Category: Astronomy

MOST, Canada?s first space telescope, celebrates its first birthday today, but its latest surprising results could spoil the party for other astronomers whose earlier results are now being questioned.

The MOST team used their tiny but powerful satellite as a stellar stethoscope to take the pulse of one of the best-known stars in the Galaxy, called Procyon (PRO-see-yon), and were shocked to discover their cosmic patient is a ?flat liner?. The star shows none of the pulsations predicted by over 20 years of earlier theory and observations from Earth. The journal Nature will publish these unexpected findings on July 1.

?The lack of a pulse doesn’t mean the star Procyon is dead,? explained MOST Mission Scientist Dr. Jaymie Matthews of the University of British Columbia. ?But it does mean that some of our long-held theories about stars like this need to be put on the critical list. And that future space missions following in the path of MOST will have to revise their target lists and observing strategies in light of this null result.?

MOST, which stands for Microvariability and Oscillations of STars, is a Canadian Space Agency mission. UBC is the main contractor for the instrument and scientific operations of the MOST mission.

MOST is not much bigger than a suitcase but is able to measure the brightness variations of stars more precisely than any other instrument on Earth or in space. It was launched one year ago on June 30, aboard a modified Russian nuclear missile. To mark the occasion, MOST scientists celebrated with a birthday party complete with cake and dehydrated ?space? ice cream.

?MOST is only one year old, but it?s proving to be a very precocious child,? said Roger Colley, a senior official from the Canadian Space Agency. ?In its first six months of operation, MOST has already given us new perspectives on the stars we thought we knew best, the ones in our own Galactic backyard. In that way, it?s providing new insights into the Sun, the star we need to understand better to predict the future of our home planet.?

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.

Its first prime target was Procyon, the eighth brightest star in the night sky, similar to the Sun but more massive and further along in life. Astronomers had concluded that Procyon was the best candidate 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 Procyon up to eight times per minute for 32 days, with lapses totalling only seven hours over that entire time. Accumulating about 250,000 individual measurements, MOST reached a level of light-measuring precision at least 10 times better than the best ever achieved before from Earth or space. The MOST team was surprised to find that Procyon was not vibrating, and soon showed that a more careful treatment of stellar models indicated that it should indeed be stable.

The lack of waves detected on the surface of Procyon has ironically generated waves in the worldwide community of stellar astronomers. These results contradict theories and observational evidence that had mounted over the last 20 years. Several planned international space missions have been designed based on the firm belief that stars like Procyon pulsate. The MOST findings mean target lists and observing strategies for these satellites may have to be seriously revamped.

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.

MOST (Microvariability & Oscillations of STars) is a Canadian Space Agency mission. UBC is the main contractor for the instrument and scientific operations of the MOST 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.

MOST is tracked and operated through a global network of ground stations located at UTIAS, UBC and the University of Vienna.

Other partners include the Harvard-Smithsonian Center for Astrophysics, Universit? de Montr?al, and St. Mary?s University in Halifax.

For more information on MOST, visit: www.astro.ubc.ca/MOST/

For more information on the Canadian Space Agency, visit: www.space.gc.ca/asc/eng/default.asp

Original Source: UBC News Release

What would our Milky Way galaxy look like if we could travel outside it and snap a picture? It might look a lot like a new image by NASA’s Spitzer Space Telescope of a spiral galaxy called NGC 7331 – a virtual twin of our Milky Way.

The picture, which can be viewed at http://photojournal.jpl.nasa.gov/catalog/PIA06322 , shows our twin as never before. Its swirling arms spin outward from a central bulge of light, which is outlined by a ring of actively forming stars.

“Being inside our galaxy makes it difficult to see what’s going on in the center,” said Dr. J.D. Smith, a member of the team that observed NGC 7331, and an astronomer at the University of Arizona, Tucson. “By looking at a very similar galaxy, we gain a bird’s eye-view of what the entire Milky Way might look like.”

Such an outside perspective will teach astronomers how our own galaxy, as well as others like it, might have formed and evolved.

The latest observations are the first in a large-scale effort to observe 75 nearby galaxies with Spitzer’s highly sensitive infrared eyes. Called Spitzer Infrared Nearby Galaxies Survey, the program will combine Spitzer data with that from other ground- and space-based telescopes operating at wavelengths ranging from ultraviolet to radio to create a comprehensive map of the selected galaxies.

The program’s first target, NGC 7331, was chosen in part for its striking similarities to the Milky Way. While these so-called twin galaxies do not share the same parents, they have many features in common, including number of stars, mass, spiral arm pattern and star-formation rate of a few stars per year. Whether the Milky Way has an inner star-forming ring like that of NGC 7331 is not known. NGC 7331 is located about 50 million light-years away in the constellation Pegasus.

The new Spitzer image demonstrates the power of the telescope’s infrared eyes to dissect galaxies into their various parts. Taken by the telescope’s infrared array camera, the false-colored picture readily distinguishes NGC 7331’s arms (brownish red), central bulge (blue) and star-forming ring (yellow). The composition of materials making up these regions was also revealed by the Spitzer observations: the central bulge consists primarily of older stars; the ring possesses a large amount of gas and dusty organic molecules called polycyclic aromatic hydrocarbons, which typically glow when illuminated by newborn stars; and the arms contain these same dust grains to a lesser degree. Polycyclic aromatic hydrocarbons are also found on Earth, on burnt toast and in car exhaust among other places.

Data from Spitzer’s infrared spectrograph instrument were also used to show that the center of NGC 7331 harbors either an unusually high concentration of massive stars, or a moderately active black hole about the same size as the one lurking at the core of our galaxy.

These findings will appear in two papers in the September issue of a special supplement to the Astrophysical Journal. Dr. Michael W. Regan of the Space Telescope Institute, Baltimore, Md., is lead author of a paper detailing observations from the infrared array camera, and Smith is lead author of a paper on the infrared spectrograph results. The Spitzer Infrared Nearby Galaxies Survey project is conducted by a team of about 25 scientists from 12 institutions, and is led by principal investigator Dr. Robert C. Kennicutt of the University of Arizona, Tucson.

Launched August 25, 2003, the Spitzer Space Telescope is the fourth of NASA’s Great Observatories, a program that also includes the Hubble Space Telescope, Chandra X-ray Observatory and Compton Gamma Ray Observatory.

JPL manages the Spitzer Space Telescope mission for NASA’s Office of Space Science, Washington, D.C. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. JPL is a division of Caltech. Spitzer’s infrared spectrograph was built by Cornell University, Ithaca, N.Y., and Ball Aerospace Corporation, Boulder, Colo. The instrument’s development was led by Dr. Jim Houck of Cornell. Spitzer’s infrared array camera was built by NASA Goddard Space Flight Center, Greenbelt, Md. The camera’s development was led by Dr. Giovanni Fazio of Smithsonian Astrophysical Observatory, Cambridge, Mass.

Additional information about the Spitzer Space Telescope is available at http://www.spitzer.caltech.edu.

Original Source: NASA/JPL News Release

An international team of astronomers, studying the left-over remnants of stars like our own Sun, have found a remarkable object where the nuclear reactor that once powered it has only just shut down. This star, the hottest known white dwarf, H1504+65, seems to have been stripped of its entire outer regions during its death throes leaving behind the core that formed its power plant.

Scientists from the United Kingdom, Germany and the USA focused two of NASA’s space telescopes, the Chandra X-ray observatory and the Far Ultraviolet Spectroscopic Explorer (FUSE), onto H1504+65 to probe its composition and measure its temperature. The data revealed that the stellar surface is extremely hot, 200,000 degrees, and is virtually free of hydrogen and helium, something never before observed in any star. Instead, the surface is composed mainly of carbon and oxygen, the ‘ashes’ of the fusion of helium in a nuclear reactor. An important question we must answer is why has this unique star lost the hydrogen and helium, which usually hide thestellar interior from our view?

Professor Martin Barstow (University of Leicester) said. ‘Studying the nature of the ashes of dead stars give us important clues as to how stars like the Sun live their lives and eventually die. The nuclear waste of carbon and oxygen produced in the process are essential elements for life and are eventually recycled into interstellar space to form new stars, planets and, possibly, living beings.’

Professor Klaus Werner (University of TUbingen) said. ‘We realized that this star has, on astronomical time scales, only very recently shut down nuclear fusion (about a hundred years ago). We clearly see the bare, now extinct reactor that once powered a bright giant star.’

Dr Jeffrey Kruk (Johns Hopkins University) said: ‘Astronomers have long predicted that many stars would have carbon-oxygen cores near the end of their lives, but I never expected we would actually be able to see one. This is a wonderful opportunity to improve our understanding of the life-cycle of stars.’

The Chandra X-ray data also reveal the signatures of neon, an expected by-product of helium fusion. However, a big surprise was the presence of magnesium in similar quantities. This result may provide a key to the unique composition of H1504+65 and validate theoretical predictions that, if massive enough, some stars can extend their lives by tapping yet another energy source: the fusion of carbon into magnesium. However, as magnesium can also be produced by helium fusion, proof of the theory is not yet ironclad. The final link in the puzzle would be the detection of sodium, which will require data from yet another observatory: the Hubble Space Telescope. The team has already been awarded time on the Hubble Space Telescope to search for sodium in H1504+65 next year, and will, hopefully, discover the final answer as to the origin of this unique star.

Original Source: RAS News Release

For the past several years, a team of University of California astrophysicists working at Los Alamos National Laboratory have been using a cluster of roughly 300 computer processors to model some of the most intriguing aspects of the Universe. Called the Space Simulator, this de facto supercomputer has not only proven itself to be one of the fastest supercomputers in the world, but has also demonstrated that modeling and simulation of complex phenomena, from supernovae to cosmology, can be done on a fairly economical basis.

According to Michael Warren, one of the Space Simulator’s three principal developers, “Our goal was to acquire a computer which would deliver the highest performance possible on the astrophysics simulations we wanted to run, while remaining within the modest budget that we were allotted. Building the Space Simulator turned out to be a excellent choice.”

The Space Simulator is a 294-node Beowulf cluster with theoretical peak performance just below 1.5 teraflops, or trillions of floating point operations per second. Each Space Simulator processing node looks much like a computer you would find at home than at a supercomputer center, consisting of a Pentium 4 processor, 1 gigabyte of 333 MHz SDRAM, an 80 gigabyte hard drive and a gigabit
Ethernet card. Each individual node cost less than $1,000 and the entire system cost under $500,000. The cluster achieved Linpack performance of 665.1 gigaflops per second on 288 processors in October 2002, making it the 85th fastest computer in the world, according to the 20th TOP500 list (see www.top500.org). A gigaflop is a billion floating-point operations per second.

Since 2002, the Space Simulator has moved down to #344 on the most recent TOP500 list as faster computers are built, but Warren and his colleagues are not worried. They built the Space Simulator to do specific astrophysics research, not to compete with other computers. It was never designed to compete with Laboratory’s massive supercomputers and, in fact, is not scalable enough to do so.

The Space Simulator has been used almost continuously for theoretical astrophysics simulations since it was built, and has spent much of the past year calculating the evolution of the Universe. The first results of that work were recently presented at a research conference in Italy by Los Alamos postdoctoral research associate Luis Teodoro. Further analysis of the simulations, in collaboration with Princeton University professor Uros Seljak, will soon be published in the prestigious journal Monthly Notices of the Royal Astronomical Society. In addition to simulating the structure and evolution of the Universe, the Space Simulator has been used to study the explosions of massive stars and to help understand the X-ray emission from the center of our galaxy.

The Space Simulator is actually the Laboratory’s third generation Beowulf cluster. The first was Loki, which was constructed in 1996 from 16 200 MHz Pentium Pro processors. Loki was followed by the Avalon cluster, which consisted of 144 alpha processors. The Space Simulator follows the same basic architecture as these previous Beowulf machines, but is the first to use Gigabit Ethernet as the network fabric, and requires significantly less space than a cluster using typical computers. The Space Simulator runs parallel N-body algorithms, which were originally designed for astrophysical applications involving gravitational interactions, but have since been used to model more complex particle systems.

In addition to Warren, the developers of the Space Simulator include Los Alamos staff members Chris Fryer and Patrick Goda.

Los Alamos’ Laboratory-Directed Research and Development (LDRD) program provided funding for the Space Simulator research. LDRD funds basic and applied research and development focusing on employee-initiated creative proposals selected at the discretion of the Laboratory director.

Los Alamos National Laboratory is operated by the University of California for the National Nuclear Security Administration (NNSA) of the U.S. Department of Energy and works in partnership with NNSA’s Sandia and Lawrence Livermore national laboratories to support NNSA in its mission.

Los Alamos enhances global security by ensuring the safety and reliability of the U.S. nuclear deterrent, developing technologies to reduce threats from weapons of mass destruction, and solving problems related to defense, energy, environment, infrastructure, health and national security concerns.

Original Source: LANL News Release

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