Category: Astronomy

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

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

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

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

Image credit: NASA

Astronomers believe that the Sun creates and destroys antimatter as part of its natural process of fusion reaction, but new observations from NASA’s Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spacecraft has brought new insights into the process. The antimatter is formed in solar flares when fast-moving particles accelerated by the flare are smashed into slower-moving particles in the Sun’s atmosphere (enough antimatter is created in just one flare to power the United States for two years). Surprisingly, the antimatter isn’t destroyed right away; instead, it’s carried by the flare to another region of the Sun before being destroyed.

The best look yet at how a solar explosion becomes an antimatter factory gave unexpected insights into how the tremendous explosions work. The observation may upset theories about how the explosions, called solar flares, create and destroy antimatter. It also gave surprising details about how they blast subatomic particles to almost the speed of light.

Solar flares are among the most powerful explosions in the solar system; the largest can release as much energy as a billion one-megaton nuclear bombs. A team of researchers used NASA’s Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spacecraft to take pictures of a solar flare on July 23, 2002, using the flare’s high-energy X-rays and gamma radiation.

“We are taking pictures of flares in an entirely new color, one invisible to the human eye, so we expect surprises, and RHESSI gave us a couple already,” said Dr. Robert Lin, a faculty member in the Dept. of Physics at the University of California, Berkeley, who is the Principal Investigator for RHESSI.

Gamma-rays and X-rays are the most energetic forms of light, with a particle of gamma ray light at the top of the scale carrying millions to billions of times more energy than a particle of visible light. The results are part of a series of papers about the RHESSI observation to be published in Astrophysical Journal Letters October 1.

Antimatter annihilates normal matter in a burst of energy, inspiring science fiction writers to use it as a supremely powerful source to propel starships. Current technology only creates minute quantities, usually in miles-long machines employed to smash atoms together, but scientists discovered the July 2002 flare created a half-kilo (about one pound) of antimatter, enough to power the entire United States for two days. According to the RHESSI images and data, this antimatter was not destroyed where expected.

Antimatter is often called the “mirror image” of ordinary matter, because for every type of ordinary matter particle, an antimatter particle can be created that is identical except for an opposite electric charge or other fundamental properties.

Antimatter is rare in the present-day universe. However, it can be created in high-speed collisions between particles of ordinary matter, when some of the energy from the collision goes into the production of antimatter. Antimatter is created in flares when the fast-moving particles accelerated during the flare collide with slower particles in the Sun’s atmosphere.

According to flare theory, these collisions happen in relatively dense regions of the solar atmosphere, because many collisions are required to produce significant amounts of antimatter. Scientists expected that the antimatter would be annihilated near the same places, since there are so many particles of ordinary matter to run into. “Antimatter shouldn’t get far,” said Dr. Gerald Share of the Naval Research Laboratory, Washington, D.C., lead author of a paper on RHESSI’s observations of the antimatter destruction in the July 23 flare.

However, in a cosmic version of the shell game, it appears that this flare might have shuffled antimatter around, producing it in one location and destroying it in another. RHESSI allowed the most detailed analysis to date of the gamma rays emitted when antimatter annihilates ordinary matter in the solar atmosphere. The analysis indicates that the flare’s antimatter might have been destroyed in regions where high temperatures made the particle density 1,000 times lower than where the antimatter should have been created.

Alternatively, perhaps there is no “shell game” at all, and flares are able to create significant amounts of antimatter in less dense regions, or flares somehow may be able to maintain dense regions despite high temperatures, or the antimatter was created “on the run” at high speeds, and the high-speed creation gave the appearance of a high-temperature region, according to the team.

Solar flares are also capable of blasting electrically charged particles in the Sun’s atmosphere (electrons and ions) to almost the speed of light (about 186,000 miles per second or 300,000 km/sec.). The new RHESSI observation revealed that solar flares somehow sort particles, either by their masses or their electric charge, as they propel them to ultra-high speeds.

“This discovery is a revolution in our understanding of solar flares,” said Dr. Gordon Hurford of the University of California, Berkeley, who is lead author of one of fifteen papers on this research.

The solar atmosphere is a gas of electrically charged particles (electrons and ions). Since these particles feel magnetic forces, they are constrained to flow along magnetic fields that permeate the Sun’s atmosphere. It is believed that solar flares happen when magnetic fields in the Sun’s atmosphere become twisted and suddenly snap to a new configuration, like a rubber band breaking when overstretched. This is called magnetic reconnection.

Previously, scientists believed that the particles in the solar atmosphere were accelerated when they were dragged along with the magnetic field as it snapped to a new shape, like a stone in a slingshot. However, if it were this simple, all the particles would be shot in the same direction. The new observations from RHESSI show that this is not so; heavier particles (ions) end up in a different location than lighter particles (electrons).

“The result is as surprising as gold miners blasting a cliff face and discovering that the explosion threw all the dirt in one direction and all the gold in another direction,” said Dr. Craig DeForest, a solar researcher at the South West Research Inst. Boulder, Colo.

The means by which flares sort particles by mass is unknown; there are many possible mechanisms, according to the team. Alternatively, the particles could be sorted by their electric charge, since ions are positively charged and electrons negatively charged. If this is so, an electric field would have to be generated in the flare, since particles move in different directions in an electric field according to their charge. In either case, magnetic reconnection still provides the energy, but the acceleration process is more complex.

The clue that tipped scientists off to this surprising behavior was the RHESSI observation that gamma rays from the July 23 flare were not emitted from the same locations that emitted the X-rays, as theory predicts. According to solar flare theories, electrons and ions are accelerated to high-speeds during the flare and race down arch-shaped magnetic structures. The electrons slam into the denser solar atmosphere near the two footpoints of the arches, emitting X-rays when they encounter electrically charged protons there that deflect them. Gamma rays should be emitted from the same locations when the high-speed ions also crash into these regions.

While RHESSI observed two X-ray emitting regions at the footpoints, as expected, it only detected a diffuse gamma-ray glow centered at a different location some 15,000 kilometers (approximately 9,300 miles) south of the X-ray sites.

“Each new discovery shows we are only just beginning to understand what happens in these gigantic explosions,” said Dr. Brian Dennis of NASA’s Goddard Space Flight Center, Greenbelt, Md., who is the Mission Scientist for RHESSI. RHESSI was launched February 5, 2002, with the University of California, Berkeley, responsible for most aspects of the mission, and NASA Goddard responsible for program management and technical oversight.

Source: NASA News Release

Image credit: NASA

The spectre of global warming and rising ocean levels have been a concern for many years, but NASA has some real numbers to help measure the situation. According to the Topex/Poseidon and Jason satellites, sea levels have been rising an average of 2.8 millimetres a year since observations began in 1992. Whether rising sea levels are caused by human impact or a natural cycle still isn’t clear, but the impact is already being felt in coastal communities around the world with water inundating low-level areas and an increased rate of beach erosion.

Stack two dimes on top of each other. Their height is a tiny fraction less than global sea level is rising each year. The increase looks small, but the consequences are potentially huge. Rising sea level threatens to inundate low-lying regions, such as the Chesapeake, and dramatically increase coastal and beach erosion around the world.

While tide gauges have been used to determine sea level for hundreds of years, the most complete global measurements now come from space. “Tide gauges can’t detect an increase in the rate of sea level rise soon enough to be useful for detecting climate change,” says Bruce Douglas, a senior researcher at Florida International University, Miami, Fla. “Tide gauges can’t measure everywhere. They’re on practically every rock in the ocean, the problem is there just aren’t enough rocks.”

In contrast, the Topex/Poseidon satellite observes the entire ocean and has been making precise measurements of global sea level since it was launched in 1992. Its successor, Jason, is now continuing the same ocean observations.

“Right now Topex/Poseidon has been seeing an average yearly increase of 2.8 millimeters (0.11 inches) in global sea level,” says University of Colorado engineering professor Dr. Steve Nerem, a member of the Topex/Poseidon and Jason 1 science team.

Global sea level is the average of all local rates. If global sea level is rising by 2.8 millimeters a year, the local rate in some areas is much higher, as much as 5 millimeters (0.2 inches) or more over long periods. In some areas it is less.

One of the big questions facing scientists and the public, especially the more than two billion of us who live within 100 kilometers (62 miles) of a coast, about the rise in sea level is “why?”

“We don’t know yet exactly what is causing it,” says Nerem. “The jury is still out.” The current rise in global sea level could be part of some natural, yet unidentified, decades-long climate pattern, Nerem says. “During 1997-1998 El Ni?o, the global average went up 15 millimeters (0.6 inches) as a result of increased ocean temperatures and then went down again.”

However, sea level is a barometer of climate change, and the rise could be a result of a warming Earth. “While the rate of increase we see is consistent with climate change models, we can’t say for sure if that is the cause,” Nerem says. “We’re just starting to ask those questions.”

“It looks like sea level rise as we now observe it began in the middle of the 19th century,” says Douglas, an expert on the history of sea level rise and its consequences. “We have a preponderance of evidence that the current rate is considerably faster than for the previous several thousand years, although there is still some disagreement among scientists about this.”

The two major factors that determine sea level are temperature and ocean mass. Warm water expands and raises sea level. Water added to the ocean from melting glaciers or ice sheets also causes sea level to go up. Figuring out just how much of the current sea level rise is due to each of these factors is difficult.

“Our best guess is that thermal expansion accounts for about 0.5 millimeters (.02 inches) per year rise in sea level or five centimeters (2 inches) per 100 years,” says Douglas. “If global sea level is rising at more than 20 centimeters (8 inches) per hundred years, then where is the water coming from? Mountain glaciers could account for three or four centimeters (1.2 to 1.6 inches), so that leaves Earth’s great ice sheets in Greenland and Antarctica. Are they losing or gaining? That’s a controversial question.”

Scientists expect to have some answers soon. NASA’s new Grace mission will be able to calculate the ocean’s mass, helping pinpoint whether rising sea level is a result of more water in the ocean or expansion due to warming waters. A new generation of tide gauges and monitoring devices provide details on sea level changes in specific locations.

Meanwhile, Jason continues the global sea level measurements begun by Topex/Poseidon more than 11 years ago, building up a record of sea level change that may help explain the past and predict the future. Ironically, Topex/Poseidon was never expected to be able to make precise enough measurements to monitor something as small as millimeter changes in global sea level. “It’s a 100 times more accurate than we expected it to be before launch,” says Douglas. Jason 1 may improve on these measurements even more.

Original Source: NASA/JPL News Release

Image credit: ESO

An international team of astronomers have used the European Southern Observatory’s Very Large Telescope (VLT) to look deep into space and see galaxies located 12.6 billion light-years away – these galaxies are being seen when the Universe was only 10% of its current age. Few galaxies this old have been found, and this new collection has helped the astronomers conclude that they are a part of a cosmic Dark Age, when luminous galaxies were rarer – there were many more only 500 million years later.

Using the ESO Very Large Telescope (VLT), two astronomers from Germany and the UK [2] have discovered some of the most distant galaxies ever seen. They are located about 12,600 million light-years away.

It has taken the light now recorded by the VLT about nine-tenths of the age of the Universe to traverse this huge distance. We therefore observe those galaxies as they were at a time when the Universe was very young, less than about 10% of its present age. At this time, the Universe was emerging from a long period known as the “Dark Ages”, entering the luminous “Cosmic Renaissance” epoch.

Unlike previous studies which resulted in the discovery of a few, widely dispersed galaxies at this early epoch, the present study found at least six remote citizens within a small sky area, less than five per cent the size of the full moon! This allowed understanding the evolution of these galaxies and how they affect the state of the Universe in its youth.

In particular, the astronomers conclude on the basis of their unique data that there were considerably fewer luminous galaxies in the Universe at this early stage than 500 million years later.

There must therefore be many less luminous galaxies in the region of space that they studied, too faint to be detected in this study. It must be those still unidentified galaxies that emit the majority of the energetic photons needed to ionise the hydrogen in the Universe at that particularly epoch.

From the Big Bang to the Cosmic Renaissance
Nowadays, the Universe is pervaded by energetic ultraviolet radiation, produced by quasars and hot stars. The short-wavelength photons liberate electrons from the hydrogen atoms that make up the diffuse intergalactic medium and the latter is therefore almost completely ionised. There was, however, an early epoch in the history of the Universe when this was not so.

The Universe emanated from a hot and extremely dense initial state, the so-called Big Bang. Astronomers now believe that it took place about 13,700 million years ago.

During the first few minutes, enormous quantities of protons, neutrons and electrons were produced. The Universe was so hot that protons and electrons were floating freely: the Universe was fully ionised.

After some 100,000 years, the Universe had cooled down to a few thousand degrees and the nuclei and electrons now combined to form atoms. Cosmologists refer to this moment as the “recombination epoch”. The microwave background radiation we now observe from all directions depicts the state of great uniformity in the Universe at that distant epoch.

However, this was also the time when the Universe plunged into darkness. On one side, the relic radiation from the primordial fireball had been stretched by the cosmic expansion towards longer wavelengths and was therefore no more able to ionise the hydrogen. On the contrary, it was trapped by the hydrogen atoms just formed. On the other side, no stars nor quasars had yet been formed which could illuminate the vast space. This sombre era is therefore quite reasonably dubbed the “Dark Ages”. Observations have not yet been able to penetrate into this remote age – our knowledge is still rudimentary and is all based on theoretical calculations.

A few hundred million years later, or at least so astronomers believe, some very first massive objects had formed out of the huge clouds of gas that had moved together. The first generation of stars and, somewhat later, the first galaxies and quasars, produced intensive ultraviolet radiation. That radiation could not travel very far, however, as it would be immediately absorbed by the hydrogen atoms which were again ionised in this process.

The intergalactic gas thus again became ionised in steadily growing spheres around the ionising sources. At some moment, these spheres had become so big that they overlapped completely: the fog over the Universe had lifted !

This was the end of the Dark Ages and, with a term again taken over from human history, is sometimes referred as the “Cosmic Renaissance”. Describing the most significant feature of this period, astronomers also call it the “epoch of reionisation”.

Finding the Most Distant Galaxies with the VLT
To cast some light on the state of the Universe at the end of the Dark Ages, it is necessary to discover and study extremely distant (i.e. high-redshift [2]) galaxies. Various observational methods may be used – for instance, distant galaxies have been found by means of narrow-band imaging (e.g., ESO PR 12/03), by use of images that have been gravitationally enhanced by massive clusters, and also serendipitously.

Matthew Lehnert from the MPE in Garching, Germany, and Malcolm Bremer from the University of Bristol, UK, used a special technique that takes advantage of the change of the observed colours of a distant galaxy that is caused by absorption in the intervening intergalactic medium. Galaxies at redshifts of 4.8 to 5.8 [2] can be found by looking for galaxies which appear comparatively bright in red optical light and which are faint or undetected in the green light. Such “breaks” in the light distribution of individual galaxies provide strong evidence that the galaxy might be located at high redshift and that its light started on its long journey towards us, only some 1000 million years after the Big Bang.

For this, they first used the FORS2 multi-mode instrument on the 8.2-m VLT YEPUN telescope to take extremely “deep” pictures through three optical filters (green, red and very-red) of a small area of sky (40 square arcmin, or approx. 5 percent the size of the full moon). These images revealed about 20 galaxies with large breaks between the green and red filters, suggesting that they were located at high redshift. Spectra of these galaxies were then obtained with the same instrument, in order to measure their true redshifts.

“The key to the success of these observations was the use of the great new red-enhanced detector available on FORS2”, says Malcolm Bremer.

The spectra indicated that six galaxies are located at distances corresponding to redshifts between 4.8 and 5.8; other galaxies were closer. Surprisingly, and to the delight of the astronomers, one emission line was seen in another faint galaxy that was observed by chance (it happened to be located in one of the FORS2 slitlets) that may possibly be located even further away, at a redshift of 6.6. If this would be confirmed by subsequent more detailed observations, that galaxy would be a contender for the gold medal as the most distant one known!

The Earliest Known Galaxies
The spectra revealed that these galaxies are actively forming stars and are probably no older than 100 million years, perhaps even younger. However, their numbers and observed brightness suggest that luminous galaxies at these redshifts are fewer and less luminous than similarly selected galaxies nearer to us.

“Our findings show that the combined ultraviolet light from the discovered galaxies is insufficient to fully ionise the surrounding gas”, explains Malcom Bremer. “This leads us to the conclusion that there must be many more smaller and less luminous galaxies in the region of space that we studied, too faint to be detected in this way. It must be these still unseen galaxies that emit the majority of the energetic photons necessary to ionise the hydrogen in the Universe.”

“The next step will be to use the VLT to find more and fainter galaxies at even higher redshifts”, adds Matthew Lehnert. “With a larger sample of such distant objects, we can then obtain insight into their nature and the variation of their density in the sky.”

A British Premiere
The observations presented here are among the first major discoveries by British scientists since the UK became a member of ESO in July 2002. Richard Wade from the Particle Physics and Astronomy Research Council (PPARC), which funds the UK subscription to ESO, is very pleased: “In joining the European Southern Observatory, UK astronomers have been granted access to world-leading facilities, such as the VLT. These exciting new results, of which I am sure there will be many more to come, illustrate how UK astronomers are contributing with cutting-edge discoveries.”

More information
The results described in this Press Release are about to appear in the research journal Astrophysical Journal (” Luminous Lyman Break Galaxies at z>5 and the Source of Reionization” by M. D. Lehnert and M. Bremer). It is available electronically as astro-ph/0212431.

Notes
[1]: This is a coordinated ESO/PPARC Press Release. The PPARC version of the release can be found here.

[2]: This work was carried out by Malcolm Bremer (University of Bristol, The United Kingdom) and Matthew Lehnert (Max-Planck-Institut f?r Extraterrestrische Physik, Garching, Germany).

[3]: The measured redshifts of the galaxies in the Bremer Deep Field are z = 4.8-5.8, with one unexpected (and surprising) redshift of 6.6. In astronomy, the redshift denotes the fraction by which the lines in the spectrum of an object are shifted towards longer wavelengths. The observed redshift of a remote galaxy provides an estimate of its distance. The distances indicated in the present text are based on an age of the Universe of 13.7 billion years. At the indicated redshift, the Lyman-alpha line of atomic hydrogen (rest wavelength 121.6 nm) is observed at 680 to 920 nm, i.e. in the red spectral region.

Original Source: ESO News Release

Image credit: ESA

The European Space Agency’s Ulysses spacecraft has confirmed that the Sun’s 11-year cycle that causes it to switch magnetic poles allows interstellar dust to enter our Solar System in greater quantities. The Sun normally puts a protective magnetic bubble around the solar system to push dust around us, but during this pole-switch, the bubble disappears for a little while. Astronomers believe this will increase the amount of material that falls on the Earth to 40,000 tonnes of dust a day – it won’t really cause a problem; however, we may be able to see some more faint falling stars.

Astronomers once thought they understood how the Sun worked. A large ball of gas, generating energy by nuclear fusion, it also created a magnetic field enclosing Earth and the other planets in a gigantic magnetic bubble.

This bubble protected us from the dusty cosmic debris that shoots through space beyond the Solar System. Thanks to ESA’s solar polewatcher Ulysses, that picture is changing…

11-year switch
Ulysses has revealed a complexity to the Sun’s magnetic field that astronomers had never imagined. The Sun’s magnetic field consists of a north pole, where the field flows out of the Sun and a south pole, where the field reenters. Usually, these line up, more-or-less, with the rotation axis of the Sun. Every 11 years the Sun reaches a peak of activity that triggers the magnetic poles to exchange places. The reversal was thought to be a rapid process but, thanks to Ulysses, astronomers now know it is gradual and could take as much as seven years to complete.

During this slow-motion reversal, the line connecting the poles – known as the magnetic axis – comes close to the Sun’s equator and is swept through space like the beam of a light house. Eventually it passes through this region and lines up with the opposite pole.

Imagine if this happened on Earth! Compasses would become useless, given that they rely on the fact that Earth’s magnetic axis is roughly coincident with its rotation axis, which passes through the North and South geographic Pole. Although it seems surprising, magnetic pole reversals have happened on Earth also. The last time was about 740 000 years ago. After studying magnetic rocks, scientists conclude that field reversals on Earth take place once every 5000 to 50 million years (but are impossible to predict). Reversals on the Sun, however, are almost as regular as clockwork – every 11 years, with its magnetic axis changing position for most of that time.

More shooting stars
Earth’s magnetic field is more stable because it arises in the metal-dominated regions in the deep interior of the planet. The Sun’s field, however, comes from a high-temperature, electrified gas called plasma so it is a much more volatile thing. Loops of the magnetic field can burst through the surface of the Sun and when they do, they create the dark patches known as sunspots.

Astronomers are still studying the precise reasons behind the Sun’s 11-year magnetic flips. However, using Ulysses, they have now shown that, when the Sun’s magnetic axis points near its equator, it allows much more cosmic dust to enter the Solar System than normal. What does that mean for us?

If there is more dust in the Solar System, more of it will fall on Earth also. Scientists estimate that in the coming years, about 40 000 tonnes of dust could fall on Earth every day. However, most of it will be so small that it will burn up in the atmosphere before reaching the ground. This will certainly increase the number of faint shooting stars during the next 11 years, but fortunately the Earth will not become a dustier place!

Original Source: ESA News Release

Image credit: NSF

Astronomers have used the accuracy of the National Science Foundation’s Very Long Baseline Array (VLBA) to pinpoint the distance to a pulsar. The object, called PSR B0656+14, was previously thought to be up to 2,500 light-years away but it was at the same location in the sky as a supernova remnant which is only 1,000 light years away. This was thought to be a coincidence, but the new measurement from the VLBA pegs the pulsar at 950 light years away; the same distance as the remnant – they were both created by the same supernova blast.

Location, location, and location. The old real-estate adage about what’s really important proved applicable to astrophysics as astronomers used the sharp radio “vision” of the National Science Foundation’s Very Long Baseline Array (VLBA) to pinpoint the distance to a pulsar. Their accurate distance measurement then resolved a dispute over the pulsar’s birthplace, allowed the astronomers to determine the size of its neutron star and possibly solve a mystery about cosmic rays.

“Getting an accurate distance to this pulsar gave us a real bonanza,” said Walter Brisken, of the National Radio Astronomy Observatory (NRAO) in Socorro, NM.

The pulsar, called PSR B0656+14, is in the constellation Gemini, and appears to be near the center of a circular supernova remnant that straddles Gemini and its neighboring constellation, Monoceros, and is thus called the Monogem Ring. Since pulsars are superdense, spinning neutron stars left over when a massive star explodes as a supernova, it was logical to assume that the Monogem Ring, the shell of debris from a supernova explosion, was the remnant of the blast that created the pulsar.

However, astronomers using indirect methods of determining the distance to the pulsar had concluded that it was nearly 2500 light-years from Earth. On the other hand, the supernova remnant was determined to be only about 1000 light-years from Earth. It seemed unlikely that the two were related, but instead appeared nearby in the sky purely by a chance juxtaposition.

Brisken and his colleagues used the VLBA to make precise measurements of the sky position of PSR B0656+14 from 2000 to 2002. They were able to detect the slight offset in the object’s apparent position when viewed from opposite sides of Earth’s orbit around the Sun. This effect, called parallax, provides a direct measurement of distance.

“Our measurements showed that the pulsar is about 950 light-years from Earth, essentially the same distance as the supernova remnant,” said Steve Thorsett, of the University of California, Santa Cruz. “That means that the two almost certainly were created by the same supernova blast,” he added.

With that problem solved. the astronomers then turned to studying the pulsar’s neutron star itself. Using a variety of data from different telescopes and armed with the new distance measurement, they determined that the neutron star is between 16 and 25 miles in diameter. In such a small size, it packs a mass roughly equal to that of the Sun.

The next result of learning the pulsar’s actual distance was to provide a possible answer to a longstanding question about cosmic rays. Cosmic rays are subatomic particles or atomic nuclei accelerated to nearly the speed of light. Shock waves in supernova remnants are thought to be responsible for accelerating many of these particles.

Scientists can measure the energy of cosmic rays, and had noted an excess of such rays in a specific energy range. Some researchers had suggested that the excess could come from a single supernova remnant about 1000 light-years away whose supernova explosion was about 100,000 years ago. The principal difficulty with this suggestion was that there was no accepted candidate for such a source.

“Our measurement now puts PSR B0656+14 and the Monogem Ring at exactly the right place and at exactly the right age to be the source of this excess of cosmic rays,” Brisken said.

With the ability of the VLBA, one of the telescopes of the NRAO, to make extremely precise position measurements, the astronomers expect to improve the accuracy of their distance determination even more.

“This pulsar is becoming a fascinating laboratory for studying astrophysics and nuclear physics,” Thorsett said.

In addition to Brisken and Thorsett, the team of astronomers includes Aaron Golden of the National University of Ireland, Robert Benjamin of the University of Wisconsin, and Miller Goss of NRAO. The scientists are reporting their results in papers appearing in the Astrophysical Journal Letters in August.

The VLBA is a continent-wide system of ten radio- telescope antennas, ranging from Hawaii in the west to the U.S. Virgin Islands in the east, providing the greatest resolving power, or ability to see fine detail, in astronomy. Dedicated in 1993, the VLBA is operated from the NRAO’s Array Operations Center in Socorro, New Mexico.

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

Original Source: NRAO News Release

Image credit: NASA

Astronomers believe that gamma-ray bursts, the most powerful explosions in the Universe, may be generating ultrahigh-energy cosmic rays, the most energetic particles in the Universe. These cosmic rays have baffled astronomers because they’re moving faster than if they were thrown out of a supernova. Evidence gathered by NASA’s de-orbited Compton Gamma-Ray Observatory showed that in one instance of a gamma ray burst, these high-energy particles dominated the area giving a connection between them, but this is hardly enough evidence to say they’re conclusively linked.

The most powerful explosions in the universe, gamma-ray bursts, may generate the most energetic particles in the universe, known as the ultrahigh-energy cosmic rays (UHECRs), according to a new analysis of observations from NASA’s Compton Gamma-Ray Observatory.

Researchers report in the August 14 edition of Nature of a newly identified pattern in the light from these enigmatic bursts that could be explained by protons moving within a hair’s breadth of light speed.

These protons, like shrapnel from an explosion, could be UHECRs. Such cosmic rays are rare and constitute an enduring mystery in astrophysics, seemingly defying physical explanation, for they are simply far too energetic to have been generated by well-known mechanisms such as supernova explosions.

“Cosmic rays ‘forget’ where they come from because, unlike light, they are whipped about in space by magnetic fields,” said lead author Maria Magdalena Gonzalez of the Los Alamos National Laboratory in New Mexico and graduate student at the University of Wisconsin. “This result is an exciting chance to possibly see evidence of them being produced at their source.”

Gamma-ray bursts — a mystery scientists are finally beginning to unravel — can shine as brilliantly as a million trillion suns, and many may be from an unusually powerful type of exploding star. The bursts are common yet random and fleeting, lasting only seconds.

Cosmic rays are atomic particles (for example, electrons, protons or neutrinos) moving close to light speed. Lower-energy cosmic rays bombard the Earth constantly, propelled by solar flares and typical star explosions. UHECRs, with each atomic particle carrying the energy of a baseball thrown in the Major Leagues, are a hundred-million times more energetic than the particles produced in the largest human-made particle accelerators.

Scientists say the UHECRs must be generated relatively close to the Earth, for any particle traveling farther than 100 million light years would lose some of its energy by the time it reached us. Yet no local source of ordinary cosmic rays seems powerful enough to generate a UHECR.

The Gonzalez-led paper focuses not specifically on UHECR production but rather a new pattern of light seen in a gamma-ray burst. Digging deep into the Compton Observatory archives (the mission ended in 2000), the group found that a gamma-ray burst from 1994, named GRB941017, appears different from the other 2,700-some bursts recorded by this spacecraft. This burst was located in the direction of the constellation Sagitta, the Arrow, likely ten billion light years away.

What scientists call gamma rays are photons (light particles) covering a wide range of energies, in fact, over a million times wider than the energies our eyes register as the colors in a rainbow. Gonzalez’s group looked at the higher-energy gamma-ray photons. The scientists found that these types of photons dominated the burst: They were at least three times more powerful on average than the lower-energy component yet, surprisingly, thousands of times more powerful after about 100 seconds.

That is, while the flow of lower-energy photons hitting the satellite’s detectors began to ease, the flow of higher-energy photons remained steady. The finding is inconsistent with the popular “synchrotron shock model” describing most bursts. So what could explain this enrichment of higher-energy photons?

“One explanation is that ultrahigh-energy cosmic rays are responsible, but exactly how they create the gamma rays with the energy patterns we saw needs a lot of calculating,” said Dr. Brenda Dingus of LANL, a co-author on the paper. “We’ll be keeping some theorists busy trying to figure this out.”

A delayed injection of ultrahigh-energy electrons provides another way to explain the unexpectedly large high-energy gamma-ray flow observed in GRB 941017. But this explanation would require a revision of the standard burst model, said co-author Dr. Charles Dermer, a theoretical astrophysicist at the U.S. Naval Research Laboratory in Washington. “In either case, this result reveals a new process occurring in gamma-ray bursts,” he said.

Gamma-ray bursts have not been detected originating within 100 million light years from Earth, but through the eons these types of explosions may have occurred locally. If so, Dingus said, the mechanism her group saw in GRB 941017 could have been duplicated close to home, close enough to supply the UHECRs we see today.

Other bursts in the Compton Observatory archive may have exhibited a similar pattern, but the data are not conclusive. NASA’s Gamma-ray Large Area Space Telescope (GLAST), scheduled for launch in 2006, will have detectors powerful enough to resolve higher-energy gamma-ray photons and solve this mystery.

Co-authors on the Nature report also include Ph.D. graduate student Yuki Kaneko, Dr. Robert Preece, and Dr. Michael Briggs of the University of Alabama in Huntsville. This research was funded by NASA and the Office of Naval Research.

UHECRs are observed when they crash into our atmosphere, as is illustrated in the figure. The energy from the collision produces an air shower of billions of subatomic particles and flashes of ultraviolet light, which are detected by special instruments.

The National Science Foundation and international collaborators have sponsored instruments on the ground, such as the High Resolution Fly’s Eye in Utah (http://www.cosmic-ray.org/learn.html) and the Auger Observatory in Argentina (http://www.auger.org/). In addition, NASA is working with the European Space Agency to place the Extreme Universe Space Observatory (http://aquila.lbl.gov/EUSO/) on the International Space Station. The proposed OWL mission would, from orbit, look downward towards air showers, viewing a region as large as Texas.

These scientists record the flashes and take a census of the subatomic shrapnel, working backward to calculate how much energy a single particle needs to make the atmospheric cascade. They arrive at a shocking figure of 10^20 electron volts (eV) or more. (For comparison, the energy in a particle of yellow light is 2 eV, and the electrons in your television tube are in the thousand electron volt energy range.)

These ultrahigh-energy particles experience the bizarre effects predicted by Einstein’s theory of special relativity. If we could observe them coming from a remote corner of the cosmos, say a hundred million light years away, we’d have to be patient — it will take a hundred million years to complete the journey. However, if we could travel with the particles, the trip is over in less than a day due to the dilation of time of rapidly moving objects as measured by an observer.

The highest energy cosmic rays cannot even reach us if produced from distant sources, because they collide and lose energy with the cosmic microwave photons left over from the big bang. Sources of these cosmic rays must be found relatively close to us, at a distance of several hundred million light years. Stars that explode as gamma-ray bursts are found within this distance, so intensive observational efforts are underway to find gamma-ray burst remnants distinguished by radiation halos made by the cosmic rays.

Few kinds of celestial objects possess the extreme conditions required to blast particles to UHECR speeds. If gamma-ray bursts produce UHECRs, they probably do so by accelerating particles in jets of matter ejected from the explosion at close to the speed of light. Gamma-ray bursts have the power to accelerate UHECRs, but the gamma-ray bursts observed so far have been remote, billions of light years away. This doesn’t mean they can’t happen nearby, within the UHECR cutoff distance.

A leading contender for long-lived kinds of gamma-ray bursts like GRB941017 is the supernova/collapsar model. Supernovae happen when a star many times more massive than the Sun exhausts its fuel, causing its core to collapse under its own gravity while its outer layers are blown off in an immense thermonuclear explosion. Collapsars are a special type of supernova where the core is so massive it collapses into a black hole, an object so dense that nothing, not even light, can escape its gravity within the black hole’s event horizon. However, observations indicate black holes are sloppy eaters, ejecting material that passes near, but does not cross, their event horizons.

In a collapsar, the star’s core forms a disk of material around the newly formed black hole, like water swirling around a drain. The black hole consumes most of the disk, but some matter is blasted in jets from the poles of the black hole. The jets tear through the collapsing star at close to the speed of light, and then punch through gas surrounding the doomed star. As the jets crash into the interstellar medium, they create shock waves and slow down. Internal shocks also form in the jets as their leading edges slow and are slammed from behind by a stream of high-speed matter. The shocks accelerate particles that generate gamma rays; they could also accelerate particles to UHECR speeds, according to the team.

“It’s like bouncing a ping pong ball between a paddle and a table,” said Dingus. “As you move the paddle closer to the table, the ball bounces faster and faster. In a gamma-ray burst, the paddle and the table are shells ejected in the jet. Turbulent magnetic fields force the particles to ricochet between the shells, accelerating them to almost the speed of light before they break free as UHECRs.”

Detection of neutrinos from gamma-ray bursts would clinch the case for cosmic ray acceleration by gamma-ray bursts. Neutrinos are elusive particles made when high-energy protons collide with photons. Neutrinos have no electrical charge, so still point back to the direction of their source.

The National Science Foundation is currently building IceCube (http://icecube.wisc.edu/), a cubic kilometer detector located in the ice under the South Pole, to search for neutrino emission from gamma-ray bursts. However, the characteristics of nature’s highest-energy particle accelerators remain an enduring mystery, though acceleration by the exploding stars that make gamma-ray bursts has been in favor ever since Mario Vietri (Universita di Roma) and Eli Waxman (Weizmann Institute) proposed it in 1995.

The team believes that while other explanations are possible for this observation, the result is consistent with UHECR acceleration in gamma-ray bursts. They saw both low-energy and high-energy gamma rays in the GRB941017 explosion. The low-energy gamma rays are what scientists expect from high-speed electrons being deflected by intense magnetic fields, while the high-energy rays are what’s expected if some of the UHECRs produced in the burst crash into other photons, creating a shower of particles, some of which flash to produce the high-energy gamma rays when they decay.

The timing of the gamma-ray emission is also significant. The low-energy gamma rays faded away relatively quickly, while the high-energy gamma rays lingered. This makes sense if two different classes of particles – electrons and the protons of the UHECRs – are responsible for the different gamma rays. “It’s much easier for electrons than protons to radiate their energy. Therefore, the emission of low-energy gamma rays from electrons would be shorter than the high-energy gamma rays from the protons,” said Dingus.

The Compton Gamma Ray Observatory was the second of NASA’s Great Observatories and the gamma-ray equivalent to the Hubble Space Telescope and the Chandra X-ray Observatory. Compton was launched aboard the Space Shuttle Atlantis in April 1991, and at 17 tons, was the largest astrophysical payload ever flown at that time. At the end of its pioneering mission, Compton was deorbited and re-entered the Earth’s atmosphere on June 4, 2000.

Original Source: NASA News Release