 ± 0.4 Mpc). Later, after some refinement of the technique, a distance of 32 ± 3 Mly (9.8 ± 0.8 Mpc) was measured. This was even further refined in 2003 to be 29.6 ± 2.5 Mly (9.1 ± 0.8 Mpc).

The average distance measured through these two techniques is 29.3 Mly (9.0 Mpc) with an uncertainty of 1.6 Mly (0.5 Mpc).

Nearby galaxies and galaxy group information:

The Sombrero Galaxy lies within a complex, filament-like cloud of galaxies that extends to the south of the Virgo Cluster. However, it is unclear as to whether the Sombrero Galaxy is part of a formal galaxy group. Hierarchical methods for identifying groups, which determine group membership by considering whether individual galaxies belong to a larger aggregate of galaxies, typically produce results showing that the Sombrero Galaxy is part of a group that includes NGC 4487, NGC 4504, NGC 4802, UGCA 289, and possibly a few other galaxies.However, results that rely on the percolation method (i.e. the "friends-of-friends" method), which links individual galaxies together to determine group membership, indicate that either the Sombrero Galaxy is not in a group or that it may only be part of a galaxy pair with UGCA 287.

Amateur astronomy observation information:

The Sombrero Galaxy is located 11.5° west of Spica and 5.5° northeast of Eta Corvi. Although the galaxy is visible with 7x35 binoculars or a 4-inch (100 mm) amateur telescope,an 8-inch (200 mm) telescope is needed to distinguish the bulge from the disk, and a 10 or 12-inch (300 mm) telescope is needed to see the dark dust lane.