Posted on by Fraser Cain

Spirit Sees Layered Rock in Nearby Hills

Image credit: NASA/JPL
More than a month into bonus time after a successful primary mission on Mars, NASA’s Spirit rover has sighted possibly layered rock in hills just ahead, while twin Opportunity has extended its arm to pockmarked stones on a crater rim to gather clues of a watery past.

Both robotic geologists of the Mars Exploration Rover Project remain healthy. Engineers at NASA’s Jet Propulsion Laboratory, Pasadena, Calif., quickly restored Spirit from two unexpected computer reboots in May triggered by low- probability software glitches. “We had bad luck to hit two very unlikely scenarios just eight days apart, but in both cases the software team was able to figure out the problem within a day,” said Joe Snyder, a Lockheed Martin software engineer on JPL’s rover team.

Spirit has driven more than 2.9 kilometers (1.8 miles) since arriving at Mars five months ago, more than three-fourths of that since completing its three-month primary mission. It now has only about 400 meters (440 yards) to go — possibly less than a week of driving — before reaching the base of a range of hills informally named “Columbia Hills,” which scientists identified in January as a desirable but potentially unreachable destination for the rover.

“This is the first time we’ve ever had a close look at hills on Mars,” said Dr. James Rice of Arizona State University, Tempe, a member of the rovers’ science team. In 1997, hills called “Twin Peaks” tantalized scientists from only about one kilometer (1,100 yards) away from the Mars Pathfinder landing site. “We could only observe Twin Peaks from a distance and wonder about them, but now with a more capable rover we can get to Columbia Hills,” Rice said. He spoke at a press briefing today at JPL.

Rocks in Columbia Hills may provide insight both into both how hills form on Mars and whether the ancient environment at this part of Mars was wet. Images Spirit has taken as it nears the hills already show boulders and potential rock outcrops. “These rocks are much older than what we’ve been driving across,” Rice said. “We could find a lot of geological history locked in them. They may be some of the oldest material ever seen on Mars.”

On the rim of stadium-sized “Endurance Crater,” halfway around Mars from Spirit, Opportunity has been using its microscopic imager to examine the texture of rocks, adding information about a past lake or sea environment that also left its mark in the smaller crater, “Eagle,” where Opportunity landed.

“We’re looking at rocks that have very interesting surface textures,” said science-team member Dr. Wendy Calvin of the University of Nevada, Reno. “These rocks appear to be from the same geological layer as the outcrop at Eagle Crater, but they have some differences from what we saw there.” One rock called “Pyrrho” on the Endurance rim has a braided ripple pattern. Another, “Diogenes,” compared with rocks seen earlier, has more of the disc-shaped cavities that scientists interpret as sites where crystals formed in the rocks, then disappeared as the chemistry of water in the rocks varied.

From an overlook point on the southeastern edge of Endurance, Opportunity used its panoramic camera and miniature thermal emission spectrometer to study the inside of the crater, supplementing a similar survey made earlier from the western edge. Both instruments can be used to assess mineral composition from a distance. “We see a strong basaltic character in the sand at the bottom and in some of the rocks in the wall of the crater,” Calvin said. That is a contrast to the sulfate-rich composition of the overlying layer, which resembles the Eagle Crater outcrop. “We expect the basaltic material to tell us about environmental conditions from an earlier time,” she said.

Scientists and engineers are evaluating the potential science benefits of sending Opportunity into Endurance Crater and assessing whether the rover would be able to climb back out. A decision about whether to enter the crater will be based on those factors.

Mission controllers have begun frequent use of a “deep sleep” mode for Opportunity, reported JPL’s Matt Wallace, mission manager. It is a more complete overnight shutdown that conserves energy but at a calculated tradeoff of risking damage to the miniature thermal emission spectrometer. The strategy has approximately tripled the amount of time the solar-powered rover can work during the day. So far, the spectrometer has survived, but as the martian winter advances, scientists expect to lose the use of that instrument.

JPL, a division of the California Institute of Technology in Pasadena, manages the Mars Exploration Rover project for NASA’s Office of Space Science, Washington, D.C. Images and additional information about the project are available from JPL at http://marsrovers.jpl.nasa.gov and from Cornell University, Ithaca, N.Y., at http://athena.cornell.edu.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Chandra Finds a Gamma Ray Blast Remnant

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

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

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

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

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

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

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

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

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

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

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

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

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

Original Source: Chandra News Release

Posted on by Fraser Cain

Super-Clusters of Galaxies Give Clues to the Big Bang

Image credit: ESO
Clusters of galaxies are very large building blocks of the Universe. These gigantic structures contain hundreds to thousands of galaxies and, less visible but equally interesting, an additional amount of “dark matter” whose origin still defies the astronomers, with a total mass of thousands of millions of millions times the mass of our Sun. The comparatively nearby Coma cluster, for example, contains thousands of galaxies and measures more than 20 million light-years across. Another well-known example is the Virgo cluster at a distance of about 50 million light-years, and still stretching over an angle of more than 10 degrees in the sky!

Clusters of galaxies form in the densest regions of the Universe. As such, they perfectly trace the backbone of the large-scale structures in the Universe, in the same way that lighthouses trace a coastline. Studies of clusters of galaxies therefore tell us about the structure of the enormous space in which we live.

The REFLEX survey
Following this idea, a European team of astronomers, under the leadership of Hans B?hringer (MPE, Garching, Germany), Luigi Guzzo (INAF, Milano, Italy), Chris A. Collins (JMU, Liverpool), and Peter Schuecker (MPE, Garching) has embarked on a decade-long study of these gargantuan structures, trying to locate the most massive of clusters of galaxies.

Since about one-fifth of the optically invisible mass of a cluster is in the form of a diffuse very hot gas with a temperature of the order of several tens of millions of degrees, clusters of galaxies produce powerful X-ray emission. They are therefore best discovered by means of X-ray satellites.

For this fundamental study, the astronomers thus started by selecting candidate objects using data from the X-ray Sky Atlas compiled by the German ROSAT satellite survey mission. This was the beginning only – then followed a lot of tedious work: making the final identification of these objects in visible light and measuring the distance (i.e., redshift) of the cluster candidates.

The determination of the redshift was done by means of observations with several telescopes at the ESO La Silla Observatory in Chile, from 1992 to 1999. The brighter objects were observed with the ESO 1.5-m and the ESO/MPG 2.2-m telescopes, while for the more distant and fainter objects, the ESO 3.6-m telescope was used.

Carried out at these telescopes, the 12 year-long programme is known to astronomers as the REFLEX (ROSAT-ESO Flux Limited X-ray) Cluster Survey. It has now been concluded with the publication of a unique catalogue with the characteristics of the 447 brightest X-ray clusters of galaxies in the southern sky. Among these, more than half the clusters were discovered during this survey.

Constraining the dark matter content
Galaxy clusters are far from being evenly distributed in the Universe. Instead, they tend to conglomerate into even larger structures, “super-clusters”. Thus, from stars which gather in galaxies, galaxies which congregate in clusters and clusters tying together in super-clusters, the Universe shows structuring on all scales, from the smallest to the largest ones. This is a relict of the very early (formation) epoch of the Universe, the so-called “inflationary” period. At that time, only a minuscule fraction of one second after the Big Bang, the tiny density fluctuations were amplified and over the eons, they gave birth to the much larger structures.

Because of the link between the first fluctuations and the giant structures now observed, the unique REFLEX catalogue – the largest of its kind – allows astronomers to put considerable constraints on the content of the Universe, and in particular on the amount of dark matter that is believed to pervade it. Rather interestingly, these constraints are totally independent from all other methods so far used to assert the existence of dark matter, such as the study of very distant supernovae (see e.g. ESO PR 21/98) or the analysis of the Cosmic Microwave background (e.g. the WMAP satellite). In fact, the new REFLEX study is very complementary to the above-mentioned methods.

The REFLEX team concludes that the mean density of the Universe is in the range 0.27 to 0.43 times the “critical density”, providing the strongest constraint on this value up to now. When combined with the latest supernovae study, the REFLEX result implies that, whatever the nature of the dark energy is, it closely mimics a Universe with Einstein’s cosmological constant.

A giant puzzle
The REFLEX catalogue will also serve many other useful purposes. With it, astronomers will be able to better understand the detailed processes that contribute to the heating of the gas in these clusters. It will also be possible to study the effect of the environment of the cluster on each individual galaxy. Moreover, the catalogue is a good starting point to look for giant gravitational lenses, in which a cluster acts as a giant magnifying lens, effectively allowing observations of the faintest and remotest objects that would otherwise escape detection with present-day telescopes.

But, as Hans B?hringer says: “Perhaps the most important advantage of this catalogue is that the properties of each single cluster can be compared to the entire sample. This is the main goal of surveys: assembling the pieces of a gigantic puzzle to build the grander view, where every single piece then gains a new, more comprehensive meaning.”

Original Source: ESO News Release

Posted on by Fraser Cain

SpaceShipOne’s Launch Date Set

Image credit: Scaled
A privately-developed rocket plane will launch into history on June 21 on a mission to become the world?s first commercial manned space vehicle. Investor and philanthropist Paul G. Allen and aviation legend Burt Rutan have teamed to create the program, which will attempt the first non-governmental flight to leave the earth?s atmosphere.

SpaceShipOne will rocket to 100 kilometers (62 miles) into sub-orbital space above the Mojave Civilian Aerospace Test Center, a commercial airport in the California desert. If successful, it will demonstrate that the space frontier is finally open to private enterprise. This event could be the breakthrough that will enable space access for future generations.

Allen, founder and chairman of Vulcan Inc, is financing the project. Along with Allen, Vulcan?s technology research and development team — which takes the lead in developing high impact science and technology projects for Allen — has been active in the project?s development and management.

“This flight is one of the most exciting and challenging activities taking place in the fields of aviation and aerospace today,” said Paul G. Allen, sole sponsor in the SpaceShipOne program. “Every time SpaceShipOne flies we demonstrate that relatively modest amounts of private funding can significantly increase the boundaries of commercial space technology. Burt Rutan and his team at Scaled Composites have accomplished amazing things by conducting the first mission of this kind without any government backing.”

Today?s announcement came after SpaceShipOne completed a May 13th, 2004 test flight in which pilot Mike Melvill reached a height of 211,400 feet (approximately 40 miles), the highest altitude ever reached by a non-government aerospace program.

Sub-orbital space flight refers to a mission that flies out of the atmosphere but does not reach the speeds needed to sustain continuous orbiting of the earth. The view from a sub-orbital flight is similar to being in orbit, but the cost and risks are far less.

The pilot (to be announced at a later date) of the up-coming June sub-orbital space flight will become the first person to earn astronaut wings in a non-government sponsored vehicle, and the first private civilian to fly a spaceship out of the atmosphere.

?Since Yuri Gagarin and Al Shepard?s epic flights in 1961, all space missions have been flown only under large, expensive Government efforts. By contrast, our program involves a few, dedicated individuals who are focused entirely on making spaceflight affordable,? said Burt Rutan. ?Without the entrepreneur approach, space access would continue to be out of reach for ordinary citizens. The SpaceShipOne flights will change all that and encourage others to usher in a new, low-cost era in space travel.?

SpaceShipOne was designed by Rutan and his research team at the California-based aerospace company, Scaled Composites. Rutan made aviation news in 1986 by developing the Voyager, the only aircraft to fly non-stop around the world without refueling.

?To succeed takes more than the work of designers and builders?, Rutan said, ?The vision, the will, the commitment and the courage to direct the program is the most difficult hurdle. We are very fortunate to have the financial support and the confidence of a visionary like Paul Allen to make this effort possible.?

To reach space, a carrier aircraft, the White Knight, lifts SpaceShipOne from the runway. An hour later, after climbing to approximately 50,000 feet altitude just east of Mojave, the White Knight releases the spaceship into a glide. The spaceship pilot then fires his rocket motor for about 80 seconds, reaching Mach 3 in a vertical climb. During the pull-up and climb, the pilot encounters G-forces three to four times the gravity of the earth.

SpaceShipOne then coasts up to its goal height of 100 km (62 miles) before falling back to earth. The pilot experiences a weightless environment for more than three minutes and, like orbital space travelers, sees the black sky and the thin blue atmospheric line on the horizon. The pilot (actually a new astronaut!) then configures the craft?s wing and tail into a high-drag configuration. This provides a ?care-free? atmospheric entry by slowing the spaceship in the upper atmosphere and automatically aligning it along the flight path. Upon re-entry, the pilot reconfigures the ship back to a normal glider, and then spends 15 to 20 minutes gliding back to earth, touching down like an airplane on the same runway from which he took off. The June flight will be flown solo, but SpaceShipOne is equipped with three seats and is designed for missions that include pilot and two passengers.

Unlike any previous manned space mission, the June flight will allow the public to view, up close, the takeoff and landing as well as the overhead rocket boost to space. This will be an historic and unique spectator opportunity. Information for the general public on attending the event is available at www.scaled.com.

Based on the success of the June space flight attempt, SpaceShipOne will later compete for the Ansari X Prize, an international competition to create a reusable aircraft that can launch three passengers into sub-orbital space, return them safely home, then repeat the launch within two weeks with the same vehicle.

The Discovery Channel and Vulcan Productions are producing RUTAN?S RACE FOR SPACE (wt), a world premiere television special that documents the entire process of the historic effort to create the first privately-funded spacecraft. From design to flight testing to the moments of the actual launch and return, the special takes viewers behind-the-scenes for the complete, inside story of this historic aerospace milestone. RUTAN?S RACE FOR SPACE will be broadcast later this year.

Original Source: Scaled News Release

Posted on by Fraser Cain

NASA Considering Robotic Mission to Save Hubble

Image credit: University of Maryland
NASA Administrator Sean O’Keefe today announced the agency’s decision to pursue the feasibility of a robotic servicing mission to the Hubble Space Telescope (HST). NASA initiated the first step toward enabling such a mission with the release of a Request for Proposals today. The due date for proposal submissions is July 16, 2004.

“This is the first step in a long process of developing the best options to save Hubble,” Administrator O’Keefe said. “We are on a tight schedule to assure a Hubble servicing mission toward the end of calendar year 2007. But we must act promptly to fully explore this approach.”

Although the primary goal of a robotic mission is to install a deorbit module on the HST, NASA is studying the feasibility of performing other tasks. The tasks could include installing new batteries, gyros and possibly science instruments that would enhance the observatory’s ability to peer even more deeply into the universe. The final decision about specific robotic tasks will be made after all proposals have been thoroughly reviewed.

Original Source: NASA News Release

Posted on by Fraser Cain

Spitzer Shows the Pinwheel Nebula

Image credit: NASA/JPL
Like nosy neighbors, astronomers are spying on one of the nearest galaxies to our Milky Way. In studying the Pinwheel Galaxy, also known as Messier 33 (M33), they seek not malicious gossip but new knowledge as they search for clues to how galaxies like our own are born, live, and die. Today at the 204th meeting of the American Astronomical Society in Denver, Colorado, astronomers from the University of Minnesota, the Harvard-Smithsonian Center for Astrophysics (CfA), and the University of Arizona unveiled new infrared images of M33 taken by NASA’s Spitzer Space Telescope. The photos reveal features of the galaxy never before visible.

About 50,000 light-years across, the spiral galaxy M33 is half the diameter of the Milky Way. It lies 3 million light-years from the Milky Way, which places it among the Local Group of galaxies. Its nearness and viewing angle give astronomers an excellent opportunity to study M33’s physical and chemical processes.

“With the Andromeda Galaxy, it’s one of the two nearest large spiral galaxies comparable to the Milky Way. Since it’s so close, we can get a nice panoramic view. It’s a great object for detailed study,” said Smithsonian astronomer Steven Willner (CfA).

“M33 is a gigantic laboratory where you can watch dust being created in novae and supernovae, being distributed in the winds of giant stars, and being reborn in new stars,” said University of Minnesota researcher and lead author Elisha Polomski. By studying M33, “you can see the Universe in a nutshell.”

Because it operates at infrared wavelengths, the Spitzer Space Telescope detects details hidden to the human eye and to telescopes that operate in visible light. Spitzer collects light at wavelengths measured in microns-millionths of a meter. The new pictures were taken in light at wavelengths ranging from 3.5 to 24 microns.

“At 3.5 microns, we see stars,” said University of Minnesota astronomy professor Robert Gehrz, a member of the M33 observation team. “At eight microns, we see warm dust that’s about 130 degrees Fahrenheit. At 24 microns, we’re picking up cool dust that’s between minus 100 and minus 190 degrees Fahrenheit.” Spitzer’s cameras also operate at 70 and 160 microns.

Observations of M33’s cool components are expected to reveal much about the “metabolism” of galaxies. A galaxy is akin to a living body, in which food substances are broken down to build the body, and the waste and decomposition products of a body are recycled to feed new life. For example, the iron in Earth’s core was forged in the bellies of large, luminous stars, and the heavier elements-all the way to uranium, the heaviest naturally occurring element-were created in supernova explosions. The deaths of those stars sprayed interstellar space with dust and gas, some of which clumped together in a disk that coalesced to form the sun and its planets.

The Spitzer team will examine the Pinwheel Galaxy in detail for the next two and a half years, studying the processes that circulate energy and chemical elements through the galaxy to build up, destroy, and recycle the building blocks of stars and planets. The researchers expect to identify new star-forming regions, red giant stars, novae and supernovae, thereby mapping out the evolutionary process of stars in M33 and comparing it to the process in our own Galaxy.

The NASA Jet Propulsion Laboratory (JPL) manages the Spitzer Space Telescope mission for NASA’s Office of Space Science, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. JPL is a division of Caltech.

Note: This release is being issued jointly with the University of Minnesota and the University of Arizona.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

Original Source: Harvard CfA News Release

Posted on by Fraser Cain

Black Hole at the Heart of a Nebula

Image credit: Harvard CfA
Most galaxies, including the Milky Way, are filled with giant clouds of gas and dust called nebulae that appear as dark silhouettes against the starry background. Nebulae shine only when illuminated or excited by nearby energy sources.

Usually, the energy source is one or more stars. But today at the 204th meeting of the American Astronomical Society in Denver, Colorado, Smithsonian astrophysicist Philip Kaaret (Harvard-Smithsonian Center for Astrophysics) announced that one nebula is illuminated by X-rays from a black hole. Moreover, the brightness of the nebula suggests that the X-ray source may be an intermediate-mass black hole many times larger than most stellar black holes.

This surprising find offers only the second known example of a black hole-illuminated nebula, after LMC X-1 in the Large Magellanic Cloud, and the first example of a nebula powered by an intermediate-mass black hole.

“Astronomers always get excited about new things, and this nebula is certainly something new. Finding it is like getting a royal flush the first time you play poker – it’s that rare,” said Kaaret.

Initially discovered by Manfred Pakull and Laurent Mirioni (University of Strasbourg), the nebula is located 10 million light-years away in the dwarf irregular galaxy Holmberg II. Two years ago, Pakull and Mirioni noted that it seemed to be associated with an ultraluminous X-ray source.

By combining observations from NASA’s Hubble Space Telescope and Chandra X-ray Observatory with those from ESA’s XMM-Newton spacecraft, Kaaret and his colleagues, Martin Ward (University of Leicester) and Andreas Zezas (CfA), pinpointed the X-ray source at the center of the nebula. Moreover, the mystery source is pouring out X-rays at a tremendous rate, shining one million times brighter in X-rays than the Sun shines at all wavelengths of light combined.

The observations by Kaaret and his associates indicate that those X-rays are generated by a black hole gobbling matter from a young, massive companion star at a rate of about one Earth mass every four years. That modest accretion rate is sufficient to ionize and light up a huge 100-light-year-wide swath of the surrounding nebula.

The X-ray emissions provide an important clue to the nature of the black hole. Some astronomers have suggested that X-rays from the source in Holmberg II and similar bright sources are beamed in the Earth’s direction like a searchlight. Such beaming would make the X-ray source appear brighter than it really is, thereby making the black hole appear more massive than it really is.

Kaaret’s data contradict that view, showing instead that the black hole in Holmberg II sends out X-rays evenly in all directions. Therefore, its brightness suggests that it must be more massive than any stellar black hole in our own Galaxy, weighing in at more than 25 times the mass of the Sun and likely more than 40 solar masses. That would rank it as an “intermediate-mass” black hole.

“It’s not easy to explain how intermediate-mass black holes form. Since we only have a few examples to study, every new find is important,” said Kaaret.

This research will be published in a paper co-authored by Kaaret, Ward and Zezas in an upcoming issue of the Monthly Notices of the Royal Astronomical Society.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

Original Source: Harvard CfA News Release

Posted on by Fraser Cain

Catching Stars in the Act of Forming Planets

Image credit: Harvard CfA
How old is too old? Pro football players tend to peak in their late 20s, and few continue their careers beyond the age of 35. For young stars, the peak age for planet formation is around 1 to 3 million years. By 10 million years old, their resources are exhausted and they retire to a life on the stellar “main sequence.”

Using telescopes on the ground and in space, a team of astronomers led by Lee W. Hartmann and Aurora Sicilia-Aguilar (Harvard-Smithsonian Center for Astrophysics) is studying Sun-like stars in their waning formative years, within clusters older than previously explored. They seek to refine our understanding of planet formation by studying dusty protoplanetary disks around such stars. Their results, presented today at the 204th meeting of the American Astronomical Society in Denver, Colorado, better define the time span during which planets might form.

“While the planets that may be forming cannot be detected directly,” said Sicilia-Aguilar, “we can see changes in the circumstellar dusty accretion disks caused as the planets sweep up and accumulate mass.”

“The data also has shown dramatic differences between stars of 3 and 10 million years of age: the younger stars frequently have dusty disks capable of forming planets, while such disks are essentially absent in the older population,” she continued.

The team used data from the Smithsonian Institution’s Whipple Observatory telescopes, the WIYN telescope at Kitt Peak National Observatory, and from the Spitzer Space Telescope (the latter made available as part of the Guaranteed Time Program of Infrared Array Camera PI Giovanni Fazio), to make these findings.

“We are trying to understand the evolution of protoplanetary disks around stars not too different from the Sun,” said team leader Lee W. Hartmann. “Many stars about 1 million years old have disks, but by 10 million years, almost none have disks. We are trying to find stars at an in-between age and `catch them in the act’ of forming planets.”

Circumstellar dust disks enshroud young stars, and astronomers understand this to be a common feature of stellar evolution and of possible planetary system formation. The initial protoplanetary disks contain the gas and dust that provide the raw materials for the formation of later planetary systems.

“After stars form planets in their disks and clear out most of the material-either by accretion onto the star, accretion onto planets, or ejection-small amounts of dust can remain in so-called ‘debris disks.’ Most or all of this debris dust is thought to be continuously generated by the collision of small bodies, much like the zodiacal light in our solar system,” said Hartmann.

The team is presenting the first identification of low mass stars in the young clusters Trumpler 37 and NGC 7160. (These clusters are loose associations of stars that have formed together in the comparatively recent past.) “The cluster members confirm the age estimates of 1 to 5 million years for Tr37 and 10 million years for NGC 7160,” said Sicilia-Aguilar.

“We do find active accretion in some of the stars in Tr37. The average accretion rate is equivalent to swallowing up 10 Jupiter masses in a million years,” said Sicilia-Aguilar. “This is consistent with models of viscous disk evolution.”

“In comparison, we have detected no signs of active accretion so far in the older cluster NGC 7160, suggesting that disk accretion ends within 10 million years. This probably coincides with the major phase of giant planet formation.”

Trumpler 37 is of more immediate interest, said Hartmann, because we hope to find stars with Jupiter-size planets that are still accumulating material from the disks, so the disks are not completely cleared out yet. However, there may be a few objects in the 10 million-year-old cluster NGC 7160 that are also still forming their giant planets. Not all disks evolve at the same rate.

“Thus we expect eventually to find out more about the frequency of debris disks, and the rate at which the dust in such disks is removed, by studying the 10-million-year-old cluster NGC 7160 and comparing it to Trumpler 37,” said Hartmann.

In addition to Sicilia-Aguilar and Hartmann, team members include Cesar Briceno (Centro de Investigaciones de Astronomia), James Muzerolle (University of Arizona), and Nuria Calvet (Smithsonian Astrophysical Observatory). This work was supported by NASA grant NAG5-9670.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

Original Source: Harvard CfA News Release

Posted on by Fraser Cain

New Black Holes Found in a Virtual Observatory

Image credit: ESA
A European team has used the Astrophysical Virtual Observatory (AVO) to find 30 supermassive black holes that had previously escaped detection behind masking dust clouds. The identification of this large population of long-sought ?hidden? black holes is the first scientific discovery to emerge from a Virtual Observatory. The result suggests that astronomers may have underestimated the number of powerful supermassive black holes by as much as a factor of five.

Black holes collect dust. They lurk at the centres of active galaxies in environments not unlike those found in violent tornadoes on Earth. Just as in a tornado, where debris is often found spinning about the vortex, so in a black hole, a dust torus surrounds its waist. In some cases astronomers can look along the axis of the dust torus from above or from below and have a clear view of the black hole. Technically these objects are then called ?type 1 sources?. ?Type 2 sources? lie with the dust torus edge-on as viewed from Earth so our view of the black hole is totally blocked by the dust over a range of wavelengths from the near-infrared to soft X-rays.

While many dust-obscured low-power black holes (called ?Seyfert 2s?) have been identified, until recently few of their high-power counterparts were known. The identification of a population of high-power obscured black holes and the active galaxies in which they live has been a key goal for astronomers and will lead to greater understanding and a refinement of the cosmological models describing our Universe.

The European AVO science team led by Paolo Padovani from Space Telescope-European Coordinating Facility and the European Southern Observatory in Munich, Germany, now announces the discovery of a whole population of the obscured, powerful supermassive black holes. Thirty of these objects were found in the so-called GOODS (Great Observatories Origins Deep Survey) fields. The GOODS survey consists of two areas that include some of the deepest observations from space- and ground-based telescopes, including the NASA/ESA Hubble Space Telescope, and have become the best studied patches in the sky.

Padovani and the team used an innovative technique. Using a Virtual Observatory (VO) they combined information from multiple wavelengths from Hubble, ESO?s Very Large Telescope and NASA’s Chandra. This unprecedented team effort by the largest telescopes in the world made this discovery possible. The majority of the sources are so faint that it is currently not possible to take spectra of them and the VO techniques made it possible for the researchers to work seamlessly with images and catalogues from many different sources.

According to Paolo Padovani: ?This discovery means that surveys of powerful supermassive black holes have so far underestimated their numbers by at least a factor of two, and possibly by up to a factor of five.?

The paper describing these results has just been accepted by the European journal Astro?nomy & Astrophysics and will be published in an upcoming issue. This is the first refereed scientific paper based on end-to-end use of Virtual Observatory tools. The results in the paper show that the VO has evolved beyond the demonstration level to become a real research tool.

The European Astrophysical Virtual Observatory (AVO), funded partly by the European Commission, is the specific VO used for this project. With this work AVO demonstrates cutting-edge science by giving astronomers easy access to manipulation of image and catalogue data on remote computer networks. Until now objects were normally identified by taking a spectrum with a telescope, but now science is moving into an era where objects are pinpointed efficiently by using easily accessible multiwavelength information.

“These discoveries highlight the kind of scientific impact that Virtual Observatory technologies and standards will have on astronomy world-wide”, said Peter Quinn (European Southern Observatory), director of the AVO. “The Astrophysical Virtual Observatory wants to continue to work with astronomers in Europe to enable more discoveries like this, using combined data from ground- and space-based observatories”.

The team already has plans to investigate the new population of dusty black holes by using even more telescopes: the European Southern Observatory?s Very Large Telescope (near-infrared), NASA?s Spitzer Space Telescope (far-infrared) using emerging new VO tools. This will give further insight into the nature of these sources.

Original Source: ESA News Release

Posted on by Fraser Cain

Detailed Image of Saturn’s Storms

Image credit: NASA/JPL/Space Science Institute
Several dark spots, or storms, are huddled in the mid-latitude region of Saturn’s southern hemisphere. The largest of these storms is about 3000 kilometers (1860 miles) across, or about as wide as Japan is long. Also visible are light-colored, lacy cloud patterns indicative of atmospheric turbulence. The image was taken with the narrow angle camera through a near-infrared filter on May 7, 2004 from a distance of 28.2 million kilometers (17.5 million miles) from Saturn. Image scale is 168 kilometers (104 miles) per pixel. The image has been contrast-enhanced to aid visibility.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA’s Office of Space Science, Washington, D.C. The imaging team is based at the Space Science Institute, Boulder, Colorado.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org.

Original Source: CICLOPS News Release