BERKELEY, CA By measuring polarized light from an unusual exploding star, an international team of astrophysicists and astronomers has worked out the first detailed picture of a Type Ia supernova and the distinctive star system in which it exploded.
Using the European Southern Observatory's Very Large Telescope in Chile, the researchers determined that supernova 2002ic exploded inside a flat, dense, clumpy disk of dust and gas, previously blown away from a companion star. Their work suggests that this and some other precursors of Type Ia supernovae resemble the objects known as protoplanetary nebulae, well known in our own Milky Way galaxy.
Lifan Wang of Lawrence Berkeley National Laboratory, Dietrich Baade of the European Southern Observatory (ESO), Peter H=F6flich and J. Craig Wheeler of the University of Texas at Austin, Koji Kawabata of the National Astronomical Observatory of Japan, and Ken'ichi Nomoto of the University of Tokyo report their findings in the 20 March 2004 issue of Astrophysical Journal Letters.
Type II and some other supernovae occur when the cores of very massive stars collapse and explode, leaving behind extremely dense neutron stars or even black holes. Type Ia supernovae, however, explode by a very different mechanism.
"A Type Ia supernova is a metallic fireball," explains Berkeley Lab's Wang, a pioneer in the field of supernova spectropolarimetry. "A Type Ia has no hydrogen or helium but lots of iron, plus radioactive nickel, cobalt, and titanium, a little silicon, and a bit of carbon and oxygen. So one of its progenitors must be an old star that has evolved to leave behind a carbon-oxygen white dwarf. But carbon and oxygen, as nuclear fuels, do not burn easily. How can a white dwarf explode?"
The most widely accepted Type Ia models assume that the white dwarf -- roughly the size of Earth but packing most of the mass of the sun -- accretes matter from an orbiting companion until it reaches 1.4 solar masses, known as the Chandrasekhar limit. The now superdense white dwarf ignites in a mighty thermonuclear explosion, leaving behind nothing but stardust.
Other schemes include the merger of two white dwarfs or even a lone white dwarf that re-accretes the matter shed by its younger self. Despite three decades of searching, however, until the discovery and subsequent spectropolarimetric studies of SN 2002ic, there was no firm evidence for any model.
In November of 2002, Michael Wood-Vasey and his colleagues in the Department of Energy's Nearby Supernova Factory based at Berkeley Lab reported the discovery of SN 2002ic, shortly after its explosion was detected almost a billion light-years away in an anonymous galaxy in the constellation Pisces.
In August of 2003, Mario Hamuy from the Carnegie Observatories and his colleagues reported that the source of the copious hydrogen-rich gas in SN 2002ic was most likely a so-called Asymptotic Giant Branch (AGB) star, a star in the final phases of its life, with three to eight times the mass of the sun -- just the sort of star that, after it has blown away its outer layers of hydrogen, helium, and dust, leaves behind a white dwarf.
Moreover, this seemingly self-contradictory supernova -- a Type Ia with hydrogen -- was in fact similar to other hydrogen-rich supernovae previously designated Type IIn. This in turn suggested that, while Type Ia supernovae are indeed remarkably similar, there may be wide differences among their progenitors.
Because Type Ia supernovae are so similar and so bright -- as bright or brighter than whole galaxies -- they have become the most important astronomical standard candles for measuring cosmic distances and the expansion of the universe. Early in 1998, after analyzing dozens of observations of distant Type Ia supernovae, members of the Department of Energy's Supernova Cosmology Project based at Berkeley Lab, along with their rivals in the High-Z Supernova Search Team based in Australia, announced the astonishing discovery that the expansion of the universe is accelerating.
Cosmologists subsequently determined that over two-thirds of the universe consists of a mysterious something dubbed "dark energy," which stretches space and drives the accelerating expansion. But learning more about dark energy will depend on careful study of many more distant Type Ia supernovae, including a better knowledge of what kind of star systems trigger them.
If the dust cloud or explosion is spherical and uniformly smooth, all orientations are equally represented and the net polarization is zero. But if the object is not spherical -- shaped like a disk or a cigar, for example -- more light will oscillate in some directions than in others.
Even for quite noticeable asymmetries, net polarization rarely exceeds one percent. Thus it was a challenge for the ESO spectropolarimetry instrument to measure faint SN 2002ic, even using the powerful Very Large Telescope. It took several hours of observation on four different nights to acquire the necessary high-quality polarimetry and spectroscopy data.
The team's observations came nearly a year after SN 2002ic was first detected. The supernova had grown much fainter, yet its prominent hydrogen emission line was six times brighter. With spectroscopy the astronomers confirmed the observation of Hamuy and his associates, that ejecta expanding outward from the explosion at high velocity had run into surrounding thick, hydrogen-rich matter.
Only the new polarimetric studies, however, could reveal that most of this matter was shaped as a thin disk. The polarization was likely due to the interaction of high-speed ejecta from the explosion with the dust particles and electrons in the slower-moving surrounding matter. Because of the way the hydrogen line had brightened long after the supernova was first observed, the astronomers deduced that the disk included dense clumps and had been in place well before the white dwarf exploded.
"These startling results suggest that the progenitor of SN 2002ic was remarkably similar to objects that are familiar to astronomers in our own Milky Way, namely protoplanetary nebulae," says Wang. Many of these nebulae are the remnants of the blown-away outer shells of Asymptotic Giant Branch stars. Such stars, if rotating rapidly, throw off thin, irregular disks.
Thus it's more likely that a white dwarf companion in the SN 2002ic system was already busily collecting matter long before the nebula formed. Because the protoplanetary phase lasts only a few hundred years, and assuming a Type Ia supernova typically takes a million years to evolve, only about a thousandth of all Type Ia supernovae are expected to resemble SN 2002ic. Fewer still will exhibit its specific spectral and polarimetric features, although "it would be extremely interesting to search for other Type Ia supernovae with circumstellar matter," Wang says.
Nevertheless, says Dietrich Baade, principal investigator of the polarimetry project that used the VLT, "it's the assumption that all Type Ia supernovae are basically the same that permits the observations of SN 2002ic to be explained."
Binary systems with different orbital characteristics and different kinds of companions at different stages of stellar evolution can still give rise to similar explosions, through the accretion model. Notes Baade, "The seemingly peculiar case of SN 2002ic provides strong evidence that these objects are in fact very much alike, as the stunning similarity of their light curves suggests."
By showing the distribution of the gas and dust, spectropolarimetry has demonstrated why Type Ia supernovae are so much alike even though the masses, ages, evolutionary states, and orbits of their precursor systems may differ so widely."On the hydrogen emission from the Type Ia supernova 2002ic," by Lifan Wang, Dietrich Baade, Peter Hoeflich, J. Craig Wheeler, Koji Kawabata, and Ken'ichi Nomoto, appears in the 20 March 2004 issue of Astrophysical Journal Letters (vol 604, no 1, part 2, p L53).
Seventeen years ago, astronomers spotted the brightest stellar explosion ever seen since the one observed by Johannes Kepler 400 years ago. Called SN 1987A, the titanic supernova explosion blazed with the power of 100,000,000 suns for several months following its discovery on Feb. 23, 1987. Although the supernova itself is now a million times fainter than 17 years ago, a new light show in the space surrounding it is just beginning.
This image, taken Nov. 28, 2003 by the Advanced Camera for Surveys aboard NASA's Hubble Space Telescope, shows many bright spots along a ring of gas, like pearls on a necklace. These cosmic "pearls" are being produced as a supersonic shock wave unleashed during the explosion slams into the ring at more than a million miles per hour. The collision is heating the gas ring, causing its innermost regions to glow. Curiously, one of the bright spots on the ring [at 4 o'clock] is a star that happens to lie along the telescope's line of sight.
Astronomers detected the first "hot spot" in 1996, but now they see dozens of them all around the ring. The temperature of the flares surges from a few thousand degrees to a million degrees Fahrenheit. Individual hot spots cannot be seen from ground-based telescopes. Only Hubble can resolve them.
And, more hot spots are coming. In the next few years, the entire ring will be ablaze as it absorbs the full force of the crash. The glowing ring is expected to become bright enough to illuminate the star's surroundings, thus providing astronomers with new information on how the star ejected material before the explosion.
The elongated and expanding object in the middle of the ring is debris from the supernova blast. The glowing debris is being heated by radioactive elements, principally titanium 44, that were created in the supernova explosion. The debris will continue to glow for many decades.
The ring, about a light-year across, already existed when the star exploded. Astronomers believe the star shed the ring about 20,000 years before the supernova blast.
The violent death of a star 20 times more massive than the Sun, called a supernova, created this stellar drama. The star actually exploded about 160,000 years ago, but it has taken that long for its light to reach Earth. The supernova resides in the Large Magellanic Cloud, a nearby small galaxy that is a satellite or our Milky Way galaxy.
Since its launch in 1990, the Hubble telescope has watched the supernova drama unfold, taking periodic snapshots of the gradually fading ring. Now, the orbiting observatory will continue to monitor the ring as it brightens from this collision.
Credit: NASA, P. Challis, R. Kirshner (Harvard-Smithsonian Center for Astrophysics) and B. Sugerman (STScI)Electronic images, animation, and additional information are available at:
Austin, Texas University of Texas at Austin astronomers have invented an inexpensive method to determine if other solar systems like our own exist.
Among the more than 100 stars now known to have planets, astronomers have found few systems similar to ours. It's unknown if this is because of technological limitations or if our system is truly a rare configuration. The McDonald Observatory astronomers=B9 novel search method uses a Depression-era telescope mated with today=B9s technology.
Astronomers Don Winget and Edward Nather, graduate students Fergal Mullally and Anjum Mukadem, and colleagues are looking for the "leftovers" of solar systems like ours. Their method searches for the pieces of such a solar system after its star has died, by exploiting a trait of ancient, burnt-out Suns called "white dwarfs."
University of Texas astronomers Bill Cochran and Ted von Hippel are also involved, along with S.O. Kepler of Brazil's Universidade Federal de Rio Grande dol Sul and Antonio Kanaan of Brazil's Universidade Federal de Santa Catarina.
Astronomers know that as Sun-like stars use up their nuclear fuel, their outer layers will expand, and the star will become a "red giant" star. When this happens to the Sun, in about five billion years, they expect it will swallow Mercury and Venus, perhaps not quite reaching Earth. Then the Sun will blow off its outer layers and will exist for a few thousand years as a beautiful, wispy planetary nebula. The Sun's leftover core will then be a white dwarf, a dense, dimming cinder about the size of Earth. And, most importantly, it likely will still be orbited by the outer planets of our solar system.
Once a Sun-like system reaches this state, WingeT's team may be able to find it. Their method is based on more than three decades of research on the variability (that is, changes in brightness) of white dwarfs. In the early 1980s, University of Texas astronomers discovered that some white dwarfs vary, or "pulsate," in regular bursts. More recently, Winget and colleagues discovered that about one-third of these pulsating white dwarfs (PWDs) are more reliable timekeepers than atomic clocks and most millisecond pulsars.
These pulsations are the key to detecting planets. Planets orbiting a stable PWD star will affect observations of its timekeeping, appearing to cause periodic variations in the patterns of pulses coming from the star. That=B9s because the planet orbiting the PWD drags the star around as it moves. The change in distance between the star and Earth with change the amount of time taken for the light from the pulsations to reach Earth. Because the pulses are very stable, astronomers can calculate the difference between the observed and expected arrival time of the pulses and deduce the presence and properties of the planet. (This method is similar to that used in the discoveries of the so-called "pulsar planets." The difference is, the pulsar companions are not thought to have formed with their stars, but only after those stars had exploded in supernovae.)
"This search will be sensitive to white dwarfs which were initially between one and four times as massive as the Sun, and should be able to detect planets within two to 20 AU from their parent star. This means we'll be probing inside the habitable zone for some stars," Winget said. (An AU, or astronomical unit, is the distance between Earth and the Sun.) "Basically, detecting Jupiter at Jupiter's distance with this technique is easy. It's duck soup," he said.
Easy, but not quick. Outer planets, orbiting their stars at large distances, can take more than a decade to complete one orbit. Therefore, it can take many years of observations to definitively detect a planet orbiting a white dwarf.
"You need to look for a long time for a full orbit," Winget said. "A half-orbit or a third of an orbit will tell us something's going on there. But for a planet at Jupiter's distance, a half-orbit is still six years." Winget added that for this method, "detecting Jupiter at Uranus' distance is easier, but takes even longer."
For the PWD planet search, Nather conceived a specialized new instrument for McDonald Observatory's 2.1-meter Otto Struve Telescope. He and Mukadam designed and built the instrument, called Argos, to measure the amount of light coming from target stars. Specifically, Argos is a "CCD photometer" -- a photon counter that uses a charge-coupled device to record images. Located at the prime focus of the Struve Telescope, Argos has no optics other than the telescope's 2.1-meter primary mirror. Copies of Argos are now being built at other observatories around the world.
Mullally continues the search for planets around white dwarfs with Argos on the Struve Telescope. He currently has 22 target stars, most of which were identified through the Sloan Digital Sky Survey.
When the team finds promising planet candidates with Argos, they will follow up using the 9.2-meter Hobby-Eberly Telescope (HET) at McDonald Observatory.
"If we find large planets orbiting at large distances, that's a good clue that there might be smaller planets closer in. In that case, what you do is pound away on that target with the largest telescope you have access to," Winget said. The HET will enable more precise timing of the PWD's pulses, and thus be able to pinpoint smaller planets.
This search will be able to study types of stars unable to be studied with the doppler spectroscopy method =8B the most successful planet search method to date =8B Winget said. Because of idiosyncrasies in the make-up of Sun-like stars, the doppler spectroscopy method is not very sensitive in looking for planets around stars twice as massive as the Sun. Roughly half of the stars in Winget=B9s study will be white dwarfs that were originally these types of stars. For this reason, the PWD study at McDonald can be instrumental in scouting and assessing targets and observing strategies for NASA space missions planned in the next two decades, specifically the Space Interferometry Mission, Terrestrial Planet Finder, and Kepler spacecraft.This research is funded by a NASA Origins grant, as well as an Advanced Research Project grant from the State of Texas. Through funding from the Texas Higher Education Agency, two secondary schoolteachers (Donna Slaughter of Stony Point High School in Round Rock, Texas, and Chris Cotter of Lanier High School in Austin) have been directly involved in this research. Plans are now underway extend this involvement to other teachers, and the students in their classrooms by bringing the science, scientists, and the Observatory directly into the classroom using the Internet. Cotter and his colleagues at Lanier High School are currently involved with Mullally in testing this concept.
Press contact: Kurt Riesselmann, Fermilab Public Affairs, 630-840-3351, firstname.lastname@example.org
Batavia, Ill.- With the completion of its hundredth surface detector, the Pierre Auger Observatory, under construction in Argentina, this week became the largest cosmic-ray air shower array in the world. Managed by scientists at the Department of Energy's Fermi National Accelerator Laboratory, the Pierre Auger project so far encompasses a 70-square-mile array of detectors that are tracking the most violent-and perhaps most puzzling-processes in the entire universe.
Cosmic rays are extraterrestrial particles-usually protons or heavier ions-that hit the Earth's atmosphere and create cascades of secondary particles. While cosmic rays approach the earth at a range of energies, scientists long believed that their energy could not exceed 1020 electron volts, some 100 million times the proton energy achievable in Fermilab's Tevatron, the most powerful particle accelerator in the world. But recent experiments in Japan and Utah have detected a few such ultrahigh energy cosmic rays, raising questions about what extraordinary events in the universe could have produced them.
"How does nature create the conditions to accelerate a tiny particle to such an energy?" asked Alan Watson, physics professor at the University of Leeds, UK, and spokesperson for the Pierre Auger collaboration of 250 scientists from 14 countries. "Tracking these ultrahigh-energy particles back to their sources will answer that question."
Scientific theory can account for the sources of low- and medium-energy cosmic rays, but the origin of these rare high-energy cosmic rays remains a mystery. To identify the cosmic mechanisms that produce microscopic particles at macroscopic energy, the Pierre Auger collaboration is installing an array that will ultimately comprise 1,600 surface detectors in an area of the Argentine Pampa Amarilla the size of Rhode Island, near the town of MalargUe, about 600 miles west of Buenos Aires. The first 100 detectors are already surveying the southern sky.
"These highest-energy cosmic rays are messengers from the extreme universe," said Nobel Prize winner Jim Cronin, of the University of Chicago, who conceived the Auger experiment together with Watson. "They represent a great opportunity for discoveries."
The highest-energy cosmic rays are extremely rare, hitting the Earth's atmosphere about once per year per square mile. When complete in 2005, the Pierre Auger observatory will cover approximately 1,200 square miles (3,000 square kilometers), allowing scientists to catch many of these events.
"Our experiment will pick up where the AGASA experiment has left off," said project manager Paul Mantsch, Fermilab, referring to the Akeno Giant Air Shower Array (AGASA) experiment in Japan. "At highest energies, the astonishing results from the two largest cosmic-ray experiments appear to be in conflict. AGASA sees more events than the HiRes experiment in Utah, but the statistics of both experiments are limited."
The Pierre Auger project, named after the pioneering French physicist who first observed extended air showers in 1938, combines the detection methods used in the Japanese and Utah experiments. Surface detectors are spaced one mile apart. Each surface unit consists of a 4-foot-high cylindrical tank filled with 3,000 gallons of pure water, a solar panel, and an antenna for wireless transmission of data. Sensors register the invisible particle avalanches, triggered at an altitude of six to twelve miles just microseconds earlier, as they reach the ground. The particle showers strike several tanks almost simultaneously.
In addition to the tanks, the new observatory will feature 24 HiRes-type fluorescence telescopes that can pick up the faint ultraviolet glow emitted by air showers in mid-air. The fluorescence telescopes, which can only be operated during dark, moonless nights, are sensitive enough to pick up the light emitted by a 4-watt lamp traveling six miles away at almost the speed of light.
"It is a really beautiful thing that we have a hybrid system," said Watson. "We can look at air showers in two modes. We can measure their energy in two independent ways."The Pierre Auger collaboration is in the process of preparing a proposal for a second site of its observatory, to be located in the United States. Featuring the same design as the Argentinean site, the second detector array would scan the northern sky for the sources of the most powerful cosmic rays. Funding for the $55 million Pierre Auger Observatory in Argentina has come from 14 member nations. The U.S. contributes 20 percent of the total cost, with support provided by the Office of Science of the Department of Energy and by the National Science Foundation. A list of all participating institutions is available at http://auger.cnrs.fr/collaboration.html Fermilab is a national laboratory funded by the Office of Science of the U.S. Department of Energy, operated by Universities Research Association, Inc. Photos are available at:
Astronomers have finally identified the progenitor star system of a Type Ia supernova. The culprit that triggered the stellar explosion is a surprisingly normal star just a few times more massive than the Sun.
Type Ia supernovae are luminous objects that have been used as cosmological beacons to study the expansion and geometry of the Universe. Two separate teams have reported on-going observations of distant supernovae of this type that indicate the presence of a repulsive force, termed dark energy, causing the expansion of the Universe to accelerate.
"A great worry in this work has been that astronomers do not understand exactly how these supernovae are produced," says Mario Hamuy, a Hubble fellow at the Carnegie Observatories in Pasadena, CA, lead author of a paper in the August 7 issue of Nature magazine. "We have been searching for a progenitor system for two decades, and now we finally have a suspect clearly identified."
The generally accepted model for a Type Ia supernova consists of a binary system with a white dwarf star (a dense and dim stellar object near the end of its life) that undergoes a sudden thermonuclear explosion. But no one had observed anything about the companion star or the processes which ultimately lead to the explosion.
"In theory, some transfer of mass must occur between the companion star and the white dwarf before the explosion," Hamuy explains, "yet no evidence has ever been found for gas around a Type Ia supernova."
Based on a strong signal of hydrogen in ground-based spectroscopic observations of Supernova 2002ic from Las Campanas Observatory, scientists in Chile and the U.S. have concluded that the source of this Type Ia supernova consisted of a white dwarf that suddenly exploded after gaining hydrogen gas blown off by its gravitational partner.
"The amount of hydrogen-rich circumstellar gas detected is considerable," says Nicholas Suntzeff, an astronomer at the Cerro Tololo Inter-American Observatory in Chile and a co-author of the paper.
"The most reasonable conclusion is that the stellar system was made up of a white dwarf and a common asymptotic giant branch star about three to seven times the mass of the Sun, which proceeded to lose a large amount of its hydrogen in the form of a wind, due to instabilities in the late stages of its evolution," Suntzeff adds. "Some of this hydrogen settled on the companion white dwarf, driving its mass up to the point where the white dwarf incinerated within just a few seconds in a potent thermonuclear event."
Type Ia supernovae are important explosions in the buildup of heavy elements in the Universe. More than half of the iron peak elements in the Solar System, such as iron and nickel, come from the ashes of previous Type Ia explosions.
"We can't understand the buildup of the elements in the stars in galaxies unless we know precisely what is blowing up - what it is made of, and how long it takes to get to the point of the explosion," explains astronomer Mark Phillips of Carnegie Observatories, a co-author of the paper.
So far, the extremely faint galaxy that spawned the system which led to Supernova 2002ic has not been identified.
The redshift of the light from the supernova, however, allowed the astronomers to measure the distance to the explosion at 945 million light-years (290 megaparsecs) from Earth.
"The search for a progenitor for Type Ia supernovae has gone on for so long that it almost became a point of embarrassment for scientists in the field," Suntzeff notes. "Supernova 2002ic may not be the prototype for all Type Ia's, but it is certainly the first crack in the puzzle."
The first identified progenitor of any supernova was massive star Sn-69 202, which was the source of the famous Supernova 1987A, a nearby example of the "core collapse" class of supernovae known as Type II, which begin with stars at least 10 times as massive as the Sun. Five more progenitors of these core collapse-type of supernovae have been found since then.An image of SN 2002ic from this study is available at:
Las Campanas Observatory is operated by the Carnegie Observatories, founded in 1904 by George Ellery Hale. It is one of six departments of the private, nonprofit Carnegie Institution of Washington (www.CarnegieInstitution.org), a pioneering force in basic scientific research since 1902.Cerro Tololo Inter-American Observatory is part of the National Optical Astronomy Observatory (NOAO) in Tucson, which is operated by the Association of Universities for Research in Astronomy (AURA) Inc., under a cooperative agreement with the NSF.
An X-ray movie of the Vela pulsar, made from a series of observations by NASA's Chandra X-ray Observatory, reveals a spectacularly erratic jet that varies in a way never seen before. The jet of high-energy particles whips about like an untended firehose at about half the speed of light. This behavior gives scientists new insight into the nature of jets from pulsars and black holes.
http://chandra.harvard.edu/photo/2003/vela_pulsar/Best of Chandra Images
Scientists have pieced together the key elements of a gamma-ray burst, from star death to dramatic black hole birth, thanks to a "Rosetta stone" found on March 29, 2003.
This telling March 29 burst in the constellation Leo, one of the brightest and closest on record, reveals for the first time that a gamma-ray burst and a supernova -- the two most energetic explosions known in the Universe -- occur simultaneously, a quick and powerful one-two punch.
The results appear in the June 19 issue of Nature. The burst was detected by NASA's High-Energy Transient Explorer (HETE) and observed in detail with the European Southern Observatory's Very Large Telescope (VLT) at the Paranal Observatory in Chile.
"We've been waiting for this one for a long, long time," said Dr. Jens Hjorth, University of Copenhagen, lead author on one of three Nature letters. "The March 29 burst contains all the missing information. It was created through the core collapse of a massive star."
The team said that the "Rosetta stone" burst also provides a lower limit on how energetic gamma-ray bursts truly are and rules out most theories concerning the origin of "long bursts," lasting longer than two seconds.
Gamma-ray bursts temporarily outshine the entire Universe in gamma-ray light, packing the energy of over a million billion suns. Yet these explosions are fleeting -- lasting only seconds to minutes - -- and occur randomly from all directions on the sky, making them difficult to study.
A supernova is associated with the death of a star about eight times as massive as the Sun or more. Its core implodes, forming either a neutron star or (if there is enough mass) a black hole. The star's surface layers blast outward, forming the colorful patterns typical of supernova remnants. Scientists have suspected gamma-ray bursts and supernovae were related, but they have had little observational evidence, until March 29.
"The March 29 burst changes everything," said co-author Dr. Stan Woosley, University of California, Santa Cruz. "With this missing link established, we know for certain that at least some gamma-ray bursts are produced when black holes, or perhaps very unusual neutron stars, are born inside massive stars. We can apply this knowledge to other burst observations."
GRB 030329, named after its detection date, occurred relatively close, approximately 2 billion light years away (at redshift 0.1685). The burst lasted over 30 seconds. ("Short bursts" are less than 2 seconds long.) GRB 030329 is among the 0.2 percent brightest bursts ever recorded. Its afterglow lingered for weeks in lower-energy X-ray and visible light.
With the VLT, Hjorth and his colleagues uncovered evidence in the afterglow of a massive, rapidly expanding supernova shell, called a hypernova, at the same position and created at the same time as the afterglow. The following scenario emerged:
A bluish Wolf-Rayet star -- containing about 10 solar masses worth of helium, oxygen and heavier elements -- rapidly depleted its fuel, triggering the Type Ic supernova / gamma-ray burst event. The core collapsed, without the star's outer part knowing. A black hole formed inside surrounded by a disk of accreting matter, and, within a few seconds, launched a jet of matter away from the black hole that ultimately made the gamma-ray burst.
The jet passed through the outer shell of the star and, in conjunction with vigorous winds of newly forged radioactive nickel-56 blowing off the disk inside, shattered the star. Meanwhile, collisions among pieces of the jet moving at different velocities, all very close to light speed, created the gamma-ray burst. This "collapsar" model, introduced by Woosley in 1993, best explains the observation of GRB 030329, as opposed to the "supranova" and "merging neutron star" models.
"This does not mean that the gamma-ray burst mystery is solved," Woosley said. "We are confident that long bursts involve a core collapse, probably creating a black hole. We have convinced most skeptics. We cannot reach any conclusion yet, however, on what causes short gamma-ray bursts."
Short bursts might be caused by neutron star mergers. A NASA-led international satellite named Swift, to be launched in January 2004, will "swiftly" locate gamma-ray bursts and may capture short-burst afterglows, which have yet to be detected.
The VLT is the world's most advanced optical telescope, comprising four 8.2-meter reflecting Unit Telescopes and, in the future, four moving 1.8-meter Auxiliary Telescopes for interferometry. HETE was built by MIT as a mission of opportunity under the NASA Explorer Program, with collaboration among U.S. universities, Los Alamos National Laboratory, and scientists and organizations in Brazil, France, India, Italy and Japan. For new gamma-ray burst animation, refer to:http://www.gsfc.nasa.gov/topstory/2003/0618rosettaburst.html
Within 90 min, a new, very bright light source (the "optical afterglow") was detected in the same direction by means of a 40-inch telescope at the Siding Spring Observatory (Australia) and also in Japan. The gamma-ray burst was designated GRB 030329, according to the date.
And within 24 hours, a first, very detailed spectrum of this new object was obtained by the UVES high-dispersion spectrograph on the 8.2-m VLT KUEYEN telescope at the ESO Paranal Observatory (Chile). It allowed to determine the distance as about 2,650 million light-years (redshift 0.1685).
Continued observations with the FORS1 and FORS2 multi-mode instruments on the VLT during the following month allowed an international team of astronomers  to document in unprecedented detail the changes in the spectrum of the optical afterglow of this gamma-ray burst. Their detailed report appears in the June 19 issue of the research journal "Nature".
The spectra show the gradual and clear emergence of a supernova spectrum of the most energetic class known, a "hypernova." This is caused by the explosion of a very heavy star - presumably over 25 times heavier than the Sun. The measured expansion velocity (in excess of 30,000 km/sec) and the total energy released were exceptionally high, even within the elect hypernova class.
From a comparison with more nearby hypernovae, the astronomers are able to fix with good accuracy the moment of the stellar explosion. It turns out to be within an interval of plus/minus two days of the gamma-ray burst. This unique conclusion provides compelling evidence that the two events are directly connected.
These observations therefore indicate a common physical process behind the hypernova explosion and the associated emission of strong gamma-ray radiation. The team concludes that it is likely to be due to the nearly instantaneous, non-symmetrical collapse of the inner region of a highly developed star (known as the "collapsar" model).
The March 29 gamma-ray burst will pass into the annals of astrophysics as a rare "type-defining event", providing conclusive evidence of a direct link between cosmological gamma-ray bursts and explosions of very massive stars.The full text of this Press Release, with two photos (ESO PR Photos 17a-b/03) and all related links, is available at:
Despite major observational efforts, it is only within the last six years that it has become possible to pinpoint with some accuracy the sites of some of these events. With the invaluable help of comparatively accurate positional observations of the associated X-ray emission by various X-ray satellite observatories since early 1997, astronomers have until now identified about fifty short-lived sources of optical light associated with GRBs (the "optical afterglows").
Most GRBs have been found to be situated at extremely large ("cosmological") distances. This implies that the energy released in a few seconds during such an event is larger than that of the Sun during its entire lifetime of more than 10,000 million years. The GRBs are indeed the most powerful events since the Big Bang known in the Universe, cf. ESO PR 08/99 and ESO PR 20/00.
During the past years circumstantial evidence has mounted that GRBs signal the collapse of massive stars. This was originally based on the probable association of one unusual gamma-ray burst with a supernova ("SN 1998bw", also discovered with ESO telescopes, cf. ESO PR 15/98). More clues have surfaced since, including the association of GRBs with regions of massive star-formation in distant galaxies, tantalizing evidence of supernova-like light-curve "bumps" in the optical afterglows of some earlier bursts, and spectral signatures from freshly synthesized elements, observed by X-ray observatories.
The corresponding distance is about 2,650 million light-years. This is the nearest normal GRB ever detected, therefore providing the long-awaited opportunity to test the many hypotheses and models which have been proposed since the discovery of the first GRBs in the late 1960's.
With this specific aim, the ESO-lead team of astronomers  now turned to two other powerful instruments at the ESO Very Large Telescope (VLT), the multi-mode FORS1 and FORS2 camera/spectrographs. Over a period of one month, until May 1, 2003, spectra of the fading object were obtained at regular rate, securing a unique set of observational data that documents the physical changes in the remote object in unsurpassed detail.
This is based on the gradual "emergence" with time of a supernova-type spectrum, revealing the extremely violent explosion of a star. With velocities well in excess of 30,000 km/sec (i.e., over 10% of the velocity of light), the ejected material is moving at record speed, testifying to the enormous power of the explosion.
Hypernovae are rare events and they are probably caused by explosion of stars of the so-called Wolf-Rayet" type . These WR-stars were originally formed with a mass above 25 solar masses and consisted mostly of hydrogen. Now in their WR-phase, having stripped themselves of their outer layers, they consist almost purely of helium, oxygen and heavier elements produced by intense nuclear burning during the preceding phase of their short life.
"We have been waiting for this one for a long, long time", says Jens Hjorth, "this GRB really gave us the missing information. From these very detailed spectra, we can now confirm that this burst and probably other long gamma-ray bursts are created through the core collapse of massive stars. Most of the other leading theories are now unlikely."
The astronomers determined that the hypernova explosion (designated SN 2003dh ) documented in the VLT spectra and the GRB-event observed by HETE-II must have occurred at very nearly the same time. Subject to further refinement, there is at most a difference of 2 days, and there is therefore no doubt whatsoever, that the two are causally connected.
"Supernova 1998bw whetted our appetite, but it took 5 more years before we could confidently say, we found the smoking gun that nailed the association between GRBs and SNe" adds Chryssa Kouveliotou of NASA. "GRB 030329 may well turn out to be some kind of 'missing link' for GRBs."
In conclusion, GRB 030329 was a rare "type-defining" event that will be recorded as a watershed in high-energy astrophysics.
Thousands of years prior to this explosion, a very massive star, running out of hydrogen fuel, let loose much of its outer envelope, transforming itself into a bluish Wolf-Rayet star . The remains of the star contained about 10 solar masses worth of helium, oxygen and heavier elements.
In the years before the explosion, the Wolf-Rayet star rapidly depleted its remaining fuel. At some moment, this suddenly triggered the hypernova/gamma-ray burst event. The core collapsed, without the outer part of the star knowing. A black hole formed inside, surrounded by a disk of accreting matter. Within a few seconds, a jet of matter was launched away from that black hole.
The jet passed through the outer shell of the star and, in conjunction with vigorous winds of newly formed radioactive nickel-56 blowing off the disk inside, shattered the star. This shattering, the hypernova, shines brightly because of the presence of nickel. Meanwhile, the jet plowed into material in the vicinity of the star, and created the gamma-ray burst which was recorded some 2,650 million years later by the astronomers on Earth. The detailed mechanism for the production of gamma rays is still a matter of debate but it is either linked to interactions between the jet and matter previously ejected from the star, or to internal collisions inside the jet itself.
This scenario represents the "collapsar" model, introduced by American astronomer Stan Woosley (University of California, Santa Cruz) in 1993 and a member of the current team, and best explains the observations of GRB 030329.
"This does not mean that the gamma-ray burst mystery is now solved", says Woosley. "We are confident now that long bursts involve a core collapse and a hypernova, likely creating a black hole. We have convinced most skeptics. We cannot reach any conclusion yet, however, on what causes the short gamma-ray bursts, those under two seconds long."
Notes: Members of the Gamma-Ray Burst Afterglow Collaboration at ESO (GRACE) team include Jens Hjorth, Pal Jakobsson, Holger Pedersen, Kristian Pedersen and Darach Watson (Astronomical Observatory, NBIfAFG, University of Copenhagen, Denmark), Jesper Sollerman (Stockholm Observatory, Sweden), Palle Moeller (ESO-Garching, Germany), Johan Fynbo (Department of Physics and Astronomy, University of Aarhus, Denmark), Stan Woosley (Department of Astronomy and Astrophysics, University of California, Santa Cruz, USA), Chryssa Kouveliotou (NSSTC, Huntsville, Alabama, USA), Nial Tanvir (Department of Physical Sciences, University of Hertfordshire, UK), Jochen Greiner (Max-Planck-Institut fuer extraterrestrische Physik, Garching, Germany), Michael Andersen (Astrophysikalisches Institut, Potsdam, Germany), Alberto Castro-Tirado (Instituto de Astrofisica de Andalucia, Granada, Spain), Jose Mar=EDa Castro Ceron, Andy Fruchter, Javier Gorosabel and James Rhoads (Space Telescope Science Institute, Baltimore, Maryland, USA), Lex Kaper, Evert Rol, Ed van den Heuvel and Ralph Wijers (Astronomical Institute Anton Pannekoek, Amsterdam, Netherlands), Sylvio Klose (Thueringer Landessternwarte Tautenburg, Germany), Nicola Masetti and Eliana Palazzi (Istituto di Astrofisica Spaziale e Fisica Cosmica - Sezione di Bologna, CNR, Italy), Elena Pian (INAF, Osservatorio Astronomico di Trieste, Italy) and Paul Vreeswijk (ESO-Santiago, Chile)
Chandra X-ray Observatory Press Release, 9/19/02
Just when it seemed like the summer movie season had ended, two of NASA's Great Observatories have produced their own action movie. Multiple observations made over several months with NASA's Chandra X-ray Observatory and the Hubble Space Telescope captured the spectacle of matter and antimatter propelled to near the speed of light by the Crab pulsar, a rapidly rotating neutron star the size of Manhattan.
NASA Press release 02-178
Just when it seemed the summer movie season had ended, two of NASA's Great Observatories have produced their own action movie. Multiple observations made over several months with NASA's Chandra X-ray Observatory and the Hubble Space Telescope captured the spectacle of matter and antimatter propelled to nearly the speed of light by the Crab pulsar, a rapidly rotating neutron star the size of Manhattan.
"Through this movie, the Crab Nebula has come to life," said Jeff Hester of Arizona State University in Tempe, lead author of a paper in the September 20 issue of The Astrophysical Journal Letters. "We can see how this awesome cosmic generator actually works."
The Crab was first observed by Chinese astronomers in 1054 A.D. and has since become one of the most studied objects in the sky. By combining the power of Chandra and Hubble, the movie reveals features never before seen in still images. By understanding the Crab, astronomers hope to unlock the secrets of how similar objects across the universe are powered.
Bright wisps can be seen moving outward at half the speed of light to form an expanding ring, visible in both X-ray and optical images. These wisps appear to originate from a shock wave that shows up as an inner X-ray ring. This ring consists of about two dozen knots that form, brighten and fade, jitter around, and occasionally undergo outbursts that give rise to expanding clouds of particles, but remain in roughly the same location.
"These data leave little doubt that the inner X-ray ring is the location of the shock wave that turns the high-speed wind from the pulsar into extremely energetic particles," said Koji Mori of Penn State University in University Park, a coauthor of the paper.
Another dramatic feature of the movie is a turbulent jet that lies perpendicular to the inner and outer rings. Violent internal motions are obvious, as is a slow motion outward into the surrounding nebula of particles and magnetic field.
"The jet looks like steam from a high-pressure boiler," said David Burrows of Penn State, another coauthor of the paper, "except when you realize you are looking at a stream of matter and anti-matter electrons moving at half the speed of light!"
The inner region of the Crab Nebula around the pulsar was observed with Hubble on 24 occasions between August 2000 and April 2001 at 11-day intervals, and with Chandra on eight occasions between November 2000 and April 2001. The Crab was observed with Chandra's Advanced CCD Imaging Spectrometer and Hubble's Wide-Field Planetary Camera. http://chandra.harvard.edu/photo/2002/0052/
May 19, 2002
See Scientific American for April 2002: "Ripples in Spacetime" by
W. Wayt Gibbs. He discusses the LIGO program extensively.
Jerry Ostriker, Cambridge University, then at Princeton: "I have always believed that detecting gravitational waves will provide us insights obtainable in no other way. That said, I think that the LIGO program has been an egregious waste of funds--funds that could have been used for more productive science."
Kip Thorne, Caltech:
"Theorists have a very poor track record for predicting whqat we will see when a new window is opened on the universe. Early radio telescopes discovered that the signals were much stronger than theorists expected. That happened again when the x-ray window opened in the 1960s.... In some sense, opening the gravitational window will give us a more radically different view on the universe than those previous advances did."
NASA Goddard Press Release, April 22, 2002
They are old but not forgotten. Nearby "retired" quasar galaxies, billions of years past their glory days as the brightest beacons in the Universe, may be the current source of rare, high-energy cosmic rays, the fastest-moving bits of matter known and whose origin has been a long-standing mystery, according to scientists at NASA and Princeton University.
The scientists have identified four elliptical galaxies that may have started this second career of cosmic-ray production, all located above the handle of the Big Dipper and visible with backyard telescopes. Each contains a central black hole of at least 100 million solar masses that, if spinning, could form a colossal battery sending atomic particles, like sparks, shooting off towards Earth at near light speed.
These findings were discussed April 22, 2002, in a press conference at the joint meeting of the American Physical Society and the High Energy Astrophysics Division of the American Astronomical Society in Albuquerque, N.M. The team includes Dr. Diego Torres of Princeton University and Drs. Elihu Boldt, Timothy Hamilton and Michael Loewenstein of NASA's Goddard Space Flight Center in Greenbelt, Md.
Quasar galaxies are thousands of times brighter than ordinary galaxies, fueled by a central black hole swallowing copious amounts of interstellar gas. In galaxies with so-called quasar remnants, the black hole nucleus is no longer a strong source of radiation.
"Some quasar remnants might not be so lifeless after all, keeping busy in their later years," said Torres. "For the first time, we see the hint of a possible connection between the arrival directions of ultra-high energy cosmic rays and locations on the sky of nearby dormant galaxies hosting supermassive black holes."
Ultra high-energy cosmic rays represent one of astrophysics' greatest mysteries. Each cosmic ray -- essentially a single sub-atomic particle such as a proton traveling just shy of light speed -- packs as much energy as a major league baseball pitch, over 40 million trillion electron volts. (The rest energy of a proton is about a billion electron volts.) The particles' source must be within 200 million light years of Earth, for cosmic rays from beyond this distance would lose energy as they traveled through the murk of the cosmic microwave radiation pervading the Universe. There is considerable uncertainty, however, over what kinds of objects within 200 million light years could generate such energetic particles.
"The very fact that these four giant elliptical galaxies are apparently inactive makes them viable candidates for generating ultra high-energy cosmic rays," said Boldt. Drenching radiation from an active quasar would dampen cosmic-ray acceleration, sapping most of their energy, Boldt said.
The team concedes it cannot determine if the black holes in these galaxies are spinning, a basic requirement for a compact dynamo to accelerate ultra-high energy cosmic rays. Yet scientists have confirmed the existence of at least one spinning supermassive black hole, announced in October 2001. The prevailing theory is that supermassive black holes spin up as they accrete matter, absorbing orbital energy from the infalling matter.
Ultra-high-energy cosmic rays are detected by ground-based observatories, such as the Akeno Giant Air Shower Array near Yamanashi, Japan. They are extremely rare, striking the Earth's atmosphere at a rate about one per square kilometer per decade. Construction is underway for the Auger Observatory, which will cover 3,000 square kilometers (1,160 square miles) on an elevated plain in western Argentina. A proposed NASA mission called OWL (Orbiting Wide-angle Light-collectors) would detect the highest-energy cosmic rays by looking down on the atmosphere from space.
Loewenstein joins NASA Goddard's Laboratory for High Energy Astrophysics as a research associate with the University of Maryland, College Park. Hamilton, also a member of the Lab, is a National Research Council fellow.
For images of the "retired" quasar galaxies, refer to:
The "standard" stellar-evolution track generally accepted as of 2002 has neutron stars held up by neutron degeneracy intermediate between white dwarfs held up by electron degeneracy and black holes, which are not held up against gravity at all. But two independent measurements, both made with the Chandra X-ray Observatory and reported in April 2002, both indicate objects that are too small and too cold to match the expectation of the neutron-star model. Jeremy Drake of the Harvard-Smithsonian Center for Astrophysics and colleagues reported that RXJ1856 is "only" 0.7 million kelvins, lower than expected for a neutron star, and a diameter of "only" 20 km, smaller than expected. David Helfand of Columbia and colleagues observed 3C58, the radio designationn for the remnant of a supernova, and found a temperature of 1.0 million kelvins, also lower than expected.
The solution may be that these stars are not made only of the up and
down quarks that make up neutrons but also have "strange" quarks
(described in the cosmology chapter of the textbook). Such "strange
matter" may leave the resulting stars in a state different from that
of ordinary neutron stars. (In the early 1900s, some particles were
found that took longer to decay than expected, and were called
"strange particles." They were later explained as incorporating a
third type of quark beyond the "up" and "down" quarks that make up
ordinary matter, and it was called a "strange quark." The "charmed
quark," found later, is the other member of its pair.)
NRAO Press Release, March 11, 2002
Astronomers using the National Science Foundation's Very Large Array (VLA) radio telescope have found a pulsar -- a spinning, superdense neutron star -- that apparently is considerably younger than previously thought. This finding, combined with the discovery in 2000 of a pulsar that was older than previously thought, means that many assumptions astronomers have made about how pulsars are born and age must be reexamined, according to the researchers.
"We are learning that each individual pulsar is a very complicated object, and we should assume nothing about it," said Bryan Gaensler, of the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA. "Our work makes it more difficult to put pulsars into neat categories, but ultimately will yield new insights into how pulsars are born," he added. The research is reported in the March 10 edition of the Astrophysical Journal Letters.
The astronomers studied a pulsar called B1951+32 and a supernova remnant called CTB 80, both nearly 8,000 light-years from Earth. The supernova remnant is the shell of debris from the explosion of a giant star. The explosion resulted from the giant star's catastrophic collapse into the superdense neutron star. By observing the pulsar and the supernova remnant from 1989 to 2000 with the VLA, the scientists were able to measure the movement of the pulsar, which, they found, is moving directly outward from the center of the shell of explosion debris.
"We've always felt that, if you see a pulsar and a supernova remnant close together, the pulsar had been born in an explosion at the center of the supernova remnant, but this is the first time that actual observational measurement shows a pulsar moving away from the center of the supernova remnant. It's nice to finally have such an example," said Joshua Migliazzo of the Center for Space Research at the Massachusetts Institute of Technology, another one of the researchers.
By tracking the pulsar's motion for more than a decade, the astronomers were able to calculate that it is traveling through space at more than 500,000 miles per hour. At that speed, the pulsar required about 64,000 years to travel from its birthplace -- the site of the supernova explosion -- to its present location. That means, the astronomers say, that the pulsar is about 64,000 years old.
This age, however, differs significantly from the age estimated by another method which has been used by astronomers for decades. This method uses measurements of the rotation rate of the neutron star and the tiny amount by which that rotation slows over time to arrive at an estimate called the pulsar's "characteristic age." For B1951+32, that method produced an estimated age of 107,000 years.
"Now we have a pulsar that is much younger than we thought. In 2000, a different pulsar was shown to be significantly older than we thought. That means that some of the assumptions that have gone into estimating the ages of these objects are unjustified," Migliazzo said.
The pulsar's rotation is thought to slow because the neutron star's powerful magnetic field acts as a giant dynamo, emitting light, radio waves and other electromagnetic radiation as the star rotates. The energy lost by emitting the radiation results in the star's rotation slowing down.
Previous estimates of pulsar ages have assumed that all pulsars are born spinning much faster than we see them now, that the physical characteristics of the pulsar such as its mass and magnetic-field strength do not change with time, and that the slowdown rate can be estimated by applying the physics of a magnet spinning in a vacuum.
"With one pulsar older than the estimates and one younger, we now realize that we have to question all three of these assumptions," said Gaensler.
Further research, the scientists say, should help them understand more about the conditions under which pulsars form and just how they get their spin in the first place. Neutron stars are formed in a fraction of a second as a massive star collapses onto itself, compressing its matter to the density of an atomic nucleus. During the collapse, the neutron star is thought to receive numerous "kicks" that spin it up.
The measurements of B1951+32's position were made in 1989, 1991, 1993 and 2000, with the VLA. The 2000 observations also used the Pie Town station of NSF's Very Long Baseline Array (VLBA), which improved the precision of the measurements. The other pulsar, which was found to be older than its estimated age, is called B1757-24 or "the duck." The report on its motion and age was published in Nature in July of 2000.
In addition to Gaensler and Migliazzo, the researchers are: Donald Backer of the University of California-Berkeley; Benjamin Stappers of ASTRON in the Netherlands; Eric Van Der Swaluw of the Dublin Institute for Advanced Studies in Ireland; and Richard Strom of ASTRON and the University of Amsterdam in the Netherlands.
The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.
As of 2002, Sirius B is 5.5" southeast of Sirius, and will gradually increase its separation until it is 11.3" away toward the east-northeast in 2022. Sue French describes her observations and these details in Sky & Telescope for March 2002, p. 88. She saw Sirius B with her 105-mm (4-inch) refractor.
A team of astronomers using the National Science Foundation's Very Large Array (VLA) radio telescope has caught an old star during the very brief period of its transformation into a planetary nebula, a shining bubble of glowing gas with a hot remnant star at its center.
"This is the first time that anyone has seen a star that is so clearly going through this transformation stage," said Yolanda Gomez, an astronomer at the Institute for Astronomy at the National Autonomous University in Mexico City, Mexico. "We believe this star began to enter its planetary-nebula phase only after 1984," she added. The researchers reported their findings in the November 15 edition of the scientific journal Nature.
At the end of their lives, stars like our Sun eject gas into space before starting to contract under their own gravity into white dwarf stars. The gravitational contraction heats up the star, making it pour out energetic ultraviolet light. The ultraviolet light tears apart molecules in the gas ejected earlier by the star and rips electrons from the atoms in the gas. This makes the gas glow, producing often-beautiful shining shells and other shapes.
Once the remnant star has heated up sufficiently to produce large amounts of ultraviolet light, molecules in the gas ejected earlier are destroyed rapidly. "We are seeing radio waves emitted by water molecules in this planetary nebula," said Gomez, who added, "The water molecules, we believe, are all destroyed within only 100 years of the beginning of this stage, so we are seeing this star during an extremely brief transition period of its life."
The astronomers used the VLA to observe a planetary nebula called K3-35, 16,000 light-years from Earth in the constellation Vulpecula (the small fox). This object has a doughnut-shaped ring of gas around its center and lobes of outflowing material, similar to structures seen in other planetary nebulae.
The researchers were surprised to find regions near the star in which water molecules are amplifying, or strengthening radio-wave emission at a frequency of 22 GigaHertz, in the same manner that a laser amplifies light waves. They found these regions, called masers, in the doughnut-shaped structure surrounding the central star, as well as at the end of much larger lobes of gas extending from the star. The doughnut-shaped ring has a radius of more than twice the distance from the Sun to Pluto. The masers at the ends of the lobes are more than 100 times more distant from the star.
By analyzing their VLA observations as well as earlier observations of the object by other astronomers, the research team concludes that K3-35 has only just begun its transformation into a planetary nebula.
"This is extremely exciting, because we now have a 'laboratory' for watching this process take place over the next few years," Luis Miranda of the Institute of Andalucia in Spain said. "We don't fully understand everything we see in this object, but know that we are going to learn much valuable information about this process by watching it develop," he added.
"We are very lucky to have caught this star during such a very brief but important period of its life," agreed Guillem Anglada of the Harvard- Smithsonian Institute for Astrophysics in Cambridge, MA; and Jose Torrelles of the Institute for Space Studies of Catalyunya in Barcelona, Spain, the other members of the team.
A VLA image of K3-35 is available on the NRAO Web page, at:
The Antarctic Muon and Neutrino Detector Array (AMANDA) has detected its first neutrinos. AMANDA uses the clear ice under the south pole to provide interactions with incoming neutrinos.
A nice article, "Antarctic Dreams," about the project appeared in The Sciences, March/April 1999, pp. 19-24.
Information on gravitational wave detectors can be found at:
STScI Press Release
Astronomers using NASA's Hubble Space Telescope have taken their first direct look, in visible light, at a lone neutron star. This offers a unique opportunity to pinpoint its size and to narrow theories about the composition and structure of this bizarre class of gravitationally collapsed, burned out stars.
By successfully characterizing the properties of an isolated neutron star, astrophysicists have an opportunity to better understand the transition matter undergoes when subjected to the extraordinary pressures and temperatures found in the intense gravitational field of a neutron star.
The Hubble results show the star is very hot, and can be no larger than 16.8 miles (28 kilometers) across. These results prove that the object must be a neutron star, for no other known type of object can be this hot and small.
"This puts the neutron star uncomfortably close to the theoretical limit of how small a neutron star should be," says Fred Walter of the State University of New York at Stony Brook. "With this observation we can begin to rule out some of the many models of the internal structure of neutron stars." The observation results, made by Walter and Lynn Matthews (also of SUNY), are reported in the Sept. 25 issue of Nature magazine.
Neutron stars, which are created in some supernovae, are so dense because the electrons and protons that form normal matter have been squeezed into neutrons and other exotic subatomic particles. Neutron star matter is the densest form of matter known to exist. (Theoretically, a piece of neutron star surface weighing as much as a fleet of battleships would be small enough to be held in the palm of your hand.)
The Hubble observations, combined with earlier data, promise to help astronomers refine the mathematical description -- called the equation of state -- of the complex transformations matter undergoes at extraordinary densities not found on Earth. Equations of state are well understood for "everyday" matter such as water, which can transition between gaseous, liquid and solid states. But the behavior of matter under extreme temperatures and pressures found on a neutron star, is not well understood.
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