Category: Astronomy

Image credit: CfA
When choosing a Valentine’s Day gift for a wife or girlfriend, you can’t go wrong with diamonds. If you really want to impress your favorite lady this Valentine’s Day, get her the galaxy’s largest diamond. But you’d better carry a deep wallet, because this 10 billion trillion trillion carat monster has a cost that’s literally astronomical!

“You would need a jeweler’s loupe the size of the Sun to grade this diamond!” says astronomer Travis Metcalfe (Harvard-Smithsonian Center for Astrophysics), who leads a team of researchers that discovered the giant gem. “Bill Gates and Donald Trump together couldn’t begin to afford it.”

When asked to estimate the value of the cosmic jewel, Ronald Winston, CEO of Harry Winston Inc., indicated that such a large diamond probably would depress the value of the market, stating, “Who knows? It may be a self-deflating prophecy because there is so much of it.” He added, “It is definitely too big to wear!”

The newly discovered cosmic diamond is a chunk of crystallized carbon 50 light-years from the Earth in the constellation Centaurus. (A light-year is the distance light travels in a year, or about 6 trillion miles.) It is 2,500 miles across and weighs 5 million trillion trillion pounds, which translates to approximately 10 billion trillion trillion carats, or a one followed by 34 zeros.

“It’s the mother of all diamonds!” says Metcalfe. “Some people refer to it as ‘Lucy’ in a tribute to the Beatles song ‘Lucy In The Sky With Diamonds.'”

The diamond star completely outclasses the largest diamond on Earth, the 530-carat Star of Africa which resides in the Crown Jewels of England. The Star of Africa was cut from the largest diamond ever found on Earth, a 3,100-carat gem.

The huge cosmic gem (technically known as BPM 37093) is actually a crystallized white dwarf. A white dwarf is the hot core of a star, left over after the star uses up its nuclear fuel and dies. It is made mostly of carbon and is coated by a thin layer of hydrogen and helium gases.

For more than four decades, astronomers have thought that the interiors of white dwarfs crystallized, but obtaining direct evidence became possible only recently.

“The hunt for the crystal core of this white dwarf has been like the search for the Lost Dutchman’s Mine. It was thought to exist for decades, but only now has it been located,” says co-author Michael Montgomery (University of Cambridge).

The white dwarf studied by Metcalfe, Montgomery, and Antonio Kanaan (UFSC Brazil), is not only radiant but also harmonious. It rings like a gigantic gong, undergoing constant pulsations.

“By measuring those pulsations, we were able to study the hidden interior of the white dwarf, just like seismograph measurements of earthquakes allow geologists to study the interior of the Earth. We figured out that the carbon interior of this white dwarf has solidified to form the galaxy’s largest diamond,” says Metcalfe.

Our Sun will become a white dwarf when it dies 5 billion years from now. Some two billion years after that, the Sun’s ember core will crystallize as well, leaving a giant diamond in the center of our solar system.

“Our Sun will become a diamond that truly is forever,” says Metcalfe.

A paper announcing this discovery has been submitted to The Astrophysical Journal Letters for publication.

Original Source: CfA News Release

Image credit: Hubble
Many examples are known where a galaxy acts as a gravitational lens, producing multiple images on the sky of a more distant object like a bright quasar hidden behind it. But there has been a persistent mystery for over 20 years: Einstein’s general theory of relativity predicts there should be an odd number of images, yet almost all observed lenses have only 2 or 4 known images. Now, astronomer Joshua Winn of the Harvard-Smithsonian Center for Astrophysics (CfA) and two former CfA colleagues, David Rusin (now at the University of Pennsylvania) and Christopher Kochanek (The Ohio State University), have identified a third, central image of a lensed quasar. Radio observations of the system known as PMN J1632-0033 in the constellation Ophiuchus uncovered a faint central image, which can be used to investigate the properties of the lensing galaxy and the supermassive black hole expected to lie at its center.

“Finding this central image is interesting in its own right, but is even more important for what it can tell us about the lensing galaxy. This offers us a new tool for studying galaxies so far away that, even to the Hubble Space Telescope, they’re just faint smudges,” said Winn.

Quasars are extremely distant and bright objects believed to be powered by supermassive black holes. They shine brightly by converting the gravitational energy of matter falling into the black hole into light and other types of radiation, such as radio waves.

In gravitational lensing, light rays from a quasar which pass close to a galaxy are bent by the galaxy’s gravitational field, much as they would be bent when passing through a glass lens. The denser the center of a galaxy, and the stronger its gravity, the fainter the central image will be. Yet this central image, whose light has passed closest to the middle of the lensing galaxy, can tell us much about that galaxy’s core. That opportunity makes finding such central images particularly desirable.

In the system PMN J1632-0033, a radio-loud quasar at redshift z=3.42 (a distance of about 11.5 billion light-years) is being lensed by an elliptical galaxy at redshift z~1 (about 8 billion light-years away). Two images of the quasar were known to exist, and a third, very faint radio source was suspected to be the central image. However, that third source was right on top of the lensing galaxy, and so might have been intrinsic to the lensing galaxy itself.

By observing the radio “color,” or spectrum, of all three images using the National Science Foundation’s Very Large Array and Very Long Baseline Array, Winn and his colleagues provided compelling evidence that the third source is indeed the quasar’s central image. Its spectrum is essentially identical to the other two images, except at low frequencies where some of the radio energy was absorbed by the lensing galaxy.

The geometry and properties of the quasar’s three images already are telling us about the core of the lensing galaxy. For example, its central black hole weighs less than 200 million solar masses. Also, its surface density (amount of matter as projected against the plane of the sky) at the location of the central image is more than 20,000 solar masses per square parsec. (For comparison, the surface density of the Milky Way near our sun is about 50 solar masses per square parsec.) Both figures for the lensing galaxy agree with expectations based on detailed observations of galaxies hundreds of times closer to the Earth.

“Almost all of our knowledge about galaxy centers comes from studying very nearby galaxies. The remarkable thing about central images is that you can get similar information about the cores of galaxies hundreds of times farther away, and billions of years younger than our neighboring galaxies,” said Winn.

This research is available online at http://arxiv.org/abs/astro-ph/0312136 and will be published in the February 12, 2004 issue of the journal Nature.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

Original Source: Harvard CfA News Release

Image credit: NRAO
A team of astronomers using the National Science Foundation’s Robert C. Byrd Green Bank Telescope (GBT) has made the first conclusive detection of what appear to be the leftover building blocks of galaxy formation — neutral hydrogen clouds — swarming around the Andromeda Galaxy, located in the Andromeda constellation, the nearest large spiral galaxy to the Milky Way.

This discovery may help scientists understand the structure and evolution of the Milky Way and all spiral galaxies. It also may help explain why certain young stars in mature galaxies are surprisingly bereft of the heavy elements that their contemporaries contain.

“Giant galaxies, like Andromeda and our own Milky Way, are thought to form through repeated mergers with smaller galaxies and through the accretion of vast numbers of even lower mass ‘clouds’ — dark objects that lack stars and even are too small to call galaxies,” said David A. Thilker of the Johns Hopkins University in Baltimore, Maryland. “Theoretical studies predict that this process of galactic growth continues today, but astronomers have been unable to detect the expected low mass ‘building blocks’ falling into nearby galaxies, until now.”

Thilker’s research is published in the Astrophysical Journal Letters. Other contributors include: Robert Braun of the Netherlands Foundation for Research in Astronomy; Rene A.M. Walterbos of New Mexico State University; Edvige Corbelli of the Osservatorio Astrofisico di Arcetri in Italy; Felix J. Lockman and Ronald Maddalena of the National Radio Astronomy Observatory (NRAO) in Green Bank, West Virginia; and Edward Murphy of the University of Virginia.

The Milky Way and Andromeda were formed many billions of years ago in a cosmic neighborhood brimming with galactic raw materials — among which hydrogen, helium, and cold dark matter were primary constituents. By now, most of this raw material has probably been gobbled up by the two galaxies, but astronomers suspect that some primitive clouds are still floating free.

Previous studies have revealed a number of clouds of neutral atomic hydrogen that are near the Milky Way but not part of its disk. These were initially referred to as high-velocity clouds (HVCs) when they were first discovered because they appeared to move at velocities difficult to reconcile with Galactic rotation.

Scientists were uncertain if HVCs comprised building blocks of the Milky Way that had so far escaped capture, or if they traced gas accelerated to unexpected velocities by energetic processes (multiple supernovae) within the Milky Way. The discovery of similar clouds bound to the Andromeda Galaxy strengthens the case that at least some of these HVCs are indeed galactic building blocks.

Astronomers are able to use radio telescopes to detect the characteristic 21-centimeter radiation emitted naturally by neutral atomic hydrogen. The great difficulty in analyzing these low-mass galactic building blocks has been that their natural radio emission is extremely faint. Even those nearest to us, clouds orbiting our Galaxy, are hard to study because of serious distance uncertainties. “We know the Milky Way HVCs are relatively nearby, but precisely how close is maddeningly tough to determine,” said Thilker.

Past attempts to find missing satellites around external galaxies at well-known distances have been unsuccessful because of the need for a very sensitive instrument capable of producing high-fidelity images, even in the vicinity of a bright source such as the Andromeda Galaxy.

One might consider this task similar to visually distinguishing a candle placed adjacent to a spotlight. The novel design of the recently commissioned GBT met these challenges brilliantly, and gave astronomers their first look at the cluttered neighborhood around Andromeda.

The Andromeda Galaxy was targeted because it is the nearest massive spiral galaxy. “In some sense, the rich get richer, even in space,” said Thilker. “All else being equal, one would expect to find more primordial clouds in the vicinity of a large spiral galaxy than near a small dwarf galaxy, for instance. This makes Andromeda a good place to look, especially considering its relative proximity — a mere 2.5 million light-years from Earth.”

What the GBT was able to pin down was a population of 20 discrete neutral hydrogen clouds, together with an extended filamentary component, which, the astronomers believe, are both associated with Andromeda. These objects, seemingly under the gravitational influence of Andromeda’s halo, are thought to be the gaseous clouds of the “missing” (perhaps dark-matter dominated) satellites and their merger remnants. They were found within 163,000 light-years of Andromeda.

Favored cosmological models have predicted the existence of these satellites, and their discovery could account for some of the missing “cold dark matter” in the Universe. Also, confirmation that these low-mass objects are ubiquitous around larger galaxies could help solve the mystery of why certain young stars, known as G-dwarf stars, are chemically similar to ones that evolved billions of years ago.

As galaxies age, they develop greater concentrations of heavy elements formed by the nuclear reactions in the cores of stars and in the cataclysmic explosions of supernovae. These explosions spew heavy elements out into the galaxy, which then become planets and get taken up in the next generation of stars.

Spectral and photometric analysis of young stars in the Milky Way and other galaxies, however, show that there are a certain number of young stars that are surprisingly bereft of heavy elements, making them resemble stars that should have formed in the early stages of galactic evolution.

“One way to account for this strange anomaly is to have a fresh source of raw galactic material from which to form new stars,” said Murphy. “Since high-velocity clouds may be the leftover building blocks of galaxy formation, they contain nearly pristine concentrations of hydrogen, mostly free from the heavy metals that seed older galaxies.” Their merger into large galaxies, therefore, could explain how fresh material is available for the formation of G-dwarf stars.

The Andromeda Galaxy, also known as M31, is one of only a few galaxies that are visible from Earth with the unaided eye, and is seen as a faint smudge in the constellation Andromeda. When viewed through a modest telescope, Andromeda also reveals that it has two prominent satellite dwarf galaxies, known as M32 and M110. These dwarfs, along with the clouds studied by Thilker and collaborators, are doomed to eventually merge with Andromeda. The Milky Way, M33, and the Andromeda Galaxy plus about 40 dwarf companions, comprise what is known as the “Local Group.”

Today, Andromeda is perhaps the most studied galaxy other than the Milky Way. In fact, many of the things we know about the nature of galaxies like the Milky Way were learned by studying Andromeda, since the overall features of our own galaxy are disguised by our internal vantage point. “In this case, Andromeda is a good analogue for the Milky Way,” said Murphy. “It clarifies the picture. Living inside the Milky Way is like trying to determine what your house looks like from the inside, without stepping outdoors. However, if you look at neighbors’ houses, you can get a feeling for what your own home might look like.”

The GBT is the world’s largest fully steerable radio telescope.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Original Source: NRAO News Release

Image credit: RAS
In recent years, astronomers have obtained detailed measurements of the cosmic microwave background radiation – the ‘echo’ from the birth of the Universe during the Big Bang.

These results appear to indicate with remarkable precision that our Universe is dominated by mysterious ‘cold dark matter’ and ‘dark energy’. But now a group of UK astronomers has found evidence that the primordial microwave echoes may have been modified or ‘corrupted’ on their 13 billion year journey to the Earth.

The results from a team at the University of Durham, led by Professor Tom Shanks, are based on a new analysis of data from NASA’s Wilkinson Microwave Anisotropy Probe (WMAP) satellite.

The team has found that nearby galaxy clusters appear to lie in regions of sky where the microwave temperature is lower than average. This behaviour could be accounted for if the hot gas in the galaxy clusters has interacted with the Big Bang photons as they passed by and corrupted the information contained in this echo of the primordial fireball. Russian physicists R. A. Sunyaev and Ya. B. Zeldovich predicted such an effect in the early 1970’s, shortly after the discovery of the cosmic microwave background radiation.

This Sunyaev-Zeldovich effect has previously been seen in the cases of detailed observations of the microwave background in the vicinity of a few rich galaxy clusters and the WMAP team themselves have reported seeing the effect in their own data, close to cluster centres.

Now the Durham team has found evidence that hot gas in the clusters may influence the microwave background maps out to a radius of nearly 1 degree from the galaxy cluster centres, a much larger area than previously detected. This suggests that the positions of “clusters of clusters” or “superclusters” may also coincide with cooler spots in the pattern of microwave background fluctuations.

“The photons in the microwave background radiation are scattered by electrons in nearby clusters,” said Professor Shanks. “This causes important changes to the radiation by the time it reaches us.”

“If the galaxy clusters located several billion light years from Earth also have the same effect, then we must consider whether it is necessary to modify our interpretation of the satellite maps of the microwave background radiation.”

If the Durham result is confirmed, then the consequences for cosmology could be highly significant. The signature for dark energy and dark matter lies in the detailed structure of the ripples detected in the microwave background, tiny temperature variations that were created at a time when the radius of the Universe was a thousand times smaller than it is today.

If this primordial pattern has been corrupted by processes taking place in the recent past, long after galaxies and galaxy clusters formed, then it will, at best, complicate the interpretation of the microwave echo and, at worst, begin to undermine the previous evidence for both dark energy and cold dark matter.

“The power of this wonderful WMAP data is that it indicates that interpreting the microwave background ‘echo’ may be less straightforward than previously thought,” said team member Sir Arnold Wolfendale (previously Astronomer Royal).

The WMAP team has already reported that their measurements of the Big Bang’s microwave echo may have been compromised by the process of galaxy formation at an intermediate stage in the Universe’s history. They presented evidence that gas heated by first-born stars, galaxies and quasars may have also corrupted the microwave signal when the Universe was 10 or 20 times smaller than at the present day. Thus both the WMAP and Durham results suggest that the microwave echo of the Big Bang may have had to come through many more obstacles on its journey to the Earth than had previously been thought, with consequent possible distortion of the primordial signal.

“Our results may ultimately undermine the belief that the Universe is dominated by an elusive cold dark matter particle and the even more enigmatic dark energy,” said Professor Shanks.

Although the observational evidence for the standard model of cosmology remains strong, the model does contain very uncomfortable aspects. These arise first because it is based on two pieces of “undiscovered physics” – cold dark matter and dark energy – neither of which has been detected in the laboratory. Indeed, the introduction of these two new components greatly increases the complication of the standard Big Bang inflationary model.

The problems of dark energy run particularly deep: for example, its observed density is so small that it may be quantum mechanically unstable. It also creates problems for the theories of quantum gravity, which suggest that we may live in a Universe with 10 or 11 dimensions, all of them shrunk, with the exceptions of three in space and one in time.

Many theorists would therefore like an escape route from today’s standard model of cosmology and it remains to be seen how far these observations discussed by the Durham group will go in this direction. But if correct, they suggest that the rumours that we are living in a “New Era of Precision Cosmology” may prove to be premature!

Original Source: RAS News Release

Image credit: Gemini
Like a doctor trying to understand an elderly patient’s sudden demise, astronomers have obtained the most detailed observations ever of an old but otherwise normal massive star just before and after its life ended in a spectacular supernova explosion.

Imaged by the Gemini Observatory and Hubble Space Telescope (HST) less than a year prior to the gigantic explosion, the star is located in the nearby galaxy M-74 in the constellation of Pisces. These observations allowed a team of European astronomers led by Dr. Stephen Smartt of the University of Cambridge, England to verify theoretical models showing how a star like this can meet such a violent fate.

The results were published in the January 23, 2004 issue of the journal Science. This work provides the first confirmation of the long-held theory that some of the most massive (yet normal) old stars in the Universe end their lives in violent supernova explosions.

“It might be argued that a certain amount of luck or serendipity was involved in this finding,” said Dr. Smartt. “However, we’ve been searching for this sort of normal progenitor star on its deathbed for some time. I like to think that finding the superb Gemini and HST data for this star is a vindication of our prediction that one day we had to find one of these stars in the immense data archives that now exist.” Click here for more details on Dr. Smartt’s ongoing supernova program.

During the last few years, Smartt’s research team has been using the most powerful telescopes, both in space and on the ground, to image hundreds of galaxies in the hope that one of the millions of stars in these galaxies will some day explode as a supernova. In this case, the renowned Australian amateur supernova hunter, Reverend Robert Evans, made the initial discovery of the explosion (identified as SN203gd) while scanning galaxies with a 12-inch (31cm) backyard telescope from his home in New South Wales, Australia in June, 2003.

Following Evans’ discovery, Dr. Smartt’s team quickly followed up with detailed observations using the Hubble Space Telescope. These observations verified the exact position of the original or “progenitor” star. Using this positional data, Smartt and his team dug through data archives and discovered that observations by the Gemini Observatory and HST contained the combination of data necessary to reveal the nature of the progenitor.

The Gemini data was obtained during the commissioning of the Gemini Multi-Object Spectrograph (GMOS) on Mauna Kea, Hawaii in 2001. These data were also used to produce a stunning high-resolution image of the galaxy that clearly shows the red progenitor star. Click here for the full resolution Gemini image.

Armed with the earlier Gemini and HST observations Smartt’s team was able to demonstrate that the progenitor star was what astronomers classify as a normal red supergiant. Prior to exploding, this star appeared to have a mass about 10 times greater, and a diameter about 500 times greater than that of our Sun. If our sun were the size of the progenitor it would engulf the entire inner solar system out to about the planet Mars.

Red supergiant stars are quite common in the universe and an excellent example can be easily spotted during January from almost anywhere on the Earth by looking at Betelgeuse, the bright red shoulder star in the constellation of Orion (see finder chart here.) Like SN2003gd, it is believed that Betelgeuse could meet the same explosive fate at any time from next week to thousands of years from now.

After SN2003gd exploded, the team observed its gradually fading light for several months using the Isaac Newton Group of telescopes on La Palma. These observations demonstrated that this was a normal type II supernova, which means that the ejected material from the explosion is rich in hydrogen. Computer models developed by astronomers have long predicted that red supergiants with extended, thick atmospheres of hydrogen would produce these type II supernovae but until now have not had the observational evidence to back up their theories. However, the fantastic resolution and depth of the Gemini and Hubble images allowed the Smartt team to estimate the temperature, luminosity, radius and mass of this progenitor star and reveal that it was a normal large, old star. “The bottom-line is that these observations provide a strong confirmation that the theories for both stellar evolution and the origins of these cosmic explosions are correct,” said co-author Seppo Mattila of Stockholm Observatory.

This is only the third time astronomers have actually seen the progenitor of a confirmed supernova explosion. The others were peculiar type II supernovae: SN 1987A, which had a blue supergiant progenitor, and SN 1993J, which emerged from a massive interacting binary star system. Click here for more details.

Dr. Smartt concludes, “Supernova explosions produce and distribute the chemical elements that make up everything in the visible Universe ? especially life. It is critical that we know what type of stars produce these building blocks if we are to understand our origins.”

Archived Gemini and HST data was critical to the success of this project. “This discovery is a perfect example of archival data’s immense value to new scientific projects,” said Dr. Colin Aspin who is the Gemini Scientist responsible for the development of the Gemini Science Archive (GSA). He continued, “this discovery demonstrates the spectacular results that can be realized by using archival data and stresses the importance of developing the GSA for future generations of astronomers.”

The Gemini Multi-Object Spectrograph used to make the Gemini observations are twin instruments built as a joint partnership between Gemini, the Dominion Astrophysical Observatory, Canada, the UK Astronomy Technology Centre and Durham University, UK. Separately, the U.S. National Optical Astronomy Observatory provided the detector subsystem and related software. GMOS is primarily designed for spectroscopic studies where several hundred simultaneous spectra are required, such as when observing star and galaxy clusters. GMOS also has the ability to focus astronomical images on its array of over 28 million pixels.

The Isaac Newton Group of Telescopes (ING) is an establishment of the Particle Physics and Astronomy Research Council (PPARC) of the United Kingdom, the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO) of the Netherlands and the Instituto de Astrof?sica de Canarias (IAC) in Spain. The ING operates the 4.2 metre William Herschel Telescope, the 2.5 metre Isaac Newton Telescope, and the 1.0 metre Jacobus Kapteyn Telescope. The telescopes are located in the Spanish Roque de Los Muchachos Observatory on La Palma which is operated by the Instituto de Astrof?sica de Canarias (IAC).

Background Information:

Supernovae are among the most energetic phenomena observed in the entire Universe. When a star of more than about eight times the mass of our Sun reaches the end of its nuclear fuel reserve, its core is no longer stable from collapsing under its own immense weight. As the core of the star collapses, the outer layers are ejected in a fast-moving shock wave. This huge energy release results in a supernova that is about one billion times brighter than our Sun, and is comparable to the brightness of an entire galaxy. After destroying itself, the core of the star becomes either a neutron star or a black hole.

The team is composed of Stephen J. Smartt, Justyn R. Maund, Margaret A. Hendry, Christopher A. Tout, and Gerald F. Gilmore (University of Cambridge, UK), Seppo Mattila (Stockholm Observatory, Sweden), and Chris R. Benn (Isaac Newton Group of Telescopes, Spain).

Original Source: Gemini News Release

Image credit: PPARC
The discovery of a unique phenomenon: a beautiful set of expanding X-ray halos surrounding a gamma-ray burst which have never been seen before, (see Movie link at end), has been announced by an international team of astronomers led by Dr Simon Vaughan of the University of Leicester. The research has been accepted for publication in the Astrophysical Journal.

Gamma-ray bursts (GRB) are the most energetic form of radiation in the Universe and can be used to probe any material between Earth and the burst. In this case, the GRB lies behind the plane of our Galaxy, so its light has to travel through the gas and dust in the Galactic disc to reach us.

ESA’s gamma ray observatory satellite ‘Integral’ detected the 30 second long GRB 031203 on December 3rd 2003 and the halos were discovered in a follow-up observation that started 6 hours after the burst with ESA’s ‘XMM-Newton’ X-ray space telescope.

Commenting on the discovery, Professor Ian Halliday, Chief Executive of the UKs Particle Physics and Astronomy Research Council (PPARC) said Gamma-ray bursts are the most violent events in the Universe. Unlike the serene beauty of the stars that we can see with our eyes, the Gamma Ray Universe is a place of dramatic explosions, cosmic collisions and matter being sucked into black holes.

Halliday added This is a wonderful example of two of ESAs most advanced observatories in which UK scientists have made a significant contribution, working in harmony to reveal a new level of scientific understanding.

The fading X-ray emission from the GRB – the afterglow – is clearly seen in the image from the X-ray cameras on XMM-Newton. Uniquely, two rings centred on the afterglow were also seen. Dr Vaughan said “These rings are due to dust in our own Galaxy which is illuminated by the X-rays from the gamma-ray burst. The dust scatters some of the X-rays causing the rings, in the same way as fog scatters the light from a car’s headlights.” He added “Its like a shout in a cathedral; the shout of the gamma-ray burst is louder, but the Galactic reverberation, seen as the rings, is more beautiful.”

Due to the finite speed of light, X-rays from more distant dust reach us later, giving rise to the appearance of expanding rings. Dr Vaughan said “We expect to see an expanding ring on the sky if the dust is in a sheet roughly in the plane of the sky, but as we see two rings there must be two dust sheets between us and the GRB. Understanding how dust is distributed in our Galaxy is important. Dust helps cool gas clouds which can then collapse to form stars and planets. Knowing where dust is located helps astronomers determine where star and planet formation is likely to occur.”

Expanding X-ray dust scattering rings have never been seen before. Slower moving rings seen in visible light around a very few supernovae are caused by a similar effect.

The two halos are due to thin sheets of dust at 2,900 and 4,500 light-years away; the astronomers accurately measured the distances from the expansion rate of the halos. The distances have an uncertainty of just 2%, a remarkable level of accuracy for an object in our Galaxy. The nearest dust sheet is probably part of the Gum nebula, a bubble of hot gas resulting from many supernova explosions. The GRB itself is thought to have occurred in a small galaxy about a billion light-years away (one of the closest GRB galaxies).

Astronomers are still trying to understand the mysterious gamma-ray bursts. Some occur with the supernova explosion of a massive star when it has used up all of its fuel, although only stars which have lost their outer layers and which collapse to make a black hole seem able to make a GRB.

Today Integral and XMM-Newton provide astronomers with their most powerful facilities for studying gamma-ray bursts, but 2004 will see the launch of “Swift”, a new NASA mission with major UK involvement, which will be dedicated to GRBs. This will work in concert with the two ESA satellite observatories, providing more opportunities for discoveries in this cutting edge field. UK participation in Integral, XMM-Newton and Swift is funded by the Particle Physics and Astronomy Research Council.

Original Source: PPARC

Image credit: NOAO

A Chinese and US astronomer have discovered a young star at the heart of the Rosette Nebula that is ejecting a complex jet of material with knots and bow shocks. Normally these stars are hidden from the view of optical telescopes by the surrounding nebula, but severe ultraviolet radiation from nearby massive stars has cleared out the area. This gives astronomers have a rare opportunity to study how a young star like this forms. The Rosette Nebula is located 1,500 light-years away in the constellation of Monoceros.

A duo of Chinese and American astronomers have discovered a young star in the fierce environs of the Rosette Nebula that is ejecting a complex jet of material riddled with knots and bow shocks.

Stripped of its normally opaque surroundings by the intense ultraviolet radiation produced by nearby massive stars, this young stellar object is likely one of the last of its generation in this region of space. Its tenuous state of existence exposes the limitations that young stars?and perhaps even sub-stellar objects such as brown dwarfs and large planets?face in attempting to form in such a violent environment.

A close-up image from this study of the young star, and a striking, newly reprocessed wide-field image of the colorful Rosette Nebula, are available above.

?Most young stars are embedded in very dense molecular clouds, which makes our view of the early stages of star formation normally impossible with optical telescopes,? says Travis Rector of the University of Alaska Anchorage, co-author of a paper on the young stellar object (YSO) in the December 2003 issue of Astrophysical Journal Letters. ?This is one of only a few cases where a protostar is visible, making it a valuable discovery that will be studied in detail.?

Optical images of the jet taken at the WIYN 0.9-meter telescope at the National Science Foundation?s Kitt Peak National Observatory in Arizona show a highly-collimated jet, now known as Rosette HH1, stretching for more than 8,000 astronomical units (1 AU = 150 million kilometers). It contains a prominent knot and hints of others, which can be interpreted as ?bullets? of material being ejected from the rapidly rotating YSO at hypersonic velocities on the order of 2,500 kilometers per second. Bow shocks on the other side of the YSO suggest the existence of a degenerated counterjet extending in the opposite direction.

These interpretations of the jet were bolstered by optical spectroscopy of the jet system taken by co-author Jin Zeng Li of the Chinese Academy of Sciences in Beijing using the 2.16-meter telescope of the National Astronomical Observatories of China.

?If it is indeed a counterjet, it may be the only existing observational evidence of how bipolar jets evolve into monopoles, or at least highly asymmetric jets,? according to Jin Zeng Li. ?This suggests that this infant star has been starved of material as its accretion disk is evaporated, leaving a very low-mass star. In some cases, this process might result in an isolated brown dwarf or planetary mass object, offering a potential evolutionary solution for such lone objects that have been spotted in the Orion Nebula and other nearby hotspots in the Milky Way.?

Located an estimated 1,500 light-years from Earth in the constellation Monoceros, the Rosette Nebula is a spectacular region of ionized hydrogen excavated by the strong stellar winds from hot O- and B-type stars in the center of the young open cluster NGC 2244. It is a region of on-going star formation with an age of about three million years.

Kitt Peak National Observatory is part of the National Optical Astronomy Observatory, Tucson, Ariz., which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under a cooperative agreement with the National Science Foundation.

Original Source: NOAO News Release

Image credit: NOAO

Astronomers from NASA’s Jet Propulsion Laboratory have measured the distance to the Pleiades star cluster to greatest precision ever. After a decade’s worth of interferometric measurements, the team found that the star cluster is between 434 and 446 light years from Earth. This is important because the European Hipparcos satellite previously measured a distance to the cluster that would have contradicted theoretical models of the life cycles of stars. This new measurement shows that Hipparcos was incorrect, and the established theory still holds.

The cluster of stars known as the Pleiades is one of the most recognizable objects in the night sky, and for millennia has been celebrated in literature and legend. Now, a group of astronomers has obtained a highly accurate distance to one of the stars of the Pleiades known since antiquity as Atlas. The new results will be useful in the longstanding effort to improve the cosmic distance scale, and to conduct research on the stellar life-cycle.

In the January 22 issue of the journal Nature, astronomers from the California Institute of Technology and NASA?s Jet Propulsion Laboratory, both in Pasadena, Calif., report the best-ever distance to the double-star Atlas. The star, along with “wife” Pleione and their daughters, the “seven sisters,” are the principal stars of the Pleiades that are visible to the unaided eye, although there are actually thousands of stars in the cluster. Atlas, according to the team’s decade of careful interferometric measurements, is somewhere between 434 and 446 light-years from Earth.

The range of distance to the Pleiades cluster may seem somewhat imprecise, but in fact is accurate by astronomical standards. The traditional method of measuring distance is by noting the precise position of a star and then measuring its slight change in position when Earth itself has moved to the other side of the sun. This approach can also be used to find distance on Earth: If you carefully record the position of a tree an unknown distance away, move a specific distance to your side, and measure how far the tree has apparently “moved,” then it’s possible to calculate the actual distance to the tree by using trigonometry.

However, this procedure gives only a rough distance estimate to even the nearest stars, due to the gigantic distances involved and the subtle changes in stellar position that must be measured.

The team’s new measurement settles a controversy that arose when the European satellite Hipparcos provided a much shorter distance measurement to the Pleiades than expected and contradicted theoretical models of the life cycles of stars.

This contradiction was due to the physical laws of luminosity and its relationship to distance. A 100-watt light bulb one mile away looks exactly as bright as a 25- watt light bulb half a mile away. So to figure out the wattage of a distant light bulb, we have to know how far away it is. Similarly, to figure out the “wattage” (luminosity) of observed stars, we have to measure how far away they are. Theoretical models of the internal structure and nuclear reactions of stars of known mass also predict their luminosities. So the theory and measurements can be compared.

However, the Hipparcos data provided a distance lower than that assumed from the theoretical models, thereby suggesting either that the Hipparcos distance measurements themselves were off, or else that there was something wrong with the models of the life cycles of stars. The new results show that the Hipparcos data was in error, and that the models of stellar evolution are indeed sound.

The new results come from careful observation of the orbit of Atlas and its companion — a binary relationship that wasn’t conclusively demonstrated until 1974 and certainly was unknown to ancient watchers of the sky. Using data from the Mount Wilson stellar interferometer, next to the historic Mount Wilson Observatory, and the Palomar Testbed Interferometer at Caltech’s Palomar Observatory near San Diego, the team determined a precise orbit of the binary.

Interferometry is an advanced technique that allows, among other things, for the “splitting” of two bodies so far away that they normally appear as a single blur, even in the biggest telescopes. Knowing the orbital period and combining it with orbital mechanics allowed the team to infer the distance between the two bodies, and with this information, to calculate the distance of the binary to Earth.

“For many months I had a hard time believing our distance estimate was 10 percent larger than that published by the Hipparcos team,” said the lead author, Xiao Pei Pan of JPL. “Finally, after intensive rechecking, I became confident of our result.”

Coauthor Shrinivas Kulkarni, a Caltech astronomy and planetary science professor, said, “Our distance estimate shows that all is well in the heavens. Stellar models used by astronomers are vindicated by our value.”

“Interferometry is a young technique in astronomy and our result paves the way for wonderful returns from the Keck interferometer and the anticipated Space Interferometry Mission that is expected to be launched in 2009,” said coauthor Michael Shao of JPL, prinicipal investigator for that planned mission, and for the Keck Interferometer, which links the two 10-meter telescopes at the Keck Observatory in Hawaii. The Palomar Testbed Interferometer was designed and built by a team of researchers from JPL led by Mark Colavita and Shao. It served as an engineering testbed for the Keck Interferometer.

Original Source: NASA/JPL News Release

Image credit: John Rowe

The search for Earthlike planets begins with the search for Sunlike stars. At the top of the list is a reasonably nearby star called 37 Gem; located in the Gemini constellation. Astronomer Maggie Turnbull was asked to make a short list of thirty candidate stars that closely matched our own Sun out of a total list 2,350 stars which are within one hundred light years from us. This short list, including 37 Gem will be used by the Terrestrial Planet Finder mission, which will search for habitable planets by looking for the visible light of oxygen or water in an Earthlike planet – a sure sign of life.

The thirty-seventh most westerly star in the constellation, Gemini, is a yellow-orange star like our own sun. The star is called 37 Geminorum, but for astrophysicist Margaret Turnbull, the star is special because it offers a case study for considering what might qualify as a good candidate for harboring habitable planets.

In building her list of stars that might support planets with liquid water and oxygen, she has to exclude suns that are extreme: either too young or too old, that rotate too fast, or that are variable enough in brightness to cause climatic chaos on any nearby world.

At a distance of 56.3 light-years away, the star 37 Gem has yet to show tell-tale signs of having such planets, or any planets–but future NASA and European telescopes are looking to target stars just like 37 Gem since they might share some of the same properties that made our own solar system habitable. More than 100 extrasolar planets have been found so far using ground-based telescopes, and estimates for the total such planets in our galaxy may total in the billions of candidate worlds.

Working from the University of Arizona in Tucson, Maggie Turnbull was asked to make a short list of thirty star candidates that most closely resembled other suns capable of supporting the conditions for life to flourish. Starting her search among stars less than one hundred light-years away yielded about 2,350 stars to consider further.

Turnbull recently presented her results to a group of scientists from NASA’s space-telescope project, the Terrestrial Planet Finder (TPF), which will search for habitable planets by using visible light with the “signature” of water and/or oxygen from an Earth-type planet. After TPF’s scheduled launch around 2013, will follow the European Darwin project involving six space telescopes.

The stellar list was pared down from an even larger list (17,129 stars within 450 light-years, or 140 parsecs), which Turnbull and adviser Jill Tarter of the SETI Institute first published in Astrophysical Journal. The list became known as the Catalog of Nearby Habitable Stellar Systems (or HabCat ). Their article published in August, entitled “Target Selection for SETI: I. A Catalog of Nearby Habitable Stellar Systems,” expanded previous candidate lists by nearly ten-fold, or an order-of-magnitude.

To support complex life, a candidate star must be the right color, brightness, and age. If it is a middle-aged star like our own, it will have burned through enough fusionable light elements to produce heavier metals like iron, but not so old that it is collapsing or so young that life is only a distant future prospect. Based on what fragments we know about how complex life appeared on Earth, Turnbull’s search aims to find the ‘Goldilocks’ of stars that seems ‘just right’.

So why 37 Gem?
37 Geminorum lies in the northwest part of constellation Gemini , named after the Twins. For amateur astronomers with a good backyard telescope, 37 Gem is visible. In Greek mythology, the Gemini twins sailed with Jason in the quest for the Golden Fleece; during a storm, the twins helped save their ship ARGO from sinking, and so the constellation became much valued by sailors.

Most stars like Gem 37 are grouped into a small number of spectral classes, based roughly on the color of light they emit. Called the Henry Draper Catalog, the star compendium lists spectral classes in seven broad categories, from the hottest to the coolest stars. These types are designated, in order of decreasing temperature, by the letters O, B, A, F, G, K, and M. The nomenclature is rooted in long-obsolete ideas about stellar evolution, but the terminology remains. Our sun, classified on a finer scale as a typical ‘G2V’ dwarf, is approximately 4.5 billion years old. The candidate star, 37 Gem, is similarly middle-aged, but somewhat older by a billion years, at 5.5 billion years.

The spectra of G-type stars like our own (and 37 Gem) are dominated by certain chemical elements, as signaled by their characteristic spectral lines (or emissions). The elements of most current interest are metals, particularly for those star-signatures rich in iron, calcium, sodium, magnesium, and titanium. In astronomical terms, compared to our sun’s classification as a typical G2V dwarf, 37 Gem has a slightly hotter surface temperature. Thus Turnbull’s prime pick–37 Gem– is catalogued as a G0V dwarf–meaning it is also a yellow-orange main sequence dwarf star. Because G stars are characterized by the presence of these metallic lines and a weak hydrogen spectra, they share a common age, mass, and luminosity.

Otherwise, 37 Gem is close to our own solar twin, or a Gemini-like counterpart to the Sun: 1.1 times our sun’s mass, 1.03 times its diameter, and 1.25 times its luminosity.

Luminosities are “perhaps the most important information”, Turnbull told Astrobiology Magazine, “we use in determining the habitability of nearby stars” for complex life, because luminosity indicates which phase of life the star is in, and that in turn dictates how long the star will remain stable.

Astrobiology Magazine had the opportunity to talk with Maggie Turnbull at the Steward Observatory in Tucson about how to select stellar candidates for habitability.

Astrobiology Magazine (AM): Your recent survey began looking at around 100-light years distant from our Sun, and all stars inwards from that radius, correct? That was the visual sphere for starting the search?

Margaret Turnbull (MT): There are about 2,350 Hipparcos stars within 30 parsecs (90 light
years), the maximum distance for the Terrestrial Planet Finder (TPF) mission. There are about 5,000 total stars within that distance, but we are only looking at Hipparcos stars so my starting list is 2,350 stars long.

AM: Have you ever gotten hold of a backyard telescope to see 37 Gem?

MT: It should certainly be visible with a backyard telescope, but no, I haven’t looked at it with my own eyes! Because of the photometry (measuring its brightness) and spectroscopy (measuring its composition) I have looked at, I feel like I “know” it without ever having seen it.

However, there is more observing to be done for 37 Gem. For example, we do need to carry out high resolution infrared imaging of this star before we can say it should be a target–if we discover that there is a lot of debris floating around, we’ll have to take it off the list.

AM: Was the star, 37 Gem, much different from number two on the list of the thirty best candidates?

MT: Actually, the “best” stars are all very similar to one another, and in reality it doesn’t make much sense to try to rank them. 37 Gem happens to be one of the very nearest stars that also satisfies the engineering criteria, so at this time it looks like a very good candidate for the TPF search.

AM: Just out of curiousity, what star was officially number two on the list?

MT: When you are only going to look at thirty stars, they all better be “number one.” That is, every star we observe has to be of primary interest to the mission, because we have no time to waste. We are still in the process of precisely defining the primary mission goal.

If the goal is to look at range of spectral types, then the top stars may include very nearby K or M stars, but if the goal is to look at 30 of the most Sun-like stars, then stars like 18 Sco (a solar twin at 14 parsecs in the Constellation Scorpius), beta CVn (the “hound”), or 51 Peg (“Pegasus”, the flying horse) may end up being our best bets.

AM: Are there one or two pieces of missing data that would help the classification hone in better on star candidates?

MT: At this time, high-resolution infrared imaging is the missing piece of data that we definitely need. We need to know if these stars have dusty debris disks that would make it hard to detect planets orbiting there.

The Sun has a substantial amount of zodiacal dust because Jupiter is constantly stirring up the asteroid belt and as the asteroids collide they add dust to the Solar System.

A similar level of dust around other stars might not ruin our chances of seeing planets, but we’d certainly like to keep that to a minimum.

AM: What are your future plans for the stellar list in support of the Terrestrial Planet Finder and Darwin missions?

MT: I haven’t yet presented my ‘final’ list to the TPF science working group on Nov 18th and 19th at the US Naval Observatory, during a meeting with others who are creating their own lists.

I have already presented my methodology to the group, but now we will be meeting with engineers who will explain to us the constraints of the instrument and we will have to refine further the list to accommodate their criteria.

Their criteria will include things like: can’t have a companion star within several arcseconds even if the companion is not a concern for planet stability, because the extra light will contaminate the field of view; can’t look at stars fainter than about 6th magnitude; can only look at stars at least ~60 degrees away from the Sun during the whole year, etc.

AM: You published your first catalog of habitable stars in August of this year, and there is a part two to that classification. What are the main plans for Part II of the HabCat?

MT: Jill Tarter and I have recently submitted a second paper on the SETI target list which will appear in the Astrophysical Journal Supplements in December. This paper gives a list of old, high metallicity open clusters, the nearest 100 stars regardless of stellar type, and about 250,000 main sequence stars from the Tycho Catalogue, all of which will be observed by the Allen Telescope Array (ATA) whenever a HabCat star isn’t available for us to observe.

The primary ATA beam will be pointed by radio astronomers, and they will be making very high resolution maps of their own targets, while at the same time we will be observing HabCat stars (or stars from our lists in Paper 2) for SETI.

AM: Finally, are the missions, Kepler and TPF, planning the kinds of enhancements that would yield a detection of more Earth-sized planets, not just gas giants, for a given star in their surveys?

MT: Yes. Kepler will give us an indication of how common terrestrial planets are by watching thousands of sun-like stars for “transits”–events where the planet actually passes in front of the star it is orbiting and temporarily blocks a little of the star’s light.

Terrestrial Planet Finder will follow up on this by actually imaging planets orbiting the nearest stars, and telling us whether these planets have atmopheres by taking spectra.

We can look for water, oxygen, and carbon dioxide, and if we’re lucky we may even see some direct indications of life in the form of a vegetation signature or strong atmospheric disequilibrium, such as the simultaneous presence of oxygen and methane (due to the simultaneous presence of plants and methanogen bacteria on Earth).

What’s Next
Any mission to detect and spectroscopically characterize terrestrial planets around other stars must be designed so that it can detect diverse types of terrestrial planets with a useful outcome. Such missions are now under study–the Terrestrial Planet Finder (TPF), by NASA, and Darwin by ESA, the European Space Agency. The principal goal of TPF/Darwin is to provide data to the biologists and atmospheric chemists.

The TPF/Darwin concept hinges on the assumption that one can screen extrasolar planets for habitability spectroscopically. For such an assumption to be valid, we must answer the following questions. What makes a planet habitable and how can they be studied remotely? What are the diverse effects that biota might exert on the spectra of planetary atmospheres? What false positives might we expect? What are the evolutionary histories of atmospheres likely to be? And, especially, what are robust indicators of life?

TPF/Darwin must survey nearby stars for planetary systems that include terrestrial sized planets in their habitable zones (“Earth-like” planets). Through spectroscopy, TPF/Darwin must determine whether these planets have atmospheres and establish whether they are habitable.

The Kepler mission is also scheduled for launch into solar orbit in October 2006. Kepler is intended as a mission to determine the frequency of inner planets near the habitable zone of a wide range of stars. Kepler will simultaneously observe 100,000 stars in our galactic “neighborhood,” looking for Earth-sized or larger planets within the “habitable zone” around each star – the not-too-hot, not-too-cold zone where liquid water might exist on a planet.

To highlight the difficulty of detecting an Earth-sized planet orbiting a distant star, Kepler’s principal investigator, William Borucki of NASA Ames points out it would take 10,000 Earths to cover the Sun’s disk. One NASA estimate says Kepler should discover 50 terrestrial planets if most of those found are about Earth’s size, 185 planets if most are 30 percent larger than Earth and 640 if most are 2.2 times Earth’s size. In addition, Kepler is expected to find almost 900 giant planets close to their stars and about 30 giants orbiting at Jupiter-like distances from their parent stars.

Because most of the gas giant planets found so far orbit much closer to their stars than Jupiter does to the Sun, Borucki believes that during the four- to six-year mission, Kepler will find a large proportion of planets quite close to stars. If that proves true, he says, “We expect to find thousands of planets.”

Using present methods, astronomers today would find it very difficult to detect an Earth-sized planet around the star 37 Gem. Past analyses have however ruled out some choices. For instance, a giant planet like our own Jupiter or Saturn does not orbit around 37 Gem. These studies have suggested that giant planets of one-tenth to 10 times the mass of Jupiter do not exist close to 37 Gem (within 0.1 to four astronomical units, or one earth-sun distance, AUs, see also Cummings et al, 1999 ). Because of the challenges of finding dim planets near to much brighter stars, almost all of the extrasolar planets found so far are like our own Jupiter–massive, probably gaseous, and unlikely to harbor conditions for life owing to their close proximity to a parent star.

But conditions around 37 Gem might support smaller, inner planets like Venus or Earth. No one knows. Only future surveys will have the instrumentation capable of finding such Earth-like planets.

Models of stars like 37 Gem, do however, support the possible existence of at least one stable orbit for an Earth-like planet (with liquid water) centered around one earth-sun distance (1.12 AU). Such a presumed planet would orbit between the distances of Earth and Mars in our Solar System. This undiscovered planet, if it can be detected in future studies, would have a year that lasts more than 450 days, or an orbital period of around 1.3 Earth-years.

Since oxygen-generating life on Earth took about two billion years to take hold, stars much younger than this would likely not have had sufficient time for life to evolve towards any complex forms. Given the billions of years required for evolution of life on earth, scientists could question whether life would stand a chance in a shorter-lived solar system. Hotter, more massive stars have always been considered less likely to harbor life but not because they would be too hot. Planets could still enjoy temperate climates, just further out than Earth is from the Sun, and at orbits farther away from the its own parent star. The first problem of habitability is one of time, not temperature. Hotter stars tend to burn out faster — perhaps too fast for life to develop there.

Original Source: Astrobiology Magazine

Image credit: UA

Astronomers with the University of Arizona tested a new infrared camera on the 6.5-metre MMTO telescope, and produced an extremely detailed image of planetary nebula IC 2149. The object, located 3,600 light-years away, consists of a cloud of dust and gas shed from a dying star. The image is so clear because of the telescope’s adaptive optics system, which removes distortion caused by the Earth’s atmosphere – the telescope’s secondary mirror changes shape thousands of times a second to compensate for fluctuations in the light.

Astronomers testing a new near-infrared camera on southern Arizona’s 6.5-meter (21-foot) MMTO telescope have produced a sharp, detailed image of an aged planetary nebula basking in the light of its several-thousand-times brighter dying central star.

It is the most detailed wide-angle picture yet taken using the large telescope’s unique adaptive optics system, a technique that removes atmospheric blurring.

Astronomers from the University of Arizona’s Steward Observatory and Center for Astronomical Adaptive Optics made this picture of Planetary Nebula IC 2149 from exposures taken at the UA/Smithsonian MMT Observatory on 8,550-foot Mount Hopkins, Ariz. The planetary nebula, a cloud of gas and dust shed from a dying star, is 3,600 light-years away and 1.5 trillion miles (2.5 trillion kilometers) across.

The observers used UA astronomer Donald W. McCarthy’s near-infrared camera ARIES to search for specific gases in the star’s debris. They took images in three infrared colors of light, then combined them into a single false-color image.

While astronomers took the images, the large telescope’s secondary mirror changed its shape thousands of times each second to compensate in real-time for atmospheric turbulence that distorts starlight. The MMTO’s ultra-thin, 2-foot-diameter secondary mirror focuses light as steadily as if Earth had no atmosphere. For more about the MMTO’s superb adaptive optics, click here.

The resulting images demonstrate two benefits of the MMTO’s adaptive optics system, McCarthy and UA astronomy graduate student Patrick A. Young said.

First, the images are about three times sharper than images obtained with UA’s NICMOS cameras on the Hubble Space Telescope, and they are as sharp as Hubble images at shorter visible wavelengths.

Second, the sharper images show faint structure close to bright objects like stars in much greater detail. The image of IC2149 shows a contorted mixture of gas and dust several thousand times dimmer than the star itself. The halo around the star is the size of solar systems.

The team selected Planetary Nebula IC 2149 for the engineering tests of ARIES from 10 candidate targets during their telescope time last October, Young said.

“What you are seeing here is a star, a little less massive than the sun, that has used up all the fuel at its nuclear-burning core,” Young said. “Unable to produce energy, the core starts to contract, and turns into a ball of carbon and oxygen the size of the Earth. This gravitational contraction releases a lot of energy, and that causes the star to shed its outer atmosphere. The material we are actually seeing in the picture is the gas and dust being lit up by the light from the central star.”

Their observations suggest that all of the molecular hydrogen in the nebula has been destroyed by radiation from the central star, leaving only ionized hydrogen. Added to other evidence, this indicates that the nebula is several thousands of years old, Young said. Most planetary nebulae disperse and vanish in less than 10,000 years. The gas and dust ejected by the dying star contain heavy elements from which future planets may form.

Original Source: University of Arizona News Release