Astronomers discovered a new asteroid, four days after it made a near miss of the Earth. The object, now called 2002 EM7, was between 40 and 80 metres across and missed the planet by a distance of only 480,200 kilometres – the 9th-closest brush ever recorded; roughly the distance from the Earth to the moon. Had it actually hit the Earth, it could have flattened a city and caused thousands of deaths.
Six Telescopes Acting as One
Image credit: USNO
Astronomers from several US observatories announced that they have successfully merged the light from six independent telescopes to form a single, high-resolution image of a distant multi-star system. To create an image with this level of detail, a single telescope would need to be 50-metres across – bigger than anything that currently exists. This technique, called interferometry, has been done with pairs of telescopes before, but never with as many as six.
Astronomers from the U.S. Naval Observatory (USNO), the Naval Research Laboratory (NRL), and Lowell Observatory announced today that they have successfully combined the light from six independent telescopes to form a single, high-resolution image of a distant multiple-star system. This is the first time that this has ever been accomplished in the optical region of the electromagnetic spectrum. The Navy Prototype Optical Interferometer (NPOI) at Lowell Observatory’s Anderson Mesa site near Flagstaff, Arizona observed the triple star system Eta Virginis, located about 130 light-years away from Earth.
“This development makes it possible to ‘synthesize’ telescopes with apertures in excess of hundreds of meters,” says Dr. Kenneth Johnston, Scientific Director of the Naval Observatory. “It will lead to the direct imaging of the surfaces of stars and of star spots, analogous to the sunspots on the Sun. This technology can also be applied to space systems for remote sensing of the Earth and other objects in the solar system, as well as stars and galaxies.”
Optical interferometers combine the light from several independent telescopes to form a “synthetic” telescope whose ability to make a high-resolution image is proportional to the maximum separation of the telescopes. They are the answer to the prohibitive costs and immense technical difficulties of building extremely large, monolithic single-mirror telescopes. Since the rate at which a giant telescope aperture is synthesized with an interferometer array is equal to the number of combinations between any two telescopes of the array, the combination of the six NPOI telescopes has more than quadrupled NPOI’s capability to collect data over its competitors.
USNO and NRL, in collaboration with Lowell Observatory and with funding from the Office of Naval Research and the Oceanographer of the Navy, joined forces in 1991 to build the instrument. Stellar observations have been conducted with a three-station array since its “first light” in 1996.
However, due to the technical difficulty associated with linking even a small number of separate telescopes, the high-resolution capabilities of optical interferometers have only been used to date on relatively simple stellar sources. Basic questions, such as a star’s apparent diameter or the existence and motions of nearby stellar companions, are easily answered for such sources. However, to increase the spatial resolution and sensitivity to stellar structure, interferometers must link more telescopes together to provide an even sampling of the synthesized aperture. Three combined telescopes provide three mea-surements in the synthesized aperture, but six telescopes provide 15 combinations.
To merge the six beams, the NPOI team has designed a new type of hybrid beam combiner. In addition, new hardware and control systems have been developed to uniquely encode every possible telescope combination in the recorded data so that the information necessary for the alignment and superposition of the starlight wave-fronts and the image reconstruction may be properly decoded.
The field of interferometry is a rapidly developing one, with giants like the twin Keck 10-meter telescopes having achieved “first fringes” last year, and the European Southern Observatory’s VLTI planning to combine the light from four 8-meter telescopes. More modest but versatile imaging interferometers like CHARA, COAST, and IOTA have also been operating for a few years, but NPOI is the first to combine light from a full array of six telescopes.
In the near future, NPOI will be commissioning all of the remaining stations onto which any of the six telescopes can be mounted for a maximum array size of 430 meters, the largest baseline of all current imaging interferometer projects.
Stellar astrophysics will be revolutionized by the capability to directly image stars other than the Sun. Ultimately, when employed in space with the experience collected from ground-based experiments, optical interferometry may develop the capability to image Jupiter-sized planets orbiting distant stars.
“Remember the early days of radio interferometry and look at the world- wide arrays we routinely use today,” says Dr. Johnston. “We’ve gone from simple two-element arrays to continent-sized ones with 10 or more antennas that produce extremely fine-scale images of distant quasars. We are standing on the brink of achieving similar results for visible-light sources.”
Original Source: US Naval Observatory News Release
Grace Satellites Launched
Image credit: NASA
NASA and the German Center for Air and Space Flight successfully launched the Gravity Recovery and Climate Experiment, or “Grace” today. The twin-satellite mission lifted off on Sunday from Russia’s Plesetsk Cosmodrome on board a Rockot launch vehicle. Once in their final orbit, the satellites will separate to a distance of 220km apart, and will begin producing a high-definition gravity map of the Earth’s surface to help scientists understand some of the factors that affect climate change.
NASA and the German Center for Air and Space Flight today successfully launched the Gravity Recovery and Climate Experiment, or “Grace,” mission into Earth orbit at 1:21:27 a.m. Pacific time from Russia’s Plesetsk Cosmodrome. The mission, comprised of identical twin satellites, will precisely measure Earth’s shifting water masses and map their effects on Earth’s gravity field.
The five-year Grace mission-the first launch of NASA’s Earth System Science Pathfinder program-will be a scientific boon to researchers who study Earth with space-based instruments. The monthly gravity maps generated by Grace will be up to 1,000 times more accurate than those currently in use, substantially improving the accuracy of many techniques used by oceanographers, hydrologists, glaciologists, geologists and other scientists to study phenomena that influence climate. These phenomena range from shallow and deep ocean currents, water movement on and beneath Earth’s surface, and the movement and changing mass of ice sheets, to sea-level heights, sea-level rise and changes in the structure of the solid Earth.
Under partly cloudy, cold skies, the Grace twins lifted off on a Russian Rockot launch vehicle. Riding over 1,500,000 newtons (approximately 350,000 pounds) of thrust, the rocket headed northward over the Arctic Ocean and Alaska, then south across the Pacific Ocean and Antarctica before heading north again over Africa and Europe. At 85 minutes, 38 seconds into the mission-or 2:47 a.m. Pacific time-the satellites separated from the launch vehicle’s third stage above Africa into a polar orbit 500 kilometers (311 miles) above Earth.
Ground controllers successfully acquired the spacecraft’s signal from the German Space Operations Center’s ground tracking station in Weilheim, Germany at 2:49 a.m. Pacific time. Initial telemetry reports received by the Grace team show both satellites to be in excellent health.
Following separation, the leading Grace satellite began pulling away from the trailing satellite at a relative speed of about 0.5 meters (1.6 feet) per second. Over the course of the next four days, the satellites will be spaced 220 kilometers (137 miles) apart- a little more than the distance between Los Angeles and San Diego.
As they race around the globe 16 times a day, the satellites will sense minute variations in Earth’s surface mass below and corresponding variations in Earth’s gravitational pull. Regions of slightly stronger gravity will affect the lead satellite first, pulling it slightly away from the trailing satellite. By measuring the constantly changing distance between the two satellites using an extremely sensitive microwave ranging system and combining that data with precise positioning measurements from Global Positioning System instruments, scientists will be able to construct a precise Earth gravity map.
During the next two and a half weeks, basic satellite operations will be established. During a subsequent three-week commissioning phase, Grace’s science instruments and supporting systems will be powered up, evaluated and calibrated. The performance of the Grace system for measuring Earth gravity will then be validated over the following six months. The mission then enters its observational phase, during which routine operational data products will be made available to scientists.
Additional information about the Grace program is available on the Internet at:
http://www.csr.utexas.edu/grace .
Grace is a joint partnership between NASA and the German Center for Air and Space Flight (Deutsches Zentrum fur Luft und Rumfahrt, or DLR). NASA’s Jet Propulsion Laboratory, Pasadena, Calif., manages the U.S. portion of the project for NASA’s Office of Earth Science, Washington. Science data processing, distribution, archiving and product verification are managed under a cooperative arrangement between JPL and the University of Texas’ Austin-based Center for Space Research in the United States and Germany’s Earth Research Center (or GeoForschungsZentrum).
JPL is a division of the California Institute of Technology in Pasadena.
Original Source: NASA/JPL News Release
Tightest Binary System Discovered
Image credit: ESO
Astronomers have discovered a pair of white dwarf stars that revolve around each other at a distance of only 80,000km (1/5th the distance between the Earth and the Moon) – the closest binary system ever discovered. The system, known as RX J0806.3+1527, was investigated with the European Southern Observatory’s Very Large Telescope (VLT), and observers noticed that the object dimmed once every five minutes suggesting a binary system.
Observations with ESO’s Very Large Telescope (VLT) in Chile and the Italian Telescopio Nazionale Galileo (TNG) on the Canary Islands during the past two years have enabled an international group of astronomers [1] to unravel the true nature of an exceptional binary stellar system.
This system, designated RX J0806.3+1527, was first discovered as an X-ray source of variable brightness – once every five minutes, it “switches off” for a short moment. The new observations have shown beyond doubt that this period reflects the orbital motion of two “white dwarf” stars that revolve around each other at a distance of only 80,000 km. Each of the stars is about as large as the Earth and this is the shortest orbital period known for any binary stellar system.
The VLT spectrum displays lines of ionized helium, indicating that the presence of an exceedingly hot area on one of the stars – a “hot spot” with a temperature of approx. 250,000 degrees. The system is currently in a rarely seen, transitory evolutionary state.
An amazing stellar binary system
One year is the time it takes the Earth to move once around the Sun, our central star. This may seem quite fast when measured on the scale of the Universe, but this is a snail’s motion compared to the the speed of two recently discovered stars. They revolve around each other 100,000 times faster; one full revolution takes only 321 seconds, or a little more than 5 minutes! It is the shortest period ever observed in a binary stellar system.
This is the surprising conclusion reached by an international team of astronomers led by GianLuca Israel of the Astronomical Observatory of Rome [1], and based on detailed observations of the faint light from these two stars with some of the world’s most advanced telescopes. The record-holding binary stellar system bears the prosaic name RX J0806.3+1527 and it is located north of the celestial equator in the constellation Cancer (The Crab).
The scientists also find that the two partners in this hectic dance are most likely a dying white dwarf star, trapped in the strong gravitational grip of another, somewhat heavier star of the same exotic type. The two Earth-size stars are separated by only 80,000 kilometers, a little more than twice the altitude of the TV-broadcasting satellites in orbit around the Earth, or just one fifth of the distance to the Moon.
The orbital motion is very fast indeed – over 1,000 km/sec, and the lighter star apparently always turns the same hemisphere towards its companion, just as the Moon in its orbit around Earth. Thus, that star also makes one full turn around its axis in only 5 minutes, i.e. its “day” is exactly as long as its “year”.
The discovery of RX J0806.3+1527
The visible light emitted by this unusual system is very faint, but it radiates comparatively strong X-rays. It was due to this emission that it was first detected as a celestial X-ray source of unknown origin by the German ROSAT space observatory in 1994. Later it was found to be a periodically variable source [2]. Once every 5 minutes, the X-ray radiation disappears for a couple of minutes. It was recently studied in greater detail by the NASA Chandra observatory.
The position of the X-ray source in the sky was localised with sufficient accuracy to reveal a very faint visible-light emitting object in the same direction, over one million times weaker than the faintest star that can be seen by unaided eye (V-magnitude 21.1). Follow-up observations were carried out with several world class telescopes, including the ESO Very Large Telescope (VLT) at the Paranal Observatory in Chile, and also the Telescopio Nazionale Galileo (TNG), the Italian 4-m class observatory at the Roche de Muchachos Observatory on La Palma in the Canary Islands.
The nature of RX J0806.3+1527
The observations in visible light also showed the same effect: RX J0806.3+1527 was getting dimmer once every 5 minutes, while no other periodic modulation was seen. By observing the spectrum of this faint object with the FORS1 multi-mode instrument on the 8.2-m VLT ANTU telescope, the astronomers were able to determine the composition of RX J0806.3+1527. It was found to contain large amounts of helium; this is unlike most other stars, which are mainly made up of hydrogen.
“At the outset, we thought that this was just another of the usual binary systems that emit X-rays”, says Gianluca Israel. “None of us could imagine the real nature of this object. We finally solved the puzzle by eliminating all other possibilities one by one, while we kept collecting more data. As the famous detective said: when you have eliminated the impossible, whatever remains, however improbable, must be the truth!”.
Current theory predicts that the two stars, which are bound together by gravity in this tight system, produce X rays when one of them acts as a giant “vacuum cleaner”, drawing gas off its companion. That star has already lost a significant fraction of its mass during this process.
The incoming matter impacts at high speed on the surface of the other star and the corresponding area – a “hot spot” – is heated to some 250,000 ?C, whereby X rays are emitted. This radiation disappears for a short time during each orbital revolution when this area is on the far side of the accreting star, as seen from the Earth.
A very rare class of stars
Our Sun is a normal star of comparatively low mass and it will eventually develop into a white dwarf star. Contrary to the violent demise of heavier stars in a glorious supernova explosion, this is a comparatively “quiet” process during which the star slowly cools while losing energy. It shrinks until it finally becomes as small as the Earth.
The Sun is a single star. However when a solar-like star is a member of a binary system, the evolution of its component stars is more complicated. During an initial phase, one star continues to move along an orbit that is actually inside the outer, very tenuous atmospheric layers of its companion. Then the system rids itself of this matter and develops into a binary system with two orbiting white dwarf stars, like RX J0806.3+1527.
Systems in which the orbital period is very short (less than 1 hour) are referred to as AM Canis Venaticorum (AM CVn) systems, after first known binary star of this rare class. It is likely that such systems, after having reached a minimum orbital period of a few minutes, then begin to evolve towards longer orbital periods. This indicates that RX J0806.3+1527 is now at the very beginning of the “AM CVn phase”.
Gravitational waves
With its extremely short orbital period, RX J0806.3+1527 is also a prime candidate for the detection of the elusive gravitational waves, predicted by Einstein’s General Theory of Relativity. They have never been measured directly, but their existence has been revealed indirectly in binary neutron star systems.
A planned gravitational wave space experiment, the European Space Agency’s Laser Interferometer Space Antenna (LISA) that will be launched in about 10 years’ time, will be sufficiently sensitive to be able to reveal this radiation from RX J0806.3+1527 with a high degree of confidence. Such an observational feat would open an entirely new window on the universe.
Original Source: ESO News Release
Young Pulsar Defies Theories
Astronomers working with the National Science Foundation’s Very Large Array have found a pulsar that is much younger than previously thought. The team tracked the movement of a pulsar, located 8,000 light years from Earth, against the remains of the supernova that created it. By calculating the distance it had moved, they were able to calculate the point at which they were at the same place – 64,000 years ago. Using a different method of calculating age, astronomers had previously pegged the pulsar as 107,000 years old. (source: NSF)
Shuttle Prepares for Morning Landing
The weather in Florida is looking good for Tuesday morning’s landing of the space shuttle Columbia. Assuming everything goes as planned (there’s slight chance of rain, but nothing that would delay the landing), Columbia will land at the Kennedy Space Center at 0932 GMT (4:32am EST). The mission got off to a rocky start when one of the shuttle’s coolant lines was blocked, but controllers say that it won’t pose a risk when the shuttle heats up as it re-enters the Earth’s atmosphere. (source: Reuters)
Shuttle Lands Safely
The space shuttle Columbia and its crew of seven astronauts landed safely Tuesday morning after completing their mission to upgrade the Hubble Space Telescope. The shuttle landed precisely on schedule, at 0932 GMT (4:32am EST) at the Kennedy Space Center, and the crew performed the customary post-flight inspection of the shuttle. The next shuttle mission is schedule for three weeks from now, when Atlantis will dock with the International Space Station. (source: AP)
Search for Planets Gets Closer to Home
Image credit: NASA
Locating the faint evidence of planets circling distant stars used to require high performance optics, like those on the Hubble Space Telescope, but two scientists are putting together a system for NASA that should do the trick with off-the-shelf components for less than $100,000. The system will watch a 5-degree square of sky continuously (about 100x the area of the full moon in the sky), searching for stars which “wink” regularly when a planet obscures it. (source: NASA/JPL)
It could fit on your desk, and it’s made mostly from parts bought at a camera shop, but two scientists believe their new instrument will help them find a slew of large planets orbiting stars in our Milky Way galaxy.
“An amateur astronomer could do this, except maybe for the debugging of the software, which requires several people working 10 hours a day,” said Dr. David Charbonneau of the California Institute of Technology in Pasadena. “But it’s easy to understand what’s going on and cheap to build the equipment. That’s why everyone thinks it’s an ideal project, if it works.”
The assembly of the new instrument is a cooperative effort between Charbonneau and Dr. John Trauger of NASA’S Jet Propulsion Laboratory in Pasadena, which is managed by Caltech. “David’s approach promises to locate new planets orbiting distant stars. The instrument is simple and straightforward, taking advantage of spare parts and computer code we already have on hand at JPL, and we hope to have it up and running in a few months,” Trauger said.
Charbonneau and his colleagues will soon use their gizmo to begin a three-year survey for extra-solar planets at Palomar Observatory in San Diego County. The instrument is based on a standard telephoto lens for a 35-millimeter camera. It will sweep the skies, looking for “hot Jupiters,” or large, gaseous planets, as their fast orbits take them in front of other stars, into the line of sight between a star and Earth. Astronomers will watch for the “wink” from the star as an orbiting planet partially blocks its light.
Charbonneau, a recent import to the Caltech astronomy staff from the Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass., is a leading authority on the search for such “transiting planets.”
The new instrument uses a standard 300-millimeter Leica camera lens, with a charge-coupled device, or CCD. The CCD, which costs $22,000, will be mounted in a specially constructed camera housing to fit at the back of the lens. The entire device will be fitted onto an inexpensive equatorial mount, available at many stores carrying amateur astronomical equipment.
“Basically, the philosophy of this project is that, if we can buy the stuff we need off the shelf, we’ll buy it,” Charbonneau said. The project costs $100,000, a fraction of the cost of most large Earth and space-based telescopes.
The Palomar staff will provide a small dome for the instrument, and the system will be automated so it can be operated remotely. The new telescope will be linked with an existing weather system, which will monitor atmospheric conditions and determine whether the dome should be opened.
Charbonneau will be able to photograph a single square of sky about five degrees by five degrees. About 100 full moons or an entire constellation could fit in that field of view. With special software Charbonneau helped develop at Harvard-Smithsonian and the National Center for Atmospheric Research, he will compare many pictures of the same patch of sky to see if any of the thousands of stars in each field has “winked.”
If the software reveals a star has dimmed slightly, it could mean a planet passed in front of the star between exposures. Repeated measurements will allow Charbonneau to measure the orbital period and size of each planet. Further work with the 10-meter (33-foot) telescopes at Keck Observatory at Mauna Kea, Hawaii, will provide spectrographic data, and thus, will infer more detailed information about the planet.
Weather permitting, Charbonneau will gather up to 300 images a night. With 20 good nights per month, about 6,000 images would be gathered each month for computer analysis. The ideal time will be in the fall and winter, when the Milky Way is in view, and an extremely high number of stars can be squeezed into each photograph.
“It’s estimated that about one in three stars in our field of view will be like the Sun, and one percent of Sun-like stars have a hot Jupiter, or a gas giant that is so close to the star that its orbit is about four or five days,” Charbonneau said. “One-tenth of this 1-percent will be inclined in the right direction so that it will pass in front of the star, so maybe one in 3,000 stars will have a planet we can detect. Or if you want to be conservative, about one in 6,000.”
Original Source: NASA/JPL News Release
Success! Columbia Releases Upgraded Hubble
After five days of repairs, the newly upgraded Hubble Space Telescope was released from the space shuttle Columbia. Over the past week, spacewalking astronauts outfitted Hubble with new solar panels, power controller, pointing mechanism, and an advanced camera – 10 times more powerful than its previous system. During this mission, the astronauts set a record for time spent spacewalking, spending a total of 35 hours, 55 minutes outside the shuttle. Columbia is due to return to Earth on Tuesday morning.
Hubble Reveals Bow Shock Around Young Star
Image credit: Hubble
Even though the Hubble Space Telescope is out of commission while it’s upgraded, older images are still being released to the public. This image, actually taken back in 1995, reveals how a bow shock has formed around a young, hot star located in the Orion Nebula. The star, LL Ori emits a powerful solar wind that collides with the slower moving gas of the Orion Nebula. This bow shock, similar to that found at the front of a boat, is formed where the two winds collide.
NASA’s Hubble Space Telescope continues to reveal various stunning and intricate treasures that reside within the nearby, intense star-forming region known as the Great Nebula in Orion. One such jewel is the bow shock around the very young star, 1998 WW31, featured in this Hubble Heritage image.
Named for the crescent-shaped wave made by a ship as it moves through water, a bow shock can be created in space when two streams of gas collide. LL Ori emits a vigorous solar wind, a stream of charged particles moving rapidly outward from the star. Our own Sun has a less energetic version of this wind that is responsible for auroral displays on the Earth.
The material in the fast wind from LL Ori collides with slow-moving gas evaporating away from the center of the Orion Nebula, which is located to the lower right in this Heritage image. The surface where the two winds collide is the crescent-shaped bow shock seen in the image.
Unlike a water wave made by a ship, this interstellar bow shock is a three-dimensional structure. The filamentary emission has a very distinct boundary on the side facing away from LL Ori, but is diffuse on the side closest to the star, a characteristic common to many bow shocks.
A second, fainter bow shock can be seen around a star near the upper right-hand corner of the Heritage image. Astronomers have identified numerous shock fronts in this complex star-forming region and are using this data to understand the many complex phenomena associated with the birth of stars.
This image was taken in February 1995 as part of the Hubble Orion Nebula mosaic. A close visitor in our Milky Way galaxy, the nebula is only 1,500 light-years from Earth. The filters used in this color composite represent oxygen, nitrogen, and hydrogen emissions.
Original Source: Hubble News Release