Youngest Millisecond Pulsar Discovered

In three years, NASA's Fermi has detected more than 100 gamma-ray pulsars, but something new has appeared. Among a type of pulsar with ages typically numbering a billion years or more, Fermi has found one that appears to have been born only millions of years ago.

Credit: NASA's Goddard Space Flight Center

By Max Planck Institute for Radio Astronomy, Bonn, Germany, Max Planck Society, Munich, Germany

Published : November 3, 2011

Paulo Freire from the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn and his collaborators have discovered the first gamma-ray pulsar in a globular cluster using the Large Area Telescope onboard the Fermi Gamma-ray Space Telescope. The pulsar, labeled J1823-3021A, is located in the globular cluster NGC 6624 in Sagittarius, not far from the direction to the galactic center. At a distance of approximately 27,000 light-years, it is also the most distant pulsar ever detected in gamma rays. Its extreme gamma-ray luminosity implies that it is the youngest millisecond pulsar discovered to date and that its magnetic field is much larger than previously predicted by pulsar recycling theories. It suggests the existence of a whole new population of such extreme objects forming at the same rate as the more normal millisecond pulsars.

When the cores of massive stars run out of nuclear fuel, they collapse catastrophically, a phenomenon known as a supernova. This spectacular event marks the birth of a neutron star: a ball of neutrons, a single giant atomic nucleus with a radius of about 6-10 miles (10-16 kilometers) and about half a million times the Earth's mass. A pulsar is a rapidly rotating neutron star for which we can detect pulsations (normally at radio, but now also at gamma-ray wavelengths), modulated by the rotation of the object — like a lighthouse. Ordinary pulsars have rotation periods between 16 milliseconds and 8 seconds. Even faster rotating are the so-called millisecond pulsars (MSPs), which can have rotation periods as fast as 1.4 milliseconds — corresponding to 43,000 rotations per minute. They are thought to have been spun up by accretion of matter from a companion star, a theory that is supported by the observation that roughly 80 percent of MSPs are found in binary systems.

MSPs possess extraordinary long-term rotational stability, which is in some cases similar to those of the best atomic clocks on Earth. They are basically giant flywheels in space where nothing disturbs their rotation. They are being used to test Einstein's general theory of relativity, search for gravitational waves, and study the properties of the super-dense matter at their center.

"We have discovered more than 100 of these objects in globular clusters with radio telescopes," said Freire. "Thanks to the sensitivity of the Large Area Telescope on the Fermi satellite, we have been able, for the first time, to see one of them in gamma rays."

Globular clusters are ancient swarms of hundreds of thousands of stars bound together by their mutual gravity. They produce many binary systems of the kind that lead to the formation of millisecond pulsars. One of these clusters is NGC 6624 in Sagittarius. At a distance of about 27,000 light-years, it is in the proximity of the galactic center. A total of six pulsars have been discovered in this globular cluster to date, three of these to be announced soon. The first pulsar found in NGC 6624 was J1823-3021A. With a rotation period of 5.44 milliseconds (11,000 rotations/minute), it is the most luminous radio pulsar found in a globular cluster to date. It has been timed since its discovery in 1990 with several large radio telescopes, in particular with the Lovell Telescope of the University of Manchester/England and with the radio telescope at Nançay/France.

"To our surprise, we found the pulsar to be extremely bright in gamma rays, as well," said Damien Parent from the Center for Earth Observing and Space Research. "Millisecond pulsars were not supposed to be that bright. This implies an unexpectedly high magnetic field for such a fast pulsar."

"This challenges our current theories for the formation of such objects," saud Michael Kramer from MPIfR. "We are currently investigating a number of possibilities. Nature might even be forming millisecond pulsars in a way we have not anticipated."

"Whichever way these anomalous pulsars are formed, one thing appears to be clear," said Freire. "At least in globular clusters, they are so young that they are probably forming at rates comparable to the large known population of normal millisecond pulsars."

Dwarf Galaxies could uncover the nature of Dark Matter

The circled cluster of stars is the dwarf galaxy Andromeda 29, which University of Michigan astronomers have discovered. The bright star within the circle is a foreground star within our own Milky Way galaxy. This image was obtained with the Gemini Multi-Object Spectrograph at the Gemini North Telescope in Hawaii. Credit: Gemini Observstory/AURA/Eric Bell

By University of Michigan, Ann Arbor

Published : November 7, 2011

In work that could help advance astronomers' understanding of dark matter, University of Michigan researchers have discovered two additional dwarf galaxies that appear to be satellites of Andromeda, the closest spiral galaxy to Earth.

Eric Bell and Colin Slater found Andromeda XXVIII and XXIX. They did it by using a tested star-counting technique on the newest data from the Sloan Digital Sky Survey, which has mapped more than a third of the night sky. They also used follow-up data from the Gemini North Telescope in Hawaii.

At 1.7 million light-years from Andromeda, these are two of the furthest satellite galaxies ever detected. Invisible to the naked eye, the galaxies are 100,000 times fainter than Andromeda and are barely visible even through large telescopes.

These astronomers set out looking for dwarf galaxies around Andromeda to help them understand how matter relates to dark matter, an invisible substance that doesn't emit or reflect light, but is believed to make up most of the universe's mass. Astronomers believe it exists because they can detect its gravitational effects on visible matter. With its gravity, dark matter is believed to be responsible for organizing visible matter into galaxies.

"These faint, dwarf, relatively nearby galaxies are a real battleground in trying to understand how dark matter acts at small scales," Bell said. "The stakes are high."

The prevailing hypothesis is that visible galaxies are all nestled in beds of dark matter, and each bed of dark matter has a galaxy in it.
For a given volume of universe, the predictions match observations of large galaxies.

"But it seems to break down when we get to smaller galaxies," Slater said. "The models predict far more dark matter halos than we observe galaxies. We don't know if it's because we're not seeing all of the galaxies or because our predictions are wrong."

"The exciting answer," Bell said, "would be that there just aren't that many dark matter halos. This is part of the grand effort to test that paradigm."

Next NASA Mission :The Nuclear Spectroscopic Telescope Array

Figure: NuSTAR (Credit: California Institute of Technology)

The NuSTAR mission will deploy the first focusing telescopes to image the sky in the high energy X-ray (6 - 79 keV) region of the electromagnetic spectrum. Our view of the universe in this spectral window has been limited because previous orbiting telescopes have not employed true focusing optics, but rather have used coded apertures that have intrinsically high backgrounds and limited sensitivity.

During a two-year primary mission phase, NuSTAR will map selected regions of the sky in order to:

(1) take a census of collapsed stars and black holes of different sizes by surveying regions surrounding the center of own Milky Way Galaxy and performing deep observations of the extragalactic sky;

(2) map recently-synthesized material in young supernova remnants to understand how stars explode and how elements are created; and

(3) understand what powers relativistic jets of particles from the most extreme active galaxies hosting supermassive black holes.

In addition to its core science program, NuSTAR will offer opportunities for a broad range of science investigations, ranging from probing cosmic ray origins to studying the extreme physics around collapsed stars to mapping microflares on the surface of the Sun. NuSTAR will also respond to targets of opportunity including supernovae and gamma-ray bursts.

The NuSTAR instrument consists of two co-aligned grazing incidence telescopes with specially coated optics and newly developed detectors that extend sensitivity to higher energies as compared to previous missions such as Chandra and XMM. After launching into orbit on a small rocket, the NuSTAR telescope extends to achieve a 10-meter focal length. The observatory will provide a combination of sensitivity, spatial, and spectral resolution factors of 10 to 100 improved over previous missions that have operated at these X-ray energies.



Figure: NuSTAR focal plane motherboard with one of the four CdZnTe detectors installed. NuSTAR will have two such units, providing for a total of two 4K high energy X-ray cameras.

NuSTAR has two detector units, each at the focus of one of the two co-aligned NuSTAR optics units. The optical units observe the same area of sky, and the two images are combined on the ground. The focal planes are each comprised of four 32×32 pixel Cadmium-Zinc-Tellurium (CdZnTe, or CZT) detectors manufactured by eV Products. CZT detectors are state-of-the-art room temperature semiconductors that are very efficient at turning high energy photons into electrons. The electrons are then digitally recorded using custom Application Specific Integrated Circuits (ASICs) designed by the NuSTAR Caltech Focal Plane Team.

A NASA Small Explorer (SMEX) mission, NuSTAR is currently in Phase C/D and is scheduled to launch into low-Earth equatorial orbit in February 2012.

Faster than Light Experiment : OPERA

CERN Neutrinos to Gran Sasso Underground Structures

Credit : CERN

Published : 3rd October, 2011

The Oscillation Project with Emulsion-tRacking Apparatus (OPERA) is an experiment to test the phenomenon of neutrino oscillations. It exploits CERN Neutrinos to Gran Sasso (CNGS), a high-intensity and high-energy beam of muon neutrinos produced at the CERN Super Proton Synchrotron in Geneva and pointing to the Laboratori Nazionali del Gran Sasso (LNGS) underground laboratory, 733 km (455 mi) away at Gran Sasso in central Italy (Abruzzo region). OPERA is located in Hall C of LNGS and is aimed at detecting for the first time the appearance of tau neutrinos from the oscillation of muon neutrinos during their 3 millisecond travel from Geneva to Gran Sasso. Tau particles resulting from the interaction of tau neutrinos will be observed in "bricks" of photographic emulsion films interleaved with lead plates. The apparatus contains about 150,000 bricks, for a total mass of 1300 tons, and is complemented by electronic detectors (trackers and spectrometers) and ancillary infrastructure. Its construction was completed in spring 2008 and the experiment is currently collecting data.

On 31 May 2010, OPERA researchers announced the observation of a first tau neutrino candidate event in a muon neutrino beam. In September 2011, CERN and OPERA announced that time of flight measurements made by their collaboration had indicated muon neutrinos traveling at faster than lightspeed. While acknowledging that such a measurement would be a major discovery if correct, many physicists,and the OPERA team itself, have expressed skepticism that OPERA's measurements are sufficiently free of error. Experimental groups such as the MINOS Experiment at Fermilab and the T2K experiment are planning to attempt to replicate the result, while others in the physics community search for any experimental errors which might account for it.

OPERA needs an intense and energetic beam of muon neutrinos traveling a distance of hundreds of kilometers to detect the appearance of oscillated tau neutrinos. A beam of this type is generated by collisions of accelerated protons with a graphite target after focusing the particles produced (pions and kaons in particular) in the desired direction. The products of their decays, muons and neutrinos, continue to travel in generally the same direction as the parent particle. Muon neutrinos produced in this way at CERN pass through the Earth's crust reaching OPERA after a 730 km journey.

OPERA is located in Hall C of the Gran Sasso underground labs. Construction started in 2003, and the apparatus was completed in summer 2008. The taus resulting from the interaction of tau neutrinos will be observed in "bricks" of photographic films (nuclear emulsion) interleaved with lead sheets. Each brick has an approximate weight of 8.3 kg and the two OPERA supermodules contain about 150,000 bricks arranged into parallel walls and interleaved with plastic scintillator counters. Each supermodule is followed by a magnetic spectrometer for momentum and charge identification of penetrating particles. During the data collection, a neutrino interaction is tagged in real time by the scintillators and the spectrometers, which also provide the location of the bricks where the neutrino interaction occurred. These bricks are extracted from the walls asynchronously with respect to the beam to allow for film development, scanning and for the topological and kinematic search of tau decays.

NASA Space Telescopes Reveal Secrets of Supermassive Black Hole

This image of the distant active galaxy Markarian 509 was taken in April 2007 with the Hubble Space Telescope's Wide Field Camera 2.

Credit: NASA, ESA, G. Kriss (STScI), and J. de Plaa (SRON Netherlands Institute for Space Research); Acknowledgment: B. Peterson (Ohio State University)

Published: 29th September, 2011

A fleet of spacecraft including NASA's Hubble Space Telescope has uncovered unprecedented details in the surroundings of a supermassive black hole. Observations reveal huge bullets of gas being driven away from the gravitational monster and a corona of very hot gas hovering above the disk of matter that is falling into the black hole.A team led by Jelle Kaastra of SRON Netherlands Institute for Space Research made use of data from ESA's XMM-Newton and INTEGRAL spacecraft (which study X-rays and gamma rays, respectively), the Hubble Space Telescope (for ultraviolet observations with the COS instrument), and NASA's Chandra (X-ray) Observatory and Swift (gamma-ray) satellites.

The black hole that the team chose to study lies at the heart of the galaxy Markarian 509 (Mrk 509), nearly 500 million light-years away. This black hole is colossal, containing 300 million times the mass of the Sun, and is growing more massive every day as it continues to feed on surrounding matter, which glows brightly as it forms a rotating disk around the black hole. Mrk 509 was chosen because it is known to vary in brightness, which indicates that the flow of matter is turbulent.

The above image of Mrk 509 was taken in April 2007 with Hubble's Wide Field Planetary Camera 2. But using a large number of telescopes that are sensitive to different wavelengths of light gave astronomers unprecedented coverage running from the infrared, through the visible, ultraviolet, X-rays, and into the gamma-ray band.The study is presented in a series of seven papers in the journal Astronomy and Astrophysics, with more expected to be published in coming months.

A method to detect the collision of stars with an elusive type of black hole

Princeton and New York University researchers have simulated the effect of a primordial black hole passing through a star. Primordial black holes are among the objects hypothesized to make up dark matter — the invisible substance thought to constitute much of the universe — and astronomers could use the researchers' model to finally observe the elusive black holes. This image illustrates the resulting vibration waves as a primordial black hole (white dots) passes through the center of a star. The different colors correspond to the density of the primordial black hole and strength of the vibration.

Credit: Tim Sandstrom

By Princeton University, Princeton, New Jersey

Published: September 22, 2011

Scientists looking to capture evidence of dark matter — the invisible substance thought to constitute much of the universe — may find a helpful tool in the recent work of researchers from Princeton University in New Jersey and New York University (NYU).

The team unveiled a ready-made method for detecting the collision of stars with an elusive type of black hole, which is on the short list of objects believed to make up dark matter. Such a discovery could serve as observable proof of dark matter and provide a much deeper understanding of the universe’s inner workings.

Researchers Shravan Hanasoge from Princeton and Michael Kesden from NYU simulated the visible result of a primordial black hole passing through a star. Theoretical remnants of the Big Bang, primordial black holes possess the properties of dark matter and are one of various cosmic objects thought to be the source of the mysterious substance, but they have yet to be observed.

If primordial black holes are the source of dark matter, the sheer number of stars in the Milky Way galaxy — roughly 100 billion — makes an encounter inevitable. Unlike larger black holes, a primordial black hole would not “swallow” the star, but instead cause noticeable vibrations on the star’s surface as it passes through.

Thus, as the number of telescopes and satellites probing distant stars in the Milky Way increases, so do the chances to observe a primordial black hole as it slides harmlessly through one of the galaxy’s billions of stars, Hanasoge said. The computer model developed by Hanasoge and Kesden can be used with these current solar-observation techniques to offer a more precise method for detecting primordial black holes than existing tools.

“If astronomers were just looking at the Sun, the chances of observing a primordial black hole are not likely, but people are now looking at thousands of stars,” Hanasoge said.

“There’s a larger question of what constitutes dark matter, and, if a primordial black hole were found, it would fit all the parameters — they have mass and force so they directly influence other objects in the universe, and they don’t interact with light. Identifying one would have profound implications for our understanding of the early universe and dark matter.”

Although dark matter has not been observed directly, galaxies are thought to reside in extended dark-matter halos based on documented gravitational effects of these halos on galaxies’ visible stars and gas. Like other proposed dark-matter candidates, primordial black holes are difficult to detect because they neither emit nor absorb light, stealthily traversing the universe with only subtle gravitational effects on nearby objects.

Because primordial black holes are heavier than other dark-matter candidates, however, their interaction with stars would be detectable by existing and future stellar observatories, Kesden said. When crossing paths with a star, a primordial black hole’s gravity would squeeze the star, and then, once the black hole passed through, cause the star’s surface to ripple as it snaps back into place.

“If you imagine poking a water balloon and watching the water ripple inside, that’s similar to how a star’s surface appears,” Kesden said.

“By looking at how a star’s surface moves, you can figure out what’s going on inside. If a black hole goes through, you can see the surface vibrate.”

Eyeing the Sun’s surface for hints of dark matter
Kesden and Hanasoge used the Sun as a model to calculate the effect of a primordial black hole on a star’s surface. Kesden, whose research includes black holes and dark matter, calculated the masses of a primordial black hole as well as the likely trajectory of the object through the Sun. Hanasoge, who studies seismology in the Sun, Earth, and stars, worked out the black hole’s vibrational effect on the Sun’s surface.

NASA’s Tim Sandstrom created video simulations of the researchers’ calculations using the Pleiades supercomputer at the Ames Research Center in California. One clip shows the vibrations of the Sun’s surface as a primordial black hole — represented by a white trail — passing through its interior. A second movie portrays the result of a black hole grazing the Sun’s surface.

Marc Kamionkowski from Johns Hopkins University in Baltimore, Maryland, said that the work serves as a toolkit for detecting primordial black holes, because Hanasoge and Kesden have provided a thorough and accurate method that takes advantage of existing solar observations.

“It’s been known that as a primordial black hole went by a star, it would have an effect, but this is the first time we have calculations that are numerically precise,” Kamionkowski said. “This is a clever idea that takes advantage of observations and measurements already made by solar physics. It’s like someone calling you to say there might be a million dollars under your front doormat. If it turns out to not be true, it cost you nothing to look. In this case, there might be dark matter in the data sets astronomers already have, so why not look?”

One significant aspect of Kesden and Hanasoge’s technique, Kamionkowski said, is that it narrows a significant gap in the mass that can be detected by existing methods of trolling for primordial black holes.

The search for primordial black holes has thus far been limited to masses too small to include a black hole, or so large that “those black holes would have disrupted galaxies in heinous ways we would have noticed,” Kamionkowski said. “Primordial black holes have been somewhat neglected, and I think that’s because there has not been a single, well-motivated idea of how to find them within the range in which they could likely exist.”

The current mass range in which primordial black holes could be observed was set based on previous direct observations of Hawking radiation — the emissions from black holes as they evaporate into gamma rays — as well as the bending of light around large stellar objects, Kesden said. The difference in mass between those phenomena, however, is enormous even in astronomical terms. Hawking radiation can only be observed if the evaporating black hole’s mass is less than 100 quadrillion grams. On the other end, an object must be larger than 100 septillion (24 zeroes) grams for light to visibly bend around it. The search for primordial black holes covered a swath of mass that spans a factor of 1 billion, Kesden said — similar to searching for an unknown object with a weight somewhere between that of a penny and a mining dump truck.

He and Hanasoge suggest a technique to give that range a much-needed trim and established more specific parameters for spotting a primordial black hole. The pair found through their simulations that a primordial black hole larger than 1 sextillion (21 zeroes) grams — roughly the mass of an asteroid — would produce a noticeable effect on a star’s surface.

“Now that we know primordial black holes can produce detectable vibrations in stars, we could try to look at a larger sample of stars than just our own Sun,” Kesden said.

“The Milky Way has 100 billion stars, so about 10,000 detectable events should be happening every year in our galaxy if we just knew where to look.”

A huge doughnut-shaped cloud of water vapor created by Enceladus

Water vapor and ice erupt from Saturn's moon Enceladus, the source of a newly discovered doughnut-shaped cloud around Saturn.

Credit: NASA/JPL/Space Science Institute

Published: September 22, 2011

Chalk up one more feat for Saturn's intriguing moon Enceladus. The small, dynamic moon spews out dramatic plumes of water vapor and ice — first seen by NASA's Cassini spacecraft in 2005. It possesses simple organic particles and may house liquid water beneath its surface. Its geyser-like jets create a gigantic halo of ice, dust, and gas around Enceladus that helps feed Saturn's E ring. Now, thanks again to those icy jets, Enceladus is the only moon in our solar system known to substantially influence the chemical composition of its parent planet.

In June, the European Space Agency (ESA) announced that its Herschel Space Observatory, which has important NASA contributions, had found a huge doughnut-shaped cloud, or torus, of water vapor created by Enceladus encircling Saturn. The torus is more than 373,000 miles (600,000 kilometers) across and about 37,000 miles (60,000 km) thick. It appears to be the source of water in Saturn's upper atmosphere.

Though it is enormous, the cloud had not been seen before because water vapor is transparent at most visible wavelengths of light, but Herschel could see the cloud with its infrared detectors. "Herschel is providing dramatic new information about everything from planets in our own solar system to galaxies billions of light-years away," said Paul Goldsmith from NASA's Jet Propulsion Laboratory in Pasadena, California.

The discovery of the torus around Saturn did not come as a complete surprise. NASA's Voyager and Hubble missions had given scientists hints of the existence of water-bearing clouds around Saturn. Then in 1997, ESA’s Infrared Space Observatory confirmed the presence of water in Saturn's upper atmosphere. NASA's Submillimeter Wave Astronomy Satellite also observed water emission from Saturn at far-infrared wavelengths in 1999.

While a small amount of gaseous water is locked in the warm, lower layers of Saturn's atmosphere, it can't rise to the colder, higher levels. To get to the upper atmosphere, water molecules must be entering Saturn's atmosphere from somewhere in space. But from where and how? Those were mysteries until now.

Build the model, and the data will come
The answer came by combining Herschel's observations of the giant cloud of water vapor created by Enceladus' plumes with computer models that researchers had already been developing to describe the behavior of water molecules in clouds around Saturn.

One of these researchers is Tim Cassidy from the University of Colorado, Boulder. "What's amazing is that the model, which is one iteration in a long line of cloud models, was built without knowledge of the observation,” said Cassidy. “Those of us in this small modeling community were using data from Cassini, Voyager, and the Hubble telescope, along with established physics. We weren't expecting such detailed 'images' of the torus, and the match between model and data was a wonderful surprise."

The results show that, though most of the water in the torus is lost to space, some of the water molecules fall and freeze on Saturn's rings, while a small amount — about 3 to 5 percent — gets through the rings to Saturn's atmosphere. This is just enough to account for the water that has been observed there.

Herschel's measurements combined with the cloud models also provided new information about the rate at which water vapor is erupting out of the dark fractures known as "tiger stripes" on Enceladus' southern polar region. Previous measurements by the Ultraviolet Imaging Spectrograph (UVIS) instrument aboard the Cassini spacecraft showed that the moon is ejecting about 440 pounds (200 kilograms) of water vapor every second.

"With the Herschel measurements of the torus from 2009 and 2010 and our cloud model, we were able to calculate a source rate for water vapor coming from Enceladus," said Cassidy. "It agrees very closely with the UVIS finding, which used a completely different method."

"We can see the water leaving Enceladus, and we can detect the end product — atomic oxygen — in the Saturn system," said Cassini UVIS science team member Candy Hansen from the Planetary Science Institute in Tucson, Arizona. "It's very nice with Herschel to track where it goes in the meantime."

While a small fraction of the water molecules inside the torus end up in Saturn's atmosphere, most are broken down into separate atoms of hydrogen and oxygen. "When water hangs out in the torus, it is subject to the processes that dissociate water molecules, first to hydrogen and hydroxide, and then the hydroxide dissociates into hydrogen and atomic oxygen," said Hansen. “This oxygen is dispersed through the Saturn system. Cassini discovered atomic oxygen on its approach to Saturn before it went into orbit insertion. At the time, no one knew where it was coming from. Now we do."

"The profound effect this little moon Enceladus has on Saturn and its environment is astonishing," said Hansen.

Total Eclipse: Dark of the Moon

The December 21, 2010, lunar eclipse dazzled viewers across North America. This image is a two-exposure combination taken in Mead, Colorado, by attaching a digital camera to a 4-inch telescope.
Photo by Richard McCoy

by Michael E. Bakich
Published: June 6, 2011

Don't get scared. This title is not from Hollywood Movies. The first lunar eclipse of 2011 occurs June 15. The timing and the placement of the Moon in its orbit does not favor the Western Hemisphere, however.

Skywatchers can see the entire event from the eastern half of Africa, the Middle East, central Asia, and western Australia. At mid-eclipse, the Moon will lie near the zenith for observers situated in Réunion or Mauritius in the Indian Ocean.

Observers throughout Europe will miss the early stages of the eclipse because they occur before moonrise. But except for northern Scotland and northern Scandinavia, Europeans with clear skies will see totality (when the Moon lies completely within Earth’s umbra).

Likewise, eastern Asia, eastern Australia, and New Zealand will miss the last stages of eclipse because they occur after moonset, but, like those in Europe, most inhabitants will see the total phase. Observers in eastern Brazil, Uruguay, and Argentina also will witness totality. Unfortunately, none of the eclipse will be visible from North America.

A lunar eclipse occurs when the Moon in its orbit passes into Earth’s shadow. Because the Sun isn’t a point of light, the shadow has two parts — the inner, darker umbra and the outer, lighter penumbra. If the entire Moon enters the umbra, the eclipse is total. If the umbra hides only part of our satellite, the eclipse is partial.

This eclipse’s umbral phase begins at 18h22m56s UT (2:22:56 p.m. EDT). As the Moon dips deeper into our planet’s shadow during the next hour or so, darkness gradually overtakes the brilliant orb.

Earth’s shadow takes almost exactly 1 hour to envelop the Moon. Totality begins at 19h22m30s UT (3:22:30 p.m. EDT).

The Moon won’t disappear from view, however. Some sunlight passing through Earth’s atmosphere falls on the lunar surface. The cleaner our atmosphere is, the “lighter” the eclipse will be. “Dark” eclipses generally occur after large volcanic eruptions when the atmosphere contains more dust.

What color will the Moon turn at mideclipse? During previous total eclipses, the Moon has appeared brown, orange, crimson, and brick red. Lunar eclipses exhibit a range of shades because sunlight passing through Earth’s atmosphere during totality becomes scattered and reddened. It’s this dim glow that fills Earth’s shadow and lights the eclipsed Moon. The sky certainly will grow darker, allowing the bright summer stars surrounding our nearest celestial neighbor to spring back to prominence.

Totality lasts 100 minutes, which is rather long. The last eclipse to exceed this duration was in July 2000. During totality, the Moon’s southern edge may appear slightly darker than its northern side. This disparity occurs because the Moon’s southern limb lies a bit closer to the center of Earth’s shadow. After totality ends at 21h02m42s UT (5:02:42 p.m. EDT), it takes the Moon another 60 minutes to leave Earth’s umbra.

Astronomy magazine Contributing Editor Ray Shubinski describes the upcoming eclipse as a missed opportunity: “It’s too bad that nobody in North America will see the eclipse. Luckily, we don’t have all that long to wait until the next one.”

The eclipse to which Shubinski refers will occur December 10. But it won’t be perfect, either. For North Americans, that eclipse will still be in progress as the Moon sets. The farther west you live, however, the larger fraction of the eclipse you will see before moonset. The entire event will be visible for inhabitants of Asia and Australia under clear skies.

NASA probes suggest magnetic bubbles reside at edge of solar system

Old and new views of the heliosheath. Red and blue spirals are the gracefully curving magnetic field lines of orthodox models. New data from Voyager add a magnetic froth (inset) to the mix.
Photo by NASA

By NASA Headquarters, Washington, D.C.
Published: June 9, 2011

While using a new computer model to analyze Voyager data, scientists found the Sun’s distant magnetic field is made up of bubbles approximately 100 million miles wide. The bubbles are created when magnetic field lines reorganize. The new model suggests the field lines are broken up into self-contained structures disconnected from the solar magnetic field. The findings are described in the June 9 edition of the Astrophysical Journal.

Like Earth, the Sun has a magnetic field with a north pole and a south pole. The field lines are stretched outward by the solar wind or a stream of charged particles emanating from the star that interacts with material expelled from others in our corner of the Milky Way galaxy.

The Voyager spacecraft, more than nine billion miles away from Earth, are traveling in a boundary region. In that area, the solar wind and magnetic field are affected by material expelled from other stars in our corner of the Milky Way galaxy.

“The Sun’s magnetic field extends all the way to the edge of the solar system,” said astronomer Merav Opher of Boston University. “Because the Sun spins, its magnetic field becomes twisted and wrinkled, a bit like a ballerina’s skirt. Far, far away from the Sun, where the Voyagers are, the folds of the skirt bunch up.”

Understanding the structure of the Sun’s magnetic field will allow scientists to explain how galactic cosmic rays enter our solar system and help define how our star interacts with the rest of the galaxy.

So far, much of the evidence for the existence of the bubbles originates from an instrument aboard the spacecraft that measures energetic particles. Investigators are studying more information and hoping to find signatures of the bubbles in the Voyager magnetic field data.

“We are still trying to wrap our minds around the implications of the findings,” said University of Maryland physicist Jim Drake, one of Opher’s colleagues.

A new class of stellar explosions

The four supernovae discovered by the Palomar Transient Factory, (from top to bottom) PTF09atu, PTF09cnd, PTF09cwl, and PTF10cwr, are shown both before (left) and after (right) explosion.
Photo by Caltech/Robert Quimby/Nature

By California Institute of Technology, Pasadena
Published: June 10, 2011

They’re bright and blue — and a bit strange. They’re a new type of stellar explosion that was recently discovered by a team of astronomers led by the California Institute of Technology (Caltech). Among the most luminous in the cosmos, these new kinds of supernovae could help researchers better understand star formation, distant galaxies, and what the early universe might have been like.

“We’re learning about a whole new class of supernovae that wasn’t known before,” said Robert Quimby, a Caltech postdoctoral scholar and lead author on the paper. In addition to finding four explosions of this type, the team also discovered that two previously known supernovae, whose identities had baffled astronomers, also belong to this new class.

Quimby first made headlines in 2007 when — as a graduate student at the University of Texas at Austin — he discovered what was then the brightest supernova ever found: 100 billion times brighter than the Sun and 10 times brighter than most other supernovae. Dubbed 2005ap, it was also a little odd. For one thing, its spectrum — the chemical fingerprint that tells astronomers what the supernova is made of, how far away it is, and what happened when it blew up — was unlike any seen before. It also showed no signs of hydrogen, which is commonly found in most supernovae.

At around the same time, astronomers using the Hubble Space Telescope discovered a mysterious supernova called SCP 06F6. This supernova also had an odd spectrum, though there was nothing that indicated this cosmic blast was similar to 2005ap.

Caltech's Shri Kulkarni, a co-author on the paper, recruited Quimby to become a founding member of the Palomar Transient Factory (PTF). The PTF is a project that scans the skies for flashes of light that weren’t there before — flashes that signal objects called transients, many of which are supernovae. As part of the PTF, Quimby and his colleagues used the 1.2-meter Samuel Oschin Telescope at Palomar Observatory to discover four new supernovae. After taking spectra with the 10-meter Keck telescopes in Hawaii, the 5.1-meter telescope at Palomar, and the 4.2-meter William Herschel Telescope in the Canary Islands, the astronomers discovered that all four objects had an unusual spectral signature.

Quimby then realized that if you slightly shifted the spectrum of 2005ap — the supernova he had found a couple of years earlier — it looked a lot like these four new objects. The team then plotted all the spectra together. “Boom — it was a perfect match,” he recalled.

The astronomers soon determined that shifting the spectrum of SCP 06F6 similarly aligned it with the others. In the end, it turned out that all six supernovae are siblings, and that they all have spectra that are very blue — with the brightest wavelengths shining in the ultraviolet.

According to Quimby, the two mysterious supernovae — 2005ap and SCP 06F6 — had looked different from one another because 2005ap was 3 billion light-years away while SCP 06F6 was 8 billion light-years away. More-distant supernovae have a stronger cosmological redshift, a phenomenon in which the expanding universe stretches the wavelength of the emitted light, shifting supernovae spectra toward the red end.

The four new discoveries, which had features similar to 2005ap and SCP 06F6, were at an intermediate distance, providing the missing link that connected the two previously unexplained supernovae. “That’s what was most striking about this — that this was all one unified class,” said Mansi Kasliwal, a Caltech graduate student and co-author on the paper.

Although astronomers now know these supernovae are related, no one knows much else. “We have a whole new class of objects that can’t be explained by any of the models we’ve seen before,” Quimby says. What the researchers do know about them is that they are bright and hot — 10,000 to 20,000 kelvins; that they are expanding rapidly at 6,000 miles per second (10,000 km/s); that they lack hydrogen; and that they take about 50 days to fade away — much longer than most supernovae, whose luminosity is often powered by radioactive decay. So there must be some other mechanism that’s making them so bright.

One possible model that would create an explosion with these properties involves a pulsating star about 90 to 130 times the mass of the Sun. The pulsations blow off hydrogen-free shells, and when the star exhausts its fuel and explodes as a supernova, the blast heats up those shells to the observed temperatures and luminosities.

A second model requires a star that explodes as a supernova but leaves behind what’s called a magnetar, a rapidly spinning dense object with a strong magnetic field. The rotating magnetic field slows the magnetar down as it interacts with the sea of charged particles that fills space, releasing energy. The energy heats the material that was previously blown off during the supernova explosion and can naturally explain the brightness of these events.

The newly discovered supernovae live in dim, small collections of a few billion stars called dwarf galaxies. (Our own Milky Way has 200 to 400 billion stars.) The supernovae, which are almost a hundred times brighter than their host galaxies, illuminate their environments like distant street lamps lighting up dark roads. They work as a kind of backlight, enabling astronomers to measure the spectrum of the interstellar gas that fills the dwarf galaxies in which the supernovae reside, and revealing each galaxy’s composition. Once an observed supernova fades a couple of months later, astronomers can directly study the dwarf galaxy — which would have remained undetected if it weren’t for the supernova.

These supernovae could also reveal what ancient stars might have been like because they most likely originate from stars around a hundred times more massive than the Sun — stars that would have been very similar to the first stars in the universe.

“It is really amazing how rich the night sky continues to be,” Kulkarni said. “In addition to supernovae, the Palomar Transient Factory is making great advances in stellar astronomy as well.”