Early Supernovae Seeded the Universe With Elements

Image source: CfA

According to cosmologists, the early Universe only had a mixture of hydrogen, helium and other lighter elements, but none of the heaver elements required for life – like carbon. From the original gasses, giant stars formed – some were 200 times larger than our Sun – lived for a brief time, often just a few million years. These giant stars converted up to 50% of their material into heaver elements, mostly iron, before exploding violently as supernovae. The James Webb telescope, due for launch after 2011 will be so sensitive it should be able to look back to watch these supernovae happening.

The early universe was a barren wasteland of hydrogen, helium, and a touch of lithium, containing none of the elements necessary for life as we know it. From those primordial gases were born giant stars 200 times as massive as the Sun, burning their fuel at such a prodigious rate that they lived for only about 3 million years before exploding. Those explosions spewed elements like carbon, oxygen and iron into the void at tremendous speeds. New simulations by astrophysicists Volker Bromm (Harvard-Smithsonian Center for Astrophysics), Naoki Yoshida (National Astronomical Observatory of Japan) and Lars Hernquist (CfA) show that the first, “greatest generation” of stars spread incredible amounts of such heavy elements across thousands of light-years of space, thereby seeding the cosmos with the stuff of life.

This research is posted online at http://arxiv.org/abs/astro-ph/0305333 and will be published in an upcoming issue of The Astrophysical Journal Letters.

“We were surprised by how violent the first supernova explosions were,” says Bromm. “A universe that was in a pristine state of tranquility was rapidly and irreversibly transformed by a colossal input of energy and heavy elements, setting the stage for the long cosmic evolution that eventually led to life and intelligent beings like us.”

Approximately 200 million years after the Big Bang, the universe underwent a dramatic burst of star formation. Those first stars were massive and fast-burning, quickly fusing their hydrogen fuel into heavier elements like carbon and oxygen. Nearing the end of their lives, desperate for energy, those stars burned carbon and oxygen to form heavier and heavier elements until reaching the end of the line with iron. Since iron cannot be fused to create energy, the first stars then exploded as supernovae, blasting the elements that they had formed into space.

Each of those first giant stars converted about half of its mass into heavy elements, much of it iron. As a result, each supernova hurled up to 100 solar masses of iron into the interstellar medium. The death throes of each star added to the interstellar bounty. Hence, by the remarkably young age of 275 million years, the universe was substantially seeded with metals.

That seeding process was aided by the structure of the infant universe, where small protogalaxies less than one-millionth the mass of the Milky Way crammed together like people on a crowded subway car. The small sizes of and distances between those protogalaxies allowed an individual supernova to rapidly seed a significant volume of space.

Supercomputer simulations by Bromm, Yoshida, and Hernquist showed that the most energetic supernova explosions sent out shock waves that flung heavy elements up to 3,000 light-years away. Those shock waves swept huge amounts of gas into intergalactic space, leaving behind hot “bubbles,” and triggered new rounds of star formation.

Supernova expert Robert Kirshner (CfA) says, “Today this is a fascinating theory, based on our best understanding of how the first stars worked. In a few years, when we build the James Webb Space Telescope, the successor to the Hubble Space Telescope, we should be able to see these first supernovae and test Volker’s ideas. Stay tuned!”

Lars Hernquist notes that the second generation of stars contained heavy elements from the first generation – seeds from which rocky planets like Earth could grow. “Without that first, ‘greatest generation’ of stars, our world would not exist.”

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: CfA News Release

Astronomers Find a Transparent Galaxy

Image credit: Hubble

It turns out that a collection of stars orbiting the Andromeda galaxy are actually the remnants of another galaxy being torn apart and consumed, according to new research from astronomers at Case University. They only realized it was a separate galaxy after charting the velocities of several of its stars. Astronomers failed to detect it before now because much of the galaxy is located in front of Andromeda’s bright galactic disk. The discovery will give astronomers further evidence to support the theory that smaller galaxies merge together to form larger, more complex galaxies.

Case Western Reserve University astronomers have announced the discovery of a new galaxy, termed Andromeda VIII. The new galaxy is so widespread and transparent that astronomers did not suspect its existence until they mapped the velocity of stars thought to belong to the well-known and nearby large Andromeda spiral galaxy and found them to move independently of Andromeda.

Heather Morrison, Paul Harding and Denise Hurley-Keller of Case’s department of astronomy and George Jacoby of the WIYN Observatory, will report their discovery in an upcoming article in Astrophysical Journal Letters.

“This is particularly exciting because it allows us to watch the ongoing growth of the nearby Andromeda galaxy from smaller galaxies,” says Morrison.

The astronomers used Case’s Burrell Schmidt telescope and the 3.5m WIYN telescope to identify the galaxy. Both telescopes are located at Kitt Peak National Observatory near Tucson, Ariz. NOAO is operated by the Association of Universities for Research in Astronomy (AURA) Inc., under a cooperative agreement with the National Science Foundation.

The newly found galaxy is being torn apart into streams of stars, which leaves a trail of stars that are strung out along the new galaxy’s orbit around the Andromeda galaxy in the way a jet’s contrail shows its route. Andromeda is the nearest large spiral galaxy to our own Milky Way galaxy two million light years away. It is visible as a hazy glowing object to the naked eye in a dark sky in the northern hemisphere and is found in the constellation of Andromeda.

Discovered over 1,000 years ago by the Persian astronomer Azophi Al-Sufi, Andromeda is a member of the Local Group of approximately 30 galaxies in the Milky Way’s celestial backyard.

In early August, Morrison finished analyzing the data of these stars from the Andromeda celestial neighborhood. “I was amazed to find a new dwarf galaxy orbiting Andromeda. It is a ‘see-thru’ galaxy, which was only discovered once we obtained velocity measurements for some of its stars, said Morrison.

She adds that the reason Andromeda VIII escaped detection was the fact that it is located in front of the bright regions of Andromeda’s galaxy disk.

Andromeda VIII’s total brightness is comparable to that of Andromeda’s well-known companion M32, a small nearby galaxy, but Andromeda VIII is spread over an area of the sky as much as ten times or more larger than M32. Its elongated shape is caused by Andromeda’s gravitational pull,
which has stretched it out due to the stronger gravity on the side nearest Andromeda.

Morrison and her collaborators also suggested that a very faint stream of stars, detected near the large Andromeda galaxy in 2001 by the Italian Astronmer R. A. Ibata and colleagues, was pulled off Andromeda VIII in an earlier passage around the parent galaxy. “Future research in this area should provide rich and fruitful results,” stated Morrison.

Theory has predicted for decades that galaxies are assembled in a “bottom-up” process, forming first as small galaxies that later merge to form large ones.

“Since 1994, when Ibata and colleagues announced the discovery of a new satellite in the process of being swallowed by the Milky Way, we have been able to see the process taking place in our own galaxy,” stated Morrison. “Now we find the same process in our nearest large neighbor.”

She adds that now it looks like Andromeda is even more inundated by small galaxies than the Milky Way. Ibata and colleagues have taken deep images of Andromeda which show a rich collection of star streams wreathed about the galaxy. Morrison and her colleagues have now identified the source of one of these star streams. They plan future observations to connect the different star streams with their progenitors, and thus learn more about the properties of the companion galaxy, the Andromeda galaxy and its elusive dark matter halo, the unseen matter that is suspected to be present in the universe.

The galaxy research was supported by a five-year National Science Foundation Early Career Development Award.

The Burrell Schmidt telescope is part of Case’s Warner and Swasey Observatory. The WIYN 3.5-meter telescope is a partnership of the University of Wisconsin, Indiana University, Yale University and the National Optical Astronomy Observatory (NOAO). NOAO is operated by the Association of Universities for Research in Astronomy (AURA) Inc., under a cooperative agreement with the National Science Foundation.

Original Source: NSF News Release

More Evidence for Dark Energy

Image credit: Hubble

Astronomers have studied the light from 11 new supernovae to help validate the evidence that some kind of “dark energy” is accelerating the Universe apart. The supernovae are a special type called Ia, which are known to be roughly the same brightness. By measuring their relative brightness, they can calculate how distant the Type Ia supernovae are. This latest data was gathered by an international team of astronomers using ground telescopes to provide followup targets for the Hubble Space Telescope. A new satellite is planned, called the SuperNova/Acceleration Probe, which will be able to discover thousands of supernova and track their explosions precisely.

A unique set of 11 distant Type Ia supernovae studied with the Hubble Space Telescope sheds new light on dark energy, according to the latest findings of the Supernova Cosmology Project (SCP), recently posted at http://www.arxiv.org/abs/astro-ph/0309368 and soon to appear in the Astrophysical Journal.

Light curves and spectra from the 11 distant supernovae constitute “a strikingly beautiful data set, the largest such set collected solely from space,” says Saul Perlmutter, an astrophysicist at Lawrence Berkeley National Laboratory and leader of the SCP. The SCP is an international collaboration of researchers from the United States, Sweden, France, the United Kingdom, Chile, Japan, and Spain.

Type Ia supernovae are among astronomy’s best “standard candles,” so similar that their brightness provides a dependable gauge of their distance, and so bright they are visible billions of light years away.

The new study reinforces the remarkable discovery, announced by the Supernova Cosmology Project early in 1998, that the expansion of the universe is accelerating due to a mysterious energy that pervades all space. That finding was based on data from over three dozen Type Ia supernovae, all but one of them observed from the ground. A competing group, the High-Z Supernova Search Team, independently announced strikingly consistent results, based on an additional 14 supernovae, also predominantly observed from the ground.

Because the Hubble Space Telescope (HST) is unaffected by the atmosphere, its images of supernovae are much sharper and stronger and provide much better measurements of brightness than are possible from the ground. Robert A. Knop, assistant professor of physics and astronomy at Vanderbilt University in Nashville, Tenn., led the Supernova Cosmology Project’s data analysis of the 11 supernovae studied with the HST and coauthored the Astrophysical Journal report with the 47 other members of the SCP.

“The HST data also provide a strong test of host-galaxy extinction,” Knop says, referring to concerns that measurements of the true brightness of supernovae could be thrown off by dust in distant galaxies, which might absorb and scatter their light. But dust would also make a supernova’s light redder, much as our sun looks redder at sunset because of dust in the atmosphere. Because the data from space show no anomalous reddening with distance, Knop says, the supernovae “pass the test with flying colors.”

“Limiting such uncertainties is crucial for using supernovae ? or any other astronomical observations ? to explore the nature of the universe,” says Ariel Goobar, a member of SCP and a professor of particle astrophysics at Stockholm University in Sweden. The extinction test, says Goobar, “eliminates any concern that ordinary host-galaxy dust could be a source of bias for these cosmological results at high-redshifts.” (See What is Host-Galaxy Extinction?)

The term for the mysterious “repulsive gravity” that drives the universe to expand ever faster is dark energy. The new data are able to provide much tighter estimates of the relative density of matter and dark energy in the universe: under straightforward assumptions, 25 percent of the composition of the universe is matter of all types, and 75 percent is dark energy. Moreover, the new data provide a more precise measure of the “springiness” of the dark energy, the pressure that it applies to the universe’s expansion per unit of density.

Among the numerous attempts to explain the nature of dark energy, some are allowed by these new measurements ? including the cosmological constant originally proposed by Albert Einstein ? but others are ruled out, including some of the simplest models of the theories known as quintessence. (See What is Dark Energy?)

High-redshift supernovae are the best single tool for measuring the properties of dark energy ? and eventually determining what dark energy is. As supernova studies with the HST demonstrate, the best place to study high-redshift supernovae is with a telescope in space, unaffected by the atmosphere.

Nevertheless, “to make the best use of a telescope in space, it’s essential to make the best use of the finest telescopes on the ground,” says SCP member Chris Lidman of the European Southern Observatory.

For the supernovae in the present study, the SCP team invented a strategy whereby the Hubble Space Telescope could quickly respond to discoveries made from the ground, despite the need to schedule HST time long in advance. Working together, the SCP and the Space Telescope Science Institute implemented the strategy to superb effect.

The current study, based on HST observations of 11 supernovae, points the way to the next generation of supernova research: in the future, the SuperNova/Acceleration Probe, or SNAP satellite, will discover thousands of Type Ia supernovae and measure their spectra and their light curves from the earliest moments, through maximum brightness, until their light has died away.

SCP’s Perlmutter is now leading an international group of collaborators based at Berkeley Lab who are developing SNAP with the support of the U.S. Department of Energy’s Office of Science. It may be that the best candidate for a correct theory of dark energy will be identified soon after SNAP begins operating. A world of new physics will open as a result.

“New constraints on omega-m, omega-lambda, and w from an independent set of eleven high-redshift supernovae observed with the HST,” by Robert A. Knop and 47 others (the Supernova Cosmology Project), will appear in the Astrophysical Journal and is currently available online at http://www.arxiv.org/abs/astro-ph/0309368.

Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research and is managed by the University of California.

Original Source: Berkeley News Release

Are We Safe from Gamma Ray Bursts?

Image credit: ESA

Gamma ray bursts (or GRBs) are the most powerful known explosions in the Universe. Although astronomers aren’t exactly sure what causes them, they’re somehow linked to supernovae explosions – it could be the formation of a black hole after the supernova explodes. When a GRB goes off, it funnels a tremendous amount of energy into two lighthouse-like beams that would probably vaporize anything out to 200 light-years away. Fortunately there aren’t any stars in our galactic neighborhood that has the potential to explode as a supernova, so we’re probably safe from such an event, but astronomers will keep looking? just to be sure.

For a few seconds every day, Earth is bombarded by gamma rays created by cataclysmic explosions in distant galaxies. Such explosions, similar to supernovae, are known as ?gamma-ray bursts? or GRBs.

Astronomers using ESA?s X-ray observatory, XMM-Newton, are trying to understand the cause of these extraordinary explosions from the X-rays given out for a day or two after the initial burst.

Danger to life?
However, the violence of the process begs the question, what happens to the space surrounding a GRB? A few years ago, some astronomers thought that a GRB might wipe out all life in its host galaxy.

That now seems to be a pessimistic view because the latest evidence shows that GRBs focus their energy along two narrow beams, like a lighthouse might do on Earth, rather than exploding in all directions like a bomb.

That does not mean that GRBs are not dangerous. Some theories suggest that anything caught in the beam, out to a distance of around 200 light years, will be vaporised.

Have there been GRBs in our own galaxy?
Although none of the recently detected GRBs seem powerful enough, events in the distant past are another question. ?There are a lot of supernova remnants in our galaxy, so I suspect that most probably there have been several GRBs as well,? says ESA astronomer Norbert Schartel.

While astronomers have yet to detect a really close GRB, they may already have picked up the most distant ones. ESA?s gamma-ray observatory, Integral, continues to collect invaluable data about GRBs on a daily basis, but last year XMM-Newton recorded the fading afterglow of X-rays that accompanied one GRB.

When Schartel and collaborators analysed the results, they found that the X-rays contained the ?fingerprints? of gas that was glowing like the X-ray equivalent of a ?neon? strip light.

Link between GRBs and exploding stars
This was the first piece of hard evidence that GRBs were linked to exploding stars, similar to supernovae. Now, XMM-Newton has captured another X-ray afterglow that shows similar features, strengthening the link.

Using these data and the discovery of visible explosions of some GRBs by NASA/ESA?s Hubble Space Telescope, astronomers have pieced together a picture of what happens.

It seems that the explosion of the star is just the first stage. The GRB itself is generated sometime later but whether that is hours, days or even weeks afterwards, no one yet knows. The GRB occurs when the centre of the exploding star turns into a ?black hole? and the X-rays are released as the GRB shock wave collides with the gas thrown off in the star?s original explosion.

Are we at risk from GRBs?
Another question still remains: could we be vaporised by a nearby GRB? The answer is no, even though there are GRBs detected almost everyday, scattered randomly throughout the Universe, it is highly unlikely. There are no stars within 200 light years of our Solar System that are of the type destined to explode as a GRB, so we do not expect to witness such an event at close range!

However, we do know that ESA?s scientific study of these fascinating ? and frightening ? cosmic events will continue for many years to come.

Original Source: ESA News Release

New Evidence About the Formation of Galaxies

Image credit: PPARC

Astronomers have long believed that galaxy formation in the early Universe was a spectacular event, with smaller groups smashing together to form larger elliptical galaxies, and star formation would have been everywhere. New data gathered by the SCUBA telescope help support this theory. A team of UK astronomers have captured images of galaxy formation 12 billion years ago, at the very limits of today’s astronomy. Their data will help astronomers understand how simple elliptical galaxies formed to help build models that could eventually help to explain how more complex spiral galaxies (like our own Milky Way) could have formed.

Revealing images produced by one of the world’s most sophisticated telescopes are enabling a team of Edinburgh astronomers to see clearly for the first time how distant galaxies were formed 12 billion years ago. Scientists from the UK Astronomy Technology Centre (UK ATC) and the University of Edinburgh have been targeting the biggest and most distant galaxies in the Universe with the world’s most sensitive submillimetre camera, SCUBA. The camera, built in Edinburgh, is operated on the James Clerk Maxwell Telescope in Hawaii. The images, published in Nature tomorrow (18 September), reveal prodigious amounts of dust-enshrouded star formation which could ultimately tell scientists more about the formation of our own galaxy.

It is thought these distant galaxies in the early Universe will evolve into the most massive elliptical galaxies seen at the present day. These giant galaxies consist of 1000 billion stars like our Sun and are found in large groups or clusters.

Dr Jason Stevens, astronomer at the UK ATC in Edinburgh explained why understanding the evolution of these galaxies is so important. “The distant, youthful Universe was a very different place to the one we inhabit today. Billions of years ago, massive galaxies are thought to have formed in spectacular bursts of star formation. These massive elliptical galaxies have relatively simple properties. We hope that by understanding how simple galaxies form we will be one step closer to understanding how our own, spiral, Milky Way galaxy formed”.

Prof. Jim Dunlop, Head of the University of Edinburgh’s Institute for Astronomy said: “For a long time astronomers have anticipated that the formation of the most massive galaxies should have been a spectacular event, but failed to find any observational evidence of massive galaxy formation from optical images. Now we have discovered that it is indeed spectacular, but because of the effects of interstellar dust, the spectacle is only revealed at submillimetre wavelengths.” The dust absorbs the bright blue light emitted by young stars. The energy from the light heats the dust and makes it glow. It is this glow that is detected by the SCUBA camera.

Dr Stevens and his colleagues suspected that these massive galaxies would form in particularly dense regions of space so they chose regions of very distant space that are known to be very dense because they contain massive radio galaxies – galaxies which emit high levels of radio waves. They found that many of the radio galaxies have near-by companion objects that had not previously been detected at any wavelength. Dr Rob Ivison, also at the UK ATC, described what they found. “The companion objects are located in the densest parts of the intergalactic medium, strung out like beads of water on a spider’s web due to the filamentary structure of the Universe”.

The SCUBA images support a popular current model of galaxy formation in which today’s massive elliptical galaxies were assembled in the early Universe in dense regions of space through the rapid merging of smaller building blocks.

Original Source: PPARC News Release

Chandra Images the Bright Side of the Moon

Image credit: Chandra

Although it’s usually peering into deep space, Chandra looked a little closer to home and inspected the Moon in the X-ray spectrum. Although the Moon doesn’t produce X-rays of its own, it does reflect the radiation of the Sun; various atoms such as oxygen, magnesium, aluminum and silicon fluoresce when the Sun’s X-rays bombard the Moon’s surface. Measuring the quantity and location of these elements will help test the theory that the Moon was formed when a Mars-sized object slammed into the Earth 4.5 billion years ago.

The Chandra observations of the bright portion of the Moon detected X-rays from oxygen, magnesium, aluminum and silicon atoms. The X-rays are produced by fluorescence when solar X-rays bombard the Moon’s surface.

According to the currently popular “giant impact” theory for the formation of the Moon, a body about the size of Mars collided with the Earth about 4.5 billion years ago. This impact flung molten debris from the mantle of both the Earth and the impactor into orbit around the Earth. Over the course of tens of millions of years, the debris stuck together to form the Moon. Measuring the amount and distribution of aluminum and other elements over a wide area of the Moon will help to test the giant impact theory.

Chandra’s observations have also solved a decade-long mystery about X-rays detected by ROSAT that were thought to be coming from the dark portion of the Moon. It turns out that these X-rays only appear to come from the Moon. Chandra shows that the X-rays from the dark moon can be explained by radiation from Earth’s geocorona (extended outer atmosphere) through which orbiting spacecraft move.

The geocoronal X-rays are caused by collisions of heavy ions of carbon, oxygen and neon in the solar wind with hydrogen atoms located tens of thousands of miles above the surface of Earth. During the collisions, the solar ions capture electrons from hydrogen atoms. The solar ions then kick out X-rays as the captured electrons drop to lower energy states.

Original Source: Chandra News Release

Red Giant Spotted Swallowing its Planets

Image credit: NASA

A team of astronomers believe they’ve figured out the explanation for an unusual object V838 Monocerotis – it’s a red giant star consuming its planets as it nears the end of its life. The object recently flared up to become the brightest cool supergiant in the Milky Way – 600,000 times more luminous than our own Sun. Detailed observations showed that the object flared up three times with similar peaks; they believe this is when the star consumed three gas giants in tight orbits – one after the other. This research could help astronomers find more subtle evidence of this happening to smaller planets in other star systems.

Astronomers from Sydney University have come forth with a solution to a mysterious new object recently discovered in our Milky Way.

In a letter soon to be published in the journal Monthly Notices of the Royal Astronomical Society, Dr Alon Retter and Dr Ariel Marom from the Department of Physics suggest that this phenomenon is an expanding giant star swallowing nearby planets, an event which may one day befall our own planet.

Their research provides data to support the theory that the multi-stage eruption of the “red giant” known as V838 Monocerotis observed last year was fuelled as it engulfed three near orbiting planets. This could be the first evidence for an event that had been predicted but not known to have been observed so far. The work identifies a new group of objects with stars that swallow planets.

Astronomers had previously been unable to explain a spectacular explosion that transformed a dim innocuous star into the brightest cool supergiant in the Milky Way. The event was originally discovered by Australian amateur astronomer, Nicholas Brown in January 2002, when V838 Monocerotis suddenly became 600,000 times more luminous than our Sun. In an ordinary nova explosion, the outer layers of a compact star are ejected into space, exposing the super hot core where nuclear fusion was taking place. By contrast, V838 Monocerotis increased enormously in diameter and its outer layers cooled and were very disrupted but still conceal the giant’s core. Beautiful images taken by the Hubble Space Telescope showed evidence of a previous eruption that ejected material from this object in the past. This too is very unusual.

The Sydney team suggests that the outburst of V838 Monocerotis took place as it swallowed three massive Jupiter-like planets in succession. Evidence for this is provided through study of the shape of the light curve and comparison between the observed properties of the star and several theoretical works. In their scenario, in addition to the gravitational energy generated by the process, there may also have been a rapid release of nuclear energy as “fresh” hydrogen was driven into the hydrogen burning shell of the post-main sequence star.

Interestingly past studies have also suggested that the inner planets in our solar system, Mercury, Venus and maybe even Earth, should be eventually swallowed by the Sun. Previous research has proposed that this is in fact a common characteristic and that many giant stars have consumed planets during their evolution. The current work suggests that the engulfment of a massive planet can cause an eruption of the host star.

Explaining the methods used during their study, Dr Retter said: “The careful inspection of the light curve of V838 Monocerotis showed that the three peaks have a similar structure, namely each maximum is followed by a decline and a very weak secondary peak. The shape of the light curve prompts us to argue that V838 Mon had three events of similar nature, but probably of different strengths. The obvious candidate for such behaviour is the swallowing of massive planets in close orbits around a parent star.”

According to this work, there should be more examples of expanding giants that swallow less and lighter planets thus showing weaker and less spectacular eruptions.

Original Source: University of Sydney News Release

You’ve Got to Be Fast to Spot Burst Afterglows

Image credit: NASA

Until recently, astronomers thought that nearly two-thirds of gamma ray bursts – the most powerful known explosions in the Universe – don’t seem to leave an afterglow. It turns out, they just weren’t looking quickly enough. Gamma-ray bursts explode suddenly, last for only a few fractions of a second and then disappear. All that’s left is the afterglow, which astronomers can study to try to understand what caused the explosion. NASA’s HETE spacecraft has quickly determined the positions of 15 gamma-ray bursts and passed this info along to astronomers to follow up with optical telescopes. In this case, only one hasn’t had an afterglow. So, it appears afterglows are common, you just need to look quickly.

Astronomers have solved the mystery of why nearly two-thirds of all gamma-ray bursts, the most powerful explosions in the Universe, seem to leave no trace or afterglow: In some cases, they just weren’t looking fast enough.

New analysis from NASA’s speedy High Energy Transient Explorer (HETE), which locates bursts and directs other satellites and telescopes to the explosion within minutes (and sometimes seconds), reveals that most gamma-ray bursts likely have some afterglow after all.

Scientists announce these results today at a press conference at the 2003 Gamma Ray Burst Conference in Santa Fe, N.M., a culmination of a year’s worth of HETE data.

“For years, we thought of dark gamma-ray bursts as being more unsociable than the Cheshire Cat, not having the courtesy to leave a visible smile behind when they faded away,” said HETE Principal Investigator George Ricker of the Massachusetts Institute of Technology in Cambridge, Mass.

“Now we are finally seeing that smile. Bit by bit, burst by burst, the gamma-ray mystery is unfolding. This new HETE result implies that we now have a way to study most gamma-ray bursts, not just a meager one third.”

Gamma-ray bursts, likely announcing the birth of a black hole, last only for a few milliseconds to upwards of a minute and then fade forever. Scientists say that many bursts seem to emanate from the implosion of massive stars, over 30 times the mass of the Sun. They are random and can occur in any part of the sky at a rate of about one per day. The afterglow, lingering in lower-energy X-ray and optical light for hours or days, offers the primary means to study the explosion.

The lack of an afterglow in a whopping two thirds of all bursts had prompted scientists to speculate that the particular gamma-ray burst might be too far away (so the optical light is “redshifted” to wavelengths not detectable with optical telescopes) or the burst occurred in dusty star-forming regions (where the dust hides the afterglow).

More reasonably, Ricker said, most of the dark bursts are actually forming afterglows, but the afterglows may initially fade very quickly. An afterglow is produced when debris from the initial explosion rams into existing gas in the interstellar regions, creating shock waves and heating the gas until it shines. If the afterglow initially fades too quickly because the shock waves are too weak, or the gas is too tenuous, the optical signal may drop precipitously below the level at which astronomers can pick it up and track it. Later, the afterglow may slow down its rate of decline–but too late for optical astronomers to recover the signal.

HETE, an international mission assembled at and operated by MIT for NASA, determines a quick and accurate location for about two bursts per month. Over the past year, HETE’s tiny but powerful Soft X-ray Camera (SXC), one of three main instruments, accurately determined positions for 15 gamma-ray bursts. Surprisingly, only one out of the SXC’s fifteen bursts has proven to be dark, whereas ten would have been expected based on results from previous satellite.

An MIT-led team has concluded that the reason that afterglows are finally being found are twofold: The accurate, prompt SXC burst locations are being searched quickly and more thoroughly by optical astronomers; and the SXC bursts are somewhat brighter in X rays than the more run-of-the-mill gamma-ray bursts studied by most previous satellites, and thus the associated optical light is also brighter.

Thus, HETE seems to have accounted for all but about 15 percent of gamma-ray bursts, greatly reducing the severity of the “missing afterglow” problem. Studies planned by teams of optical astronomers over the next year should further reduce, and possibly even eliminate, the remaining discrepancy.

Gamma-ray hunters are challenged. Because of the nature of gamma-rays and X-rays, which cannot be focused like optical light, HETE locates bursts within only a few arcminutes by measuring the shadows cast by incident X-rays passing through an accurately calibrated mask within the SXC. (An arcminute is about the size of an eye of a needle held at arm’s length.) Most gamma-ray bursts are exceedingly far, so myriad stars and galaxies fill that tiny circle. Without prompt localization of a bright and fading afterglow, scientists have great difficulty locating the gamma-ray burst counterpart days or weeks later. HETE must continue to localize gamma-ray bursts to settle the discrepancy of the remaining dark bursts.

The HETE spacecraft, on an extended mission into 2004, is part of NASA’s Explorer Program. HETE is a collaboration among MIT; NASA; Los Alamos National Laboratory, New Mexico; France’s Centre National d’Etudes Spatiales (CNES), Centre d’Etude Spatiale des Rayonnements (CESR), and Ecole Nationale Superieure del’Aeronautique et de l’Espace (Sup’Aero); and Japan’s Institute of Physical and Chemical Research (RIKEN). The science team includes members from the University of California (Berkeley and Santa Cruz) and the University of Chicago, as well as from Brazil, India and Italy.

Original Source: NASA News Release

Coldest Temperature Ever Created

Image credit: NASA/JPL

Researchers from NASA and MIT have cooled sodium gas to the lowest temperature ever recorded – one-half billionth degree above absolute zero. At absolute zero temperature (-273 degrees Celsius), all molecular motion would stop completely since the cooling process has extracted all energy from the material. The gas needed to be confined in a magnetic field; otherwise it would stick to the walls of the container and be impossible to cool down. The researchers used a similar methodology that led to the Nobel Prize for Physics in 2001with the discovery of Bose-Einstein condesates (where the molecules move together in an orderly way at low temperatures).

NASA-funded researchers at the Massachusetts Institute of Technology (MIT), Cambridge, Mass., have cooled sodium gas to the lowest temperature ever recorded, one-half-billionth degree above absolute zero. This absolute temperature is the point, where no further cooling is possible.

This new temperature is six times lower than the previous record and marks the first time a gas was cooled below one nanokelvin (one billionth of a degree). At absolute zero (-273? Celsius or -460? Fahrenheit), all motion stops, except for tiny atomic vibrations, since the cooling process has extracted all energy from the particles.

By improving cooling methods, scientists have succeeded in getting closer to absolute zero. “To go below one nanokelvin is like running a mile below four minutes for the first time,” said Dr. Wolfgang Ketterle, a physics professor at MIT and co-leader of the research team.

“Ultra-low temperature gases could lead to vast improvements in precision measurements by allowing better atomic clocks and sensors for gravity and rotation,” said Dr. David E. Pritchard, MIT physics professor, pioneer in atom optics, atom interferometry, and co-leader of the team.

In 1995, a group at the University of Colorado, Boulder, Colo., and a MIT group led by Ketterle, cooled atomic gases to below one microkelvin (one millionth degree above absolute zero). In doing so, they discovered a new form of matter, the Bose-Einstein condensate, where the particles march in lockstep instead of flitting around independently. The discovery was recognized with the 2001 Nobel Prize in Physics, which Ketterle shared with his Boulder colleagues Drs. Eric Cornell and Carl Wieman.

Since the 1995 breakthrough, many groups have routinely reached nanokelvin temperatures; with three nanokelvin as the lowest temperature recorded. The new record set by the MIT group is 500 picokelvin or six times lower.

At such low temperatures, atoms cannot be kept in physical containers, because they would stick to the walls. Also, no known container can be cooled to such temperatures. To circumvent this problem, magnets surround the atoms, which keeps the gaseous cloud confined without touching it. To reach the record-low temperatures, the researchers invented a novel way of confining atoms, which they call a “gravito-magnetic trap.” The magnetic fields acted together with gravitational forces to keep the atoms trapped.

All the researchers are affiliated with the MIT physics department, the Research Laboratory of Electronics and the MIT-Harvard Center for Ultracold Atoms, funded by the National Science Foundation. Ketterle, Leanhardt and Pritchard co-authored the low-temperature paper, scheduled to appear in the September 12 issue of Science. NASA, National Science Foundation, the Office of Naval Research and the Army Research Office funded the research.

Ketterle conducts research under NASA’s Fundamental Physics in Physical Sciences Research Program, part of the agency’s Office of Biological and Physical Research, Washington. NASA’s Jet Propulsion Laboratory, Pasadena, Calif., a division of the California Institute of Technology, Pasadena, manages the Fundamental Physics program.

Original Source: NASA News Release

Electrons Surfing on a Solar Wind

Image credit: NASA

New research indicates that electrons may surf on magnetic waves driven by the solar wind, and get accelerated to the point they can cause some serious damage to spacecraft orbiting the Earth. The process is a result of the interaction between the Earth’s magnetic field and fluctuations in the density of the solar wind. As the density of the solar wind changes, it causes waves in the magnetic field to ripple back to the Earth. Electrons can be caught in these ripples and surf back to the Earth so fast they can damage delicate electronics in space.

“Killer” electrons capable of wreaking havoc on orbiting spacecraft may “surf” magnetic waves driven by the solar wind, according to a team of space scientists.

The team from Boston University and the National Oceanic and Atmospheric Administration (NOAA) combined observations from NASA and NOAA spacecraft to identify a phenomenon that explains how the solar wind makes waves in Earth’s magnetic field (magnetosphere). Ordinary electrons orbiting the Earth in the Van Allen radiation belts may boogyboard the waves, accelerating to near the speed of light, with energies 300-500 times greater than the electrons in a television screen.

The solar wind is a stream of electrically charged particles blown constantly from the Sun. The magnetosphere is a cavity formed when the solar wind encounters the Earth’s magnetic field. When the solar wind density is high and comes up against the magnetosphere, the magnetosphere gets compressed. When the wind density is low, the magnetosphere expands. The researchers discovered that the solar wind contains periodic structures of high and low density, driving a periodic “breathing” action of the magnetosphere and the global generation of magnetic waves.

It’s known that if the frequency of these waves matches the frequency of the electrons in their motion in the Van Allen belt, the electrons can be accelerated, significantly boosting their energies. The process is similar to a boogyboarder catching a wave. Some electrons “ride the wave” and gain so much energy that they can then damage expensive spacecraft.

“If we can confirm this as a significant mechanism for making the waves that accelerate ‘killer’ electrons, then scientists using data from satellites like Wind could develop advance warning for spacecraft operators that their spacecraft may be in danger of excessive and damaging radiation exposure,” said Dr. Barbara Giles, project scientist for the Polar spacecraft at NASA’s Goddard Space Flight Center, Greenbelt, Md.

When electrons become this energetic, they can penetrate to the interior of spacecraft. Once inside electronic parts, they build up static electricity that can short circuit a critical part or put the spacecraft into a bad operating mode.

“What’s new and exciting about this research is that people had always looked for mechanisms internal to the magnetosphere for generating these waves,” said Dr. Larry Kepko, research associate at Boston University and lead author of two papers on this research, one published in the Journal of Geophysical Research in June 2003 and the other in Geophysical Research Letters in 2002. “But here we’ve found an external mechanism – the solar wind itself.”

NASA’s Polar and Wind satellites, along with NOAA’s Geostationary Operational Environmental Satellite (GOES), provided the key observations leading the team to this conclusion. Polar confirmed that the waves are not local, but global. The Wind satellite was the primary source for identifying the density structures in the solar wind that drive the magnetosphere. GOES provided data about the Earth’s magnetosphere as it increased and decreased in size.

“We already knew that the solar wind has density structures and that magnetic waves can accelerate electrons,” said Dr. Harlan Spence, associate professor of astronomy at Boston University and co-author of the two papers on this research. “What we didn’t know was that the solar wind structures can be periodic and drive magnetic waves. These new observations may provide a missing link between the two.”

The ultimate source of these newly discovered solar wind structures is still a mystery, but the team speculates that the Sun may play a direct role. “The solar wind density variations are partly controlled by the pattern of magnetic reconnection, the twisting and snapping of magnetic field lines, on the surface of the Sun,” says Dr. Kepko. “Reconnection occurring in a systematic, periodic manner may produce the observed periodic density structures in the solar wind. There is some evidence that this may be occurring, but further research is required to establish a definitive link.”

The Van Allen radiation belts were discovered in 1958 by Dr. James Van Allen and his team at the University of Iowa with Explorers 1 and 3, the first satellites successfully launched by the United States. They are belts of electrically charged particles trapped by the Earth’s magnetic field. Since the particles are electrically charged (mostly protons and electrons), they feel magnetic forces and are constrained to spiral around invisible lines of magnetic force that comprise the Earth’s magnetic field. There are actually two donut-shaped belts in the Van Allen system, one inside the other with the Earth in the “hole” of the inner belt. The inner belt, made up of high-speed protons, is located at altitudes between 430 and 7,500 miles (about 700 to 12,000 km) above the Earth. The outer belt is made of high-speed electrons and appears at altitudes between 15,500 and 25,000 miles (about 25,000 to 40,000 km) above Earth. Spacecraft operators try to avoid orbits in these regions, but sometimes these altitudes are best for a particular mission, or the spacecraft must pass through the belts during part of its orbit or to escape the Earth entirely.

NASA’s Polar and Wind satellites, together known as the “Global Geospace Science Program,” are dedicated to helping scientists understand how particles and energy from the Sun flow through, and interact with, the Earth’s space environment.

NOAA is dedicated to gathering data about the oceans, the atmosphere, space, and the Sun. Its GOES satellite system is the basic element for U.S. weather monitoring and forecasting. Dr. Howard Singer from NOAA is a third co-author on the 2002 paper about this research.

Original Source: NASA News Release