Category: Astronomy

Image credit: NRAO
A team of scientists using the National Science Foundation’s Robert C. Byrd Green Bank Telescope (GBT) has discovered two new molecules in an interstellar cloud near the center of the Milky Way Galaxy. This discovery is the GBT’s first detection of new molecules, and is already helping astronomers better understand the complex processes by which large molecules form in space.

The 8-atom molecule propenal and the 10-atom molecule propanal were detected in a large cloud of gas and dust some 26,000 light-years away in an area known as Sagittarius B2. Such clouds, often many light-years across, are the raw material from which new stars are formed.

“Though very rarefied by Earth standards, these interstellar clouds are the sites of complex chemical reactions that occur over hundreds-of-thousands or millions of years,” said Jan M. Hollis of the NASA Goddard Space Flight Center in Greenbelt, Md. “Over time, more and more complex molecules can be formed in these clouds. At present, however, there is no accepted theory addressing how interstellar molecules containing more than 5 atoms are formed.”

So far, about 130 different molecules have been discovered in interstellar clouds. Most of these molecules contain a small number of atoms, and only a few molecules with eight or more atoms have been found in interstellar clouds. Each time a new molecule is discovered, it helps to constrain the formation chemistry and the nature of interstellar dust grains, which are believed to be the formation sites of most complex interstellar molecules.

Hollis collaborated with Anthony Remijan, also of NASA Goddard; Frank J. Lovas of the National Institute of Standards and Technology in Gaithersburg, Md.; Harald Mollendal of the University of Oslo, Norway; and Philip R. Jewell of the National Radio Astronomy Observatory (NRAO) in Green Bank, W.Va. Their results were accepted for publication in the Astrophysical Journal Letters.

In the GBT experiment, three aldehyde molecules were observed and appear to be related by simple hydrogen addition reactions, which probably occur on the surface of interstellar grains. An aldehyde is a molecule that contains the aldehyde group (CHO): a carbon atom singly bonded to a hydrogen atom and double-bonded to an oxygen atom; the remaining bond on that same carbon atom bonds to the rest of the molecule.

Starting with previously reported propynal (HC2CHO), propenal (CH2CHCHO) is formed by adding two hydrogen atoms. By the same process propanal (CH3CH2CHO) is formed from propenal.

After these molecules are formed on interstellar dust grains, they may be ejected as a diffuse gas. If enough molecules accumulate in the gas, they can be detected with a radio telescope. As the molecules rotate end-for-end, they change from one rotational energy state to another, emitting radio waves at precise frequencies. The “family” of radio frequencies emitted by a particular molecule forms a unique “fingerprint” that scientists can use to identify that molecule. The scientists identified the two new aldehydes by detecting a number of frequencies of radio emission in what is termed the K-band region (18 to 26 GHz) of the electromagnetic spectrum.

“Interstellar molecules are identified by means of the frequencies that are unique to the rotational spectrum of each molecule,” said Lovas. “These are either directly measured in the laboratory or calculated from the measured data. In this case we used the calculated spectral frequencies based on an analysis of the literature data.”

Complex molecules in space are of interest for many reasons, including their possible connection to the formation of biologically significant molecules on the early Earth. Complex molecules might have formed on the early Earth, or they might have first formed in interstellar clouds and been transported to the surface of the Earth.

Molecules with the aldehyde group are particularly interesting since several biologically significant molecules, including a family of sugar molecules, are aldehydes.

“The GBT can be used to fully explore the possibility that a significant amount of prebiotic chemistry may occur in space long before it occurs on a newly formed planet,” said Remijan. “Comets form from interstellar clouds and incessantly bombard a newly formed planet early in its history. Craters on our Moon attest to this. Thus, comets may be the delivery vehicles for organic molecules necessary for life to begin on a new planet.”

Laboratory experiments also demonstrate that atomic addition reactions — similar to those assumed to occur in interstellar clouds — play a role in synthesizing complex molecules by subjecting ices containing simpler molecules such as water, carbon dioxide, and methanol to ionizing radiation dosages. Thus, laboratory experiments can now be devised with various ice components to attempt production of the aldehydes observed with the GBT.

“The detection of the two new aldehydes, which are related by a common chemical pathway called hydrogen addition, demonstrates that evolution to more complex species occurs routinely in interstellar clouds and that a relatively simple mechanism may build large molecules out of smaller ones. The GBT is now a key instrument in exploring chemical evolution in space,” said Hollis.

The GBT is the world’s largest fully steerable radio telescope; it is operated by the NRAO.

“The large diameter and high precision of the GBT allowed us to study small interstellar clouds that can absorb the radiation from a bright, background source. The sensitivity and flexibility of the telescope gave us an important new tool for the study of complex interstellar molecules,” said Jewell.

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

Original Source: NRAO News Release

Image credit: Canadian Space Agency
MOST, Canada?s first space telescope, is shaking up the way astronomers think about stars — and putting a new spin on the life story of our own Sun — by allowing astronomers to see in unprecedented detail how stars shake and spin.

The first results from MOST, a Canadian Space Agency mission which was also the first scientific satellite to be launched by Canada in over 30 years, include the detection of a strong ?pulse? in a young adult star called eta Bootis, and a bad case of stellar acne and hyperactivity in a ?pre-teen? version of the Sun, kappa 1 Ceti. These data offer a unique perspective on what our own Sun may have been like in its youth.

?All this talk of stellar pulses and hyperactivity must sound like ER Meets Star Trek,? admitted MOST Mission Scientist Dr. Jaymie Matthews of the University of British Columbia, who presented the findings today in a keynote address to the annual meeting of the Canadian Astronomical Society in Winnipeg. ?But we really are doing diagnostic check-ups of stars at different points in their lives, by placing them under intensive observation for weeks at a time.?

Matthews made the presentation to a gathering of physicists, astrophysicists, and medical physicists at a unique conference of Canadian physics societies (CAP/CASCA/COMP/BSC CONGRESS 2004) hosted by the Department of Physics and Astronomy at the University of Manitoba in celebration of the Faculty of Science’s 100th anniversary.

These are ambitious results from a Canadian-built and -operated orbiting observatory which is no bigger than a suitcase but can monitor the brightnesses of stars with unmatched precision and thoroughness. MOST, which stands for Microvariability and Oscillations of STars, was launched into orbit last summer and has been collecting data for the last few months.

?MOST is a major advance in the way astronomers study stars, made possible by innovative Canadian technology,? noted Canadian Space Agency President, Dr. Marc Garneau. ?It is the world?s most precise light meter, capable of recording variations as small as one ten thousandth of a percent in the brightness of a star.?

How small is that?

?If all the lights in all the offices of the Empire State Building were on at night,? explains Dr. Garneau, ?you could dim the total light by 1/10,000th of a percent if you pulled down just one window blind by only one centimetre.?

From its vantage point in polar orbit, 820 km high, the tiny MOST space telescope can stare at stars without interruption for up to eight weeks. No other observatory or network of telescopes, including the Hubble, can do this. The unique combination of precision and time coverage enables MOST to look for subtle vibrations in stars that will reveal secrets hidden beneath their surfaces. It also gives MOST the best chance to detect light directly from planets outside our Solar System and study their atmospheres and weather.

MOST is a Canadian Space Agency mission. Dynacon Inc. of Mississauga, Ontario, is the prime contractor for the satellite and its operation, with the University of Toronto Institute for Aerospace Studies (UTIAS) as a major subcontractor. The University of British Columbia (UBC) is the main contractor for the instrument and scientific operations of the MOST mission. MOST is tracked and operated through a global network of ground stations located at UTIAS, UBC and the University of Vienna.

The MOST Canadian space telescope was launched from northern Russia in June 2003 aboard a former Soviet ICBM (Intercontinental Ballistic Missile) converted to peaceful use. Weighing only 54 kg, this suitcase-sized microsatellite is packed with a small telescope and electronic camera to study stellar variability.

One of its early targets was the star eta Bootis, a slightly more massive and younger version of the Sun. Astronomers had picked out this star as one of the best candidates for the new technique of ?asteroseismology? — using surface vibrations to probe the inside of a star, similar to how geophysicists use earthquake vibrations to probe the Earth?s core.

MOST monitored eta Bootis for 28 days without interruption, placing the star under a 24-hour scientific ?stake-out? that revealed behaviour that was hidden from the limited view possible for Earth-bound telescopes. Accumulating almost a quarter of a million individual measurements of this star, MOST reached a level of light-measuring precision at least 10 times better than the best ever achieved before from Earth or space.

The data reveal the star is vibrating, but at a pitch well below the range of human hearing. The stellar melody should allow the MOST team of scientists, including Dr. David Guenther of the Canadian Institute for Computational Astrophysics at St. Mary?s University, Halifax, to determine the age and structure of eta Bootis. ?We?re now in a position to explore new physics in stars, with observations like these,? said Dr. Guenther.

Before observing eta Bootis, while still in the shakedown phase of its mission, MOST was aimed for testing purposes at a fainter star called kappa 1 Ceti. Astronomers already suspected this was a younger version of our Sun, with an age of about 750 million years. The Sun?s age is about 4.5 billion years, and it?s just entering middle age. In terms of a human life, the Sun would be about 45 years old while kappa 1 Ceti would be eight years old ? barely a pre-teen.

Like many human kids, Kappa 1 Ceti is hyperactive, flaring up from time to time, and spinning with much more kinetic energy than sedate older stars like the Sun. It also has a severe case of acne — dark spots on its face which are much larger than those visible on the Sun’s surface. The MOST data, following Kappa 1 Ceti for 29 days, show in exquisite detail how the spots move across the visible side of the star as it spins once every nine days or so. And because a star is not solid, different parts of its gaseous surface spin at different rates. MOST has been able to measure this effect directly in a star other than the Sun for the first time. These results are being prepared for submission to The Astrophysical Journal.

Future targets for MOST include other stars representing the Sun at various stages in its life, and stars known to have giant planets. MOST is designed to be able to register the tiny changes in brightness that will occur as a planet orbits its parent star. The way in which the light changes will tell astronomers about the atmospheric composition of these mysterious worlds, and even if they have clouds.

?It?s like doing a weather report for a planet outside our Solar System,? says Dr. Jaymie Matthews, MOST Mission Scientist, of the University of British Columbia.

Original Source: UBC News Release

Image credit: ESO
Using ESO’s Very Large Telescope at Paranal and a suite of ground- and space-based telescopes in a four-year long study, an international team of astronomers has measured for the first time the mass of an ultra-cool star and its companion brown dwarf. The two stars form a binary system and orbit each other in about 10 years.

The team obtained high-resolution near-infrared images; on the ground, they defeated the blurring effect of the terrestrial atmosphere by means of adaptive optics techniques. By precisely determining the orbit projected on the sky, the astronomers were able to measure the total mass of the stars. Additional data and comparison with stellar models then yield the mass of each of the components.

The heavier of the two stars has a mass around 8.5% of the mass of the Sun and its brown dwarf companion is even lighter, only 6% of the solar mass. Both objects are relatively young with an age of about 500-1,000 million years.

These observations represent a decisive step towards the still missing calibration of stellar evolution models for very-low mass stars.

Telephone number star
Even though astronomers have found several hundreds of very low mass stars and brown dwarfs, the fundamental properties of these extreme objects, such as masses and surface temperatures, are still not well known. Within the cosmic zoo, these ultra-cool stars represent a class of “intermediate” objects between giant planets – like Jupiter – and “normal” stars less massive than our Sun, and to understand them well is therefore crucial to the field of stellar astrophysics.

The problem with these ultra-cool stars is that contrary to normal stars that burn hydrogen in their central core, no unique relation exists between the luminosity of the star and its mass. Indeed, luminosities and surface temperatures of ultra-cool dwarf stars depend both on their age and their mass. An older, somewhat more massive ultra-cool dwarf can thus have exactly the same temperature as a younger, less massive one.

It is therefore a basic goal of modern astrophysics to obtain independently the masses of an ultra-cool dwarf star. This is in principle possible by studying such objects that are members in a binary system.

This is precisely what an international team of astronomers has now done in a four-year long study of a binary stellar system with an ultra-cool dwarf star, using a plethora of top telescopic facilities, including ESO’s Very Large Telescope, as well as Keck I and Gemini North in Hawaii and also the Hubble Space Telescope. This system – with the telephone number name of 2MASSW J0746425+2000321 – is located at a distance of 40 light-years.

The astronomers used high-angular-resolution imaging to see both stars in the binary system and to measure their motion over a four-year period. However, this is more easily said than done, as the separation on the sky between the two stars is quite small: between 0.13 and 0.22 arcsec. This corresponds to the size of a 1-Euro coin, seen at a distance of about 25 km.

This separation is so small that it is normally not possible to differentiate the two stars due to the blurring effect of atmospheric turbulence (the “seeing”). It is therefore necessary to use the technique of adaptive optics. This wonderful method is based on the measurement of the image quality in real-time and sending corresponding corrective signals up to 100 times every second to a small deformable mirror, located in front of the detector. As the mirror continuously modifies its shape, the disturbing effect of the turbulence is neutralised. Applied at the VLT, this technique has resulted in images which are at least ten times sharper than the “seeing” and which therefore show many more details in the observed objects.

At the Very Large Telescope, the astronomers used the state-of-the-art adaptive optics NACO instrument. Says Herv? Bouy, principal author of the paper presenting the results described here: “NACO offers the possibility to work in the infrared and is therefore ideally suited for the study of ultra-cool stars, which emit most of their light in this wavelength range. With the combination of the high efficiency of NACO and the VLT, and the excellent atmospheric conditions prevailing at Paranal, we were able to achieve very sharp images of this binary stellar system, almost as good as if the telescope were located in space.”

Ultra-cool and on diet
During their four-year long study, seven different relative positions of the two components of the binary system were measured and Herv? Bouy and his co-workers were able to determine with good precision the stellar orbits. They find that the two stars revolve around each other once every 10 years and that their physical separation is only 2.5 times the distance of the Earth to the Sun – as astronomers say, 2.5 Astronomical Units. Using Kepler’s laws, it is then straightforward to derive the total mass of the system. The obtained value is less than 15 % of the mass of the Sun.

The astronomers then used the photometric data of each star obtained in several wavebands, as well as spectra obtained with the Hubble Space Telescope to study the two objects in more detail. Using the latest stellar models of the group of the Ecole Normale Sup?rieure de Lyon, they found that both stars have roughly the same surface temperature, around 1500 ?C (1800 K). For a star, this is ultra-cool indeed – by comparison, the surface temperature of the Sun is more than three times higher.

Using theoretical models, the team also found that the two stars are rather young (in astrophysical terms) – their age is between 500 and 1,000 million years only. The more massive of the two has a mass between 7.5 and 9.5% the mass of the Sun, while its companion has a mass between 5 and 7% of the solar mass.

Objects weighing less than about 7% of our Sun have been variously called “Brown Dwarfs”, “Failed Stars” or “Super Planets”. Indeed, since they have no sustained energy generation by thermal nuclear reactions in their interior, many of their properties are more similar to those of giant gas planets in our own solar system such as Jupiter, than to stars like the Sun.

The system 2MASSW J0746425+2000321 is thus apparently made up of a brown dwarf orbiting a slightly more massive ultra-cool dwarf star. It is a true “Rosetta stone” in the new field of low-mass stellar astrophysics and further studies will surely provide more valuable information about these objects in the transitional zone between stars and planets.

Original Source: ESO News Release

Image credit: NRAO
Astronomers using a global combination of radio telescopes to study a stellar explosion some 30 million light-years from Earth have likely discovered either the youngest black hole or the youngest neutron star known in the Universe. Their discovery also marks the first time that a black hole or neutron star has been found associated with a supernova that has been seen to explode since the invention of the telescope nearly 400 years ago.

A supernova is the explosion of a massive star after it exhausts its supply of nuclear fuel and collapses violently, rebounding in a cataclysmic blast that spews most of its material into interstellar space. What remains is either a neutron star, with its material compressed to the density of an atomic nucleus, or a black hole, with its matter compressed so tightly that its gravitational pull is so strong that not even light can escape it.

A team of scientists studied a supernova called SN 1986J in a galaxy known as NGC 891. The supernova was discovered in 1986, but astronomers believe the explosion actually occurred about three years before. Using the National Science Foundation’s Very Long Baseline Array (VLBA), Robert C. Byrd Green Bank Telescope (GBT), and Very Large Array (VLA), along with radio telescopes from the European VLBI Network, they made images that showed fine details of how the explosion evolves over time.

“SN 1986J has shown a brightly-emitting object at its center that only became visible recently. This is the first time such a thing has been seen in any supernova,” said Michael Bietenholz, of York University in Toronto, Ontario. Bietenholz worked with Norbert Bartel, also of York University, and Michael Rupen of the National Radio Astronomy Observatory (NRAO) in Socorro, New Mexico, on the project. The scientists reported their findings in the June 10 edition of Science Express.

“A supernova is likely the most energetic single event in the Universe after the Big Bang. It is just fascinating to see how the smoke from the explosion is blown away and how now after all these years the fiery center is unveiled. It is a textbook story, now witnessed for the first time,” Bartel said.

Analysis of the bright central object shows that its characteristics are different from the outer shell of explosion debris in the supernova.

“We can’t yet tell if this bright object at the center is caused by material being sucked into a black hole or if it results from the action of a young pulsar, or neutron star,” said Rupen.

“It’s very exciting because it’s either the youngest black hole or the youngest neutron star anybody has ever seen,” Rupen said. The youngest pulsar found to date is 822 years old.

Finding the young object is only the beginning of the scientific excitement, the astronomers say.

“We’ll be watching it over the coming years. First, we hope to find out whether it’s a black hole or a neutron star. Next, whichever it is, it’s going to give us a whole new view of how these things start and develop over time,” Rupen said.

For example, Rupen explained, if the object is a young pulsar, learning the rate at which it is spinning and the strength of its magnetic field would be extremely important for understanding the physics of pulsars.

The scientists point out that it will be important to observe SN 1986J at many wavelengths, not just radio, but also in visible light, infrared and others.

In addition, the astronomers also now want to look for simiilar objects elsewhere in the Universe.

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

Original Source: NRAO News Release

Image credit: Orbital Sciences
Using NASA’s Far Ultraviolet Spectroscopic Explorer (FUSE) satellite, researchers have for the first time detected molecular nitrogen in interstellar space, giving them their first detailed look into how the universe’s fifth most-abundant element behaves in an environment outside the Solar System.

This discovery, made by astronomers at The Johns Hopkins University, Baltimore, promises to enhance understanding not only of the dense regions between the stars, but also of the very origins of life on Earth.

“Detecting molecular nitrogen is vital for improved understanding of interstellar chemistry,” said David Knauth, a post-doctoral fellow at Johns Hopkins and first author of a paper in the June 10 issue of Nature. “And because stars and planets form from the interstellar medium, this discovery will lead to an improved understanding of their formation, as well.”

Nitrogen is the most prevalent element of Earth’s atmosphere. Its molecular form, known as N2, consists of two combined nitrogen atoms. A team of researchers led by Knauth and physics and astronomy research scientist and co-author B-G Andersson continued investigations of N2 that began in the 1970s with the Copernicus satellite. At least 10,000 times more sensitive than Copernicus, FUSE – a satellite-telescope designed at and operated by Johns Hopkins for NASA – allowed the astronomers to probe the dense interstellar clouds where molecular nitrogen was expected to be a dominant player.
“Astronomers have been searching for molecular nitrogen in interstellar clouds for decades,” said Dr. George Sonneborn, FUSE Project Scientist at NASA Goddard Space Flight Center, Greenbelt, Md. “Its discovery by FUSE will greatly improve our knowledge of molecular chemistry in space.”

The astronomers faced several challenges along the way, including the fact that they were peering through dusty, dense interstellar clouds which blocked a substantial amount of the star’s light. In addition, the researchers confronted a classic Catch-22: Only the brightest stars emitted enough of a signal to allow FUSE to detect molecular nitrogen’s presence, but many of those stars were so bright they threatened to damage the satellite’s exquisitely-sensitive detectors.

HD 124314, a moderately-reddened star in the southern constellation of Centaurus, ended up being the first sight line where researchers could verify molecular nitrogen’s presence. This discovery is an important step in ascertaining the complicated process of how much molecular nitrogen exists in the interstellar medium and how its presence varies in different environments.

“For nitrogen, most models say that a major part of the element should be in the form of N2, but as we had not been able to measure this molecule, it’s been very hard to test whether those models and theories are right or not. The big deal here is that now we have a way to test and constrain those models,” Andersson said.

Launched on June 24, 1999, FUSE seeks to understand several fundamental questions about the Universe. What were the conditions shortly after the Big Bang? What are the properties of interstellar gas clouds that form stars and planetary systems? How are the chemical elements made and dispersed throughout our galaxy?

FUSE is a NASA Explorer mission. Goddard manages the Explorers Program for the Office of Space Science at NASA Headquarters in Washington, D.C. For more on the FUSE mission, go the website at: http://fuse.pha.jhu.edu

Original Source: NASA News Release

Image credit: Berkeley Lab
In a case of the plot thickening as the mystery unfolds, the Higgs boson has just gotten heavier, even though the subatomic particle has yet to be found. In a letter to the scientific journal Nature, published in the June 10, 2004 issue, an international collaboration of scientists working at the Tevatron accelerator of the Fermi National Accelerator Laboratory (Fermilab), report the most precise measurements yet for the mass of the top quark ? a subatomic particle that has been found ? and this requires an upward revision for the long-postulated but still undetected Higgs boson.

“Since the top quark mass we are reporting is a bit higher than previously measured, it means the most likely value of the Higgs mass is also higher,” says Ron Madaras, a physicist with the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), who heads the local participation in the D-Zero experiment at the Tevatron. “The most likely Higgs mass has now been increased from 96 to 117 GeV/c2” ? GeV/c2 is a common particle-physics unit of mass; the mass of the proton measures about 1 GeV/c2 ? “which means it’s probably beyond the sensitivity of current experiments, but very likely to be found in future experiments at the Large Hadron Collider being built at CERN.”

The Higgs boson has been called the missing link in the Standard Model of Particles and Fields, the theory that’s been used to explain fundamental physics since the 1970s. Prior to 1995 the top quark was also missing, but then the experimental teams working at the Tevatron’s two large detector systems, D-Zero and CDF, were able to discover it independently.

Scientists believe that the Higgs boson, named for Scottish physicist Peter Higgs, who first theorized its existence in 1964, is responsible for particle mass, the amount of matter in a particle. According to the theory, a particle acquires mass through its interaction with the Higgs field, which is believed to pervade all of space and has been compared to molasses that sticks to any particle rolling through it. The Higgs field would be carried by Higgs bosons, just as the electromagnetic field is carried by photons.

“In the Standard Model, the Higgs boson mass is correlated with top quark mass,” says Madaras, “so an improved measurement of the top quark mass gives more information about the possible value of the Higgs boson mass.”

According to the Standard Model, at the beginning of the universe there were six different types of quarks. Top quarks exist only for an instant before decaying into a bottom quark and a W boson, which means those created at the birth of the universe are long gone. However, at Fermilab’s Tevatron, the most powerful collider in the world, collisions between billions of protons and antiprotons yield an occasional top quark. Despite their brief appearances, these top quarks can be detected and characterized by the D-Zero and CDF experiments.

In announcing the D-Zero results, experiment cospokesperson John Womersley said, “An analysis technique that allows us to extract more information from each top quark event that occurred in our detector has yielded a greatly improved precision of plus or minus 5.3 GeV/c2 in the top mass measurement, compared with previous measurements. The new measurement is comparable to the precision of all previous top quark mass measurements put together. When this new result is combined with all other measurements from both the D-Zero and CDF experiments, the new world average for the top mass becomes 178.0 plus or minus 4.3 GeV/c2.”

The D-Zero detector system consists of a central tracking detector array, a hermetic calorimeter for measuring energy, and a large solid-angle muon detector system. Berkeley Lab designed and built the two electromagnetic end-cap calorimeters and also the initial vertex detector, the innermost component of the tracking system. Tracking detectors supplement calorimeters by measuring particle trajectories. Only when trajectory and energy measurements are combined can scientists identify and characterize particles.

While raising the central value for the top quark mass appears to diminish the possibility that the Higgs boson could be discovered at the Tevatron, it does open a wider door for new discoveries in supersymmetry, also known as SUSY, an extension of the Standard Model that unites particles of force and matter through the existence of superpartners (sometimes referred to as “sparticles”). Supersymmetry seeks to fill gaps left by the Standard Model.

“The current mass limits or bounds that exclude supersymmetric particles are very sensitive to the top quark mass,” says Madaras. “Since the top quark mass is now higher, these limits or bounds are not as severe, which increases the chance of seeing supersymmetric particles at the Tevatron.”

Scientists from nearly 40 US universities and 40 foreign institutions contributed to the data analysis reported in the letter to Nature by the D-Zero experimental group. Berkeley Lab co-authors of the letter in addition to Madaras were Mark Strovink, Al Clark, Tom Trippe, and Daniel Whiteson.

Fermilab Director Michael Witherell said in a statement that these results do not end the story of precision measurements of the top quark mass. “The two collider detectors, D-Zero and CDF, are recording large amounts of data in Run II of the Tevatron. The CDF collaboration has recently reported preliminary new measurements of the top mass based on Run II data. The precision of the world average will improve further when their results are final. Over the next few years, both experiments will make increasingly precise measurements of the top quark mass.”

Fermilab, like Berkeley Lab, is funded by the Department of Energy?s Office of Science. In response to the Nature letter from the D-Zero group, Raymond L. Orbach, Director of the Office of Science, said: ?These important results demonstrate how our scientists are applying new techniques to existing data, producing new estimates for the mass of the Higgs boson. We eagerly await the next round of results from the vast quantities of data that are generated today at the Fermilab Tevatron.?

Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research and is managed by the University of California. Fermilab is a national laboratory funded by the Office of Science of the U.S. Department of Energy, operated by Universities Research Association, Inc.

Original Source: Berkeley Lab News Release

Image credit: U of Chicago
Astrophysicists led by the University of Chicago?s Andrey Kravtsov have resolved an embarrassing contradiction between a favored theory of how galaxies form and what astronomers see in their telescopes.

Astrophysicists base their understanding of how galaxies form on an extension of the big bang theory called the cold dark matter theory. In this latter theory, small galaxies collide and merge, inducing bursts of star formation that create the different types of massive and bright galaxies that astronomers see in the sky today. (Dark matter takes its name from the idea that 85 percent of the total mass of the universe is made of unknown matter that is invisible to telescopes, but whose gravitational effects can be measured on luminous galaxies.)

This theory fits some key data that astrophysicists have collected in recent years. Unfortunately, when astrophysicists ran supercomputer simulations several years ago, they ended up with 10 times more dark matter satellites?clumps of dark matter orbiting a large galaxy?than they expected.

?The problem has been that the simulations don?t match the observations of galaxy properties,? said David Spergel, professor of astrophysics at Princeton University. ?What Andrey?s work represents is a very plausible solution to this problem.?

Kravtsov and his collaborators found the potential solution in new supercomputer simulations they will describe in a paper that will appear in the July 10 issue of the Astrophysical Journal. ?The solution to the problem is likely to be in the way the dwarf galaxies evolve,? Kravtsov said, referring to the small galaxies that inhabit the fringes of large galaxies.

In general, astrophysicists believe that formation of very small dwarf galaxies should be suppressed. This is because gas required for continued formation of stars can be heated and expelled by the first generation of exploding supernovae stars. In addition, ultraviolet radiation from galaxies and quasars that began to fill the universe approximately 12 billion years ago heats the intergalactic gas, shutting down the supply of fresh gas to dwarf galaxies.

In the simulations, Kravtsov, along with Oleg Gnedin of the Space Telescope Science Institute and Anatoly Klypin of New Mexico State University, found that some of the dwarf galaxies that are small today have been more massive in the past and could gravitationally collect the gas they need to form stars and become a galaxy.

?The systems that appear rather feeble and anemic today could, in their glory days, form stars for a relatively brief period,? Kravtsov said. ?After a period of rapid mass growth, they lost the bulk of their mass when they experienced strong tidal forces from their host galaxy and other galaxies surrounding them.?

This galactic ?cannibalism? persists even today, with many of the ?cannibalized? dwarf galaxies becoming satellites orbiting in the gravitational pull of larger galaxies.

?Just like the planets in the solar system surrounding the sun, our Milky Way galaxy and its nearest neighbor, the Andromeda galaxy, are surrounded by about a dozen faint ?dwarf? galaxies,? Kravtsov said. ?These objects were pulled in by the gravitational attraction of the Milky Way and Andromeda some time ago during their evolution.?

The simulations had succeeded where others had failed because Kravtsov?s team analyzed simulations that were closely spaced in time at high resolution. This allowed the team to track the evolution of individual objects in the simulations. ?This is rather difficult and is not often done in analyses of cosmological simulations. But in this case it was the key to recognize what was going on and get the result,? Kravtsov said.

The result puts the cold dark matter scenario on more solid ground. Scientists had attempted to modify the main tenets of the scenario and the properties of dark matter particles to eliminate the glaring discrepancy between theory and observation of dwarf galaxies. ?It turns out that the proposed modifications introduced more problems than they solved,? Kravtsov said.

The simulations were performed at the National Center for Supercomputer Applications, University of Illinois at Urbana-Champaign, with grants provided by the National Science Foundation and the National Aeronautics and Space Administration.

Original Source: University of Chicago News Release

Image credit: NRAO
Astronomers studying gas clouds in the famous Whirlpool Galaxy have found important clues supporting a theory that seeks to explain how the spectacular spiral arms of galaxies can persist for billions of years. The astronomers applied techniques used to study similar gas clouds in our own Milky Way to those in the spiral arms of a neighbor galaxy for the first time, and their results bolster a theory first proposed in 1964.

The Whirlpool Galaxy, about 31 million light-years distant, is a beautiful spiral in the constellation Canes Venatici. Also known as M51, it is seen nearly face-on from Earth and is familiar to amateur astronomers and has been featured in countless posters, books and magazine articles.

“This galaxy made a great target for our study of spiral arms and how star formation works along them,” said Eva Schinnerer, of the National Radio Astronomy Observatory in Socorro, NM. “It was ideal for us because it’s one of the closest face-on spirals in the sky,” she added.

Schinnerer worked with Axel Weiss of the Institute for Millimeter Radio Astronomy (IRAM) in Spain, Susanne Aalto of the Onsala Space Observatory in Sweden, and Nick Scoville of Caltech. The astronomers presented their findings to the American Astronomical Society’s meeting in Denver, Colorado.

The scientists analyzed radio emission from Carbon Monoxide (CO) molecules in giant gas clouds along M51’s spiral arms. Using telescopes at Caltech’s Owens Valley Radio Observatory and the 30-meter radio telescope of IRAM, they were able to determine the temperatures and amounts of turbulence within the clouds. Their results provide strong support for a theory that “density waves” explain how spiral arms can persist in a galaxy without winding themselves so tightly that, in effect, they disappear.

The density-wave theory, proposed by Frank Shu and C.C. Lin in 1964, says that a galaxy’s spiral pattern is a wave of higher density, or compression, that revolves around the galaxy at a speed different from that of the galaxy’s gas and stars. Schinnerer and her colleagues studied a region in one of M51’s spiral arms that presumably has just overtaken and passed through the density wave.

Their data indicate that gas on the trailing edge of the spiral arm, which has most recently passed through the density wave, is both warmer and more turbulent than gas in the forward edge of the arm, which would have passed through the density wave longer ago.

“This is what we would expect from the density-wave theory,” Schinnerer said. “The gas that passed through the density wave earlier has had time to cool and lose the turbulence caused by the passage,” she added.

“Our results show, for the first time, how the density wave operates on a cloud-cloud scale, and how it promotes and prevents star formation in spiral arms,” Aalto said.

The next step, the scientists say, is to look at other spiral galaxies to see if a similar pattern is present. That will have to wait, Schinnerer said, because the radio emission from CO molecules that provides the information on temperature and turbulence is very faint.

“When the Atacama Large Millimeter Array (ALMA) comes on line, it will have the ability to extend this type of study to other galaxies. We look forward to using ALMA to test the density-wave model more thoroughly,” Schinnerer said. ALMA is a millimeter-wave observatory that will use 64, 12-meter-diameter dish antennas on the Atacama Desert of northern Chile. Now under construction, ALMA will provide astronomers with an unprecedented capability to study the Universe at millimeter wavelengths.

The Whirlpool Galaxy was discovered by the French comet-hunter Charles Messier on October 13, 1773. He included it as object number 51 in his now-famous catalog of astronomical objects that, in a small telescope, might be mistaken for a comet. In 1845, the British astronomer Lord Rosse discovered the spiral structure in the galaxy. For amateur astronomers using telescopes in dark-sky locations, M51 is a showpiece object.

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

Original Source: NRAO News Release

Image credit: NOAO
New observations from the WIYN 3.5-meter telescope on Kitt Peak show striking visual evidence for a galaxy being stripped bare of its star-forming material by its violent ongoing encounter with the hot gas in the center of a galaxy cluster.

This extremely disruptive process is believed to be a major influence on the evolution of galaxies and their star-forming ability over time, but direct observational evidence has been more circumstantial than incontrovertible.

A new three-color composite image of spiral galaxy NGC 4402, taken as the galaxy falls into the Virgo galaxy cluster, shows several key lines of evidence of an ongoing interaction, according to a presentation today in Denver at the 204th meeting of the American Astronomical Society.

NGC 4402 is located more than 50 million light years from Earth, in the midst of the relatively nearby Virgo cluster. As the galaxy moves toward the center of the cluster (located out of the image toward the bottom left), it experiences a ?wind? from the hot cluster gas, which can reach temperatures of millions of degrees.

?This hot wind strips out the much cooler gas and dust in the galaxy. This is important because the gas is raw material for new stars, and once this gas is stripped, the galaxy can no longer form new stars and becomes ?dead? in a sense,? says Hugh Crowl of Yale University, New Haven, CT, lead author of the paper. ?We see at least four distinct lines of evidence for declaring that this ram-pressure stripping process is cleaning out this infalling spiral galaxy.?

* First, the dust disk appears to be truncated, meaning that the light from stars extends out well beyond where gas and dust is observed. ?Since we believe that stars are born in clouds of gas and dust, this suggests that some of the material must have been stripped from the galaxy after the stars were born,? Crowl explains.
* Second, the dusty disk appears to be ?bowed? upward; that is, it has been bent by the wind blowing from the southeast (from the lower left of the image).
* Third, it appears that the light emitted by the north side of the stellar disk has been reddened and dimmed by dust that has been pushed up in front of it by the pressure of the cluster gas. Simultaneously, the dust to the south of the disk has been removed, revealing young blue stars glowing behind it.
* Finally, some of the most unusual features of NGC 4402 are the linear filaments of dust to the south of its main disk. ?These remarkable filaments originate in clumps that appear to be the densest remnants of the now displaced disk of the galaxy,? Crowl says.

The filaments are being ?ablated,? or stripped away, in an outside-in fashion, similar to the process observed in much smaller filamentary features in hot star-forming nebula such as the Eagle Nebula and Pelican Nebula. The hot galaxy cluster wind strips away the outer layers of the cloud, and the dust from these layers is then pushed away. In one case (the eastern or leftmost filament), ?we can see that the wind has either triggered star formation toward the tip of one of these dense clumps or exposed an already-existing star forming region,? Crowl adds.

The bright blue clusters of young stars in the bottom left region of the galaxy?s disk is further evidence of recently triggered star formation.

?This image clearly shows galactic disruption on a grand scale,? Crowl adds. ?It gives us much more confidence that this widely postulated process truly plays a significant role in shaping the evolution of galaxies in clusters.?

This imaging data was obtained with the help of the WIYN Tip-Tilt module, an adaptive optics device that uses a movable mirror to provide first-order compensation for the jittery motion of the incoming image caused by variable atmospheric conditions and telescope vibrations.

This result will be presented in poster 80.12 at the AAS meeting, located in the Ballroom poster session from 9:20 a.m. to 4:00 p.m. Co-authors of the paper are Jeff Kenney (Yale), J.H. van Gorkom (Columbia University), and B. Vollmer (CDS, Strasbourg).

The Wisconsin-Indiana-Yale-NOAO (WIYN) 3.5-meter telescope is located at Kitt Peak National Observatory, 55 miles southwest of Tucson, AZ. Kitt Peak National Observatory is part of the National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under a cooperative agreement with the National Science Foundation (NSF).

Original Source: NOAO News Release

Image credit: Chandra
Combined data from NASA’s Chandra X-ray Observatory and infrared observations with the Palomar 200-inch telescope have uncovered evidence that a gamma-ray burst, one of nature’s most catastrophic explosions, occurred in our Galaxy a few thousand years ago. The supernova remnant, W49B, may also be the first remnant of a gamma-ray burst discovered in the Milky Way.

W49B is a barrel-shaped nebula located about 35,000 light years from Earth. The new data reveal bright infrared rings, like hoops around a barrel, and intense X-radiation from iron and nickel along the axis of the barrel.

“These results provide intriguing evidence that an extremely massive star exploded in two powerful, oppositely directed jets that were rich in iron,” said Jonathan Keohane of NASA’s Jet Propulsion Laboratory at a press conference at the American Astronomical Society meeting in Denver. “This makes W49B a prime candidate for being the remnant of a gamma ray burst involving a black hole collapsar.”

“The nearest known gamma-ray burst to Earth is several million light years away ? most are billions of light years distant ? so the detection of the remnant of one in our galaxy would be a major breakthrough,” said William Reach, one of Keohane’s collaborators from the California Institute of Technology.

According to the collapsar theory, gamma-ray bursts are produced when a massive star runs out of nuclear fuel and the star’s core collapses to form a black hole surrounded by a disk of extremely hot, rapidly rotating, magnetized gas. Much of this gas is pulled into the black hole, but some is flung away in oppositely directed jets of gas traveling at near the speed of light.

An observer aligned with one these jets would see a gamma-ray burst, a blinding flash in which the concentrated power equals that of ten quadrillion Suns for a minute or so. The view perpendicular to the jets is a less astonishing, although nonetheless spectacular supernova explosion. For W49B, the jet is tilted out of the plane of the sky by about 20 degrees.

Four rings about 25 light years in diameter can be identified in the infrared image. These rings, which are due to warm gas, were presumably flung out by the rapid rotation of the massive star a few hundred thousand years before the star exploded. The rings were pushed outward by a hot wind from the star a few thousand years before it exploded.

Chandra’s image and spectral data show that the jets of multimillion-degree-Celsius gas extending along the axis of the barrel are rich in iron and nickel ions, consistent with their being ejected from the center of the star. This distinguishes the explosion from a conventional type II supernova in which most of the Fe and Ni goes into making the neutron star, and the outer part of the star is what is flung out. In contrast, in the collapsar model of gamma ray bursts iron and nickel from the center is ejected along the jet.

At the ends of the barrel, the X-ray emission flares out to make a hot cap. The X-ray cap is surrounded by a flattened cloud of hydrogen molecules detected in the infrared. These features indicate that the shock wave produced by the explosion has encountered a large, dense cloud of gas and dust.

The scenario that emerges is one in which a massive star formed from a dense cloud of dust, shone brightly for a few million years while spinning off rings of gas and pushing them away, forming a nearly empty cavity around the star. The star then underwent a collapsar-type supernova explosion that resulted in a gamma-ray burst.

The observations of W49B may help to resolve a problem that has bedeviled the collapsar model for gamma-ray bursts. On the one hand, the model is based on the collapse of a massive star, which is normally formed from a dense cloud. On the other hand, observations of the afterglow of many gamma-ray bursts indicate that the explosion occurred in a low-density gas. Based on the W49B data, the resolution proposed by Keohane and colleagues is that the star had carved out an extensive low-density cavity in which the explosion subsequently occurred.

“This star appears to have exploded inside a bubble it had created,” said Keohane. “In a sense, it dug its own grave.”

NASA’s Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for the Office of Space Science, NASA Headquarters, Washington. Northrop Grumman of Redondo Beach, Calif., formerly TRW, Inc., was the prime development contractor for the observatory. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass.

Original Source: Chandra News Release