Posted on by Fraser Cain

Discovery Set to Launch Tuesday Morning

The Return to Flight mission STS-114 crew. Image credit: NASA/KSC. Click to enlarge
With some work still to go, NASA is moving toward a new launch attempt for the Space Shuttle Discovery Tuesday, July 26, at 10:39 a.m. EDT. Engineers are wrapping up a troubleshooting plan to address a fuel sensor system issue that caused Space Shuttle managers to scrub the first launch attempt for the Return to Flight mission, STS-114.

At a meeting today of the Mission Management Team, Shuttle managers decided on a plan to complete outstanding work on the External Tank’s liquid hydrogen low-level fuel sensor system circuit that runs from the External Tank into the Orbiter. The plan outlines a series of steps that could culminate in a launch next Tuesday. First, engineers will complete tests to look at electromagnetic interference as a factor in the sensor system circuit malfunction. Then, workers will swap circuits for two of the sensors to provide a means to isolate the problem to the wiring or the point sensor box, should the problem recur during the countdown. Next, engineers will shore up the electrical grounding to reduce further the chance of electromagnetic interference with the sensor system.

For a Tuesday launch, the official launch countdown for Discovery will begin Saturday. During the countdown, engineers will closely watch the behavior of the sensor system circuit as the tank is filled with super-cooled propellants.

Including the first launch attempt on Tuesday, there are at least four opportunities for Discovery to launch during the current launch window, which extends until July 31. NASA managers are also looking at the possibility of additional launch opportunities in the first week of August.

For the latest information on the Space Shuttle’s Return to Flight, visit:
http://www.nasa.gov/returntoflight

Original Source: NASA News Release

Posted on by Fraser Cain

A Supernova that Won’t Fade Away

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

Posted on by Fraser Cain

Dusty Disk Could Hide a New Earth

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

Posted on by Fraser Cain

Search for Mars Methane

The impact crater, known as “Endurance”. Image credit: NASA/JPL/Cornell. Click to enlarge
Mars is the planet that refuses to say “die.” In 1996, after centuries of speculation about canals, icecaps and vegetation, NASA’s David McKay reported seeing traces of ancient bacteria in a meteorite from Mars. Scientists have debated this finding ever since, and many now believe that the intriguing traces are probably not of biological origin.

Within the last few years, however, two simple chemicals intimately associated with life on Earth have been discovered on Mars. Large amounts of frozen water were discovered at the surface, and traces of methane appeared in the atmosphere.

Water is necessary for life as we know it, and most of the methane on Earth is made by microbes. Although the twin discoveries redoubled interest in the possibility of life on Mars, nobody is suggesting that anything is living on the planet’s surface, where temperatures average minus 63 degrees Celsius and harmful ultraviolet radiation pierces the thin atmosphere.

On Mars, as on Earth, temperatures rise as you go deeper down into the planet. Somewhere between a dozen and a thousand meters below the surface, conditions may be warm enough for liquid water, which is necessary for even non-biological methane production on Earth. But could a living ecosystem be hidden deep under the martian surface? On Earth, subterranean microbes survive without sunlight, free oxygen, or contact with the surface.

The question becomes more intriguing when you consider that most deep-Earth microbes are primitive, single-celled organisms that power their metabolism with chemical energy from their environment. These microbes are called “methanogens” because they make methane as a waste product.

Three NASA missions have discovered signs of water on Mars. In 2000, Mars Global Surveyor images of gullies suggested to many that water recently flowed on the martian surface. In May 2002, the gamma ray spectrometer on Mars Odyssey found a huge deposit of hydrogen in shallow polar soil — a sure sign of water ice. Then, in December 2004, researchers using the Mars Exploration Rover Opportunity announced that they had discovered rocks that had been formed by the periodic flooding of water on the surface. Such findings support the idea that Mars was warm and wet billions of years ago.

While water is a necessary condition for life, methane may be actual evidence of life. In the past two years, three separate research groups have seen spectral signs of methane on Mars:

* In 2003, Michael Mumma of Goddard Space Flight Center (GSFC) detected methane using spectrometers at two large earthbound telescopes. He has since told several scientific meetings that large variations exist in methane concentration on Mars. In a presentation at a NASA Astrobiology Institute meeting in April 2005, Mumma said the detection of martian methane varied with geography: there was an average of 200 parts per billion (ppb) detected at the equator, and 20 to 60 ppb near the poles.

* Vladimir Krasnopolsky, a research professor at Catholic University of America in Washington D.C., also detected methane on Mars. Like Mumma, Krasnopolsky used spectrometers on Earth-based telescopes. He calculated a global average of 11 ppb, with a range of 7 to 15 ppb. The data, as Krasnopolsky reported to a European Geosciences Union meeting in April 2004, came from 1999 observations of the whole planet’s disk.

“We didn’t try to make localized measurements because we did not expect any variation from place to place,” Krasnopolsky told Astrobiology Magazine.

* In December 2004, the European Space Agency’s Mars Express delivered the first methane data from a Mars orbiter. In the journal Science, Vittorio Formisano of the Institute of the Physics of Interplanetary Space in Rome and colleagues reported measurements made with the satellite’s Planetary Fourier Spectrometer. Their measurements were similar to Krasnopolsky’s numbers: A concentration of 10 ppb, plus or minus 5 ppb.

Although the Krasnopolsky and Formisano studies independently pointed to similar concentrations of methane, some planetary scientists express skepticism because the amount detected is very faint.

“The detections have been right at the detection limit of the instruments,” says William Boynton of the University of Arizona, principal investigator on the gamma ray spectrometer on Mars Odyssey. “I’m not completely convinced it’s a solid detection yet. It’s likely, but I wouldn’t put it in the bank.”

The matter of methane

The methane on Mars was detected with spectrometry — the analysis of light waves. Because each atom and molecule emits and absorbs characteristic wavelengths of light, spectrometers can determine the composition of distant objects by measuring these wavelengths. To study gases in the atmosphere of Mars, spectroscopists use instruments that can analyze the infrared light that is emitted when solar radiation warms the planet’s surface. As that infrared radiation speeds toward Earth, gases in the martian atmosphere can block, or absorb, certain frequencies. When the infrared light is concentrated in a telescope and separated by a spectroscope’s diffraction grating, the missing wavelengths show which particular atoms or molecules have absorbed light en route to Earth. Thus, a methane “line” on a spectroscope curve is a reflection of the light that methane has blocked.

There are complications, however. When faint light from a planet is collected in a terrestrial telescope, atoms and molecules in space or in Earth’s atmosphere will block some wavelengths. Spectroscopists must compensate for these non-martian signals. And because Mars is moving relative to Earth, the absorption lines appear in the “wrong” places until additional compensations are made.

Any methane on Mars today is not a legacy of ancient conditions, because solar radiation would destroy the molecules in the atmosphere within 600 years. Instead, the methane either was brought to Mars on comets or meteorites, or it was made on Mars. If we have glimpsed some made-on-Mars methane, was it made by geological or chemical processes — or by biology?

Original Source: NASA Astrobiology

Posted on by Fraser Cain

July 26 Targeted for Discovery Launch

Space Shuttle is largely hidden by the Rotating Service Structure. Image credit: NASA/KSC. Click to enlarge
NASA is targeting Tuesday, July 26 as the earliest possible date to launch the Space Shuttle Discovery on the Return to Flight mission (STS-114). The determination was made during Monday’s meeting of the Mission Management Team (MMT) at Kennedy.

The MMT reviewed efforts by teams of engineers. The engineers are working through a troubleshooting plan to address an issue with a liquid hydrogen low-level fuel sensor circuit. The sensor circuit failed a routine prelaunch check during the countdown July 13, delaying Discovery’s first launch attempt.

NASA is still working to launch Discovery by the end of the July window that extends to the 31st. A dozen teams, with hundreds of engineers across the country, are expected to complete their battery of tests by Wednesday. While they have not isolated a cause of the sensor circuit failure, they have eliminated a number of possibilities. If the remaining tests are inconclusive, NASA could reload the External Tank with super-cooled propellants to see how the sensor circuit behaves. The tanking could be done as a test or as part of an actual launch countdown.

Commander Eileen Collins and her six Discovery crewmates come out of quarantine today for one day off. They resume quarantine and training later this week.

For the latest information about STS-114 on the Web, visit: http://www.nasa.gov/returntoflight

Original Source: NASA News Release

Posted on by Fraser Cain

Charon Passes in Front of a Star

An artist’s conception of Pluto and its moon Charon. Image credit: NASA. Click to enlarge
On a clear summer night, the stars aligned for MIT researchers watching and waiting for one small light in the heavens to be extinguished, just briefly.

Thanks to a feat of both astronomical and terrestrial alignment, a group of scientists from MIT and Williams College succeeded in observing distant Pluto’s tiny moon, Charon, hide a star. Such an event had been seen only once before, by a single telescope 25 years ago, and then not nearly as well.

The MIT-Williams consortium spotted it with four telescopes in Chile on the night of July 10-11.

The team expects to use data from this observation to assess whether Charon has an atmosphere, to measure its radius and to determine how round it is.

The data and results from the observation will be presented at the 2005 meeting of the American Astronomical Society’s Division of Planetary Sciences meeting to be held in Cambridge, England, in September.

MIT team leader James L. Elliot headed the group at the Clay Telescope at Las Campanas Observatory in Chile.

“We have been waiting many years for this opportunity. Watching Charon approach the star and then snuff it out was spectacular,” said Elliot, a professor in the Department of Earth, Atmospheric and Planetary Science and the Department of Physics at MIT in Cambridge, Mass.

Jay M. Pasachoff, team leader from Williams College in Williamstown, Mass., and a professor in that school’s Department of Astronomy, said, “It’s amazing that people in our group could get in the right place at the right time to line up a tiny body 4 billion miles away. It’s quite a reward for so many people who worked so hard to arrange and integrate the equipment and to get the observations.”

With the Clay Telescope’s 6.5-meter mirror (more than 21 feet across, the size of a large room) the researchers were able to observe changes throughout the event, which lasted less than a minute. While their electronic cameras sensitively recorded data, the light of the faint star was seen to dim and then, some seconds later, brighten. This kind of disappearance of a celestial body behind a closer, apparently larger one is known as an occultation.

Studying how the light dimmed and brightened will let the MIT-Williams consortium look for signs that Charon has an atmosphere. It has very little mass and thus little gravity to hold in an atmosphere, but it is so cold (being some 40 times farther from the sun than the Earth) that some gases could be held in place by the small amount of Charon’s gravity.

Other telescopes around Chile used by the MIT-Williams consortium included the 8-meter (more than 26 feet across) Gemini South on Cerro Pachon, the 2.5-meter (more than 8 feet across) DuPont Telescope at Las Campanas Observatory and the 0.8-meter (almost 3 feet across) telescope at the Cerro Armazones Observatory of Chile’s Catholic University of the North near Cerro Paranal.

The team had searched for a distribution of telescopes along a north-south line in Chile since the predictions of the starlight shadow of Charon were uncertain by several hundred kilometers. Since the star that was hidden is so far away, it casts a shadow of Charon that is the same size as Charon itself, about 1,200 kilometers in diameter. To see the event, the distant star, Charon and the telescopes in Chile had to be perfectly aligned. All of these telescopes had clear views of the event.

Other MIT affiliates involved in the observation were MIT graduate students Elisabeth Adams, Michael Person and Susan Kern and postdoctoral associate Amanda Gulbis.

The images from three telescopes in Chile, including the Clay Telescope, and one in Brazil, were taken with new electronic cameras and computer control obtained by MIT and Williams with an equipment grant from NASA. The expeditions were sponsored by NASA’s Planetary Astronomy Program.

A video showing the star dimming as Charon passes in front of it and then brightening again is posted on the Web at http://occult.mit.edu/research/occultations/Charon/C313.2/C313OccMovie.html.

Teams from the Observatory of Paris at Meudon and from the Southwest Research Institute in Boulder, Colo., also observed the occultation.

Original Source: MIT News Release

Posted on by Fraser Cain

How Millisecond Pulsars Spin So Fast

X-ray full-field view of the globular star cluster 47 Tucanae. Image credit: NASA/CXC/Northwestern U./C.Heinke et al. Click to enlarge
New Chandra observations give the best information yet on why such neutron stars, called millisecond pulsars, are rotating so fast. The key, as in real estate, is location, location, location – in this case the crowded confines of the globular star cluster 47 Tucanae, where stars are less than a tenth of a light year apart. Almost two dozen millisecond pulsars are located there. This large sample is a bonanza for astronomers seeking to test theories for the origin of millisecond pulsars, and increases the chances that they will find a critical transitional object such 47 Tuc W.

47 Tuc W stands out from the crowd because it produces more high-energy X-rays than the others. This anomaly points to a different origin of the X-rays, namely a shock wave due to a collision between matter flowing from a companion star and particles racing away from the pulsar at near the speed of light. Regular variations in the optical and X-ray light corresponding to the orbital period of the stars support this interpretation.

A team of astronomers from the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA pointed out that the X-ray signature and variability of the light from 47 Tuc W are nearly identical to those observed from an X-ray binary source known as J1808. They suggest that these similarities between a known millisecond pulsar and a known X-ray binary provide the long-sought link between these types of objects.

In theory, the first step toward producing a millisecond pulsar is the formation of a neutron star when a massive star goes supernova. If the neutron star is in a globular cluster, it will perform an erratic dance around the center of the cluster, picking up a companion star which it may later swap for another.

As on a crowded dance floor, the congestion in a globular cluster can cause the neutron star to move closer to its companion, or to swap partners to form an even tighter pair. When the pairing becomes close enough, the neutron star begins to pull matter away from its partner. As matter falls onto the neutron star, it gives off X-rays. An X-ray binary system has been formed, and the neutron star has made the crucial second step toward becoming a millisecond pulsar.

The matter falling onto the neutron star slowly spins it up, in the same way that a child’s carousel can be spun up by pushing it every time it comes around. After 10 to 100 million years of pushing, the neutron star is rotating once every few milliseconds. Finally, due to the rapid rotation of the neutron star, or the evolution of the companion, the infall of matter stops, the X-ray emission declines, and the neutron star emerges as a radio-emitting millisecond pulsar.

It is likely that the companion star in 47 Tuc W – a normal star with a mass greater than about an eighth that of the Sun – is a new partner, rather than the companion that spun up the pulsar. The new partner, acquired fairly recently in an exchange that ejected the previous companion, is trying to dump on the already spun-up pulsar, creating the observed shock wave. In contrast, the X-ray binary J1808 is not in a globular cluster, and is very likely making do with its original companion, which has been depleted to a brown dwarf size with a mass less than 5% that of the Sun.

Most astronomers accept the binary spin-up scenario for creating millisecond pulsars because they have observed neutron stars speeding up in X-ray binary systems, and almost all radio millisecond pulsars are observed to be in binary systems. Until now, definitive proof has been lacking, because very little is known about transitional objects between the second and final steps.

That is why 47 Tuc W is hot. It links a millisecond pulsar with many of the properties of an X-ray binary, to J1808, an X-ray binary that behaves in many ways like a millisecond pulsar, thus providing a strong chain of evidence to support the theory.

Original Source: Chandra X-ray Observatory</a

Posted on by Fraser Cain

Biggest Star Quake Ever Seen

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.

Posted on by Fraser Cain

Oldest Planetary Disk Discovered

Artist’s conception of the 25-million-year-old protoplanetary disk. Credit: David A, Aguilar (CfA) Click to enlarge
Every rule has an exception. One rule in astronomy, supported by considerable evidence, states that dust disks around newborn stars disappear in a few million years. Most likely, they vanish because the material has collected into full-sized planets. Astronomers have discovered the first exception to this rule – a 25-million-year-old dust disk that shows no evidence of planet formation.

“Finding this disk is as unexpected as locating a 200-year-old person,” said astronomer Lee Hartmann of the Harvard-Smithsonian Center for Astrophysics (CfA), lead author on the paper announcing the find.

The discovery raises the puzzling question of why this disk has not formed planets despite its advanced age. Most protoplanetary disks last only a few million years, while the oldest previously known disks have ages of about 10 million years.

“We don’t know why this disk has lasted so long, because we don’t know what makes the planetary formation process start,” said co-author Nuria Calvet of CfA.

The disk in question orbits a pair of red dwarf stars in the Stephenson 34 system, located approximately 350 light-years away in the constellation Taurus. Data from NASA’s Spitzer Space Telescope shows that its inner edge is located about 65 million miles from the binary stars. The disk extends to a distance of at least 650 million miles. Additional material may orbit farther out where temperatures are too low for Spitzer to detect it.

Astronomers estimate the newfound disk to be about 25 million years old. They calculated the age by modeling the central stars within the system, since stars and disk share the same age. The appearance of the disk itself also supports an advanced age.

“The disk looks a lot different than most other disks we’ve seen. This disk looks a lot more evolved than those around younger stars,” said Hartmann.

Hartmann and Calvet hold opposite opinions about the eventual fate of the disk around Stephenson 34.

“Most stars, by the age of 10 million years, have done whatever they’re going to do,” said Hartmann. “If it hasn’t made planets by now, it probably never will.”

Calvet disagreed. “This disk still has a lot of gas in it, so it may still form giant planets.”

Both astronomers emphasize that such debates are a natural part of the scientific process.

“Some people expect scientists to have all the answers. But research is all about exploring the edge of what is known,” said Hartmann. “That’s what makes it so exciting!”

In the future, Hartmann and Calvet plan to search for more old disks in order to learn why some disks survive so much longer than most others.

“It’s important to find more objects like this because they give us clues about the conditions that influence the formation of planets,” said Calvet.

This research will be published in The Astrophysical Journal Letters.

Original Source: CfA News Release