Category: Astronomy

Observed Fields in NGC 300. Image credit: ESO Click to enlarge
Cepheid pulsating stars have been used as distance indicators since the early discovery of Henrietta Leavitt almost a hundred years ago. From her photographic data regarding one of the Milky Way’s neighbour galaxies, the Small Magellanic Cloud, she found that the brightness of these stars closely correlate with their pulsation periods.

This period-luminosity relation, once calibrated, allows a precise distance determination of a galaxy once Cepheids have been discovered in it, and their periods and mean magnitudes have been measured.

While the Cepheid method doesn’t reach out far enough in the Universe to directly determine cosmological parameters like the Hubble constant, Cepheid distances to relatively nearby resolved galaxies have laid the foundation for such work in the past, as in the Hubble Space Telescope Key Project on the Extragalactic Distance Scale. Cepheids indeed constitute one of the first steps in the cosmic distance ladder.

The current main problem with the Cepheid method is that its dependence on a galaxy’s metallicity, that is, its content in elements more heavy than hydrogen and helium, has never been measured accurately so far. Another intriguing difficulty with the method is the fact that the total absorption of the Cepheid’s light on its way to Earth, and in particular the amount of absorption within the Cepheid’s host galaxy, must be precisely established to avoid significant errors in the distance determination.

To tackle this problem, Wolfgang Gieren (University of Concepcion, Chile) and his team devised a Large Programme at ESO: the Araucaria Project. Its aim is to obtain distances to relatively nearby galaxies with a precision better than 5 percent.

One of the key galaxies of the team’s Araucaria Project is the beautiful, near face-on galaxy NGC 300 in the Sculptor Group. In a wide-field imaging survey carried out at the ESO/MPG 2.2-m telescope on La Silla in 1999-2000, the team had discovered more than a hundred Cepheid variables spanning a broad range in pulsation period. Pictures of the galaxy, and some of its Cepheids from these data were released in ESO Press Photos 18a-h in 2002. Last year, the team presented the distance of NGC 300 as derived from these optical images in V- and I-bands.

The team complemented this unique dataset with new data taken with the ISAAC near-infrared camera and spectrometer on ESO’s 8.2-m VLT Antu telescope.

“There are three substantial advantages in the Cepheid distance work when images obtained through near-infrared passbands are used instead of optical data”, says Wolfgang Gieren. The most important gain is the fact that the absorption of starlight in the near-infrared, and particularly in the K-band, is dramatically reduced as compared to the effect interstellar matter has at visible wavelengths. A second advantage is that Cepheid light curves in the infrared have smaller amplitudes and are much more symmetrical than their optical counterparts, making it possible to measure a Cepheid’s mean K-band brightness just from a very few, and in principle from just one observation at known pulsation phase. In contrast, optical work requires the observation of full light curves to determine accurate mean magnitudes. The third basic advantage in the infrared is a reduced sensitivity of the period-luminosity relation to metallicity, and to blending with other stars in the crowded fields of a distant galaxy.

Taking this into account, one of the main purposes of the team’s Large Programme has been to conduct near-infrared follow-up observations of Cepheids in their project’s target galaxies which have previously been discovered in optical wide-field surveys.

Deep images in the J and K bands of three fields in NGC 300 containing 16 Cepheids were taken with VLT/ISAAC in 2003.

“The high quality of the data allowed a very accurate measurement of the mean J- and K- magnitudes of the Cepheids from just 2 observations of each star obtained at different times”, says Grzegorz Pietrzynski, another member of the team, also from Concepcion.

Using these remarkable data the period-luminosity relations were constructed. “They are the most accurate infrared PL relations ever obtained for a Cepheid sample in a galaxy beyond the Magellanic Clouds”, emphasizes Wolfgang Gieren.

The total absorption of light (“reddening”) of the Cepheids in NGC 300 was obtained by combining the values for the distance of the galaxy obtained in the various optical and near-infrared bands in which NGC 300 was observed. This led to the discovery that there is a very significant contribution to the total reddening from absorption intrinsic to NGC 300. This intrinsic absorption has an important effect on the determination of the distance but had not been taken into account previously.

The team was able to measure the distance to NGC 300 with the unprecedented total uncertainty of only about 3 percent. The astronomers found that NGC 300 is located 6.13 million light-years away.

Original Source: ESO News Release

This new planet is larger than Pluto. Image credit: NASA/JPL. Click to enlarge.
A planet larger than Pluto has been discovered in the outlying regions of the solar system.

The 10th planet was discovered using the Samuel Oschin Telescope at Palomar Observatory near San Diego, Calif. The discovery was announced today by planetary scientist Dr. Mike Brown of the California Institute of Technology in Pasadena, Calif., whose research is partly funded by NASA.

The planet is a typical member of the Kuiper belt, but its sheer size in relation to the nine known planets means that it can only be classified as a planet, Brown said. Currently about 97 times further from the sun than the Earth, the planet is the farthest-known object in the solar system, and the third brightest of the Kuiper belt objects.

“It will be visible with a telescope over the next six months and is currently almost directly overhead in the early-morning eastern sky, in the constellation Cetus,” said Brown, who made the discovery with colleagues Chad Trujillo, of the Gemini Observatory in Mauna Kea, Hawaii, and David Rabinowitz, of Yale University, New Haven, Conn., on January 8.

Brown, Trujillo and Rabinowitz first photographed the new planet with the 48-inch Samuel Oschin Telescope on October 31, 2003. However, the object was so far away that its motion was not detected until they reanalyzed the data in January of this year. In the last seven months, the scientists have been studying the planet to better estimate its size and its motions.

“It’s definitely bigger than Pluto,” said Brown, who is a professor of planetary astronomy.

Scientists can infer the size of a solar system object by its brightness, just as one can infer the size of a faraway light bulb if one knows its wattage. The reflectance of the planet is not yet known. Scientists can not yet tell how much light from the sun is reflected away, but the amount of light the planet reflects puts a lower limit on its size.

“Even if it reflected 100 percent of the light reaching it, it would still be as big as Pluto,” says Brown. “I’d say it’s probably one and a half times the size of Pluto, but we’re not sure yet of the final size.

“We are 100 percent confident that this is the first object bigger than Pluto ever found in the outer solar system,” Brown added.

The size of the planet is limited by observations using NASA’s Spitzer Space Telescope, which has already proved its mettle in studying the heat of dim, faint, faraway objects such as the Kuiper-belt bodies. Because Spitzer is unable to detect the new planet, the overall diameter must be less than 2,000 miles, said Brown.

A name for the new planet has been proposed by the discoverers to the International Astronomical Union, and they are awaiting the decision of this body before announcing the name.

The Jet Propulsion Laboratory manages the Spitzer Space Telescope mission for NASA’s Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at Caltech. Caltech manages JPL for NASA.

For more information and images see: http://www.nasa.gov/vision/universe/solarsystem/newplanet-072905-images.html

or http://www.astro.caltech.edu/palomarnew/sot.html

For information about NASA and agency programs on the Web, visit:

http://www.nasa.gov/home/index.

Original Source: NASA/JPL News Release

A view of the observatories atop Mount Lemmon’s summit. Image credit: Yvette Cendes. Click to enlarge.
Welcome to the world of astronomy camp. Every year, the University of Arizona astronomy camps host teenagers, adults, and educators from around the world. Taking place on Mount Lemmon, a mountain with numerous astronomical instruments near Tucson, Arizona, the camps allow the participants to become ?guest astronomers? from being housed in the professional astronomers? dormitories to learning how to use the various computer programs. The campers even get to do their own research using telescopes and instruments that would turn most professionals green with envy: a 12? equipped with a CCD camera, a 40? with a photometer, a 60? with an imager, and even a 61? with a spectrometer on nearby Mount Bigelow.

This year, the 2005 Advanced Teen Camp took place for nine days in late June and early July. The campers were diverse: 28 campers evenly divided between male and female, ranging from age 14 to age 18, from sixteen states and one foreign country. Each camper had to write an essay and have a letter of recommendation to be accepted, and all the campers arrived in Tucson excited but nervous about what to expect. ?We want this to be the best week of your life,? said Dr. Don McCarthy, a Steward Observatory astronomer and director of astronomy camp. By the last day, most campers agreed that it had been just that.

Before astronomy camp began, the campers were encouraged to begin brainstorming project ideas for research they would like to conduct during the week. The campers then had two days to refine ideas before they were written as proposals and submitted to the camp?s Telescope Allocation Committee (TAC), which then figured out an observing schedule on each telescope for the remainder of the week. After all the data had been collected and analyzed, the camp culminated on the last day with a miniature conference where each group presented their findings.

The projects that were carried out during astronomy camp varied in incredible amounts and showed just what the campers were interested in from imaging galaxies to finding the properties of planetary nebulae. One group was on the 61? every night taking data from quasars, which yielded things such as the distance and velocity of each object after careful calculation. Another group, which became all too painfully aware that astronomy is filled with problems, went through three different types of instrumentation before finally getting usable data on an asteroid?s light curve.

The campers even made observations that contributed to cutting edge astronomical research. Armed with the imaging capabilities of the 60? and the help of the Catalina Sky Survey, the campers tracked the movements for several Kuiper Belt Objects (KBOs) and conducted a search for Near Earth Objects (NEOs). The KBO group was successful in tracking the KBOs and even recovered a previously lost object. The NEO group topped even that: after ?blinking? several hundred images taken of the same parts of the sky at various times the group not only recovered several lost NEOs but discovered a completely new one themselves! The newly discovered asteroid, 2005 MG5, was discovered on the nearest point of its orbit to Earth, and was followed up on by several other observatories around the world. Not bad for a few teenagers still in high school!

When not observing or sleeping off the effects of staying up all night (to the excitement of any teenager, the campers did not have to wake before noon) the days were filled with lectures on various astronomical topics from the camp counselors on everything from the properties of reflecting telescopes to the Deep Impact mission. There was also time to observe our nearest star, the Sun, through numerous safe ways including pinhole projection and through a hydrogen alpha filter. The days were rounded off with other interesting activities, such as watching astronomy-related Simpsons episodes and numerous chess duels.

In the middle of camp, there was a break from the usual schedule for an overnight trip to Mount Graham International Observatory, which houses the Large Binocular Telescope (LBT), the Sub-Millimeter Telescope (SMT), and the Vatican Observatory (jokingly referred to as the ?pope scope?). This caused great excitement among the campers for good reason: the LBT will become the largest telescope in the world upon completion with its twin 8.4m mirrors, the first of which saw first light in 2004. Not only did the campers sleep in the telescope building, they got to see the building open up at sunset! To top it off, the campers had the opportunity to use the SMT telescope, observing various objects throughout the night in radio wavelengths not available on Mount Lemmon.

Before the campers knew it, it was the last day of camp and graduation was being held in downtown Tucson in the additional company of camper relatives. While handing out the certificates, however, the campers were roasted a little by the counselors, who singled out campers for everything from ?The Falsetto Award? to ?Greatest Fruit Lover? and ?Best Impersonation of Spock.? After numerous hugs all around and sorrowful goodbyes, the campers left for homes scattered around the globe. Would there be another reunion sometime in the future? It is likely: down the line most campers end up in the most top-notch universities, and many continue on in similar engineering and science fields. Not surprisingly, many even go on to become the next generation of astronomers, citing their week in Arizona as the primary inspiration in their decision.

What does the future hold for astronomy camp? It appears the program will soon be expanding: numerous plans are in the works for Mount Lemmon, including a brand-new 2.4 meter telescope exclusively for camp use. In the world of astronomy camp, the sky is truly the limit.

Visit the Astronomy Camp website

Written by Yvette Cendes

Ultra-violet image of the hidden spiral arms of NGC 4625. Image credit: NASA/JPL/Caltech. Click to enlarge
A new image from NASA’s Galaxy Evolution Explorer shows that a galaxy once thought to be rather plain and old is actually endowed with a gorgeous set of young spiral arms.

The unusual galaxy, called NGC 4625, is a remarkable find because it is relatively nearby. Until now, astronomers had thought that this kind of youthful glow in galaxies was a thing of the past.

“This galaxy is an amazing surprise,” said Dr. Armando Gil de Paz of the Carnegie Observatories, Pasadena, Calif., lead author of a paper appearing in the July issue of Astrophysical Journal Letters. “We are practically up-close and personal with a galaxy undergoing an evolutionary stage that was thought to occur only at the dawn of the universe, in very young and faraway galaxies.”

The image can be found at http://www.nasa.gov/centers/jpl/missions/galex.html or http://www.galex.caltech.edu/ . It offers astronomers their best look yet at what our Milky Way galaxy might have looked like in earlier times.

“We do not fully understand how stars were created in our galaxy,” said Dr. Barry Madore of the Carnegie Observatories, co-author of the new paper. “This nearby galaxy represents one of our possible histories, in which stars developed first in the galaxy core and then later in the arms.”

Previous visible-light images of NGC 4625 showed only an oval-shaped ball of light, with very faint hints of a halo of spiral arms. These arms were finally revealed to the ultraviolet eyes of the Galaxy Evolution Explorer. Their intense brightness indicates that the arms are teeming with hot, newborn stars, which shine primarily with ultraviolet light.

“The stars in the arms are about one billion years old, while the stars in the body are about ten times older,” said Gil de Paz.

NGC 4625’s spiral arms are very lengthy, extending four times beyond the size of the core of the galaxy. They represent the largest ultraviolet galactic disk discovered so far.

Also of interest in the new Galaxy Evolution Explorer image is a nearby companion galaxy, which looks very similar to NGC 4625, yet has no arms. How could this galactic duo have turned out so differently? Astronomers do not know, but some theories hold that the presence of the armless galaxy was required for NGC 4625 to grow a set.

“We know that interactions between galaxies can spur the creation of stars, but it is not clear why only one galaxy ended up with arms,” said Dr. Chris Martin of the California Institute of Technology in Pasadena, Calif, principal investigator for the Galaxy Evolution Explorer.

Previous studies of the gas distribution around the two galaxies indicate that NGC 4625 might have developed in a more dynamically stable environment, while the armless galaxy grew up in a more chaotic and turbulent setting.

Other authors of this paper include: Dr. S. Boissier, Carnegie Observatories; Dr. R. Swaters, University of Maryland, College Park; Dr. R. J. Tuffs, Max Planck Institut fur Kernphysik, Germany; Dr. K. Sheth, Caltech; Dr. R.C. Kennicutt, University of Arizona, Tucson; Drs. L. Bianchi and D. Thilker, Johns Hopkins University, Baltimore, Md.

Caltech leads the Galaxy Evolution Explorer mission and is responsible for science operations and data analysis. NASA’s Jet Propulsion Laboratory, 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. South Korea and France are the international partners in the mission.

For images and information about the Galaxy Evolution Explorer on the Internet, visit http://www.galex.caltech.edu/ .

Original Source: NASA News Release

UV image of supernova in spiral galaxy M100. Image credit: ESA/NASA/Immer et al. Click to enlarge
Scientists have found that a star that exploded in 1979 is as bright today in X-ray light as it was when it was discovered years ago, a surprise finding because such objects usually fade significantly after only a few months.

Using ESA?s XMM-Newton space observatory, a team of astronomers has discovered that this supernova, called SN 1979C, shows no sign of fading. The scientists can document a unique history of the star, both before and after the explosion, by studying rings of light left over from the blast, similar to counting rings in a tree trunk.
?This 25-year-old candle in the night has allowed us to study aspects of a star explosion never before seen in such detail,? said Dr Stefan Immler, leader of the team, from NASA?s Goddard Space Flight Center, USA. ?All the important information that usually fades away in a couple of months is still there.?

Among the many unique finds is the history of the star?s stellar wind dating back 16 000 years before the explosion. Such a history is not even known about our Sun. Also, the scientists could measure the density of the material around the star, another first. The lingering mystery, though, is how this star could fade away in visible light yet remain so radiant in X-rays.

Without fuel and thus energy to support their gravity, such stars first implode. The core reaches a critical density, and much of the collapsing matter gets bounced back out violently into space by powerful shockwaves.

Supernovae can outshine an entire galaxy and are often easily seen in neighbouring galaxies with simple amateur telescopes. Supernovae are typically half as bright after about ten days and fade steadily after that, regardless of the wavelength.

SN 1979C has in fact faded in optical light by a factor of 250 becoming barely visible with a good amateur telescope. In X-rays, however, this supernova is still the brightest object in its host galaxy, M100, in the constellation ?Coma Berenices?.

In identifying the history of the star that created SN 1979C, the team found that this star, about 18 times more massive than our Sun, produced fierce stellar winds. That material was flung into space for millions of years, creating concentric rings around the star.

The X-rays – produced after the explosion when the supernova shock caught up with the stellar wind and heated it to a temperature of several million degrees – illuminated 16 000 years? worth of stellar activity.

?We can use the X-ray light from SN 1979C as a ?time machine? to study the life of a dead star long before it exploded,? said Immler.

The detailed analysis was only possible because SN 1979C has not yet faded away. Scientists have 25 years? worth of data in a variety of wavelengths, from radio waves through to optical/ultraviolet and X-rays. They speculate that the abundance of stellar wind has provided ample material to keep SN 1979C glowing so brightly.

The team also captured a rare glimpse of the ultraviolet radiation from the supernova using XMM-Newton. The ultraviolet image independently confirms what the X-ray analysis found: that the circumstellar material ? covering a region 25 times larger than our Solar System – has a relatively high density of 10 000 atoms per cubic centimetre, or about 1000 times denser than the wind from our Sun. The ultraviolet image also shows galaxy M100 in detail never seen before.

?XMM-Newton is known among scientists as a superior X-ray observatory, but the study of SN 1979 demonstrates the importance of the satellite’s simultaneously observing ultraviolet and optical telescope,? said Dr Norbert Schartel, XMM-Newton Project Scientist at ESA’s European Space Astronomy Centre (ESAC) in Spain.

Original Source: ESA Portal

Artist’s conception of a possible collision around BD +20 307. Image credit: Gemini Observatory/Jon Lomberg. Click to enlarge
A relatively young star located about 300 light-years away is greatly improving our understanding of the formation of Earth-like planets.

The star, going by the unassuming name of BD +20 307, is shrouded by the dustiest environment ever seen so close to a Sun-like star well after its formation. The warm dust is believed to be from recent collisions of rocky bodies at distances from the star comparable to that of the Earth from the Sun. The results were based on observations done at the Gemini and W.M. Keck Observatories, and were published in the July 21 issue of the British science journal Nature.

This finding supports the idea that comparable collisions of rocky bodies occurred early in our solar system’s formation about 4.5 billion years ago. Additionally, this work could lead to more discoveries of this sort which would indicate that the rocky planets and moons of our inner solar system are not as rare as some astronomers suspect.

?We were lucky. This set of observations is like finding the proverbial needle in the haystack,? said Inseok Song, the Gemini Observatory astronomer who led the U.S.-based research team. ?The dust we detected is exactly what we would expect from collisions of rocky asteroids or even planet-sized objects, and to find this dust so close to a star like our Sun bumps the significance way up. However, I can’t help but think that astronomers will now find more average stars where collisions like these have occurred.”

For years, astronomers have patiently studied hundreds of thousands of stars in the hopes of finding one with an infrared dust signature (the characteristics of the starlight absorbed, heated up and reemitted by the dust) as strong as this one at Earth-to-Sun distances from the star. “The amount of warm dust near BD+20 307 is so unprecedented I wouldn’t be surprised if it was the result of a massive collision between planet-size objects, for example, a collision like the one which many scientists believe formed Earth’s moon,” said Benjamin Zuckerman, UCLA professor of physics and astronomy, member of NASA’s Astrobiology Institute, and a co-author on the paper. The research team also included Eric Becklin of UCLA and Alycia Weinberger formerly at UCLA and now at the Carnegie Institution.

BD +20 307 is slightly more massive than our Sun and lies in the constellation Aries. The large dust disk that surrounds the star has been known since astronomers detected an excess of infrared radiation with the Infrared Astronomical Satellite (IRAS) in 1983. The Gemini and Keck observations provide a strong correlation between the observed emissions and dust particles of the size and temperatures expected by the collision of two or more rocky bodies close to a star.

Because the star is estimated to be about 300 million years old, any large planets that might orbit BD +20 307 must have already formed. However, the dynamics of rocky remnants from the planetary formantion process might be dictated by the planets in the system, as Jupiter did in our early solar system. The collisions responsible for the observed dust must have been between bodies at least as large as the largest asteroids present today in our solar system (about 300 kilometers across). “Whatever massive collision ocurred, it managed to totally pulverize a lot of rock,” said team member Alycia Weinberger.

Given the properties of this dust, the team estimates that the collisions could not have occurred more than about 1,000 years ago. A longer history would give the fine dust (about the size of cigarette smoke particles) enough time to be dragged into the central star.

The dusty environment around BD +20 307 is thought to be quite similar, but much more tenuous than what remains from the formation of our solar system. “What is so amazing is that the amount of dust around this star is approximately one million time greater than the dust around the Sun,” said UCLA team member Eric Becklin. In our solar system the remaining dust scatters sunlight to create an extremely faint glow called the zodiacal light (see image above). It can be seen under ideal conditions with the naked eye for a few hours after evening or before morning twilight.

The team?s observations were obtained using Michelle, a mid-infrared spectrograph/imager built by the UK Astronomy Technology Centre, on the Frederick C. Gillette Gemini North Telescope, and the Long Wavelength Spectrograph (LWS) at the W.M. Keck Observatory on Keck I.

Original Source: Gemini Observatory News Release

Artist?s conception of the gamma ray flare expanding from SGR 1806-20. Image credit: NASA.Click to enlarge
A gigantic explosion on a neutron star halfway across the Milky Way galaxy, the largest such explosion ever recorded in the universe, should allow astronomers for the first time to probe the interiors of these mysterious stellar objects.

An international team of astrophysicists, combing through data from a NASA X-ray satellite, the Rossi X-ray Timing Explorer, reports in the July 20th issue of Astrophysical Journal Letters that the explosion produced vibrations within the star, like a ringing bell, that generated rapid fluctuations in the X-ray radiation it emitted into space. These X-ray pulses, emitted during each seven second rotation by the fast-spinning star, contained the frequency vibrations of the neutron star?s massive quakes.

Much as geologists probe the Earth?s interior from seismic waves produced by earthquakes and solar astronomers study the sun using shock waves traveling through the sun, the X-ray fluctuations discovered from this explosion should provide critical information about the internal structure of neutron stars.

?This explosion was akin to hitting the neutron star with a gigantic hammer, causing it to ring like a bell,? said Richard Rothschild, an astrophysicist at the University of California?s Center for Astrophysics and Space Sciences and one of the authors of the journal report. ?Now the question is, What does the frequency of the neutron star?s oscillations?the tone produced by the ringing bell?mean?

?Does it mean neutron stars are just a bunch of neutrons packed together? Or do neutron stars have exotic particles, like quarks, at their centers as many scientists believe? And how does the crust of a neutron star float on top of its superfluid core? This is a rare opportunity for astrophysicists to study the interior of a neutron star, because we finally have some data theoreticians can chew on. Hopefully, they?ll be able to tell us what this all means.?

The biggest star quakes ripped through the neutron star at an incredible speed, vibrating the star at 94.5 cycles per second. ?This is near the frequency of the 22nd key of a piano, F sharp,? said Tomaso Belloni, an Italian member of the team who measured the signals.

The international team?led by GianLuca Israel, Luigi Stella and Belloni of Italy?s National Institute of Astrophysics?discovered the oscillations from data it retrieved two days after Christmas by the Rossi X-Ray Timing Explorer, a satellite designed to study the fluctuating X-ray emissions from stellar sources. The peculiar oscillations the researchers found began three minutes after a titanic explosion on a neutron star that, for only a tenth of a second, released more energy than the sun emits in 150,000 years. The oscillations then gradually receded after about 10 minutes.

Neutron stars are the dense, rapidly spinning cores of matter that result from the crushing collapse of a star that has depleted all of its nuclear fuel and exploded in a cataclysmic event known as a supernova. The collapse is so crushing that electrons are forced into the atomic nucleus and combine with protons to become neutrons. The resulting sphere of neutrons is so dense?packing the mass of the sun in a sphere only 10 miles in diameter?that a spoonful of its matter would weigh billions of tons on Earth.

Most of the millions of neutron stars in our Milky Way galaxy produce magnetic fields that are a trillion times stronger than those of the Earth. But astrophysicists have discovered less than a dozen ultra-high magnetic neutron stars, called ?magnetars,? with magnetic fields a thousand times greater?strong enough to strip information from a credit card at a distance halfway to the moon.

These intense magnetic fields are strong enough they sometimes buckle the crust of neutron stars, causing ?star quakes? that result in the release of gamma rays, a more energetic form of radiation than X-rays. Four of these magnetars are known to do just that and are termed ?soft gamma repeaters,? or SGRS, by astrophysicists because they flare up randomly and release a series of brief bursts of gamma rays.

SGR 1806-20, the formal designation of the neutron star that exploded and sent X-rays flooding through the galaxy on December 27, 2004?producing a flash brighter than anything ever detected beyond the solar system?is one of them. The flash was so bright that it blinded all X-ray satellites in space for an instant and lit up the Earth?s upper atmosphere.

Astrophysicists suspect the burst of gamma-ray and X-ray radiation from this unusually large explosion could have come from a highly twisted magnetic field surrounding the neutron star that suddenly snapped, creating a titanic quake on the neutron star.

?The scenario was probably analogous to a twisted rubber band that finally broke and in the process released a tremendous amount of energy,? said Rothschild. ?With this energy release, the magnetic field surrounding the magnetar was presumably able to relax to a more stable configuration.?

The December 27 flash of energy was detected by several other NASA and European satellites and recorded by radio telescopes around the world. It already has been the subject of numerous scientific papers published in recent months.

?The sudden and surprising occurrence of this giant flare, which will help us learn more about the nature of magnetars and the internal make-up of neutron stars,? said Rothschild, ?underlines the importance of having satellites and telescopes with the capacity to record unusual and unpredictable phenomena in the universe.?

Other members of the international team were Pier Giorgio Casella, Simone Dall?Osso and Massimo Persic of Italy?s National Institute of Astrophysics; Yoel Rephaeli of UCSD and the University of Tel Aviv; Duane Gruber, formerly of UCSD and now at the Eureka Scientific Corporation in Oakland, Calif; and Nanda Rea of the National Institute for Space Research in the Netherlands.

Original Source: UCSD News Release

Here’s a link to the biggest stars in the Universe.

An artist’s impression of a Superwind in a young massive galaxy. Image credit: PPARC/David Hardy. Click to enlarge
A team of astronomers, led by the University of Durham, has discovered the aftermath of a spectacular explosion in a galaxy 11.5 billion light years away. Their observations, reported today (14th July 2005) in the journal Nature provide the most direct evidence yet of a galaxy being almost torn apart by explosions that produce a stream of high-speed material known as “Superwinds”. The observations were made using the 4.2 metre William Herschel Telescope on La Palma in which the UK is a major stakeholder.

Through Superwinds, galaxies are thought to blast a significant part of their gas into intergalactic space at speeds of up to several hundred miles per second. The driving force behind them is the explosion of many massive stars during an intense burst of star formation early in the galaxy’s life, possibly assisted by energy from a super massive black hole growing at its heart.

Superwinds are vital to the theory of galaxy formation for several reasons: firstly, they limit the sizes of galaxies by preventing further star formation – without them theoretical models indicate far more very bright galaxies than are actually seen in the Universe today. Secondly, they carry heavy elements – Star dust – far from their production sites in stars out into intergalactic space, providing raw material for planets and life across the Universe. Whilst the theories predicted Superwinds of this kind existed, previously observed examples were much smaller phenomena in nearby galaxies. These observations provide some of the most direct evidence yet for the existence of large-scale, galaxy-wide superwinds so far back in the history of the Universe.

The discovery of the Superwind was made by observing the gas in the halo of a galaxy (known as “LAB-2”), which at over 300,000 light years across is about three times larger than the disk of our own Milky Way galaxy. The astronomers discovered that light from hot glowing hydrogen gas is dimmed in a very specific way across the entire galaxy.

“We believe that the dimming is caused by a shell of cooled material which has been swept-up from the surroundings by a galaxy-wide Superwind explosion,” said Dr. Richard Wilman of the University of Durham. “Based on the uniformity of the absorption across the galaxy, it appears that the explosion was triggered several hundred million years earlier. This allows time for the gas to cool and to slow down from its high ejection speed, and thus to produce the absorption. As we see it, the shell is probably a few hundred thousand light years in front of its parent galaxy,” added Dr. Wilman.

Astronomers have long been puzzled about why key elements for the formation of planets and ultimately life (such as carbon, oxygen and iron) are so widely distributed throughout the Universe; only 2 billion years after the Big Bang, the remotest regions of intergalactic space have been enriched with them. The Superwind observed in this galaxy shows how such blast waves can travel through space carrying the elements formed deep within galaxies.

Crucial to the discovery and its interpretation was the ability to obtain detailed information on the gas in two-dimensions across the whole galaxy. This was made possible by a technique known as integral field spectroscopy, which is only just reaching maturity on the world’s largest telescopes.

Dr Joris Gerssen, a key member of the Durham team, explains, “Most astronomical spectroscopy is performed by placing a small aperture, or a narrow slit on the target, which for complex, extended sources such as this galaxy gives a rather incomplete picture”.

To overcome this the astronomers used an integral field spectrograph called ‘Sauron’ for a large survey of nearby galaxies, built at the Observatoire de Lyon by a collaboration of French, Dutch and UK astronomers.

Dr Gerssen added,” “Sauron is truly unique and its high efficiency means that it can more than hold its own against instruments on the world’s largest telescopes, some twice the size of the William Herschel Telescope. Nevertheless, the sheer distance of our target galaxy meant that Sauron had to stare at it for over 15 hours in order to make this discovery”.

“Sauron has provided us with the best evidence so far for an extensive outflow from a galaxy undergoing a huge starburst. These measurements are among the first steps towards understanding the physics of galaxy formation.,” commented Prof. Roger Davies, University of Oxford, one of the institutes involved on Sauron,” and we look forward to using similar two-dimensional spectrographs being built for 8m telescopes; these will probe the galaxy formation process to even earlier times.”

To date, observational evidence for Superwinds in young galaxies in the distant Universe has been largely indirect and circumstantial; efforts have focussed on searching for their subtle statistical signatures in large surveys of galaxies and intergalactic gas.

According to Prof. Richard Bower, from the University of Durham’s Institute of Computational Cosmology who initiated the research, “Astronomers have observed high-speed outflows in distant star-forming galaxies for several years, but never before have we been able to gauge their true scale from observations of a single galaxy. By taking advantage of the highly extended emission source of this galaxy, we can see the outflow as a kind of silhouette against the whole galaxy. This suggests that Superwinds are truly galaxy-wide in scale, and that they really are as important as our theories require.”

Original Source: PPARC News Release

Artist’s impression of neutron star IGR J16283-4838. Image Credit:NASA/Dana Berry. Click to enlarge
An international team of scientists has uncovered a rare type of neutron star so elusive that it took three satellites to identify it.

The findings, made with ESA?s Integral satellite and two NASA satellites, reveals new insights about star birth and death in our Galaxy. We report this discovery, highlighting the complementary nature of European and US spacecraft, on the day in which ESA?s Integral celebrates 1000 days in orbit.
The neutron star, called IGR J16283-4838, is an ultra-dense ?ember? of an exploded star and was first seen by Integral on 7 April 2005. This neutron star is about 20,000 light years away, in a ?double hiding place?. This means it is deep inside the spiral arm Norma of our Milky Way galaxy, obscured by dust, and then buried in a two-star system enshrouded by dense gas.

?We are always hunting for new sources,? said Simona Soldi, the scientist at the Integral Science Data Centre in Geneva, Switzerland, who first saw the neutron star. ?It is exciting to find something so elusive. How many more sources like this are out there??

Neutron stars are the core remains of ?supernovae?, exploded stars once about ten times as massive as our Sun. They contain about a Sun’s worth of mass compacted into a sphere about 20 kilometres across.

?Our Galaxy?s spiral arms are loaded with neutron stars, black holes and other exotic objects, but the problem is that the spiral arms are too dusty to see through,? said Dr Volker Beckmann at NASA Goddard Spaceflight Centre, lead author of the combined results.

?The right combination of X-ray and gamma-ray telescopes could reveal what is hiding there, and provide new clues about the true star formation rate in our Galaxy,? he added.

Because gamma rays are hard to focus into sharp images, the science team then used the X-ray telescope on Swift to determine a precise location. In mid April 2005, Swift confirmed that the light was ?highly absorbed?, which means the binary system was filled with dense gas from the stellar wind of the companion star.

Later the scientists used the Rossi Explorer to observe the source as it faded away. This observation revealed a familiar light signature, clinching the case for a fading high-mass X-ray binary with a neutron star.

IGR J16283-4838 is the seventh so-called ?highly absorbed?, or hidden neutron star to be identified. Neutron stars, created from fast-burning massive stars, are intrinsically tied to star formation rates. They are also energetic ?beacons? in regions too dusty to study in detail otherwise. As more and more are discovered, new insights about what is happening in the Galaxy’s spiral arms begin to emerge.

IGR J16283-4838 revealed itself with an ?outburst? on or near its surface. Neutron stars such as IGR J16283-4838 are often part of binary systems, orbiting a normal star. Occasionally, gas from the normal star, lured by gravity, crashes onto the surface of the neutron star and releases a great amount of energy. These outbursts can last for weeks before the system returns to dormancy for months or years.

Integral, the Rossi Explorer and Swift all detect X-rays and gamma rays, which are far more energetic than the visible light that our eyes detect. Yet each satellite has different capabilities. Integral has a large field of view, enabling it to scan our Milky Way galaxy for neutron stars and black hole activity.

Swift contains a high-resolution X-ray telescope, which allowed scientists to zoom in on IGR J16283-4838. The Rossi Explorer has a timing spectrometer, a device used to uncover properties of the light source, such as speed and rapid variations in the order of milliseconds.

Original Source: ESA Portal

This view of nearly 10,000 galaxies is the deepest visible-light image of the cosmos. Image credit: Hubble. Click to enlarge
One of the fastest supercomputers in the world and the first ever designed specifically to study the evolution of star clusters and galaxies is now in operation at Rochester Institute of Technology.

The new computer, built by David Merritt, professor of physics in RIT?s College of Science, uses a novel architecture to reach speeds much higher than that of standard supercomputers of comparable size.

Known as gravitySimulator, the computer is designed to solve the ?gravitational N-body problem?. It simulates how a galaxy evolves as the stars move about each other in response to their own gravity. This problem is computationally demanding because there are so many interactions to calculate requiring a tremendous amount of computer time. As a result, standard supercomputers can only carry out such calculations with thousands of stars at a time.

The new computer achieves much greater performance by incorporating special accelerator boards, called GRAPEs or Gravity Pipelines, into a standard Beowulf-like cluster. The gravitySimulator, which is one of only two machines of its kind in the world, achieves a top speed of 4 Teraflops, or four trillion calculations per second, making it one of the 100 fastest computers in the world, and it can handle up to 4 million stars at once. The computer cost over $500,000 to construct and was funded by RIT, the National Science Foundation, and NASA.

Since gravitySimulator was installed in the spring, Merritt and his associates have been using it to study the binary black hole problem- what happens when two galaxies collide and their central, supermassive black holes form a bound pair.

?Eventually the two black holes are expected to merge into a single, larger black hole,? Merritt says. ?But before that happens, they interact with the stars around them, ejecting some and swallowing others. We think we see the imprints of this process in nearby galaxies, but so far no one has carried out simulations with high enough precision to test the theory.?

Merritt and his team will also use gravitySimulator to study the dynamics of the central Milky Way Galaxy in order to understand the origin of our own black hole.

Merritt sees the gravitySimulator as an important example of RIT?s development as a major scientific research institute. ?Our unique combination of in-class instruction, experiential learning and research will be a major asset in the continued development of astrophysics and other research disciplines here at RIT,? Merritt says. ?The gravitySimulator is the perfect example of the cutting edge work we are already doing and will be a major stepping stone for the development of future scientific research.?

Original Source: RIT News Release