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Cosmic powerhouses

Astronomy on 01/05/2008 at 11:22am (UTC)

Suzaku X-ray observatory explains some of the most energetic objects in our galaxy.
Provided by NASA's Goddard Space Flight Center

An artist depicts the Suzaku X-ray observatory in Earth orbit. JAXA [View Larger Image]December 21, 2007
By working in synergy with a ground-based telescope array, the joint Japanese Aerospace Exploration Agency (JAXA)/NASA Suzaku X-ray observatory is shedding new light on some of the most energetic objects in our galaxy, but objects that remain shrouded in mystery.

These cosmic powerhouses pour out vast amounts of energy, and they accelerate particles to almost the speed of light. But very little is known about these sources because they were discovered only recently. "Understanding these objects is one of the most intriguing problems in astrophysics," says Takayasu Anada of the Institute for Space and Astronautical Science in Kanagawa, Japan.

These mysterious objects have been discovered in just the last few years by an array of four European-built telescopes named the High Energy Stereoscopic System (H.E.S.S.), located in the African nation of Namibia. H.E.S.S. indirectly detects very high-energy gamma rays from outer space. These gamma rays are the highest-energy form of light ever detected from beyond Earth, so H.E.S.S. and other similar arrays have opened up a new branch of astronomy.

Suzaku resolved an X-ray source (left) that was also seen in gamma rays by the H.E.S.S. array (right). The object, HESS J1614-518, is accelerating protons to nearly the speed of light. JAXA/H.E.S.S. [View Larger Image]The gamma rays themselves are absorbed by gases high in Earth's atmosphere. But as the gamma rays interact with air molecules, they produce subatomic particles that radiate a blue-colored light known as Cherenkov radiation. H.E.S.S. detects this blue light, whose intensity and direction reveals the energy and position of the gamma-ray source.

The H.E.S.S. observations were groundbreaking, but the array's images aren't sharp enough to reveal the exact location where particles are being accelerated or how the particles are being accelerated. To solve this problem, several teams aimed Suzaku in the direction of some of these H.E.S.S. sources. Any object capable of emitting high-energy gamma rays will also produce X-rays, and Suzaku is particularly sensitive to high-energy (hard) X-rays.

When Anada and his colleagues pointed Suzaku at a source known as HESS J1837-069 (the numerals express the object's sky coordinates), the X-ray spectrum closely resembled X-ray spectra of pulsar wind nebulae, gaseous clouds that are sculpted by winds blown off by collapsed stars known as pulsars. Pulsar wind nebulae emit hard X-rays, and their X-ray output remains relatively constant over long timescales. "The origin of the gamma-ray emission from HESS J1837-069 remains unclear, but we suspect that this source is a pulsar wind nebula from the Suzaku observation," says Anada.

NASA's Chandra X-ray Observatory and the European Space Agency's XMM-Newton X-ray Observatory have revealed that other H.E.S.S. sources are also pulsar wind nebulae. These combined gamma-ray and X-ray observations are revealing that pulsar wind nebulae are more common and more energetic than astronomers had expected.

These four telescopes comprise the H.E.S.S. array, located in the African nation of Namibia. The telescopes indirectly detect high-energy gamma rays. H.E.S.S. [View Larger Image]Another group, led by Hironori Matsumoto of the University of Kyoto in Japan, targeted Suzaku on HESS J1614-518. This source belongs to a class of objects known as "dark particle accelerators" because their ultrahigh energies suggest they are accelerating particles to near-light speed, turning them into cosmic rays. But what are these objects, and what kinds of particles are being accelerated?

Although the nature of these objects remains a mystery, Suzaku's observations do reveal the identity of the particles. When electrons are accelerated to high speeds, they spiral around magnetic field lines that permeate space, generating copious X-rays. But since protons are 2,000 times more massive than electrons, they emit few X-rays. Matsumoto and his colleagues reported at the conference that HESS J1614-518 is a very weak X-ray emitter. "This result strongly suggests that high-energy protons are being produced in this object," says Matsumoto.

Suzaku also observed two other H.E.S.S. dark particle accelerators, but found no obvious X-ray counterparts at the H.E.S.S. positions. These sources must also be weak X-ray emitters, indicating they are accelerating mostly protons. As Matsumoto says, "Using the high sensitivity of the Suzaku satellite, we can find strong candidates for the origin of cosmic rays."

Mars joins Santa in the sky Christmas Eve

astronomy on 01/05/2008 at 11:20am (UTC)

Christmas Eve will bring a lot more than Santa this year. Mars shines brightest and remains visible all night when it reaches opposition December 24. That night, the Red Planet shines brighter than any star; only the Full Moon and Venus will outshine it. An opposition occurs when Mars lies opposite from the Sun, becoming fully illuminated. Mars' oppositions happen roughly every 780 days.

Mars won't be this big or bright again until 2016. No equipment - just warm clothes - will be needed to enjoy this spectacle.

The Full Moon helps observers find Mars. On December 23, the Moon sits just 1° from the planet (one degree is equal to 2 Moon-diameters). Observers can also track Mars' westward motion against the stars of Gemini.

The Red Planet soars high in the sky for northern observers late this year as it reaches the stars of Gemini. [View Larger Image]"Use binoculars, and about every other night, see which stars lie close to Mars," says Astronomy magazine Senior Editor Michael Bakich. "By doing this, observers can learn about planetary motion."

Even under urban skies with heavy light pollution, it will be easy to see martian details with a small telescope.

Mars' closest point to Earth came December 18, when it laid 54.8 million miles away. Opposition and closest approach don't coincide because Mars has a noticeably elliptical orbit.

Mars will look almost as bright several weeks before and after December 24. Let Santa be the only one to worry if Christmas Eve presents a cloudy sky.

Make a note
Mars varies in angular measurement from 13.8" to 25.1". Angular measurement is used to describe how large a celestial object is. Mars' brightness varies from -1.5 to -2.9 magnitude.

A day on Mars is 37.4 minutes longer than a day on Earth. So, if you're observing Mars at the same time every night, its markings will appear to move 9.11° to the west each day.

Mars' declination will measure 26° 46' December 24th. Altitude is important. The less air Mars is viewed through, the better. So, if it's possible, head south to view the opposition.

For tips on viewing the opposition, read Bakich's "15 tips for observing Mars," in the December 2007 issue of Astronomy magazine.

LIGO sheds light on cosmic event

Astronomy on 01/05/2008 at 11:13am (UTC)

Gamma-ray bursts are among the most violent and energetic events in the universe, and scientists have only recently begun to understand their origins.
Provided by the California Institute of Technology

A color composite of images taken with ESO's Very Large Telescope shows the field around a GRB. The gamma-ray burst is indicated with an arrow. ESO [View Larger Image]January 4, 2008
An analysis by the international LIGO (Laser Interferometer Gravitational-Wave Observatory) Scientific Collaboration has excluded one previously leading explanation for the origin of an intense gamma-ray burst that occurred last winter.

The LIGO project, which is funded by the National Science Foundation, was designed and is operated by the California Institute of Technology and the Massachusetts Institute of Technology for the purpose of detecting cosmic gravitational waves and for the development of gravitational-wave observations as an astronomical tool. Research is carried out by the LIGO Scientific Collaboration, a group of 580 scientists at universities around the United States and in 11 foreign countries. The LIGO Scientific Collaboration interferometer network includes the GEO600 interferometer, located in Hannover, Germany, funded by the Max-Plank-Gesellschaft/Science and Technologies Facilities Council and designed and operated by scientists from the Max Planck Institute for Gravitational Physics and partners in the United Kingdom.

Each of the L-shaped LIGO interferometers (including the 2 km and 4 km detectors in Hanford, Washington, and a 4 km instrument in Livingston, Louisiana) uses a laser split into two beams that travel back and forth down long arms, each of which is a beam tube from which the air has been evacuated. The beams are used to monitor the distance between precisely configured mirrors. According to Albert Einstein's 1916 general theory of relativity, the relative distance between the mirrors will change very slightly when a gravitational wave, a distortion in space-time, produced by massive accelerating objects that propagates outward through the universe, passes by. The interferometer is constructed in such a way that it can detect a change of less than a thousandth the diameter of an atomic nucleus in the lengths of the arms relative to each other.

On February 1, 2007, the Konus-Wind, Integral, Messenger, and Swift gamma-ray satellites measured a short but intense outburst of energetic gamma rays originating in the direction of M31, the Andromeda galaxy, located 2.5 million light-years away. The majority of such short (less than 2 seconds in duration) gamma-ray bursts (GRBs) are thought to emanate from the merger and coalescence of two massive but compact objects, such as neutron stars or black hole systems. They can also come from astronomical objects known as soft gamma-ray repeaters, which are less common than binary coalescence events and emit less energetic gamma rays.

During the intense blast of gamma rays, known as GRB070201, the 4 km and 2 km gravitational-wave interferometers at the Hanford facility were in science mode and collecting data. They did not, however, measure any gravitational waves in the aftermath of the burst.

That non-detection was itself significant.

The burst had occurred along a line of sight that was consistent with it originating from one of Andromeda's spiral arms, and a binary coalescence event, the merger of two neutron stars or black holes, for example, was considered among the most likely explanations. Such a monumental cosmic event occurring in a nearby galaxy should have generated gravitational waves that would be easily measured by the ultrasensitive LIGO detectors. The absence of a gravitational-wave signal meant GRB070201 could not have originated in this way in Andromeda. Other causes for the event, such as a soft gamma-ray repeater or a binary merger from a much further distance, are now the most likely contenders.

LIGO's contribution to the study of GRB070201 marks a milestone for the project, says Caltech's Jay Marx, LIGO's executive director. "Having achieved its design goals 2 years ago, LIGO is now producing significant scientific results. The nondetection of a signal from GRB070201 is an important step toward a very productive synergy between gravitational-wave and other astronomical
communities that will contribute to our understanding of the most energetic events in the cosmos."

"This is the first time that the field of gravitational-wave physics has made a significant contribution to the gamma-ray astronomical community, by searching for GRBs in a way that electromagnetic observations cannot," adds David Reitze, a professor of physics at the University of Florida and spokesperson for the LIGO Collaboraton.

Up until now, Reitze says, astronomers studying GRBs relied solely on data obtained from telescopes conducting visible, infrared, radio, X-ray, and gamma-ray observations. Gravitational waves offer a new window into the nature of these events.

"We are still baffled by short GRBs. The LIGO observation gives a tantalizing hint that some short GRBs are caused by soft gamma repeaters. It is an important step forward," says Neil Gehrels, the lead scientist of the Swift mission at NASA's Goddard Space Flight Center.

"This result is not only a breakthrough in connecting observations in the electromagnetic spectrum to gravitational-wave searches, but also in the constructive integration of teams of complementary expertise. Our findings imply that multimessenger astronomy will become a reality within the next decade, opening a wonderful opportunity to gain insight on some of the most elusive phenomena of the universe," says Szabolcs Márka, an assistant professor of physics at Columbia University.

The next major construction milestone for LIGO will be the Advanced LIGO Project, which is expected to start in 2008. But Advanced LIGO, which will utilize the infrastructure of LIGO, will be 10 times more sensitive. Advanced LIGO will incorporate advanced designs and technologies for mirrors and lasers that have been developed by the GEO project and have allowed the GEO detector to achieve enough sensitivity to participate in this discovery despite its smaller size.

The increased sensitivity will be important because it will allow scientists to detect cataclysmic events such as black-hole and neutron-star collisions at 10-times-greater distances.

NASA Sends Spacecraft on Mission to Comet Hartley 2

Nasa on 01/05/2008 at 11:12am (UTC)

WASHINGTON - NASA has approved the retargeting of the EPOXI mission for a flyby of comet Hartley 2 on Oct. 11, 2010. Hartley 2 was chosen as EPOXI's destination after the initial target, comet Boethin, could not be found. Scientists theorize comet Boethin may have broken up into pieces too small for detection.

The EPOXI mission melds two compelling science investigations -- the Extrasolar Planet Observation and Characterization and the Deep Impact Extended Investigation. Both investigations will be performed using the Deep Impact spacecraft.

In addition to investigating comet Hartley 2, the spacecraft will point the larger of its two telescopes at nearby exosolar planetary systems in late January 2008 to observe several previously discovered planetary systems outside our solar system. It will study the physical properties of giant planets and search for rings, moons and planets as small as three Earth masses. It also will look at Earth as though it were an exosolar planet to provide data that could become the standard for characterizing these types of planets.

"The search for exosolar planetary systems is one of the most intriguing explorations of our time," said Drake Deming, EPOXI deputy principal investigator at NASA's Goddard Space Flight Center, Greenbelt, Md. "With EPOXI we have the potential to discover new worlds and even analyze the light they emit to perhaps discover what atmospheres they possess."

The mission's closest approach to the small half-mile-wide comet will be about 620 miles. The spacecraft will employ the same suite of two science instruments the Deep Impact spacecraft used during its prime mission to guide an impactor into comet Tempel 1 in July 2005.

If EPOXI's observations of Hartley 2 show it is similar to one of the other comets that have been observed, this new class of comets will be defined for the first time. If the comet displays different characteristics, it would deepen the mystery of cometary diversity.

"When comet Boethin could not be located, we went to our backup, which is every bit as interesting but about two years farther down the road," said Tom Duxbury, EPOXI project manager at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

Mission controllers at JPL began directing EPOXI towards Hartley 2 on Nov. 1. They commanded the spacecraft to perform a three-minute rocket burn that changed the spacecraft's velocity. EPOXI's new trajectory sets the stage for three Earth flybys, the first on Dec. 31, 2007. This places the spacecraft into an orbital "holding pattern" until time for the optimal encounter of comet Hartley 2 in 2010.

"Hartley 2 is scientifically just as interesting as comet Boethin because both have relatively small, active nuclei," said Michael A'Hearn, principal investigator for EPOXI at the University of Maryland, College Park.

EPOXI's low mission cost of $40 million is achieved by taking advantage of the existing Deep Impact spacecraft.

JPL manages EPOXI for NASA's Science Mission Directorate, Washington. The spacecraft was built for NASA by Ball Aerospace & Technologies Corp., Boulder, Colo.

'Dancing with the Stars' Takes on a Whole New Twist

hubblesite on 12/04/2007 at 1:32pm (UTC)

View image details What is Hubble Heritage?
A monthly showcase of new and archival Hubble images. Go to the Heritage site.
Two galaxies perform an intricate dance in this new Hubble Space Telescope image. The galaxies, containing a vast number of stars, swing past each other in a graceful performance choreographed by gravity. The pair, known collectively as Arp 87, is one of hundreds of interacting and merging galaxies known in our nearby universe.

Arp 87 is in the constellation Leo, the Lion, approximately 300 million light-years away from Earth. These observations were taken in February 2007 with the Wide Field Planetary Camera 2.

Hubble Zooms In on Heart of Mystery Comet

hubblesite on 12/04/2007 at 1:30pm (UTC)

NASA's Hubble Space Telescope has probed the bright core of Comet 17P/Holmes, which, to the delight of sky watchers, mysteriously brightened by nearly a millionfold in a 24-hour period beginning Oct. 23, 2007.

Astronomers used Hubble's powerful resolution to study Comet Holmes' core for clues about how the comet brightened. The orbiting observatory's Wide Field Planetary Camera 2 (WFPC2) monitored the comet for several days, snapping images on Oct. 29, Oct. 31, and Nov. 4. Hubble's crisp "eye" can see objects as small as 33 miles (54 kilometers) across, providing the sharpest view yet of the source of the spectacular brightening.

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