Posted on by Fraser Cain

ESO Watches Burst Afterglow for Five Weeks

Image credit: ESO

Gamma-ray bursts are some of the largest explosions in the Universe; one can generate more energy in a few seconds than the Sun creates in 10 billion years. It’s believed they’re caused when a super-massive star collapses, called a hypernova. Astronomers from the European Southern Observatory tracked the afterglow of a recent burst by using a technique called polarimetry, which lets them track the shape of the explosion. If it was a spherical explosion, the light would have random polarity, but they found that gas is flowing out in jets which are widening over time.

“Gamma-ray bursts (GRBs)” are certainly amongst the most dramatic events known in astrophysics. These short flashes of energetic gamma-rays, first detected in the late 1960’s by military satellites, last from less than one second to several minutes.

GRBs have been found to be situated at extremely large (“cosmological”) distances. The energy released in a few seconds during such an event is larger than that of the Sun during its entire lifetime of more than 10,000 million years. The GRBs are indeed the most powerful events since the Big Bang known in the Universe, cf. ESO PR 08/99 and ESO PR 20/00.

During the past years circumstantial evidence has mounted that GRBs signal the collapse of extremely massive stars, the so-called hypernovae. This was finally demonstrated some months ago when astronomers, using the FORS instrument on ESO’s Very Large Telescope (VLT), documented in unprecedented detail the changes in the spectrum of the light source (“the optical afterglow”) of the gamma-ray burst GRB 030329 (cf. ESO PR 16/03). A conclusive and direct link between cosmological gamma-ray bursts and explosions of very massive stars was provided on this occasion.

Gamma-Ray Burst GRB 030329 was discovered on March 29, 2003 by NASA’s High Energy Transient Explorer spacecraft. Follow-up observations with the UVES spectrograph at the 8.2-m VLT KUEYEN telescope at the Paranal Observatory (Chile) showed the burst to have a redshift of 0.1685 [1]. This corresponds to a distance of about 2,650 million light-years, making GRB 030329 the second-nearest long-duration GRB ever detected. The proximity of GRB 030329 resulted in very bright afterglow emission, permitting the most extensive follow-up observations of any afterglow to date.

A team of astronomers [2] led by Jochen Greiner of the Max-Planck-Institut f?r extraterrestrische Physik (Germany) decided to make use of this unique opportunity to study the polarisation properties of the afterglow of GRB 030329 as it developed after the explosion.

Hypernovae, the source of GRBs, are indeed so far away that they can only be seen as unresolved points of light. To probe their spatial structure, astronomers have thus to rely on a trick: polarimetry (see ESO PR 23/03).

Polarimetry works as follows: light is composed of electromagnetic waves which oscillate in certain directions (planes). Reflection or scattering of light favours certain orientations of the electric and magnetic fields over others. This is why polarising sunglasses can filter out the glint of sunlight reflecting off a pond.

The radiation in a gamma-ray burst is generated in an ordered magnetic field, as so-called synchrotron radiation [3]. If the hypernova is spherically symmetric, all orientations of the electromagnetic waves will be present equally and will average out, so there will be no net polarisation. If, however, the gas is not ejected symmetrically, but into a jet, a slight net polarisation will be imprinted on the light. This net polarisation will change with time since the opening angle of the jet widens with time, and we see a different fraction of the emission cone.

Studying the polarisation properties of the afterglow of a gamma-ray burst thus allows to gain knowledge about the underlying spatial structures and the strength and orientation of the magnetic field in the region where the radiation is generated. “And doing this over a long period of time, as the afterglow fades and evolves, provides us with a unique diagnostic tool for gamma-ray burst studies”, says Jochen Greiner.

Although previous single measurements of the polarisation of GRB’s optical afterglow exist, no detailed study has ever been done of the evolution of polarisation with time. This is indeed a very demanding task, only possible with an extremely stable instrument on the largest telescope… and a sufficient bright optical afterglow.

As soon as GRB 030329 was detected, the team of astronomers therefore turned to the powerful multi-mode FORS1 instrument on the VLT ANTU telescope. They obtained 31 polarimetric observations over a period of 38 days, enabling them to measure, for the first time, the changes of the polarisation of an optical gamma-ray burst afterglow with time. This unique set of observational data documents the physical changes in the remote object in unsurpassed detail.

Their data show the presence of polarisation at the level of 0.3 to 2.5 % throughout the 38-day period with significant variability in strength and orientation on timescales down to hours. This particular behaviour has not been predicted by any of the major theories.

Unfortunately, the very complex light curve of this GRB afterglow, in itself not understood, prevents a straightforward application of existing polarisation models. “It turns out that deriving the direction of the jet and the magnetic field structure is not as simple as we thought originally”, notes Olaf Reimer, another member of the team. “But the rapid changes of the polarisation properties, even during smooth phases of the afterglow light curve, provide a challenge to afterglow theory”.

“Possibly”, adds Jochen Greiner, “the overall low level of polarisation indicates that the strength of the magnetic field in the parallel and perpendicular directions do not differ by more than 10%, thus suggesting a field strongly coupled with the moving material. This is different from the large-scale field which is left-over from the exploding star and which is thought to produce the high-level of polarisation in the gamma-rays.”

Original Source: ESO News Release

Posted on by Fraser Cain

Nozomi is on a Collision Course with Mars

The Mars-bound Japanese spacecraft Nozomi, which has been plagued with problems since its launch in 1998, could be on a collision course with the Red Planet, and might crash into it if engineers can’t change its trajectory. Officials from the Japanese space agency will attempt to fire the spacecraft’s engines on December 8 to kick it into a safer orbit. But before that, they need to fix the spacecraft’s malfunctioning electrical. One worry is that Nozomi was never intended to enter Mars’ atmosphere, so it wasn’t carefully decontaminated – it could deliver Earth-based microbes to the Martian surface.

Posted on by Fraser Cain

Ancient Rivers Lasted a While on Mars

Image credit: NASA/JPL

NASA’s Mars Global Surveyor spacecraft has revealed new features on Mars that look like ancient river deltas. This discovery might help answer the mystery of how long water flowed on the surface of the Red Planet. The shape of this formation suggests that a river flowed into a body of water for quite a while, changing its course and building up layers of sediment over time. The area is about 13 km long and 11 km wide, and located in a crater in the southern hemisphere.

Newly seen details in a fan-shaped apron of debris on Mars may help settle a decades-long debate about whether the planet had long-lasting rivers instead of just brief, intense floods.

Pictures from NASA’s Mars Global Surveyor orbiter show eroded ancient deposits of transported sediment long since hardened into interweaving, curved ridges of layered rock. Scientists interpret some of the curves as traces of ancient meanders made in a sedimentary fan as flowing water changed its course over time.

“Meanders are key, unequivocal evidence that some valleys on early Mars held persistent flows of water over considerable periods of time,” said Dr. Michael Malin of Malin Space Science Systems, San Diego, which supplied and operates the spacecraft’s Mars Orbiter Camera.

“The shape of the fan and the pattern of inverted channels in it suggest it may have been a real delta, a deposit made where a river enters a body of water,” he said. “If so, it would be the strongest indicator yet Mars once had lakes.”

Malin and Dr. Ken Edgett, also of Malin Space Science Systems, have published pictures and analysis of the landform in today’s online edition of Science Express. The images with captions are available online from the Mars Orbiter Camera team, at http://www.msss.com/mars_images/moc/2003/11/13/ and from NASA’s Jet Propulsion Laboratory, Pasadena, Calif., at http://photojournal.jpl.nasa.gov/catalog/PIA04869.

The fan covers an area about 13 kilometers (8 miles) long and 11 kilometers (7 miles) wide in an unnamed southern hemisphere crater downslope from a large network of channels that apparently drained into it billions of years ago.

“This latest discovery by the intrepid Mars Global Surveyor is our first definitive evidence of persistent surface water,” commented Dr. Jim Garvin, NASA’s Lead Scientist for Mars Exploration, NASA Headquarters, Washington, D.C. “It reaffirms we are on the right pathway for searching the record of martian landscapes and eventually rocks for the record of habitats. Such localities may serve as key landing sites for future missions, such as the Mars Science Laboratory in 2009,” continued Garvin. “These astounding findings suggest that “following the water” with Mars Global Surveyor, Mars Odyssey, and soon with the Mars Exploration Rovers, is a powerful approach that will ultimately allow us to understand the history of habitats on the red planet.”

No liquid water has been detected on Mars, although one of the previous major discoveries from Mars Global Surveyor pictures suggests that some gullies have been cut in geologically recent times by the flow of ephemeral liquid water. Another NASA orbiter, Mars Odyssey, has discovered extensive deposits of near-surface ice at high latitudes. Mars’ atmosphere is now so thin that, over most of the planet, any liquid water at the surface would rapidly evaporate or freeze, so evidence of persistent surface water in the past is also evidence for a more clement past climate.

Malin and Edgett estimate that the volume of material in the delta-like fan is about one-fourth the volume of what was removed by the cutting of the upstream channels. Their analysis draws on information from Mars Global Surveyor’s laser altimeter and from cameras on Mars Odyssey and NASA’s Viking Orbiter, as well as images from the Mars Orbiter Camera.

“Because the debris in this fan is now cemented, it shows that some sedimentary rocks on Mars were deposited by water,” Edgett said. “This has been suspected, but never so clearly demonstrated before.”

The camera on Mars Global Surveyor has returned more than 155,000 pictures since the spacecraft began orbiting Mars on Sept. 12, 1997. Still, its high-resolution images cover only about three percent of the planet’s surface. Information about Mars Global Surveyor is available on the Internet at http://mars.jpl.nasa.gov/mgs.

JPL, a division of the California Institute of Technology, Pasadena, manages Mars Global Surveyor for NASA’s Office of Space Science in Washington. JPL’s industrial partner is Lockheed Martin Space Systems, Denver, which developed and operates the spacecraft. Malin Space Science Systems and the California Institute of Technology built the Mars Orbiter Camera. Malin Space Science Systems operates the camera from facilities in San Diego.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

New Cassini Image of Jupiter Released

Image credit: NASA/JPL

The team responsible for the Cassini spacecraft’s imaging system have produced the most detailed mosaic image of Jupiter ever created – the whole planet is visible down to a resolution of 60 km. The spacecraft took a series of 27 images over the course of an hour on December 29, 2000. The separate photos were then blended together on a computer to account for Jupiter’s rotation and the movement of the spacecraft.

This true color mosaic of Jupiter was constructed from images taken by the narrow angle camera onboard NASA’s Cassini spacecraft starting at 5:31 Universal time on December 29, 2000, as the spacecraft neared Jupiter during its flyby of the giant planet. It is the most detailed global color portrait of Jupiter ever produced; the smallest visible features are ~ 60 km (37 miles) across. The mosaic is composed of 27 images: nine images were required to cover the entire planet in a tic-tac-toe pattern, and each of those locations was imaged in red, green, and blue to provide true color. Although Cassini’s camera can see more colors than humans can, Jupiter here looks the way that the human eye would see it.

Cassini’s camera is digital, much like today’s popular cameras, and it takes images in each color separately as different spectral filters are rotated in front of its light-sensitive detector. Over an hour was required for this portrait. Jupiter rotated during this time, so the face it presented to the camera, and the lighting on its moving clouds, were constantly changing. In order to assemble a seamless mosaic, each image was first digitally re-positioned to reflect the planet’s appearance at the instant the first exposure was taken. Then, the lighting variation across each image was removed, and the mosaic was re-illuminated by a computer-generated ‘Sun’ from a direction that allowed all imaged portions to appear in sunlight at once. The result, which was slightly contrast-enhanced to bring out subtleties in the Jupiter atmosphere, is a view that the spacecraft would have had at the same distance from the planet but ~ 80 degrees solar phase.

Everything visible on the planet is a cloud. The parallel reddish-brown and white bands, the white ovals, and the large Great Red Spot persist over many years despite the intense turbulence visible in the atmosphere. The most energetic features are the small, bright clouds to the left of the Great Red Spot and in similar locations in the northern half of the planet. These clouds grow and disappear over a few days and generate lightning. Streaks form as clouds are sheared apart by Jupiter’s intense jet streams that run parallel to the colored bands. The prominent dark band in the northern half of the planet is the location of Jupiter’s fastest jet stream, with eastward winds of 480 km (300 miles) per hour. Jupiter’s diameter is eleven times that of Earth, so the smallest storms on this mosaic are comparable in size to the largest hurricanes on Earth.

Unlike Earth, where only water condenses to form clouds, Jupiter’s clouds are made of ammonia, hydrogen sulfide, and water. The updrafts and downdrafts bring different mixtures of these substances up from below, leading to clouds at different heights. The brown and orange colors may be due to trace chemicals dredged up from deeper levels of the atmosphere, or they may be byproducts of chemical reactions driven by ultraviolet light from the Sun. Bluish areas, such as the small features just north and south of the equator, are areas of reduced cloud cover, where one can see deeper.

Original Source: Arizona University News Release

Posted on by Fraser Cain

Three Kinds of Explosions Could Be the Same Thing

Image credit: Hubble

Three of the Universe’s largest explosions: gamma-ray bursts, X-ray flashes, and supernovae could actually come from the same event – the collapse of a supermassive star. An astronomer from Caltech has found that the different kinds of explosions seem to contain the same amount of energy, they’re just divided up differently between low and high-energy jets. NASA is going to launch a new gamma-ray detecting spacecraft, called SWIFT, which should be able to detect 100 gamma-ray busts a year. This should give scientists new targets to study.

For the past several decades, astrophysicists have been puzzling over the origin of powerful but seemingly different explosions that light up the cosmos several times a day. A new study this week demonstrates that all three flavors of these cosmic explosions–gamma-ray bursts, X-ray flashes, and certain supernovae of type Ic–are in fact connected by their common explosive energy, suggesting that a single type of phenomenon, the explosion of a massive star, is the culprit. The main difference between them is the “escape route” used by the energy as it flees from the dying star and its newly born black hole.

In the November 13 issue of the journal Nature, Caltech graduate student Edo Berger and an international group of colleagues report that cosmic explosions have pretty much the same total energy, but this energy is divided up differently between fast and slow jets in each explosion. This insight was made possible by radio observations, carried out at the National Radio Astronomy Observatory’s Very Large Array (VLA), and Caltech’s Owens Valley Radio Observatory, of a gamma-ray burst that was localized by NASA’s High Energy Transient Explorer (HETE) satellite on March 29 of this year.

The burst, which at 2.6 billion light-years is the closest classical gamma-ray burst ever detected, allowed Berger and the other team members to obtain unprecedented detail about the jets shooting out from the dying star. The burst was in the constellation Leo.

“By monitoring all the escape routes, we realized that the gamma rays were just a small part of the story for this burst,” Berger says, referring to the nested jet of the burst of March 29, which had a thin core of weak gamma rays surrounded by a slow and massive envelope that produced copious radio waves.

“This stumped me,” Berger adds, “because gamma-ray bursts are supposed to produce mainly gamma rays, not radio waves!”

Gamma-ray bursts, first detected accidentally decades ago by military satellites watching for nuclear tests on Earth and in space, occur about once a day. Until now it was generally assumed that the explosions are so titanic that the accelerated particles rushing out in antipodal jets always give off prodigious amounts of gamma radiation, sometimes for hundreds of seconds. On the other hand, the more numerous supernovae of type Ic in our local part of the universe seem to be weaker explosions that produce only slow particles. X-ray flashes were thought to occupy the middle ground.

“The insight gained from the burst of March 29 prompted us to examine previously studied cosmic explosions,” says Berger. “In all cases we found that the total energy of the explosion is the same. This means that cosmic explosions are beasts with different faces but the same body.”

According to Shri Kulkarni, MacArthur Professor of Astronomy and Planetary Science at Caltech and Berger’s thesis supervisor, these findings are significant because they suggest that many more explosions may go undetected. “By relying on gamma rays or X rays to tell us when an explosion is taking place, we may be exposing only the tip of the cosmic explosion iceberg.”

The mystery we need to confront at this point, Kulkarni adds, is why the energy in some explosions chooses a different escape route than in others.

At any rate, adds Dale Frail, an astronomer at the VLA and coauthor of the Nature manuscript, astrophysicists will almost certainly make progress in the near future. In a few months NASA will launch a gamma-ray detecting satellite known as Swift, which is expected to localize about 100 gamma-ray bursts each year. Even more importantly, the new satellite will relay very accurate positions of the bursts within one or two minutes of initial detection.

The article appearing in Nature is titled “A Common Origin for Cosmic Explosions Inferred from Calorimetry of GRB 030329.” In addition to Berger, the lead author, and Kulkarni and Frail, the other authors are Guy Pooley, of Cambridge University’s Mullard Radio Astronomy Observatory; Vince McIntyre and Robin Wark, both of the Australia Telescope National Facility; Re’em Sari, associate professor of astrophysics and planetary science at Caltech; Derek Fox, a postdoctoral scholar in astronomy at Caltech; Alicia Soderberg, a graduate student in astrophysics at Caltech; Sarah Yost, a postdoctoral scholar in physics at Caltech; and Paul Price, a postdoctoral scholar at the University of Hawaii’s Institute for Astronomy.

Original Source: Caltech News Release

Posted on by Fraser Cain

There Might Not Be Ice at the Moon’s Pole

Image credit: Cornell University

At the South Pole of the Moon, there is a region that is always in the shadow of craters which scientists have long believed could have deposits of water ice. Despite the fact that ice was detected by two spacecraft that orbited the moon, a new survey of the area by the giant Arecibo radio observatory has failed to find any surface deposits of ice. This doesn’t mean that the ice isn’t there, but it might be trapped in a large area under the surface, like lunar permafrost. Arecibo is a good instrument for detecting ice because it gives a very specific echo signature in the radio spectrum.

Despite evidence from two space probes in the 1990s, radar astronomers say they can find no signs of thick ice at the moon’s poles. If there is water at the lunar poles, the researchers say, it is widely scattered and permanently frozen inside the dust layers, something akin to terrestrial permafrost.

Using the 70-centimeter (cm)-wavelength radar system at the National Science Foundation’s (NSF) Arecibo Observatory, Puerto Rico, the research group sent signals deeper into the lunar polar surface — more than five meters (about 5.5 yards) — than ever before at this spatial resolution. “If there is ice at the poles, the only way left to test it is to go there directly and melt a small volume around the dust and look for water with a mass spectrometer,” says Bruce Campbell of the Center for Earth and Planetary Studies at the Smithsonian Institution.

Campbell is the lead author of an article, “Long-Wavelength Radar Probing of the Lunar Poles,” in the Nov. 13, 2003, issue of the journal Nature . His collaborators on the latest radar probe of the moon were Donald Campbell, professor of astronomy at Cornell University; J.F. Chandler of Smithsonian Astrophysical Observatory; and Alice Hine, Mike Nolan and Phil Perillat of the Arecibo Observatory, which is managed by the National Astronomy and Ionosphere Center at Cornell for the NSF.

Suggestions of lunar ice first came in 1996 when radio data from the Clementine spacecraft gave some indications of the presence of ice on the wall of a crater at the moon’s south pole. Then, neutron spectrometer data from the Lunar Prospector spacecraft, launched in 1998, indicated the presence of hydrogen, and by inference, water, at a depth of about a meter at the lunar poles. But radar probes by the 12-cm-wavelength radar at Arecibo showed no evidence of thick ice at depths of up to a meter. “Lunar Prospector had found significant concentrations of hydrogen at the lunar poles equivalent to water ice at concentrations of a few percent of the lunar soil,” says Donald Campbell. “There have been suggestions that it may be in the form of thick deposits of ice at some depth, but this new data from Arecibo makes that unlikely.”

Says Bruce Campbell, “There are no places that we have looked at with any of these wavelengths where you see that kind of signature.”

The Nature paper notes that if ice does exist at the lunar poles it would be considerably different from “the thick, coherent layers of ice observed in shadowed craters on Mercury,” found in Arecibo radar imaging. “On Mercury what you see are quite thick deposits on the order of a meter or more buried by, at most, a shallow layer of dust. That’s the scenario we were trying to nail down for the moon,” says Bruce Campbell. The difference between Mercury and the moon, the researchers say, could be due to the lower average rate of comets striking the lunar surface, to recent comet impacts on Mercury or to a more rapid loss of ice on the moon.

What makes the lunar poles good cold traps for water is a temperature of minus 173 degrees Celsius (minus 280 degrees Fahrenheit). The limb of the sun rises only about two degrees above the horizon at the lunar poles so that sunlight never penetrates into deep craters, and a person standing on the crater floor would never see the sun. The Arecibo radar probed the floors of two craters in permanent shadow at the lunar south pole, Shoemaker and Faustini, and, at the north pole, the floors of Hermite and several small craters within the large crater Peary. In contrast, Clementine focused on the sloping walls of Shackleton crater, whose floor can’t be “seen” from Earth. “There is a debate on how to interpret data from a rough, tilted surface,” says Bruce Campbell.

The Arecibo radar probe is a particularly good detector of thick ice because it takes advantage of a phenomenon known as “coherent backscatter.” Radar waves can travel long distances without being absorbed in ice at temperatures well below freezing. Reflections from irregularities inside the ice produce a very strong radar echo. In contrast, lunar soil is much more absorptive and does not give as strong a radar echo.

Original Source: Cornell News Release

Posted on by Fraser Cain

Mars Express is Nearly There

Image credit: ESA

The European Space Agency’s mission to Mars, Mars Express, is right on schedule to arrive at the Red Planet on December 25, 2003. The British-built Beagle 2 lander will also reach Mars the same day, but it will be released from Mars Express on December 19. Beagle 2 doesn’t have any propulsion system of its own, so it’s critical that Mars Express releases it on the right trajectory. It will plunge through Mars’ atmosphere, deploy a parachute, and then land on the surface with the help of an airbag. Assuming everything went well, it will then be able to start examining rocks searching for evidence of life.

Europe’s mission to the Red Planet, Mars Express, is on schedule to arrive at the planet on Christmas Day, 2003.

The lander, Beagle 2, is due to descend through the Martian atmosphere and touch down also on 25 December.

Mars Express is now within 20 million kilometres of the Red Planet and the next mission milestone comes on 19 December, when Mars Express will release Beagle 2. The orbiter spacecraft will send Beagle 2 spinning towards the planet on a precise trajectory.

Into orbit
Beagle has no propulsion system of its own, so it relies on correct aiming by the orbiter to find its way to the planned landing site, a flat basin in the low northern latitudes of Mars.

ESA engineers will then fire the orbiter’s main engine in the early hours of 25 December to put Mars Express into orbit around Mars (called Mars Orbit Insertion, or MOI).

Landing
When Beagle 2 begins its descent, it will be slowed by friction with the Martian atmosphere. Nearer to the surface, parachutes will deploy and large gas-filled bags will inflate to cushion the final touchdown. Beagle 2 should bounce to a halt on Martian soil early on Christmas morning.

The first day on Mars is important for the lander because it has only a few hours to collect enough sunlight with its solar panels to recharge its battery.

Waiting for signal
We then have to wait for the radio ‘life’ signal from Beagle 2, relayed through the US Mars Odyssey spacecraft, to see if the probe has survived the landing. This could take hours or even days.

If nothing is received on Christmas morning, the UK Jodrell Bank Telescope will search for the faint radio signal from Beagle 2 in the evening. The Mars Express orbiter can also search for the lander but, because of its orbit, it will not be in place to do this until early January.

If all goes well, Mars Express and Beagle 2 will then begin their main mission – trying to answer the questions of whether there has been water, and possibly life, on Mars.

Original Source: ESA News Release

Posted on by Fraser Cain

New Dark Matter Detectors

Image credit: Fermilab

Astronomers don’t know what Dark Matter is, but they can see the effect of its gravity on regular matter. One possibility is that it’s regular matter, but isn’t emitting enough light for us to see. Another idea is that Dark Matter is an exotic form of matter that’s much more massive than regular particles, but interact so weakly that they’re almost impossible to detect. Researchers with the Cryogenic Dark Matter Search II have set up a series of detectors in an old iron mine in Minnesota that’s shielded from cosmic radiation and might sense these particles.

Using detectors chilled to near absolute zero, from a vantage point half a mile below ground, physicists of the Cryogenic Dark Matter Search today (November 12) announced the launch of a quest that could lead to solving two mysteries that may turn out to be one and the same: the identity of the dark matter that pervades the universe, and the existence of supersymmetric particles predicted by particle physics theory. Scientists of CDMS II, an experiment managed by the Department of Energy’s Fermi National Accelerator Laboratory hope to discover WIMPs, or weakly interacting massive particles, the leading candidates for the constituents of dark matter-which may be identical to neutralinos, undiscovered particles predicted by the theory of supersymmetry.

“There’s this arrow from particle physics and this arrow from cosmology and they seem to be pointing to the same place,” said Case Western Reserve University’s Dan Akerib, deputy project manager of CDMS II. “Detection of a neutralino would be very big for cosmology and it would also be very big for particle physics.”

The CDMS II experiment, a collaboration of scientists from 12 institutions with support from DOE’s Office of Science and the National Science Foundation, uses a detector located deep underground in the historic Soudan Iron Mine in northeastern Minnesota. Experimenters seek signals of WIMPs, particles much more massive than a proton but interacting so weakly with other particles that thousands would pass through a human body each second without leaving a trace.

Remarkably, in the kind of convergence that gets physicists’ attention, the characteristics of this cosmic missing matter particle now appear to match those of the supersymmetric neutralino.

“Either that is a cosmic coincidence, or the universe is telling us something,” said Fermilab’s Dan Bauer, CDMS project manager.

By watching how galaxies spin-how gravity affects their contingent stars-astronomers have known for 70 years that the matter we see cannot constitute all the matter in the universe. If it did, galaxies would fly apart. Recent calculations indicate that ordinary matter containing atoms makes up only 4 percent of the energy-matter content of the universe. “Dark energy” makes up 73 percent, and an unknown form of dark matter makes up the last 23 percent.

“It is often said that this is the ultimate Copernican Revolution,” said David Caldwell, a physicist at the University of California at Santa Barbara and chair of the CDMS Executive Committee. “Not only are we not at the center of the universe, but we are not even made of the same stuff as most of the universe.”

Measurements of the cosmic microwave background, residual radiation left over from the Big Bang, have recently placed severe constraints on the nature and amount of dark matter. The lightweight neutrino can account for only a few percent of the missing mass. If neutrinos constituted the main component of dark matter, they would act on the cosmic microwave background of the universe in ways that the recent Wilkinson Microwave Anisotropy Probe should have observed-but did not.

Meanwhile, particle physicists have kept a lookout for particles that will extend the Standard Model, the theory of fundamental particles and forces. Supersymmetry, a theory that takes a big step toward the unification of all of the forces of nature, predicts that every matter particle has a massive supersymmetric counterpart. No one has yet seen one of these “superpartners.” Theory specifies the neutralino as the lightest neutral superpartner, and the most stable, a necessary attribute for dark matter. The neutralino’s predicted abundance and rate of interaction also make it a likely dark matter candidate, and Caldwell noted the impact that CDMS II could have.

“Discovery,” he said, “would be a great breakthrough, one of the most important of the century.”

Only occasionally would a WIMP hit the nucleus of a terrestrial atom, and the constant background “noise” from more mundane particle events-such as the common cosmic rays constantly showering the earth-would normally drown out these rare interactions. Placing the CDMS II detector beneath 740 meters of earth screens out most particle noise from cosmic rays. Chilling the detector to 50 thousandths of a degree above absolute zero reduces background thermal energy to allow detection of individual particle collisions. Fermilab’s Bauer estimates that with sufficiently low backgrounds, CDMS needs only a few interactions to make a strong claim for detection of WIMPs.

“The powerful technology we deploy allows an unambiguous identification of events in the crystals caused by any new form of matter,” said CDMS cospokesperson Bernard Sadoulet of the University of California at Berkeley.

Cospokesperson Blas Cabrera of Stanford University concurred.

“We believe we have the best apparatus in the world in terms of being able to identify WIMPs,” Cabrera said.

“This endeavor is a good example of cooperation between the DOE’s Office of High Energy Physics and the National Science Foundation in helping scientists address the origin of the dark matter in the universe,” said Raymond Orbach, Director of the Department of Energy’s Office of Science.

“CDMS II is the kind of innovative and pathbreaking research NSF is proud to support,” said Michael Turner, Assistant Director for Math and Physical Sciences at the National Science Foundation. “If it detects a signal it may tell us what the dark matter is and give us an important clue as to how gravity fits together with the other forces. This type of experiment shows how the universe can be used as a laboratory for getting at the some of the most basic questions we can ask as well as how DOE and NSF are working together.”

While CDMS II watches for WIMPs, scientists at Fermilab’s Tevatron particle accelerator will try to create neutralinos by smashing protons and antiprotons together.

“CDMS can tell us the mass and interaction rate of the WIMP,” said collaborator Roger Dixon of Fermilab. “But it will take an accelerator to tell us whether it’s a neutralino.”

CDMS II collaborators include Brown University, Case Western Reserve University, Fermi National Accelerator Laboratory, Lawrence Berkeley National Accelerator Laboratory, National Institute of Standards and Technology, Princeton University, Santa Clara University, Stanford University, University of California at Berkeley, University of California at Santa Barbara, University of Colorado at Denver, University of Minnesota.

Funding for the CDMS II experiment comes from the Office of Science of the U.S. Department of Energy and the Astronomy and Physics Division of the National Science Foundation.

Fermilab is a national laboratory funded by the Office of Science of the U.S. Department of Energy and operated by Universities Research Association, Inc.

Original Source: Fermilab News Release

Posted on by Fraser Cain

Pleiades Could Be Three Objects Colliding Together

Image credit: NOAO

The Pleiades star cluster has long been a favorite of astronomers, as it’s clearly visible with the naked eye, and looks even better in small telescopes and binoculars. The cluster’s wispy appearance comes from the fact that the stars are surrounded by a faint nebula. By tracking the motion of the stars and the cloud, a team of astronomers have discovered that the area is being formed by multiple clouds colliding together in the same region.

The naked-eye Pleiades star cluster has long been known to professional and amateur astronomers for the striking visible nebulosity that envelopes the cluster?s brightest stars, scattering their light like fog around a streetlamp.

Radio and infrared observations in the 1980s established that this nebulosity results from a chance encounter by the young stars of the Pleiades with an interstellar cloud, rather than being caused by debris from the cluster?s formation. New data obtained at Kitt Peak National Observatory suggest that the Pleiades are actually encountering two clouds, giving rise to an extraordinary and previously unknown occurrence: a three-body collision in the vast emptiness of interstellar space.

This new perspective on the motion of interstellar gas near the cluster comes from high-resolution spectra obtained at an adjunct facility of Kitt Peak?s 2.1-meter telescope known as the Coud? Feed. The investigator was Richard White of Smith College in Northampton, MA, who worked in collaboration with students from Smith College and Amherst College.

?The idea of the Pleiades and one gas cloud in an interstellar train wreck already made this nearby cluster an especially interesting region for astronomers seeking to understand the details of physical and chemical processes in the interstellar medium,? White says. ?The presence of a second cloud interacting with the first cloud and with the cluster creates a situation more like a three-car crash in a demolition derby, which makes the Pleiades altogether unique as natural laboratory.?

The time scale for the unfolding of the interstellar collisions in the Pleiades is several hundred thousand years. ?That is good news for those who enjoy the magnificent color images of the Pleiades images that grace textbooks and coffee table books, which suffer no danger of obsolescence,? White says. ?It is bad news for those who would like to see celestial fireworks unfolding from year to year.?

Known as the Seven Sisters for the seven stars said to be visible with the naked eye, the Pleiades (M45) consists of more than 500 stars roughly 100 million years old in a cluster located about 400 light-years from Earth.

Sodium atoms in gas found between Earth and the stars absorb two specific wavelengths of yellow starlight (the same wavelengths of yellow light emitted by low-pressure sodium streetlamps). Because of the Doppler effect (analogous to the shift in siren pitch produced when an ambulance is moving toward or away from a listener), the motion of the gas along our line of sight produces subtle shifts in the observed wavelengths.

In a paper published in the October 2003 Astrophysical Journal Supplement, White interprets the new observations of sodium atoms in the Pleiades region in the context of other recent observations of the Pleiades region. These observations include significant new optical images of the Pleiades from the Burrell Schmidt telescope on Kitt Peak, published earlier this year in the Astrophysical Journal by Steven Gibson of the University of Calgary and Kenneth Nordsieck of the University of Wisconsin, and radio maps of neutral hydrogen that formed part of Gibson?s doctoral thesis.

The orientation of features in the optical and radio imagery provides clues to gas and dust motions across the sky, which can be combined with the spectroscopically measured velocities from Kitt Peak to allow astronomers to reconstruct the three-dimensional configuration of the interstellar matter near the Pleiades.

The sodium absorption lines reveal that there always is one feature between Earth and the Pleiades stars, moving toward the cluster with a line of sight velocity of about 10 kilometers per second. White associates this feature with the Taurus-Auriga interstellar cloud complex, the bulk of which lies about 40 light-years to the east.

Toward some stars, however, there are two or more absorption features. White argues that a shock-wave from the collision between the Pleiades and gas associated with the Taurus-Auriga complex can account for splitting of one feature into three in some areas, primarily on the south and east sides of the Pleiades. However, the presence of an additional feature in the data, primarily on the west side and moving into the cluster at about 12 kilometers per second, defies understanding unless a second cloud also is converging on the Pleiades, he concludes.

The only previously known three-body collisions in interstellar space are inferred close encounters by a star and a neighboring binary or triple star system within a globular cluster or in the cores of galaxies.

Previously released images of the Pleiades from Kitt Peak that amply demonstrate the surrounding nebulosity are available in the NOAO Image Gallery (linked above).

Located 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.

Original Source: NOAO News Release

Posted on by Fraser Cain

Nearby Star is Forming a Jupiter-Like Planet

Image credit: UA

Astronomers from the University of Arizona have used a new technique called “nulling interferometry” to reveal the planetary disk around a newly-forming star. Incredibly, they discovered a gap in the disk, where a Jupiter-like planet is probably forming. This nulling technique works by combining the light from the central star in such a way that it gets canceled out. This allows fainter objects, such as dust and planets to be observed. The planet is likely several times the mass of Jupiter and orbits its star at about 1.5 billion kilometers.

University of Arizona astronomers have used a new technique called nulling interferometry to probe a dust disk around a young nearby star for the first time. They not only confirmed that the young star does have a protoplanetary disk — the stuff from which solar systems are born — but discovered a gap in the disk, which is strong evidence of a forming planet.

“It’s very exciting to find a star that we think should be forming planets, and actually see evidence of that happening,” said UA astronomer Philip Hinz.

“The bottom line is, we not only confirmed the hypothesis that this young star has a protoplanetary disk, we found evidence that a giant, Jupiter-like protoplanet is forming in this disk,” said Wilson Liu, a doctoral student and research assistant on the project.

“There’s evidence that this star is right on the cusp of becoming a main-sequence star,” Liu added. “So basically, we’re catching a star that is right at the point of becoming a main-sequence star, and it looks like it’s caught in the act of forming planets.”

Main-sequence stars are those like our sun that burn hydrogen at their cores.

Earlier this year, Hinz and Liu realized that observations of HD 100546 at thermal, or mid-infrared, wavelengths showed that the star had a dust disk.

Finding faint dust disks is “analogous to finding a lighted flashlight next to Arizona Stadium when the lights are on,” Liu said.

The nulling technique combines starlight in such a way that it is canceled out, creating a dark background where the star’s image normally would be. Because HD 100546 is such a young star, its dust disk is still relatively bright, about as bright as the star itself. The nulling technique is needed to distinguish what light comes from the star, which can be suppressed, and what comes from the extended dust disk, which nulling does not suppress.

Hinz and UA astronomers Michael Meyer, Eric Mamajek, and William Hoffmann took the observations in May 2002. They used BLINC, the only working nulling interferometer in the world, along with MIRAC, a state-of-the-art mid-infrared camera, on the 6.5-meter (21-foot) diameter Magellan telescope in Chile to study the roughly 10-million-year-old star in the Southern Hemisphere sky.

Typically, dust in disks around stars is uniformly distributed, forming a continuous, flattened, orbiting cloud of material that is hot on the inner edge but cold most of the distance to the frigid outer edge.

“The data reduction was complicated enough that we didn’t realize until later that there was an inner gap in the disk,” Hinz noted.

“We realized the disk appeared about the same size at warmer (10 micron) wavelengths and at colder (20 micron) wavelengths. The only way that could be is if there’s an inner gap.”

The most likely explanation for this gap is that it is created by the gravitational field of a giant protoplanet =AD an object that could be several times more massive than Jupiter. The researchers believe the protoplanet may be orbiting the star at perhaps 10 AU. (An AU, or astronomical unit, is the distance between Earth and the sun. Jupiter is about 5 AU from the sun.)

Astronomers from the Netherlands and Belgium had previously used the Infrared Space Observatory to study HD 100546, which is 330 light-years from Earth. They detected comet-like dust around the star and concluded that it might be a protoplanetary disk. But the European space telescope was too small to clearly see dust surrounding the star.

Hinz, who developed BLINC, has been using the nulling interferometer with two 6.5-meter telescopes for the past three years for his survey of nearby stars in search of protoplanetary systems. In addition to the Magellan telescope that covers the Southern Hemisphere, Hinz uses the 6.5-meter UA/Smithsonian MMT atop Mount Hopkins, Ariz., for the Northern Hemisphere sky.=20

Hinz developed BLINC as a technology demonstration for the Terrestrial Planet Finder mission, which is managed for NASA by the Jet Propulsion Laboratory, Pasadena, Calif. NASA, which funds Hinz’ survey, supports research on solar-system formation under its Origins program and is developing nulling interferometry for Terrestrial Planet Finder.

“Nulling interferometry is very exciting because it is one of only a few technologies that can directly image circumstellar environments,” Liu said.

Using MIRAC, the camera developed by William Hoffmann and others, was important because it is sensitive to mid-infrared wavelengths, Hinz said. Astronomers will have to look in mid-infrared wavelengths, which correspond to room temperatures, to find planets with liquid water and possible life, he said.

Hinz’ survey includes HD 100546 and other “Herbig Ae” stars, which are nearby young stars generally more massive than our sun, but are not yet main sequence stars powered by nuclear fusion.

Hinz and Liu plan to observe increasingly mature star systems, searching for ever-fainter circumstellar dust disks and planets, as they continue to improve nulling interferometry and adaptive optics technologies. Adaptive optics is a technique that eliminates the effects of Earth’s shimmering atmosphere from starlight.

Hinz and others at UA Steward Observatory are designing a nulling interferometer for the Large Binocular Telescope, which will view the sky with two 8.4-meter (27-foot) diameter mirrors on Mount Graham, Ariz., in 2005.

Original Source: UA News