Hot Spot Cosmic Accelerators
Posted: Friday, November 22, 2002
Source: NASA/Marshall Space Flight Center
Chandra X-Ray Observatory Spots Two Supermassive Black Holes In Same Galaxy
For the first time, scientists have proof two supermassive black holes exist together in the same galaxy, thanks to data from NASA's Chandra X-ray Observatory. These black holes are orbiting each other and will merge several hundred million years from now, to create an even larger black hole resulting in a catastrophic event that will unleash intense radiation and gravitational waves.
The Chandra image reveals that the nucleus of an extraordinarily bright galaxy, known as NGC 6240, contains not one, but two giant black holes, actively accreting material from their surroundings. This discovery shows that massive black holes can grow through mergers in the centers of galaxies, and that these enigmatic events will be detectable with future space-borne gravitational wave observatories.
"The breakthrough came with Chandra's ability to clearly distinguish the two nuclei, and measure the details of the X-radiation from each nucleus," said Guenther Hasinger, of the Max Planck Institute for Extraterrestrial Physics in Germany, a coauthor of an upcoming Astrophysical Journal Letters paper describing the research. "These cosmic fingerprints revealed features characteristic of supermassive black holes — a black hole, and X-rays from fluorescing iron atoms in gas near black holes," he said.
"The breakthrough came with Chandra's ability to clearly distinguish the two nuclei, and measure the details of the X-radiation from each nucleus," said Guenther Hasinger, of the Max Planck Institute for Extraterrestrial Physics in Germany, a coauthor of an upcoming Astrophysical Journal Letters paper describing the research. "These cosmic fingerprints revealed features characteristic of supermassive black holes — an excess of high-energy photons from gas swirling around a black hole, and X-rays from fluorescing iron atoms in gas near black holes," he said.
Previous X-ray observatories had shown that the central region produces X-rays, while radio, infrared and optical observations had detected two bright nuclei, but the nature of this region remained a mystery. Astronomers did not know the location of the X-ray source, or the nature of the bright nuclei.
“With Chandra, we hoped to determine which one, if either, of the nuclei was an active supermassive black hole,” said Stefanie Komossa, also of the Max-Planck, and lead author of the paper on NGC 6240. “Much to our surprise, we found that both were active black holes!”
At a distance of about 400 million light years, NGC 6240 is a prime example of a massive galaxy in which stars are forming at an exceptionally rapid rate due to a recent collision and subsequent merger of two smaller galaxies. Because of the large amount of dust and gas in such galaxies, it is difficult to peer deep into their central regions with optical telescopes. However, X-rays emanating from a galactic nucleus can penetrate the veil of gas and dust.
“The detection of a binary black hole supports the idea that black holes grow to enormous masses in the centers of galaxies by merging with other black holes, “ said Komossa. “This is important for understanding how galaxies form and evolve.”
Over the course of the next few hundred million years, the two black holes in NGC 6240, which are about 3000 light years apart, will drift toward one another and merge to form an even larger supermassive black hole. Toward the end of this process an enormous burst of gravitational waves will be produced.
These gravitational waves will spread through the universe and produce ripples in the fabric of space. These ripples would appear as minute changes in the distance between any two points and could be detected by NASA’s planned space-based detector, LISA (Laser Interferometer Space Antenna). The coalescence of massive black holes is estimated to occur several times each year in the observable universe.
“This is the first time that we see a binary black hole in action, the smoking gun evidence for something which will become a major gravitational wave burst in the future,” said Hasinger.
Chandra observed NGC 6240 for 10.3 hours with the Advanced CCD Imaging Spectrometer (ACIS). Other members of the team are Vadim Burwitz and Peter Predehl of Max Planck, Jelle Kaastra of Space Research Organization Netherlands and Y. Ikebe of the University of Maryland in Baltimore.
NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program, and TRW, Inc., Redondo Beach, Calif., is the prime contractor for the spacecraft. The Smithsonian's Chandra X-ray Center controls science and flight operations from Cambridge, Mass.
Images and additional information about this result are available at:
The original news release can be found at:
Send page by E-Mail Three Inferior Prefrontal Regions Of The Brain
Posted: Thursday, November 21, 2002
Source: American Physiological Society
Three Inferior Prefrontal Regions Of The Brain Found Receptive To Somatosensory Stimuli
November 19, 2002) - Bethesda, MD -- We know quite a bit about the orbitofrontal cortex (OFC). It is part of the frontal lobe that lies superior to the orbit of the eyes. This area of the brain plays an important role in emotional behavior, receives direct inputs from the dorsomedial thalamus, temporal cortex, ventral tegmental area, olfactory system, and the amygdala (illustration). Its outputs go to several brain regions, including the cingulate cortex, hippocampal formation, temporal cortex, lateral hypothalamus, and amygdala. Finally, it communicates with other regions of the frontal cortex. Thus its inputs provide it with information about what is happening in the environment and what plans are being made by the rest of the frontal lobes. Its outputs permit it to affect a variety of behaviors and physiological responses, including emotional responses organized by the amygdala.
However, there is still much that we do not know about this important part of the brain. Research has shown that three inferior prefrontal regions of the monkey's brain (OFC, ventral area of the principal sulcus, and the anterior frontal operculum) all receive somatosensory stimuli (indirect sensations to the body as opposed to specific stimuli such as light). Now a groundbreaking research effort has incorporated two studies, combining positron emission tomography with neutral tactile (touch) stimulation to determine if these same regions in the human brain respond accordingly.
The authors of "Somatosensory Processing in the Human Inferior Prefrontal Cortex" are Matthew C. Hagen and Jose´ V. Pardo, both from the Veterans Affairs Medical Center and the University of Minnesota Medical School, Minneapolis, MN; and David H. Zald and Tricia A. Thornton, both from Vanderbilt University, Nashville, TN. Their findings are published in the Journal of Neurophysiology, a publication of the American Physiological Society (APS).
S T U D Y 1
Thirty-three individuals (18 males, 15 females, 30 were right-handed, two left-handed, one ambidextrous, and the mean age was 38 + 15 participated. An additional ten right-handed subjects (four males, six females; mean age 35) participated in a small experiment outside of the scanner to assess the subjective evaluation of the stimulus used in this study. The stimulation entailed subjects lying with eyes closed while tactile stimulation was administered by manually applying a repetitive (approximately 2–3 Hz) tap at one of four stimulation sites (right index finger, right great toe, left index finger, left great toe). Subjects were instructed to count the number of pauses in the tactile stimulation; 0–3 pauses were administered prior to injection of the isotope or following scan acquisition. No pause in tactile stimulation was provided during the period of scan. Each subject participated in stimulation of one or more sites. Under the control condition, subjects lay resting with their eyes closed (ECR) with no somatosensory stimulation. The ten subjects selected for subjective evaluation were given the same stimulation and instructions as were delivered during the scanning sessions. All subjects were first stimulated on the toe, since the likelihood of rating the stimulus negatively appeared greatest at this site. Following the session of toe stimulation, subjects were asked to rate the pleasantness/unpleasantness of the stimulus using a Likert scale. PET imaging and analysis regional cerebral blood flow (rCBF) were estimated from normalized tissue activity (with measured attenuation correction).
Two sectors of the ventral frontal lobe accounted for most of these foci, a large area that encompassed the posterior-most portions of the inferior frontal gyrus (IFG) (pars orbitalis and triangularis) and the underlying frontal operculum. In contrast, the left hemisphere equivalent only reached statistical significance in one comparison. A second strong area of activation localized to the OFC. In all cases the activation included the right anterior orbital gyrus and the neighboring lateral orbital gyrus. Additional activations arose in other sectors of the right and left OFC, but without as much consistency. The data did not provide consistent evidence for the involvement of an area equivalent to the ventral principal sulcus in monkeys. In the subjective evaluation of the stimulus, 9 of the 10 subjects rated the tactile stimulation of the toe as neutral. One subject found it mildly unpleasant. Eight of the nine subjects rating the stimulus as neutral for the toe also found it similarly neutral for the finger. One subject found the finger stimulation mildly unpleasant, although they rated the toe stimulation as neutral. The individual that found it mildly unpleasant on the toe rated the stimulation of the finger as neutral.
S T U D Y 2
Study 1 indicated that rCBF increases in areas of the ventral frontal lobe during somatosensory stimulation. However, it remains unclear what cognitive or perceptual processes are associated with these increases. These activations could, for instance, reflect a passive sensory representation, a general attentional process (unrelated to a specific sensory modality), or a more modality-specific sensory process. To partially clarify these issues, the researchers employed an intermodal attention task. In both conditions subjects viewed a fixation point and received somatosensory stimulation. In one condition subjects were instructed to attend to the somatosensory dimension while in the other condition they attended to the visual dimension. Because the actual sensory stimulation was identical across conditions, differences in activation between conditions likely reflect modality-specific processing. In contrast, passive sensory representations or more general attentional factors should largely cancel out in this experiment.
Thirteen healthy, right-handed individuals (8 males, 5 females) participated in Study 2. Subjects fixated continuously on a 1 x 1 cm crosshair against a black background that was displayed on a 38-cm computer monitor placed 43 cm in front of their eyes. Concomitantly, tactile stimulation was administered by manually applying a repetitive von Frey hair (3–5 Hz) at one of two stimulation sites (right index finger and right great toe). During each stimulation event, the subject performed under one of two attentional conditions: count the number of pauses in the tactile stimulation and to passively fixate on the central fixation point; and count the number of times the luminance of the central fixation point dimmed and to ignore the somatosensory stimulus. No pause in tactile stimulation or change in the luminance of the fixation point occurred under either condition during scan acquisition. Thus the difference lay in the sensory modality to which the subject attended. Each subject performed one attend somatosensory/passive fixation and one attend visual/ignore somatosensory condition at each of the two stimulation sites.
The regions of interest (ROI) located in the right IFG pars triangularis/operculum showed a significant increase in rCBF with attention to the somatosensory stimulus when compared with attending to the visual stimulus. The ROI in the OFC showed a slight, though nonsignificant increase in rCBF with attention to the visual stimulus. In the pixel-wise analysis, the contrast of attending to somatosensory stimulation/passive fixation versus attend vision/ignore somatosensory produced a significant activation of the right IFG pars triangularis
The data from the two studies provide evidence for at least two discrete ventral frontal brain regions that respond to somatosensory stimulation: posterior IFG/frontal operculum and anterior OFC. Contrasts between somatosensory stimulation and resting with eyes closed produced consistent activations in these regions regardless of the site and side of stimulation. Although there are some differences in the specific locations of peak significance, the overall pattern of activity shows strong convergence across stimulation conditions.
In the first study, the largest ventral frontal area of activation was found in the posterior IFG and underlying anterior frontal opercular region. The involvement of this area in somatosensory processing is consistent with the existing, although limited, data on the neural connections in monkeys. Although the nature of the processing in this region cannot be fully determined from this study, this area of the posterior IFG appears to have a role in selective attention to touch. In the second study, subjects showed significantly greater activation under the "attend somatosensory" condition than under the "attend visual" condition. Since stimulation was identical between conditions, the modulation in activity cannot simply reflect a passive representation of touch.
In summary, the present studies clearly demonstrate the presence of inferior frontal brain regions responsive to somatosensory stimulation. The areas identified show reasonable correspondence to areas previously observed to possess somatosensory input in monkeys and thus appear to indicate a conservation of these pathways in humans. Future studies will hopefully clarify the specific task conditions that engage these areas.
Source: Journal of Neurophysiology.
The American Physiological Society (APS) was founded in 1887 to foster basic and applied science, much of it relating to human health. The Bethesda, MD-based Society has more than 10,000 members and publishes 3,800 articles in its 14 peer-reviewed journals every year.
The original news release can be found here
Send page by E-Mail Black Hole Clues To Supernova Origin
Posted: Tuesday, November 19, 2002
Source: Space Telescope Science Institute
Fast-Flying Black Hole Yields Clues To Supernova Origin
A nearby black hole, hurtling through the plane of our galaxy like a cannonball, has given what some astronomers say is their best evidence yet that stellar-mass black holes are made in supernova explosions. The black hole, called GRO J1655-40, is streaking across space at a rate of 250,000 miles per hour. That speed is four times faster than the average velocity of the stars in that galactic neighborhood. The most likely "cannon blast" is the explosive kick of a supernova, one of the universe's most titanic events.
Even though, by definition, black holes swallow light, the runaway black hole has a companion star, allowing astronomers to track it. NASA Hubble Space Telescope's sharp view allowed astronomers to measure the black hole's motion across the sky in images taken in 1995 and 2001. Combining the Hubble data with separate measurements of its radial motion toward Earth taken from ground-based telescopes yields the true "space velocity" of the black hole, and shows that it is streaking across the plane of our Milky Way in a highly elliptical orbit.
"This is the first black hole found to be moving fast through the plane of our galaxy," says Felix Mirabel of the French Atomic Energy Commission and the Institute for Astronomy and Space Physics of Argentina. "This discovery is exciting because it shows the link of a black hole to a supernova," aside from observing gamma-ray busts from hypernovae (even more powerful stellar explosions), which are believed to make black holes. Mirabel's results appear in the November 19 issue of Astronomy and Astrophysics.
Though the black hole is roughly heading in our direction, it is at a "safe" distance, 6,000 to 9,000 light-years away, in the direction of the constellation Scorpius. Mirabel believes the black hole may have been born in the inner disk of our galaxy, where the highest rate of star formation is taking place.
An aging, evolved star whirls around the black hole, completing one orbit just every 2.6 days. The hole is slowly devouring the companion, which apparently survived the supernova that originally created the black hole. This process makes blowtorch-like jets that stream away from the black hole at a significant fraction of the speed of light. It is the second "microquasar" discovered in our galaxy (meaning that it is a scaled-down model of monster black holes at the cores of extremely active galaxies, called quasars.)
Astronomers have known about stellar-mass black holes (ranging anywhere from 3.5 to approximately 15 solar masses) since the early 1970s. The only conceivable mechanism for making such black holes would be the implosion of the core of a star when it dies. The implosion sends out a shockwave that rips the rest of the star to shreds as a supernova. If the surviving core is greater than 3.5 times our Sun's mass, no forces can stop the collapse, and it will shrink to an infinitely small and dense singularity.
Astronomers have catalogued even faster-moving neutron stars catapulted by a supernova explosion. The black hole is moving relatively slower because it has much more mass and so has more resistance to being accelerated.
The original news release can be found at:
Send page by E-Mail Unexpected Findings In "Little" Big Bang
Posted: Wednesday, November 13, 2002
Source: University Of Rochester
Physicists Puzzle Over Unexpected Findings In "Little" Big Bang
Scientists have recreated a temperature not seen since the first microsecond of the birth of the universe and found that the event did not unfold quite the way they expected, according to a recent paper in Physical Review Letters. The interaction of energy, matter, and the strong nuclear force in the ultra-hot experiments conducted at the Relativistic Heavy Ion Collider (RHIC) was thought to be well understood, but a lengthy investigation has revealed that physicists are missing something in their model of how the universe works.
"It's the things you weren't expecting that are really trying to tell you something in science," says Steven Manly, associate professor of physics and astronomy at the University of Rochester and co-author of the paper. "The basic nature of the interactions within the hot, dense medium, or at least the manifestation of it, changes depending on the angle at which it's viewed. We don't know why. We've been handed some new pieces to the puzzle and we're just trying to figure out how this new picture fits together."
At RHIC in Brookhaven, NY., Manly and his collaborators on the PHOBOS experiment wanted to probe the nature of the strong nuclear force that helps bind atoms together. They smashed two atoms of gold together at velocities near the speed of light in an attempt to create what's called a "quark-gluon plasma," a very brief state where the temperature is tens of thousands of times higher than the cores of the hottest stars. Particles in this hot-soup plasma stream out, but not without bumping into other particles in the soup. It's a bit like trying to race out of a crowded room--the more people in your way, the more difficult to escape. The strength of the interactions between particles in the soup is determined by the strong force, so carefully watching particles stream out could reveal much about how the strong force operates at such high temperatures.
To simplify their observations, the researchers collided the circular gold atoms slightly off-center so that the area of impact would not be round, but shaped rather like a football--pointed at each end. This would force any streaming particles that headed out one of the tips of the football to pass through more of the hot soup than a particle exiting the side would. Differences in the number of particles escaping out the tip versus the side of the hot matter could reveal something of the nature of that hot matter, and maybe something about the strong force itself.
But a surprise was in store. Right where the gold atoms had collided, particles did indeed take longer to stream out the tips of the football than the sides, but farther from the exact point of collision, that difference evaporated. That defied a treasured theory called boost invariance.
"When we first presented this at a conference in Stony Brook, the audience couldn't believe it," says Manly. "They said, 'This can't be. You're violating boost invariance.' But we've gone over our results for more than a year, and it checks out."
Aside from revealing that scientists are missing a piece of the physics puzzle, the findings mean that understanding these collisions fully will be much more difficult than expected. No longer can physicists measure only the sweet spot where the atoms initially collided--they now must measure the entire length of the plasma, effectively making what was a two-dimensional problem into a three-dimensional one. As Manly says, this "dramatically increases the computing complexity" of any model researchers try to devise.
Modeling and understanding such collisions are extremely important because the way that the plasma cools--condensing like steam turning into water against a shower door--might shed some light on the mechanism that gives matter its very mass. Where mass itself comes from has been one of physicists chief conundrums for decades. Manly hopes that if we can understand exactly why the quark-gluon plasma behaves as it does, we might gain an insight into some of the rudiments of the world we live in.
"Understanding all the dynamics of the collision is really critical for actually trying to get the information we want," says Manly. "It may be that we have an actual clue here that something fundamental is different--something we just don't understand." Smiling, he adds, "Yet."
The original news release can be found here
Send page by E-Mail Scientist Capture On Film DNA In Action
Posted: Friday, November 8, 2002
Source: University At Buffalo
Scientist Is The First To Capture On Film DNA In Action: Work Could Lead To More Accurate Targeting Of Cancer Drugs
BUFFALO, N.Y. -- Piero Bianco produces movies. Not films that chronicle the human condition, a la Hollywood. His subject is human biology at its most basic -- the translocation and unwinding of DNA by a DNA motor protein.
Bianco, an assistant professor in the Center for Single Molecule Biophysics and the Department of Microbiology, was the first to record on videotape in real time a molecule of a particular DNA motor protein in the process of "unzipping" a double strand of bacterial DNA.
To accomplish this feat, Bianco uses a novel technique he developed called "laser tweezers." Using this tool, he can grasp and hold a DNA molecule long enough to capture the action as the double helix unwinds.
"These laser tweezers allow us to look at one molecule at a time and understand how a protein really works," Bianco said. "When you look at groups of proteins, all the nuances of individual proteins are lost. With this system we can pull a DNA molecule out of a solution and actually watch a single DNA helicase molecule (the motor protein) take an individual DNA molecule and pull it apart."
If there were an Academy Award for most important basic science film, Bianco's work surely would be in the running. Knowing how DNA unwinds, copies and repairs itself -- what starts it, stops it and why -- will make possible major advancements in cancer treatment and is vitally important to the progress of gene therapy and recombinant DNA research.
Bianco currently is focusing his investigation and his camera on a motor protein more complex than the one captured on his first film and which has a different mode of action.
His goal at UB is to videotape in real time the actions of several motor proteins that accomplish DNA unwinding and DNA repair, and to usethis knowledge to answer pressing questions about how cancer drugs work.
Since cancers are caused by uncontrolled cell growth, and DNA motor proteins make this possible by allowing DNA to copy itself, motor proteins are natural drug targets. Researchers know that many cancer drugs stop cell growth, but they don't know precisely how. Bianco is hoping to provide some details.
"We want to find out what happens when you put an anti-tumor drug in the way of the motor protein," Bianco said. "If the drug stops cell growth, we want to find out exactly how it does it. Will the protein start the unwinding with the drug present? If it starts, will it continue? Where will it stop, if at all?" The resulting movies will show how existing drugs work, and will allow researchers to test the efficacy of new drugs designed to inhibit DNA replication and repair.
Bianco developed his novel system while a postdoctoral fellow at the University of California at Davis, in collaboration with colleagues from Lawrence Livermore National Laboratory in Livermore, Calif. Creating it consumed several years, culminating in publication of the breakthrough in the journal Nature in January 2001.
Learning how a DNA motor protein functions and capturing it on film posed several vexing technical problems at the time: how to snatch a single DNA molecule, stretch it out, and hold it stable long enough to watch the helicase in action. Then there was the problem of size: DNA motor proteins, called helicases, are too small to be observed under a microscope.
Bianco solved these problems in a variety of ways. The laser tweezers form the crux of the system. By focusing an infrared laser beam through a microscope objective and aided by the laws of physics, he can create an optical trap that stops a DNA molecule in its tracks.
The molecule itself is too elusive to be caught, however, so Bianco tethers the DNA molecule to a microscopic polystyrene bead to give the tweezers something to grasp. Next he attaches a motor protein molecule to the opposite end of the DNA molecule, and tags both bead and DNA with a fluorescent dye. The dye creates an image sufficiently bright to be recorded by a micro-camera designed to perform under very-low-light conditions. Techniques weren't available earlier to bind fluorescent dye to the DNA helicase, but Bianco now has that capacity at UB.
Stretching out the molecule and initiating the action occurs in a flow cell -- a tiny, custom-made, Y-shaped apparatus the size of a microscope slide. Bianco introduces the bead and its cargo of DNA and motor protein into one channel of the flow cell (one of the arms of the "Y"), inserts ATP -- the molecular energy source -- into the other channel, and focuses an optical microscope and laser beam on the juncture of the channels.
The stretched-out molecule and its energy source flow in their separate channels into the juncture, where the action begins. The laser beam captures the polystyrene bead in its tweezers-like grip. Manipulating the laser beam, Bianco maneuvers the DNA into the path of the ATP, which jump-starts the helicase.
The breakthrough film described in Nature features a molecule of Escherichia coli helicase called RecBCD, which acts by unzipping the DNA molecule from one end to the other. That movie shows the stretched-out strands of glowing DNA becoming progressively shorter as the invisible motor protein unzips them, displacing the dye as it goes.
This action is called processive translocation. On film, it looks like a string of lights being switched off, one by one.
Once DNA strands are separated, the elemental processes of replication or repair can begin.
At UB, Bianco is adapting his novel system to investigate other, more complex bacterial helicases. The present target is RuvB, a circular nanomachine that drives a critical late step in genetic recombination called branch migration. Unlike RecBCD, this motor protein wraps itself around DNA like a doughnut on a string, carrying out translocation in a different manner. The UB set-up is equipped with two optical traps and is significantly more advanced than his former system, allowing him to work with complicated molecules such as RuvB.
The overarching goal of Bianco's research is to learn how cancer drugs interfere with translocation, which, in turn, will allow drug developers to target chemotherapy drugs to the most effective point in the process. He intends to define and film the action of several motor proteins, then begin working with four specific cancer drugs provided by collaborators at Roswell Park Cancer Institute.
"There is potential here," Bianco said, "to answer questions you could never answer any other way."
The original news release can be found here
Send page by E-Mail Innards Of A Neutron Star Revealed
Posted: Friday, November 8, 2002
Source: NASA/Goddard Space Flight Center
Exotic Innards Of A Neutron Star Revealed In A Series Of Explosions
Amid the fury of 28 thermonuclear blasts on a neutron star's surface, scientists using the European Space Agency's (ESA) XMM-Newton X-ray satellite have obtained a key measurement revealing the nature of matter inside these enigmatic objects.
The result, capturing for the first time the ratio between such an ultra-dense star's mass and radius in an extreme gravity environment, is featured in the November 7 issue of Nature. Dr. Jean Cottam of NASA's Goddard Space Flight Center in Greenbelt, Md., leads this international effort.
The neutron star -- the core remains of a star once bigger than the Sun yet now small enough to fit within the Washington Beltway -- contains densely packed matter under forces that perhaps existed at the moment of the Big Bang but which cannot be duplicated on Earth. The contents offer a crucial test for theories describing the fundamental nature of matter and energy.
Cottam and her team probed the neutron star's interior by measuring for the first time how light passing through the star's half-inch atmosphere is warped by extreme gravity, a phenomenon called the gravitational redshift. The extent of the gravitational redshift, as predicted by Einstein, depends directly on the neutron star's mass and radius. The mass-to- radius ratio, in turn, determines the density and nature of the star's internal matter, called the equation of state. "It is only during these bursts that the region is suddenly flooded with light and we were able to detect within that light the imprint, or signature, of material under extreme gravitational forces," said Cottam. The neutron star is part of a binary star system named EXO 0748-676, located in the constellation Volans, or Flying Fish, about 30,000 light-years away in the Milky Way galaxy, visible in southern skies with a large backyard telescope.
Scientists estimate that neutron stars contain the mass of about 1.4 Suns compacted into about a 10-mile-wide sphere (16 kilometers). At such density, all the space is squeezed out of the atoms inside the neutron star, and protons and electrons squeeze into neutrons, leaving a neutron superfluid, a liquid that flows without friction. By understanding the precise ratio of mass to radius, and thus pressure to density, scientists can determine the nature of this superfluid and speculate on the presence of exotic matter and forces within -- the type of phenomena that particle physicists search for in earthbound particle accelerators. Today's announcement states that EXO 0748-676's mass-to- radius ratio is 0.152 solar masses per kilometer, based on a gravitational redshift measurement of 0.35. This provides the first observational evidence that neutron stars are indeed made of tightly packed neutrons, as predicted by theory estimating mass-radius, density-pressure ratios. "Unlike the Sun, with an interior well understood, neutron stars have been like a black box," said co-author Dr. Frits Paerels of Columbia University in New York. "We have bored our first small hole into a neutron star. Now theorists will have a go at the little sample we have offered them," he said. More important, said co-author Dr. Mariano Mendez of SRON, the National Institute for Space Research in the Netherlands, "We have now established a means to probe the bizarre interior of a 10-mile-wide chunk of neutrons thousands of light-years away -- based on gravitational redshift. With the fantastic light-collecting potential of XMM-Newton, we can measure the mass-to-radius ratios of other neutron stars, perhaps uncovering a quark star." In a quark star, which is denser than a neutron star and has a different mass-to-radius ratio, neutrons are squeezed so tightly they liberate the subatomic quark particles and gluons that are the building blocks of atomic matter. To obtain its measurement, the team needed the fantastic radiance provided by thermonuclear bursts, which illuminate matter very close to the neutron star surface where gravity is strongest. The team spotted the 28 bursts during a series of XMM-Newton observations of the neutron star totaling 93 hours. There are dozens of known binary systems with neutron stars, like EXO 0748-676, where such bursting is seen several times a day, the result of gas pouring onto the neutron star from its companion star. ESA's XMM-Newton was launched in December 1999. NASA helped fund mission development and supports guest observatory time. Goddard Space Flight Center hosts the U.S. guest visitor- support center. Jean Cottam joins Goddard through a grant from the National Research Council.
Editor's Note: The original news release can be found here
Send page by E-Mail Astronomers locate oldest known star in Milky Way
Posted: Friday, November 1, 2002
By Steve Connor, Science Editor, independent.co.uk
Astronomers may have detected the oldest star in the Milky Way galaxy, which could date back to the beginning of the Universe more than 12 billion years ago.
The star lies towards the southern constellation of Phoenix, about 36,000 light years from Earth. It is among the 10,000 or so brightest stars in the sky. An analysis of its chemical composition suggests that the star, known only by its catalogue name, HE0107-5240, is almost devoid of metals. This indicates that it is a relic from the very early history of the galaxy, when it was formed after the Big Bang.
After decades of searching for such a candidate, a team led by Norbert Christlieb at the University of Hamburg in Germany found the star with the help of observations using the Anglo-Australian telescope in New South Wales and the European Southern Observatory in Chile.
Stars are the nuclear cauldrons in which the lighter elements of the Periodic Table, such as hydrogen and helium, are gradually converted into the heavier atoms that are essential for life. For many years astronomers have theorised about the existence of so-called "population III" stars, which contain minimal amounts of heavier atoms, such as iron, and which therefore date back to this much earlier age.
Catherine Pilachowski, an astronomer at Indiana University, said: "These stars would be relics from early in galactic history, before star formation and evolution polluted the primordial gas with metals."
HE0107-5240 has a metallic composition far lower than anything seen before – a metallic concentration that is about one two-hundred-thousandth that of our own star, the Sun. This is about 20 times lower than previous measurements.
Dr Pilachowski said that the results of the study, published in the journal Nature, suggest that the birth of the star could date back to about 1 billion years after the Big Bang.
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