A Bubble in Cygnus

Image Credit & Copyright: Keith Quattrocchi, Mel Helm

Adrift in the rich star fields of the constellation Cygnus, this lovely, symmetric bubble nebula was only recently recognized and may not yet appear in astronomical catalogs.

In fact, amateur astronomer Dave Jurasevich identified it as a nebula on July 6 in his images of the complex Cygnus region that included the Crescent Nebula (NGC 6888). He subsequently notified the International Astronomical Union.

Only eleven days later the same object was independently identified by Mel Helm at Sierra Remote Observatories, imaged by Keith Quattrocchi and Helm, and also submitted to the IAU as a potentially unknown nebula.

Their final composite image is seen here, including narrow-band image data that highlights the nebula's delicate outlines. What is the newly recognized bubble nebula? Like the Crescent Nebula itself, this cosmic bubble could be blown by winds from a massive Wolf-Rayet star, or it could be a spherically-shaped planetary nebula, a final phase in the life of a sun-like star.

Astronomers detect matter torn apart by black hole

Tuesday, November 18, 2008

ESO PR Photo 41c/08
Credit: ESO/APEX/2MASS/A. Eckart et al. , ESO/L. Calçada

About this image:
Left:- This is a colour composite image of the central region of our Milky Way galaxy, about 26 000 light years from Earth. Giant clouds of gas and dust are shown in blue, as detected by the LABOCA instrument on the Atacama Pathfinder Experiment (APEX) telescope at submillimetre wavelengths (870 micron). The image also contains near-infrared data from the 2MASS project at K-band (in red), H-band (in green), and J-band (in blue). The image shows a region approximately 100 light-years wide.

Rigth:- This series of three images shows an artist’s impression of a bright “blob” of gas in the disk of material surrounding the black hole in the centre of our Galaxy, Sagittarius A*. This blob of material is responsible for the flares detected by the researchers. As the blob orbits the black hole, it is stretched out, and this expansion over time causes the delay between flares being detected at near-infrared wavelengths (with the VLT) and at submillimetre wavelengths (with APEX).

VLT and APEX team up to study flares from the black hole at the Milky Way's core

Astronomers have used two different telescopes simultaneously to study the violent flares from the supermassive black hole in the centre of the Milky Way. They have detected outbursts from this region, known as Sagittarius A*, which reveal material being stretched out as it orbits in the intense gravity close to the central black hole.

The team of European and US astronomers used ESO's Very Large Telescope (VLT) and the Atacama Pathfinder Experiment (APEX) telescope, both in Chile, to study light from Sagittarius A* at near-infrared wavelengths and the longer submillimetre wavelengths respectively. This is the first time that astronomers have caught a flare with these telescopes simultaneously. The telescopes' location in the southern hemisphere provides the best vantage point for studying the Galactic Centre.

"Observations like this, over a range of wavelengths, are really the only way to understand what's going on close to the black hole," says Andreas Eckart of the University of Cologne, who led the team.

Sagittarius A* is located at the centre of our own Milky Way Galaxy at a distance from Earth of about 26 000 light-years. It is a supermassive black hole with a mass of about four million times that of the Sun. Most, if not all, galaxies are thought to have a supermassive black hole in their centre.

"Sagittarius A* is unique, because it is the nearest of these monster black holes, lying within our own galaxy," explains team member Frederick K. Baganoff of the Massachusetts Institute of Technology (MIT) in Cambridge, USA. "Only for this one object can our current telescopes detect these relatively faint flares from material orbiting just outside the event horizon."

The emission from Sagittarius A* is thought to come from gas thrown off by stars, which then orbits and falls into the black hole.

Making the simultaneous observations required careful planning between teams at the two telescopes. After several nights waiting at the two observatory sites, they struck lucky.

"At the VLT, as soon as we pointed the telescope at Sagittarius A* we saw it was active, and getting brighter by the minute. We immediately picked up the phone and alerted our colleagues at the APEX telescope," says Gunther Witzel, a PhD student from the University of Cologne.

Macarena García-Marín, also from Cologne, was waiting at APEX, where the observatory team had made a special effort to keep the instrument on standby. "As soon as we got the call we were very excited and had to work really fast so as not to lose crucial data from Sagittarius A*. We took over from the regular observations, and were in time to catch the flares," she explains.

Over the next six hours, the team detected violently variable infrared emission, with four major flares from Sagittarius A* . The submillimetre-wavelength results also showed flares, but, crucially, this occurred about one and a half hours after the infrared flares.

The researchers explain that this time delay is probably caused by the rapid expansion, at speeds of about 5 million km/h, of the clouds of gas that are emitting the flares. This expansion causes changes in the character of the emission over time, and hence the time delay between the infrared and submillimetre flares.

Although speeds of 5 million km/h may seem fast, this is only 0.5% of the speed of light. To escape from the very strong gravity so close to the black hole, the gas would have to be travelling at half the speed of light – 100 times faster than detected – and so the researchers believe that the gas cannot be streaming out in a jet. Instead, they suspect that a blob of gas orbiting close to the black hole is being stretched out, like dough in a mixing bowl, and this is causing the expansion.

The simultaneous combination of the VLT and APEX telescopes has proved to be a powerful way to study the flares at multiple wavelengths. The team hope that future observations will let them prove their proposed model, and discover more about this mysterious region at the centre of our Galaxy.

Notes for Editors

Sagittarius A* is a compact object located at the centre of our own Milky Way Galaxy, at a distance of about 26 000 light-years from Earth. In recent years, observations of stars orbiting in its strong gravitational grip have convincingly proven that Sagittarius A* must be a supermassive black hole with a mass of about four million times that of the Sun.

The members of the international team who did this research are: A. Eckart (University of Cologne, Germany), R. Schödel (Instituto de Astrofísica de Andalucía - CSIC, Spain), M. García-Marín (University of Cologne, Germany), G. Witzel (University of Cologne, Germany), A. Weiss (MPIfR, Germany), F. K. Baganoff (MIT, USA), M. R. Morris (University of California, USA), T. Bertram (University of Cologne, Germany), M. Dovčiak (Astronomical Institute of the Academy of Sciences of the Czech Republic), D. Downes (IRAM, France), W.J. Duschl (Christian-Albrechts-Universität, Germany), V. Karas (Astronomical Institute of the Academy of Sciences of the Czech Republic), S. König (University of Cologne, Germany), T. P. Krichbaum (MPIfR, Germany), M. Krips (Harvard-Smithsonian Center for Astrophysics, USA), D. Kunneriath (University of Cologne, Germany), R.-S. Lu (MPIfR, Germany), S. Markoff (Astronomical Institute 'Anton Pannekoek', Netherlands), J. Mauerhan (University of California, USA), L. Meyer (University of California, USA), J. Moultaka (LATT, France), K. Mužić (University of Cologne, Germany), F. Najarro (Centro de Astro Biologia, Madrid, Spain), J.-U. Pott (University of California, USA), K. F. Schuster (IRAM, France), L. O. Sjouwerman (NRAO, USA), C. Straubmeier (University of Cologne, Germany), C. Thum (IRAM, France), S. Vogel (University of Maryland, USA), H. Wiesemeyer (IRAM, Spain), M. Zamaninasab (University of Cologne, Germany), J. A. Zensus (MPIfR, Germany)

XMM-Newton and Integral clues on magnetic powerhouses

Credits: © 2008 Sky & Telescope: Gregg Dinderman

X-ray and gamma-ray data from ESA’s XMM-Newton and Integral orbiting observatories has been used to test, for the first time, the physical processes that make magnetars, an atypical class of neutron stars, shine in X-rays.

Neutron stars are remnants of massive stars (10-50 times as massive as our Sun) that have collapsed on to themselves under their own weight. Made almost entirely of neutrons (subatomic particles with no electric charge), these stellar corpses concentrate more than the mass of our Sun within a sphere about 20 km in diameter.

They are so compact that a teaspoon of neutron star stuff would weigh about one hundred million tons. Two other physical properties characterise a neutron star: their fast rotation and strong magnetic field.

Magnetars form a class of neutron stars with ultra-strong magnetic fields. With magnetic fields a thousand times stronger than that of ordinary neutron stars, they are the strongest known magnets in the cosmos.

In comparison, one would need 10 million million commonly-used hand magnets to generate a comparable magnetic field (most media used for data storage, for example, would be erased instantly if exposed to a magnetic field a mere million million times weaker).

So far, about 15 magnetars have been found. Five of them are known as soft gamma repeaters, or SGRs, because they sporadically release large, short bursts (lasting about 0.1 s) of low energy (soft) gamma rays and hard X-rays. The rest, about 10, are associated with anomalous X-ray pulsars, or AXPs. Although SGRs and AXPs were first thought to be different objects, we now know that they share many properties and that their activity is sustained by their strong magnetic fields.

Magnetars are different from ‘ordinary’ neutron stars because their internal magnetic field is thought to be strong enough to twist the stellar crust. Like in a circuit fed by a gigantic battery, this twist produces currents in the form of electron clouds which flow around the star. These currents interact with the radiation coming from the stellar surface, producing the X-rays.

Until now, scientists could not test their predictions, because it is not possible to produce such ultra-strong magnetic fields in laboratories on Earth.

To understand this phenomenon, a team led by Dr Nanda Rea from the University of Amsterdam used XMM-Newton and Integral data to search for these dense electron clouds around all known magnetars, for the first time.

Rea’s team found evidence that large electron currents do actually exist, and were able to measure the electron density which is a thousand times stronger than in a ‘normal’ pulsar. They have also measured the typical velocity at which the electron currents flow. With it, scientists have now established a link between an observed phenomenon and an actual physical process, an important clue in the puzzle of understanding these celestial objects.

The team is now working hard to develop and test more detailed models on the same line, to fully understand the behaviour of matter under the influence of such strong magnetic fields.

Notes for editors:

The team includes Dr Silvia Zane, from University College London, Prof. Roberto Turolla from the University of Padua, Prof. Maxim Lyutikov from Purdue University, and Dr Diego Gotz from CEA-Saclay.

The results appear in ‘Resonant cyclotron scattering in magnetars’ emission’, by N. Rea, S. Zane, R. Turolla, M. Lyutikov and D. Gotz, published in the Astrophysical Journal on 20 October 2008.

The XMM-Newton science teams are based in several European and US institutes, grouped into three instrument teams and the XMM-Newton Survey Science Centre (SSC). Science operations are managed at ESA’s European Space Astronomy Centre (ESAC), at Villanueva de la Cañada near Madrid, Spain. Spacecraft operations are managed at ESA’s European Space Operations Centre (ESOC) in Darmstadt, Germany.

Cassini Finds Mysterious New Aurora on Saturn

Wednesday, November 12, 2008

Saturn's Polar Aurora
Credit: NASA/JPL/University of Arizona

This image of the northern polar region of Saturn shows both the aurora and underlying atmosphere, seen at two different wavelengths of infrared light as captured by NASA's Cassini spacecraft.

Energetic particles, crashing into the upper atmosphere cause the aurora, shown in blue, to glow brightly at 4 microns (six times the wavelength visible to the human eye). The image shows both a bright ring, as seen from Earth, as well as an example of bright auroral emission within the polar cap that had been undetected until the advent of Cassini. This aurora, which defies past predictions of what was expected, has been observed to grow even brighter than is shown here. Silhouetted by the glow (cast here to the color red) of the hot interior of Saturn (clearly seen at a wavelength of 5 microns, or seven times the wavelength visible to the human eye) are the clouds and haze that underlie this auroral region. For a similar view of the region beneath the aurora see Saturn's North Pole Hexagon and Aurora.

This image is a composite captured with Cassini's visual and infrared mapping spectrometer.

The aurora image was taken in the near-infrared on Nov. 10, 2006, from a distance of 1,061,000 kilometers (659,000 miles), with a phase angle of 157 degrees and a sub-spacecraft planetocentric latitude of 52 degrees north. The image of the clouds was obtained by Cassini on June 15, 2008, from a distance of 602,000 kilometers (374,000 miles) and a sub-spacecraft planetocentric latitude of 73 degrees north.

Saturn has its own unique brand of aurora that lights up the polar cap, unlike any other planetary aurora known in our solar system. This odd aurora revealed itself to one of the infrared instruments on NASA's Cassini spacecraft.

"We've never seen an aurora like this elsewhere," said Tom Stallard, a scientist working with Cassini data at the University of Leicester, England. Stallard is lead author of a paper that appears in the Nov. 13 issue of the journal Nature. "It's not just a ring of auroras like those we've seen at Jupiter or Earth. This aurora covers an enormous area across the pole. Our current ideas on what forms Saturn's aurora predict that this region should be empty, so finding such a bright aurora here is a fantastic surprise."Auroras are caused by charged particles streaming along the magnetic field lines of a planet into its atmosphere. Particles from the sun cause Earth's auroras. Many, but not all, of the auroras at Jupiter and Saturn are caused by particles trapped within the magnetic environments of those planets.

Jupiter's main auroral ring, caused by interactions internal to Jupiter's magnetic environment, is constant in size. Saturn's main aurora, which is caused by the solar wind, changes size dramatically as the wind varies. The newly observed aurora at Saturn, however, doesn't fit into either category.

"Saturn's unique auroral features are telling us there is something special and unforeseen about this planet's magnetosphere and the way it interacts with the solar wind and the planet's atmosphere," said Nick Achilleos, Cassini scientist on the Cassini magnetometer team at the University College London. "Trying to explain its origin will no doubt lead us to physics which uniquely operates in the environment of Saturn."

The new infrared aurora appears in a region hidden from NASA's Hubble Space Telescope, which has provided views of Saturn's ultraviolet aurora. Cassini observed it when the spacecraft flew near Saturn's polar region. In infrared light, the aurora sometimes fills the region from around 82 degrees north all the way over the pole. This new aurora is also constantly changing, even disappearing within a 45 minute-period.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The visual and infrared mapping spectrometer team is based at the University of Arizona, Tucson.

APEX reveals glowing stellar nurseries

Glowing stellar nurseries.
ESO PR Photo 40/08
Credit: ESO/APEX/DSS2/SuperCosmos

Illustrating the power of submillimetre-wavelength astronomy, an APEX image reveals how an expanding bubble of ionised gas about ten light-years across is causing the surrounding material to collapse into dense clumps that are the birthplaces of new stars. Submillimetre light is the key to revealing some of the coldest material in the Universe, such as these cold, dense clouds.

The region, called RCW120, is about 4200 light years from Earth, towards the constellation of Scorpius. A hot, massive star in its centre is emitting huge amounts of ultraviolet radiation, which ionises the surrounding gas, stripping the electrons from hydrogen atoms and producing the characteristic red glow of so-called H-alpha emission.

As this ionised region expands into space, the associated shock wave sweeps up a layer of the surrounding cold interstellar gas and cosmic dust. This layer becomes unstable and collapses under its own gravity into dense clumps, forming cold, dense clouds of hydrogen where new stars are born. However, as the clouds are still very cold, with temperatures of around -250˚ Celsius, their faint heat glow can only be seen at submillimetre wavelengths. Submillimetre light is therefore vital in studying the earliest stages of the birth and life of stars.

The submillimetre-wavelength data were taken with the LABOCA camera on the 12-m Atacama Pathfinder Experiment (APEX) telescope, located on the 5000 m high plateau of Chajnantor in the Chilean Atacama desert. Thanks to LABOCA's high sensitivity, astronomers were able to detect clumps of cold gas four times fainter than previously possible. Since the brightness of the clumps is a measure of their mass, this also means that astronomers can now study the formation of less massive stars than they could before.

The plateau of Chajnantor is also where ESO, together with international partners, is building a next generation submillimetre telescope, ALMA, the Atacama Large Millimeter/submillimeter Array. ALMA will use over sixty 12-m antennas, linked together over distances of more than 16 km, to form a single, giant telescope.

APEX is a collaboration between the Max-Planck-Institute for Radio Astronomy (MPIfR), the Onsala Space Observatory (OSO) and ESO. The telescope is based on a prototype antenna constructed for the ALMA project. Operation of APEX at Chajnantor is entrusted to ESO.

Dusty Shock Waves Generate Planet Ingredients

Quartz-like Crystals Found in Planetary Disks
Credit: NASA/JPL-Caltech

Shock waves around dusty, young stars might be creating the raw materials for planets, according to new observations from NASA's Spitzer Space Telescope.

The evidence comes in the form of tiny crystals. Spitzer detected crystals similar in make-up to quartz around young stars just beginning to form planets. The crystals, called cristobalite and tridymite, are known to reside in comets, in volcanic lava flows on Earth, and in some meteorites that land on Earth.

Astronomers already knew that crystallized dust grains stick together to form larger particles, which later lump together to form planets. But they were surprised to find cristobalite and tridymite crystals. What's so special about these particular crystals? They require flash heating events, such as shock waves, to form.

The findings suggest that the same kinds of shock waves that cause sonic booms from speeding jets are responsible for creating the stuff of planets throughout the universe.

"By studying these other star systems, we can learn about the very beginnings of our own planets 4.6 billion years ago," said William Forrest of the University of Rochester, N.Y. "Spitzer has given us a better idea of how the raw materials of planets are produced very early on." Forrest and University of Rochester graduate student Ben Sargent led the research, to appear in the Astrophysical Journal.

Planets are born out of swirling pancake-like disks of dust and gas that surround young stars. They start out as mere grains of dust swimming around in a disk of gas and dust, before lumping together to form full-fledged planets. During the early stages of planet development, the dust grains crystallize and adhere together, while the disk itself starts to settle and flatten. This occurs in the first millions of years of a star's life.

When Forrest and his colleagues used Spitzer to examine five young planet-forming disks about 400 light-years away, they detected the signature of silica crystals. Silica is made of only silicon and oxygen and is the main ingredient in glass. When melted and crystallized, it can make the large hexagonal quartz crystals often sold as mystical tokens. When heated to even higher temperatures, it can also form small crystals like those commonly found around volcanoes.

It is this high-temperature form of silica crystals, specifically cristobalite and tridymite, that Forrest's team found in planet-forming disks around other stars for the first time. "Cristobalite and tridymite are essentially high-temperature forms of quartz," said Sargent. "If you heat quartz crystals, you'll get these compounds."

In fact, the crystals require temperatures as high as 1,220 Kelvin (about 1,740 degrees Fahrenheit) to form. But young planet-forming disks are only about 100 to 1,000 Kelvin (about minus 280 degrees Fahrenheit to 1,340 Fahrenheit) -- too cold to make the crystals. Because the crystals require heating followed by rapid cooling to form, astronomers theorized that shock waves could be the cause.

Shock waves, or supersonic waves of pressure, are thought to be created in planet-forming disks when clouds of gas swirling around at high speeds collide. Some theorists think that shock waves might also accompany the formation of giant planets.

The findings are in agreement with local evidence from our own solar system. Spherical pebbles, called chondrules, found in ancient meteorites that fell to Earth are also thought to have been crystallized by shock waves in our solar system's young planet-forming disk. In addition, NASA's Stardust mission found tridymite minerals in comet Wild 2.

Other authors of the paper include C. Tayrien, M.K. McClure, A.R. Basu, P. Mano, Dan Watson, C.J. Bohac, K.H. Kim and J.D. Green of the University of Rochester; A Li of the University of Missouri, Columbia; E. Furlan of NASA's Jet Propulsion Laboratory, Pasadena, Calif., and G.C. Sloan of Cornell University, Ithaca, N.Y.

JPL manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology, also in Pasadena. Caltech manages JPL for NASA. Spitzer's infrared spectrograph, which made the observations, was built by Cornell University, Ithaca, N.Y. Its development was led by Jim Houck of Cornell.

Our Galaxy's Central Molecular Zone

Credit: A. Ginsburg (U. Colorado - Boulder) et al.,
BGPS Team, GLIMPSE II Team

Monday, November 10, 2008

The central region of our Milky Way Galaxy is a mysterious and complex place. Pictured here in radio and infrared light, the galaxy's central square degree is highlighted in fine detail. The region is known as the Central Molecular Zone.

While much of the extended emission is due to dense gas laced with molecules, also seen are emission nebulas lit up by massive young stars, glowing supernova remnants, and the curving Galactic Center Radio Arc in purple. T

he identity and root cause for many other features remains unknown. Besides a massive black hole named Sgr A*, the Galactic Center houses the galaxy's most active star forming region. This image is not just interesting scientifically. It's esthetic beauty won first prize this year in the AUI/NRAO Image Contest.

Two Black Holes Dancing

Credit: X-ray: NASA/CXC/AIfA/D.Hudson & T.Reiprich et al.;
Radio: NRAO/VLA/NRL

This composite X-ray (blue)/radio (pink) image of the galaxy cluster Abell 400 shows radio jets immersed in a vast cloud of multimillion degree X-ray emitting gas that pervades the cluster.

November 09, 2008

The jets emanate from the vicinity of two supermassive black holes (bright spots in the image). These black holes are in the dumbbell galaxy NGC 1128,which has produced the giant radio source, 3C 75.

The peculiar dumbbell structure of this galaxy is thought to be due to two large galaxies that are in the process of merging. Such mergers are common in the relatively congested environment of galaxy clusters. An alternative hypothesis is that the apparent structure is the result of a coincidence in time when the two galaxies are passing one another, like ships in the cosmic sea.

Careful analysis of the recent Chandra and radio data on 3C 75 indicates that the galaxies and their supermassive black holes are indeed bound together by their mutual gravity. By using the shape and direction of the radio jets, astronomers were able to determine the direction of the motion of the black holes. The swept-back appearance of the radio jets is produced by the rapid motion of the galaxy through the hot gas of the cluster, in much the same way that a motorcyclist's scarf is swept back while speeding down the road.

The binary black holes in 3C 75 are about 25,000 light years apart. They are likely at an earlier stage in their evolution than the pair found in NGC 6240, which are about 3,000 light years apart. Computer simulations indicate that binary supermassive black holes gradually spiral toward each other until they coalesce to form a single, more massive black hole, accompanied by an enormous burst of gravitational waves.

These gravitational waves would spread through the Universe and produce ripples in the fabric of space, which would appear as minute changes in the distance between any two points. Sensitive gravitational wave detectors scheduled to be operational in the next decade could detect one of these events, which are estimated to occur several times each year in the observable Universe.

Crab Nebula: Fingers, Loops and Bays in The Crab Nebula

Credit: NASA/CXC/SAO/F.Seward et al

This image gives the first clear view of the faint boundary of the Crab Nebula's X-ray-emitting pulsar wind nebula.

The nebula is powered by a rapidly rotating, highly magnetized neutron star, or pulsar (white dot near the center). The combination of rapid rotating and strong magnetic field generates an intense electromagnetic field that creates jets of matter and anti-matter moving away from the north and south poles of the pulsar, and an intense wind flowing out in the equatorial direction.

The inner X-ray ring is thought to be a shock wave that marks the boundary between the surrounding nebula and the flow of matter and antimatter particles from the pulsar. Energetic electrons and positrons (antielectrons) move outward from this ring to brighten the outer ring and produce an extended X-ray glow.

The fingers, loops, and bays in the image all indicate that the magnetic field of the nebula and filaments of cooler matter are controlling the motion of the electrons and positrons. The particles can move rapidly along the magnetic field and travel several light years before radiating away their energy. In contrast, they move much more slowly perpendicular to the magnetic field, and travel only a short distance before losing their energy.

This effect can explain the long, thin, fingers and loops, as well as the sharp boundaries of the bays. The conspicuous dark bays on the lower right and left are likely due to the effects of a toroidal magnetic field that is a relic of the progenitor star.

Cygnus Trio

Credit & Copyright: J-P Metsävainio (Astro Anarchy)

Friday, November 07, 2008

In this colorful mosaic, filaments of gas and dust span some 9 degrees across central Cygnus, a nebula rich constellation along the northern Milky Way.

A trio of nebulae with popular names highlights the beautiful skyscape - the Butterfly, the Crescent, and the Tulip.
At left, the Butterfly Nebula (IC 1318), lies near bright star Gamma Cygni. The Butterfly's expansive, glowing, wing-shaped gas clouds are divided by a dark dust lane.
Near center, the Crescent Nebula (NGC 6888) is more compact, a cosmic bubble with a bright edge blown by winds from a massive Wolf-Rayet star.
On the right is the Tulip Nebula (Sh2-101), a small emission region shaped like a blossoming flower viewed from the side.

All are within a few thousand light-years of the Sun in the Orion spiral arm of our galaxy. The gorgeous mosaic is presented in false color, constructed from image data recorded through narrow band filters.

The range of colors was created by a mapping of emission from hydrogen, sulfur and oxygen atoms in the nebula to red, green, and blue hues.

The Cosmic Web - NGC 2070

The Cosmic Web - NGC 2070 by Joseph Brimacombe

Thursday, November 06, 2008

Just one glance at this incredible visage is enough to make you do a double take. This intricate net of nebular mists is known as 30 Doradus, or even more commonly as the "Tarantula", but no space spider created this web. No, sir. What spun out these gossamer strands of HII silk is one of the largest and most active star forming regions known to our local galaxy group…

When Nicolas Louis de Lacaille first saw it in 1751 through his half-inch spyglass, he knew it was something different. He wrote down that it was nebular in nature, without stars and said; "It resembles the nucleus of a small comet." Too bad he didn't realize what he was really looking at, for Lacaille was a huge fan of all things science. What he couldn't see with his primitive telescope is there really is a cluster of stars at the heart of this web… A very compact cluster stars known as R136a. And in its midst? Twelve stars… twelve very massive and luminous stars almost exclusively of spectral type O3. Even at a distance of 180,000 light years these stars light up this nebula so brightly that if it were as close to Earth as the Orion Nebula, it would cast shadows on the night.

So what else lay hidden in the 1000 light year expanse of the cosmic web? Look beyond what you can see in visible light and think like a spider… Try infra-red. With the eyes of the Spitzer Space Telescope aimed towards NGC 2070, scientists could penetrate the dust clouds throughout the Tarantula to reveal previously hidden sites of star formation. Within the luminescent nebula, holes began to appear. These voids are created by highly energetic winds spewing out from the massive stars in the central star cluster. Like the intricate designs woven by the spider, the structures at the edges of these voids are particularly interesting. Dense pillars of gas and dust, sculpted by the stellar radiation, will be the birthplace of future generations of stars!
But like the spider web… It's a place of death, too.

In 1987 one of the closest supernova events ever to occur near Earth happened in the outskirts of the Tarantula Nebula. The light from the supernova reached Earth on February 23, 1987 and not.since 1604 had humankind been witness to such an event. Even though we were witnessing something that occurred 168,000 years in the past, those X-ray and radio emission were still just as bright as the day the highly energetic electrons and particles spewed into the interstellar medium upon the explosive death of the progenitor star. Oh, there is skeletons in the web, too. Older and weaker supernovae remnants are scattered about, their signatures as faint as the imprint of a fallen leaf that has long blown away. This "Cosmic Web" is home to many supergiant stars. At any moment, a snapshot of any dense region of supergiant stars will show a mixture of newborn stars and supernovae, the signature of stars who those that have lived fast and died young.

The Bullet Cluster: Searching for Primordial Antimatter

Credit: X-ray: NASA/CXC/CfA/M.Markevitch et al.;
Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.

This view of the Bullet Cluster, located about 3.8 billion light years from Earth, combines an image from NASA's Chandra X-ray Observatory with optical data from the Hubble Space Telescope and the Magellan telescope in Chile. This cluster, officially known as 1E 0657-56, was formed after the violent collision of two large clusters of galaxies. It has become an extremely popular object for astrophysical research, including studies of the properties of dark matter and the dynamics of million-degree gas.



llustration of Antimatter/Matter Annihilation.
Credit(NASA/CXC/M. Weiss)


In the latest research, the Bullet Cluster has been used to search for the presence of antimatter leftover from the very early Universe. Antimatter is made up of elementary particles that have the same masses as their corresponding matter counterparts - protons, neutrons and electrons - but the opposite charges and magnetic properties.

The optical image shows the galaxies in the Bullet Cluster and the X-ray image (red) reveals how much hot gas has collided. If some of the gas from either cluster has particles of antimatter, then there will be annihilation between the matter and antimatter and the X-rays will be accompanied by gamma rays.

The observed amount of X-rays from Chandra and the non-detection of gamma rays from NASA's Compton Gamma Ray Observatory show that the antimatter fraction in the Bullet Cluster is less than three parts per million. Moreover, simulations of the Bullet Cluster merger show that these results rule out any significant amounts of antimatter over scales of about 65 million light years, an estimate of the original separation of the two colliding clusters.

'Ghost of Mirach' Materializes in Space Telescope Image

Credit: NASA/JPL-Caltech/DSS

NASA's Galaxy Evolution Explorer has lifted the veil off a ghost known to haunt the local universe, providing new insight into the formation and evolution of galaxies.

The eerie creature, called NGC 404, is a type of galaxy known as "lenticular." Lenticular galaxies are disk-shaped, with little ongoing star formation and no spiral arms. NGC 404 is the nearest example of a lenticular galaxy, and therefore of great interest. But it lies hidden in the glare from a red giant star called Mirach. For this reason, NGC 404 became known to astronomers as the "Ghost of Mirach."

When the Galaxy Evolution Explorer spied the galaxy in ultraviolet light, a spooky ring materialized.

"We thought this celestial ghost was essentially dead, but we've been able to show that it has an extended ring of new stars. The galaxy has a hybrid character in which the well-known, very old stellar population tells only part of the story," said David Thilker of Johns Hopkins University in Baltimore. "It's like the living dead."

Thilker and members of the Galaxy Evolution Explorer team spotted the Ghost of Mirach in images taken during the space telescope's all-sky survey. The Galaxy Evolution Explorer is a relatively low-cost NASA mission, launched in 2003, with an ambitious charge to survey the entire visible sky in ultraviolet light, a job never before accomplished. Because Earth's atmosphere absorbs ultraviolet photons -- a good thing for us living creatures who are susceptible to the damaging light -- ultraviolet telescopes must operate from space.

The first images of the Ghost of Mirach taken by the Galaxy Evolution Explorer hinted at a surrounding ultraviolet-bright extended structure. Subsequent, longer exposure observations indeed show that the lenticular galaxy is surrounded by a clumpy, never-before-seen ring of stars.

What is this mysterious ultraviolet ring doing around an otherwise nondescript lenticular galaxy? As it turns out, previous imaging with the National Science Foundation's Very Large Array radio telescope in New Mexico had discovered a gaseous ring of hydrogen that matches the ultraviolet ring observed by the Galaxy Evolution Explorer. The authors of this Very Large Array study attributed the gas ring to a violent collision between NGC 404 and a small neighboring galaxy 900 million years ago.

The ultraviolet observations demonstrate that, when the hydrogen from the collision settled into the plane of the lenticular galaxy, stars began to form in a ghostly ring. Young, relatively hot stars forming in stellar clusters sprinkled throughout NGC 404's ring give off the ultraviolet light that the Galaxy Evolution Explorer was able to see.

"Before the Galaxy Evolution Explorer image, NGC 404 was thought to contain only very old and evolved red stars distributed in a smooth elliptical shape, suggesting a galaxy well into its old age and no longer evolving significantly," said Mark Seibert of the Observatories of the Carnegie Institution of Washington in Pasadena, Calif. "Now we see it has come back to life, to grow once again."

"The Ghost of Mirach has been lucky enough to get a new lease on life through the rejuvenating, chance merger with its dwarf companion," added Thilker.

The findings indicate that the evolution of lenticular galaxies might not yet be complete. They may, in fact, continue to form stars in a slow, piecemeal fashion as they suck the raw, gaseous material for stars from small, neighboring galaxies. It seems the Ghost of Mirach might act more like a vampire than a ghost.

Caltech leads the Galaxy Evolution Explorer mission and is responsible for science operations and data analysis. NASA's Jet Propulsion Laboratory in Pasadena, Calif., manages the mission and built the science instrument. The mission was developed under NASA's Explorers Program managed by the Goddard Space Flight Center, Greenbelt, Md. Researchers sponsored by Yonsei University in South Korea and the Centre National d'Etudes Spatiales (CNES) in France collaborated on this mission.

Special stars: Gliese 105

Gliese 105 A and C
Graphic: Nasa, Hubble Telescope


A small triple system. The C star, a red dwarf, is with 2600 kelvin surface temperature the coolest known main sequence star. Its mass is just enough to start the hydrogen fusion.
The B star is a bigger red dwarf, A is a yellow-orange star.


Constellation: Cetus
Distance: 23.5 light-years
Space between Gliese 105 A and B: 1200 AU
Space between Gliese 105 A and C: 24 AU

Gliese 105 A

Spectral class: K3
Visual magnitude: 5.82
Luminosity: 0.21 * Sun
Mass: 0.81 * Sun
Diameter: 0.85 * Sun


Gliese 105 B

Spectral class: M3.5
Visual magnitude: 12
Luminosity: 0.001 * Sun
Mass: 0.21 * Sun
Diameter: 0.28 * Sun

Gliese 105 C

Spectral class: M7
Luminosity: 0.0000084 * Sun
Mass: 0.082 * Sun


Kappa Ceti:



Photo: ESO Online Digitized Sky Survey

A yellow star of sunlike measures, but with much more raving attributes. It is a superflare star with eruptions a million times heavier than those of our Sun. They are caused by disturbances of the magnetic field from a still undiscovered near companion.

Constellation: Cetus
Age: 800 million years
Distance: 29.87 light-years
Spectral class: G5
Visual magnitude: 4.83
Luminosity: 0.851 * Sun
Mass: 1 * Sun
Diameter: 0.984 * Sun
Radial velocity: 18.9 km/sec

Special star: Delta Pavonis

Photo: ESO Online Digitized Sky Survey

Delta Pavonis

The yellow star is older as our Sun, but besides very similar to it. It is one of the main targets for the search of Earth-like planets and life.

Constellation: Pavo
Distance: 19.92 light-years
Spectral class: G8
Visual magnitude: 3.55
Luminosity: 1.231 * Sun
Mass: 0.98 * Sun
Diameter: 1.188 * Sun
Radial velocity: -21.7 km/sec

Spacial Stars: Gliese 229

The red dwarf and right to it the tiny brown dwarf.
Photo: Nasa, Hubble Telescope

A pair of a red dwarf which is a flare star and a brown dwarf.

Constellation: Lepus
Age: 3 billion years
Distance: 18.8 light-years
Radial velocity: 5.2 km/sec
Space between Gliese 229 A and B: 44 AU

Gliese 229 A

Spectral class: M1

Visual magnitude: 8.15

Luminosity: 0.016×Sun

Mass: 0.46×Sun

Diameter: 0.527×Sun

Gliese 229 B(Brown Dwarf):

Luminosity: 0.000006× Sun

Mass: 0.05× Sun (45× Jupiter)

Diameter: 0.1027× Sun (1×Jupiter)

Spacial Star: Altair

Altair:

Graphic: Zina Deretsky, National Science Foundation

A blue-white star, which is quite good visible in summer on the northern hemisphere. Altair is one of the fastest rotating stars we know of. In 6.5 hours it rotates once. The smaller Sun needs 600 hours for this. Due to its fast rotation Altair is strongly oblate on its poles.

Constellation: Aquila

Age: less than 1 billion years

Distance: 16.77 light-years

Spectral class: A7

Visual magnitude: 0.77

Luminosity: 11.39× Sun

Mass: 2×Sun

Diameter: 1.631×Sun

Radial velocity: -26.1 km/sec

A list of unusual, extreme and notable stars

The Orion Nebula, a stellar nursery.
Photo: Nasa

Stars with a distance less than 2000 light-years (ordered by their distance from us):

1. Altair
2. Gliese 229
3. Delta Pavonis
4. Gliese 105
5. Kappa Ceti
6. The Methane Dwarf
7. TVLM513-46546
8. GJ 3685A
9. 18 Scorpii
10. G29-38
11. AB Doradus
12. Castor
13. Diamond Star
14. Delta Equulei
15. Gliese 710
16. DENIS-P J020529.0-1159
17. Alpha Caeli
18. Mizar and Alcor
19. Phecda
20. Diphda
21. Rotanev
22. Cor Caroli
23. II Pegasi
24. Hyadum I
25. HR 8210
26. BO Microscopii
27. Zubeneschamali
28. BD -22°5866
29. Alkes
30. Hang-loose Binary
31. Sigma Octantis
32. Gamma Comae Berenices
33. EF Eridanus
34. Alpha Arae
35. Dabih
36. AE Aquarii
37. WD0137-349
38. Chi Cygni
39. RX-J185635-375
40. GY Andromedae
41. R Coronae Australis
42. Z Camelopardalis
43. Geminga
44. L1014
45. CW Leonis
46. R Aquarii
47. Helix Nebula
48. Phi Persei
49. FK Comae Berenices
50. L1157
51. HD 12545
52. 32 Cygni
53. 2MASS J053521840546085
54. HH 34
55. V380 Orionis
56. Rosette HH1
57. Nova Persei 1901
58. Nova Herculis 1934
59. NGC 2440
60. RX J0806
61. FU Orionis
62. MACHO-LMC-5

The first planet inside a Debris Disk:A true planet

photo: The Hubble Space Telescope captured this image of a dusty disk around Fomalhaut. The inset image shows the position and motion of Fomalhaut b from 2004 to 2006. The object has the brightness one would expect of a planet similar in mass to Jupiter, given the system's age. Fomalhaut b's gravity has clearly not destroyed the disk, which also argues for planetary status. The star itself has been blotted out by an occulting disk. Click on the image for a larger view.
Paul Kalas (UC, Berkeley) / STScI / NASA

For years, astronomers have been racing one another to take the first picture of a planet orbiting another star. Over the past few years, several teams have claimed to have directly imaged an extrasolar planet. But in each case, there were lingering questions about the nature of the purported planet. The objects seem unusually massive for planets, and each orbits much farther from its host star than Pluto orbits the Sun. Many astronomers argue that these objects are more accurately described as failed stars (known as brown dwarfs) rather than true planets, because they probably formed from collapsing gas clouds, like stars.

Today, two teams of astronomers announced new exoplanet images, and in each case, I think they have the real deal. Only time and future observations will let us know for certain, but these objects have the look and feel of bona fide planets. One group found a planet orbiting Fomalhaut, the 18th brightest star in the night sky, and one of the Sun’s nearest stellar neighbors. The other team appears to have imaged three planets around a more obscure star known as HR 8799.The Fomalhaut planet was imaged by Paul Kalas (University of California, Berkeley) and his colleagues. Kalas and his team used the Hubble Space Telescope, which comes with an occulting disk that was employed to block Fomalhaut’s blazing pinpoint of light. Observations taken over several years revealed an ultra-faint moving object orbiting at a large distance from Fomalhaut.

photo:Fomalhaut is by far the brightest star in the dim constellation Piscis Austrinis. For observers at mid-northerly latitudes, it shines at 1st magnitude in the southern sky during autumn evenings. The star is 25 light-years from Earth. It belongs to spectral type A3, and is about 15 times more luminous than our Sun.

The purported planet orbits Fomalhaut at a whopping 119 astronomical units (1 a.u. is the average Earth-Sun distance). This puts it four times farther from Fomalhaut than Neptune is from the Sun. The planet, known as Fomalhaut b, orbits just inside a dusty ring of rubble that is Fomalhaut’s equivalent of our Kuiper Belt.Kalas and his colleagues cite two lines of evidence to argue that Fomalhaut b is indeed a planet. First, its extreme faintness in visible light, coupled with Fomalhaut’s estimated 100- to 300-million-year age, argues that it cooled off too quickly to be a brown dwarf, and thus has at most 2 or 3 times the mass of Jupiter. Kalas also points out a second piece of evidence: "A brown dwarf could not sit so close to the belt without completely disrupting it by gravity."

photo:This illustration compares the Fomalhaut system to our solar system. Both systems have dusty disks far from the star, but Fomalhaut's disk is much farther out. The disks come from colliding comets grinding themselves to dust. Fomalhaut's disk is analogous to our Kuiper Belt.

Given these two completely independent lines of evidence that Fomalhaut b has a very low mass, I’m buying the argument that Fomalhaut b is a genuine planet. But there is still no universally accepted definition of what distinguishes a high-mass planet from a low-mass brown dwarf. According to some astronomers, the line should be drawn at about 13 Jupiter masses — the mass at which a gaseous body can briefly fuse deuterium atoms in its core. According to that definition, Fomalhaut b is clearly a planet.

But other astronomers think the distinction should be based on formation. If a 3-Jupiter-mass object formed like a star from a collapsing gas cloud, it’s a very-low-mass brown dwarf. If it formed inside a disk, then it’s a planet. Since it’s unclear how Fomalhaut b formed, one could argue either way.The HR 8799 planets were imaged by a team led by Christian Marois (Herzberg Institute of Astrophysics, Canada). This group used the 10-meter Keck II telescope in Hawaii and the 8-meter Gemini telescope in Hawaii to image three pinpricks of infrared light orbiting HR 8799, a magnitude-6 star in the constellation Pegasus. Besides using an occulting mask to blot out the star’s light, the team used adaptive optics to compensate for the blurring effects of Earth’s atmosphere.


photo:In this image from the Keck Observatory, the light of the star HR 8799 has been blotted out by an occulting disk to reveal three faint companions, color coded as red dots. Previous positions are indicated, which allows us to see orbital motions. The system appears to be nearly face on, and the planets are all moving in the same direction and in approximately the same plane.
Christian Marois (Hertzberg Institute) / W.M. Keck Observatory, and others

But are these pinpricks of light actually planets? Based on their separations from the star and HR 8799’s measured 128-light-year distance, the bodies orbit at distances of about 24, 38, and 68 a.u. The innermost object would be halfway between Uranus and Neptune in our solar system, and the outermost would be slightly more than twice Neptune’s distance.Based on the infrared luminosity of the three companions, and the star’s estimated 60-million-year age, Marois and his team estimate the masses to be around 10, 10, and 7 Jupiters, respectively. These masses are getting uncomfortably close to the 13-Jupiter-mass lower limit for brown dwarfs. Moreover, the star’s age is not known to high precision, and astronomers have not thoroughly tested the cooling models they use to determine the masses of brown dwarfs and planets. In other words, the actual masses might exceed 13 Jupiters.

photo:This sky map shows the location of HR 8799. The star is just barely visible to the naked eye under very dark skies. The star is spectral type A5, and is about 5 to 10 times more luminous than our Sun. It is located 128 light-years from Earth. By coincidence, it lies in nearly the same direction as 51 Pegasi, the first solar-type star discovered to have a planet.

But as codiscoverer Bruce Macintosh (Lawrence Livermore National Laboratory) points out, "All three of these objects seem to be orbiting in the same plane, and they’re going around in the same direction. This would imply they formed in a protoplanetary disk, like planets do."I’m ready to buy that argument, at least for now. With three substellar companions moving in the same direction and in the same plane, the HR 8799 system looks like a scaled-up version of our own solar system. It looks a heck of a lot more like a planetary system than it resembles a multiple-star system.

I’d like to see both systems given further scrutiny so astronomers can better characterize the orbiting companions. I would also like to see detections around other stars, so we can start comparing different systems. But if I had to bet, I’d put my money on the claims that these are indeed planets. If Kalas, Marois, and their colleagues are right, they may go down in the history books as having taken the first images of extrasolar planets.

photo:This diagram compares the HR 8799 system (left) to our solar system (right). Like Fomalhaut, HR 8799 is surrounded by a dusty disk. The outermost planet is just inside the disk, just as Fomalhaut b lies just inside its disk. Both planets appear to be gravitationally sculpting their disks, but are not massive enough to destroy it. Click on the image for a larger view.

Regardless of the uncertainties in formation and semantics, these direct images represent a giant leap forward. "These discoveries are extraordinarily exciting for exoplanet science," says veteran exoplanet hunter Geoff Marcy (University of California, Berkeley). "We may be witnessing the birth of a new exoplanet era. For the first time, we may measure orbits, brightnesses, and spectra of other planets, just as astronomers have done for decades with stars, nebulae, and galaxies."

Space,Science,Technology,News related websites(part:2)

12.http://www.msnbc.msn.com
(Latest News and Article website)

13.http://cnn.com
(Latest News and Article website)

14.http://scitechdaily.com
(Science website articles and links)

15.http://newscientist.com
(Science news and articles)

16.http://discovermagazine.com
(Science news and articles)

17.http://sciam.com
(Science news and articles)

18.http://space.com
(Space news and articles)

19.http://chron.com
(Science news and articles)

20.http://eurekalert.org
(Science news and articles)

21.http://astronomy.com
(Space news and articles)

22.http://cern.ch
(CERN - European Organization for Nuclear Research)

Space,Technology,Science,News related websites(Part 1)

1.http://imraneee.blogspot.com
(The most intense website about Astronomy)

2.http://hubblesite.org
(The website of Hubble Space Telescope)

3.http://gemini.edu
(The Gemini Observatory)

4.http://livescience.com
(Science and Technology News Website)

5.http://nationalgeographic.com
(Science and Technology News Website)

6.http://sciencedaily.com
(Science and Technology News Website)

7.http://spacedaily.com
(Science and Technology News Website)

8.http://universetoday.com
(Space related website)

9.http://newscientist.com
(Science and Technology News Website)

10.http://physorg.com
(Physics related News Website)

11.http://www.spaceinfo.com.au/
(Space related Australian News Website)

Star-Eating Mass Found Near Center of Milky Way

20 September 1999

A brilliant X-ray outburst in the direction of the galactic center flared to prominence last Wednesday, turning a relatively sedate energy source into the brightest X-ray object in the sky.

Instruments aboard at least two X-ray observing spacecraft detected the flash, which was most likely produced by a huge mass of material being swallowed by a black hole or neutron star.The event has been tracked down to an area near a visible star called GM Sagittarii in the constellation Sagittarius.

That star is known to vary in brightness when observed at visible light, said Mike McCollough, a staff scientist at NASA's Marshall Space Flight Center. The existence of a high-energy X-ray source next to it means that the star is actually part of a system called an X-ray binary, a pair in which a star and an extremely dense object such as a neutron star or a black hole orbit each other, he said.

Last week's unusually energetic activity was first noticed Wednesday, said McCollough, who works on a team that analyzes data from the Burst and Transient Source Experiment (BATSE) instrument aboard the Compton Gamma Ray Observatory. That NASA spacecraft is designed to observe sources of high-energy radiation.

When McCollough heard that other instruments had detected the X-ray burst, he looked at information from the Compton instruments and noticed a brief, but huge spike in emissions from GM Sagittarii on Tuesday. The object -- which is typically some 30 times dimmer than the pulsar in the Crab nebula -- jumped to about five times brighter than that object before it dimmed again.

The Crab pulsar is usually the brightest X-ray object in the sky. It is the standard against which X-ray luminosity is commonly measured.

Sifting through data for Wednesday, McCollough found nothing for the first half of the day, he said.

"Then about 10 hours into the day we started seeing it go off. Literally within about six hours it got to about eight times the Crab," he said. "It essentially wasn't there and then it just went through the roof on us."

Meanwhile, scientists watching data from the Rossi X-ray Explorer (another spacecraft that observes X-rays) were witnessing the intense flare in X-ray emissions from Sagittarius, but at slightly less energetic X-ray wavelengths than BATSE picks up.

Within eight hours on Wednesday, Rossi scientists saw GM Sagittarii flare to more than 12 times brighter than the Crab nebula then drop just as dramatically, said William Heindl, a research scientist at the Center for Astrophysics and Space Science at the University of California at San Diego, who works with data from the Rossi observer.

The spacecraft's sky scanner measured most the activity, Heindl said, but scientists aimed the instrument's telescope into view just in time to see the object's last violent sputter -- the object had dimmed, then within a period of about 15 minutes, it flashed to about twice the brightness of the Crab before Earth obscured the spacecraft's view.

When Rossi next glimpsed GM Sagittarii, the object was quiet and dark, betraying no hint of its violent outburst, Heindl said.

The jolts in X-ray emissions both in the low-energy "soft" X-rays, measured by Rossi, and the higher-energy "hard" X-rays detected by BATSE mean that they were produced as material falls into either by a black hole or neutron star, McCollough said. The source of that material is probably the companion star that is feeding the black hole or neutron star.

Based on the new observations, the system will need to be reclassified as an X-ray binary, McCollough said. The system will likely attract a lot more attention in the coming year as scientists try to learn more about the star, its mass, and just what the high-density object beside it is, he said.


[ Important note: Due to a mix-up among astronomers, the star in this article is misidentified as GM Sagittarii. The star associated with the brilliant X-ray burst of September 15, 1999 is now called V 4641 Sagittarii. For two decades astronomers have been incorrectly calling V4641 by the name GM Sagittarii, a mistake which was recently discovered and announced on October 13, 1999. ]

Edge of Darkness: Milky Way's Black Hole 'Seen' in X-rays

Simulation of a supermassive black hole as seen from above. Hot, compressed gas swirls around the event horizon. Blue indicates the radio waves oscillating sideways; red indicates waves oscillating vertically. The bright, thin ring is due to light that has circled the black hole once before leaving its environment.

Scientists announced today some of the most compelling evidence to date for the existence of a colossal black hole at the center of the Milky Way Galaxy, also determining a new and much smaller upper limit to the diameter of the mysterious object.

Experts were already fairly sure that the black hole resided at the center of our galaxy, packing the mass of 2.6 million Suns into an area smaller than our solar system. Their confidence came from reading the motions of millions of fast-moving stars that swarm around the dense, central object.

Yet they've never seen it -- black holes by definition are invisible. And they don't really know how much space it takes up.

In fact, no one is even sure it is a black hole. It might instead be a dense concentration of exotic "dark" stars, for example.

But in the new study researchers claim to have seen the edge of darkness by spotting rapidly pulsing X-ray emissions thought to be created when superheated gas or other matter zooms beyond the point of no return, through an "event horizon" that marks the time-bending and space-warping outer limits of a black hole. "This is extremely exciting because it's the first time we have seen our own neighborhood supermassive black hole devour a chunk of material," said Frederick Baganoff of the Massachusetts Institute of Technology, who led the study. "It's as if the material there sent us a postcard before it fell in."

He said the material could be a hot gas or solid matter roughly the size of a comet. Or the pulse of emissions could possibly be the result of some intense magnetic flare, similar to solar flares seen on our Sun.

The X-ray emissions were found near a previously known strong source of radio emissions, known as Sagittarius A* (pronounced "Sagittarius A Star") at the center of the Milky Way. Astrophysicists have long suspected that the compact source of intense radio emissions is related to what's known as a supermassive black hole, the largest type of black hole and a variety suspected of anchoring many large galaxies.

The new observations, detailed here at a Chandra X-ray Observatory symposium, represent what may be the most direct evidence for the black hole's existence, several scientists said. And though they stopped short of calling it proof, researchers are hopeful that a final answer will come within a decade.

Galactic puppeteer

Most of our galaxy is relatively uncrowded. The nearest star to our Sun, for example, is 4.2 light-years away.

But roughly 10 million stars are known to orbit within a light year of the galaxy's center, dashing along at phenomenal speeds of up to 3.1 million mph (5 million kph). This concentration of stars, and the speed with which they orbit, is the main clue that something hugely massive is at the center of the Milky Way, acting like a galactic puppeteer by providing the tremendous gravity needed to tug at stars with invisible strings.

If it is in fact a black hole, then it must meet the technical definition laid out by Einstein's general theory of relativity: All its mass must be locked and hidden inside a sphere known as an event horizon, beyond which nothing -- not even light -- can escape.

Just before matter swirls into a black hole, scientists predict it will approach the speed of light and become superheated, giving off X-rays prior to entering the event horizon.

Generally, the suspected supermassive black hole at the center of the Milky Way is quiet as black holes go, rarely coughing up X-rays or other forms of light radiation. This puzzling feature has made it difficult to study and casts some doubt on whether Sagittarius A*, the radio source, really represents a black hole.

So the X-ray observations announced Wednesday eliminated some of that doubt and filled a data gap.

Intense flares

The new observations, made in October of 2000 by the Chandra space telescope orbiting Earth, span about two hours. Flares of X-rays were 45 times more powerful than typical emissions that had previously been spotted. And wild variations occurred on shorter time frames: The number of X-rays per second dropped by a factor of five over one 10-minute period and then jump again to high levels 10 minutes later.

"Such breathless variability is rarely seen in emissions from ponderous multi-million solar-mass objects," said Fulvio Melia, a researcher at the University of Arizona's Steward Observatory. This kind of activity is typically reserved for smaller objects, like neutron stars.

Melia was not involved in the study but has written an analysis of it for the Aug. 6 issue of the journal Nature, where the results will be published.

Because Chandra only sees the area near the black hole as a point in space, the X-ray peaks represent the entire output around the sphere of the event horizon. So if strong peaks of activity can build in just 10 minutes, then the entire event horizon that contributes to the total emissions must be no larger than the distance light can travel in 10 minutes -- roughly the distance from Earth to the Sun, Melia said.

This implies a size of the event horizon that is some 1,500 times smaller than previous research could determine -- much closer to the size predicted by the theory of general relativity. Though it may be as small as relativity predicts -- 5.6 million miles (9 million km) in diameter -- the new study can only say that it is no larger than 112 million miles (180 million km).

Could it be a cosmic trick?

In 1999, the same research group used Chandra to detect weak but steady X-rays near Sagittarius A*, data that has not been widely reported.

Combined, the two sets of observations strongly indicate that the radiation most likely comes directly from Sagittarius A* and not from some other object, such as a star that orbits close Sagittarius A* in some sort of "binary" configuration, Melia said.

But the observations are not entirely conclusive.

"Nature has been cruel to astronomers in other circumstances, and this probability, although small, is not zero," Melia said. He added that much more convincing evidence would come if astronomers could spot X-ray emissions and radio emissions that occur simultaneously from the same location.

Studies to look for such a convergence are underway, and an answer could come within a year, several researchers agreed.

Baganoff hopes to lead the team that makes that discovery. Will scientists then declare, once and for all, that there is a black hole at the center of the Milky Way Galaxy?

Not quite. Baganoff said researchers would have to actually image the event horizon, not just the emissions from it. If he and his colleagues spot a correlation between radio and X-ray flares in Sagittarius A* within the next year, then he said he would bet his career that the event horizon will be imaged within a decade.

But, he said, he wouldn't be quite ready to bet his life on it.

Contributing to the study were researchers from Penn State University, MIT, UCLA, Caltech, and Insititute of Space and Astronautical Science, Japan.

Simulating the Fate of Our Milky Way

Our Future: A simulation of what might happen when the Andromeda Galaxy hits ours shows tidal forces of gravity creating long plumes of material. The central regions will relatively quickly fall back together and merge into a single remnant galaxy.

When cars collide, it’s an accident. When galaxies collide, it’s Nature at work. Many astronomers believe such crashes are part of the natural evolution in the lives of galaxies and galaxy clusters, now scientists are blending scientific research and high-powered computer visual effects into vivid models of how they occur.

Astrophysicist Frank Summers, of the Space Telescope Science Institute (STScI), produced a simulated galaxy collision, using a combination of computer modeling research and the same special effects software used to make computer-generated movies.

The resulting animation shows a crash between two large spiral galaxies roughly the size of our own Milky Way and its larger neighbor Andromeda, themselves slated to collide in a few billion years.

"What makes me happy about this visualization is that it’s a presentation of accurate science to the public," Summers told. "It allows for a fluid process of education and the ability to create mental models of the universe."

Rip and tear

In his animation, Summers shows two galaxies at different planes of position, then documents their collision at a rate of about 10 million years per second. The entire sequence covers some 500 million years.

As the galaxies approach each other, they keep their spiral shapes up to the point of impact, where so-called "tidal forces" of gravity result in the formation of long plumes of stars, gas and dust called tidal tails. The centers of each galaxy then merge into one remnant core. The scenario is a likely preview for the expected interaction between the Milky Way and Andromeda galaxies, which some astronomers have already mapped out with computers models.

Summers used research data produced by astronomy professors and galactic modelers Chris Mihos, of Case Western Reserve University, and Lars Hernquist, of Harvard University. The researchers used a supercomputer to depict the collision in a project for the National Air and Space Museum's newly renovated Einstein Planetarium.

Dark matter

Astronomers who study galaxy structure spend most of their time modeling the effects of dark matter, that ubiquitous but unseen stuff that makes up most of a galaxy’s mass, Summers said. Only between 10 percent and 30 percent of a galaxy’s mass is visible, so astronomers study its rotation to determine the dark matter content, material that must be there based on known gravitational effects. They also look at how clusters of galaxies appear glued together by gravity.

By simulating collisions between galaxies, theorists can study the structures of galaxies and the architecture behind galactic clusters without having to wait the millennia it takes for such crashes to occur.

In the early days of the universe, the rate of collisions was about 10 to 100 times higher, simply because things were closer together. Although individual stars may not physically hit each other during a collision -- the space between them is still vast -- the gravitational effects of the encounter are enough to twist and distort galaxies beyond recognition.

Colliding spiral galaxies can become one elliptical galaxy, for example, which is the likely destiny for our Milky Way, astronomers say.

Galaxy building

"Mergers and interactions between galaxies are an essential part of their dynamical evolution," said John Dubinksi, an astronomy professor at University of Toronto who has modeled the eventual clash between the Milky Way and Andromeda galaxies. "The elliptical galaxies which represent around 10 percent of the galaxy population are most likely the product of a merger of two or more galaxies of nearly equal mass."

Galaxy collisions also contribute to star formation, as clouds of gas heat up and coalesce during the encounter. Observations from the Chandra X-ray Observatory suggest they may even contribute to the development of supermassive black holes.

In galaxy clusters, Dubinski said in an e-mail interview, elliptical galaxies outnumber spiral or irregular varieties. The clusters also often have a giant elliptical galaxy -- a product of many spiral galaxies merging together when the cluster first formed -- at their center.

Where we're headed

Most scientists agree that the Milky Way will cross paths with the Andromeda galaxy in about three billion years. Both galaxies are now spiral in shape, though Andromeda is about twice as large as the Milky Way.

The galaxies are separated by about 2.2 million light years (one light-year is about 6 trillion miles, or 10 trillion kilometers). That gap is closing at about 310,000 miles per hour (500,000 kph).

While a collision appears inevitable, astronomers admit that the sideways motion of Andromeda -- the galaxy’s speed perpendicular to its forward path toward the Milky Way -- could affect the encounter’s timing, but it has yet to be measured precisely. Dubinksi used an estimate of 12.4 miles per second (20 km per second) for his collision model.

"Even if the galaxies have a wider passage on the first pass, if they are on a bound orbit they are destined to merge eventually," Dubinski said. "If not on the first flyby, then within the second or third pass over the next 10 billion years, he added.

The clincher is gravity. Even if there’s enough space between the Milky Way and Andromeda to simply brush past each other at spiral arm’s length, their mutual gravity will ultimately win out, drawing the two galaxies together on successive flybys.Dubinski hopes to refine his model of the collision between the Milky Way and Andromeda galaxies in the future by modeling a system of about a trillion or so particles to match the number of stars in the two galaxies. But with the current growth in computer memory and speed, such computations won’t be possible for about 10 years, he said.

The Mice

Meanwhile, another pair of researchers has taken a pair of interacting galaxies called the Mice and worked backward to simulate what they figure has already taken place. The Mice, recently photographed by the Hubble Space Telescope's new camera, represent a collision in progress that could be very much like the pending crash of our own galaxy into Andromeda.

Joshua Barnes of the University of Hawaii worked with John Hibbard, now at the National Radio Astronomy Observatory, to animate a past that might have led to the present-day Mice.

Their computer animation shows two pinwheel galaxies falling together, swerving as they pass, and flinging out long tails of stars. At present the two galaxies have made one pass, and are coming back for a second and closer encounter. Eventually they will coalesce into a single galaxy, whose possibilities the simulation projects.

"Simulating colliding galaxies is a bit like investigating a car crash," Barnes says. "Suppose you had no witnesses, just a couple of wrecked cars. You might try different test crashes, varying things like speed and angle of impact, until you found a way to get the same damage as the original collision. That's basically what we did."

Brightest Galactic Flash Ever Detected Hits Earth

photo: Artist impression of the eruption striking Earth's magnetic field and atmosphere. Credit: NASA

18 February, 2005

A huge explosion halfway across the galaxy packed so much power it briefly altered Earth's upper atmosphere in December, astronomers said Friday.

No known eruption beyond our solar system has ever appeared as bright upon arrival.

But you could not have seen it, unless you can top the X-ray vision of Superman: In gamma rays, the event equaled the brightness of the full Moon's reflected visible light.

The blast originated about 50,000 light-years away and was detected Dec. 27. A light-year is the distance light travels in a year, about 6 trillion miles (10 trillion kilometers).

The commotion was caused by a special variety of neutron star known as a magnetar. These fast-spinning, compact stellar corpses -- no larger than a big city -- create intense magnetic fields that trigger explosions. The blast was 100 times more powerful than any other similar eruption witnessed, said David Palmer of Los Alamos National Laboratory, one of several researchers around the world who monitored the event with various telescopes."Had this happened within 10 light-years of us, it would have severely damaged our atmosphere and possibly have triggered a mass extinction," said Bryan Gaensler of the Harvard-Smithsonian Center for Astrophysics (CfA).

There are no magnetars close enough to worry about, however, Gaensler and two other astronomers told . But the strength of the tempest has them marveling over the dying star's capabilities while also wondering if major species die-offs in the past might have been triggered by stellar explosions.

'Once-in-a-lifetime'

The Sun is a middle-aged star about 8 light-minutes from us. It's tantrums, though cosmically pitiful compared to the magnetar explosion, routinely squish Earth's protective magnetic field and alter our atmosphere, lighting up the night sky with colorful lights called aurora.



photo: The burst from SGR1806-20 as seen in radio wavelength. Credit: University of Hawaii

Solar storms also alter the shape of Earth's ionosphere, a region of the atmosphere 50 miles (80 kilometers) up where gas is so thin that electrons can be stripped from atoms and molecules -- they are ionized -- and roam free for short periods. Fluctuations in solar radiation cause the ionosphere to expand and contract.

"The gamma rays hit the ionosphere and created more ionization, briefly expanding the ionosphere," said Neil Gehrels, lead scientist for NASA's gamma-ray watching Swift observatory.

Gehrels said in an email interview that the effect was similar to a solar-induced disruption but that the effect was "much smaller than a big solar flare."

Still, scientists were surprised that a magnetar so far away could alter the ionosphere.

"That it can reach out and tap us on the shoulder like this, reminds us that we really are linked to the cosmos," said Phil Wilkinson of IPS Australia, that country's space weather service.

"This is a once-in-a-lifetime event," said Rob Fender of Southampton University in the UK. "We have observed an object only 20 kilometers across [12 miles], on the other side of our galaxy, releasing more energy in a tenth of a second than the Sun emits in 100,000 years."

Some researchers have speculated that one or more known mass extinctions hundreds of millions of years ago might have been the result of a similar blast altering Earth's atmosphere. There is no firm data to support the idea, however. But astronomers say the Sun might have been closer to other stars in the past.

A similar blast within 10 light-years of Earth "would destroy the ozone layer," according to a CfA statement, "causing abrupt climate change and mass extinctions due to increased radiation."

The all-clear has been sounded, however.

"None of the known sample [of magnetars] are closer than about 4,000-5,000 light years from us," Gaensler said. "This is a very safe distance."

Cause a mystery

Researchers don't know exactly why the burst was so incredible. The star, named SGR 1806-20, spins once on its axis every 7.5 seconds, and it is surrounded by a magnetic field more powerful than any other object in the universe.

"We may be seeing a massive release of magnetic energy during a 'starquake' on the surface of the object," said Maura McLaughlin of the University of Manchester in the UK.

Another possibility is that the magnetic field more or less snapped in a process scientists call magnetic reconnection.

Gamma rays are the highest form of radiation on the electromagnetic spectrum, which includes X-rays, visible light and radio waves too.

The eruption was also recorded by the National Science Foundation's Very Large Array of radio telescopes, along with other European satellites and telescopes in Australia.

Explosive details

A neutron star is the remnant of a star that was once several times more massive than the Sun. When their nuclear fuel is depleted, they explode as a supernova. The remaining dense core is slightly more massive than the Sun but has a diameter typically no more than 12 miles (20 kilometers).

Millions of neutron stars fill the Milky Way galaxy. A dozen or so are ultra-magnetic neutron stars -- magnetars. The magnetic field around one is about 1,000 trillion gauss, strong enough to strip information from a credit card at a distance halfway to the Moon, scientists say.

Of the known magnetars, four are called soft gamma repeaters, or SGRs, because they flare up randomly and release gamma rays. The flare on SGR 1806-20 unleashed about 10,000 trillion trillion trillion watts of power.

"The next biggest flare ever seen from any soft gamma repeater was peanuts compared to this incredible Dec. 27 event," said Gaensler of the CfA.

Tsunami Connection?

Several readers wondered if the magnetar blast could be related to the December tsunami. Scientists have made no such connection. The blast affected Earth's ionosphere, which is routinely affected to a greater extent by changes in solar activity.