Credit: Chris Miller/Spaceflight Now 
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 The positions of 67 newly found gravitational lenses are shown in this image. NASA/ESA/C. Faure/J.P. Kneib [View Larger Image] Astronomers using the NASA/ESA Hubble Space Telescope have compiled a large catalog of gravitational lenses in the distant universe. The catalog contains a staggering 67 new gravitationally lensed galaxy images found around massive elliptical and lenticular-shaped galaxies. This sample demonstrates the rich diversity of strong gravitational lenses. If this sample is representative, there would be nearly half a million similar gravitational lenses in total over the whole sky. The lenses come from a recently completed, large set of observations as part of a huge project to survey a single 1.6 square degree field of sky (nine times the area of the full Moon) with several space-based and Earth-based observatories. The COSMOS project, led by Nick Scoville at the California Institute of Technology, used observations from several observatories including the Hubble Space Telescope, as well as the Spitzer Space Telescope, the XMM-Newton spacecraft, the Chandra X-Ray Observatory, the Very Large Telescope (VLT), the Subaru Telescope and CFHT. |
 This is a triple gravitational lens, an example of the rich diversity of the 67 strong gravitational lenses found in the COSMOS survey. NASA/ESA/C. Faure/J.P. Kneib [View Larger Image] Gravitational lensing occurs when light traveling towards us from a distant galaxy is magnified and distorted as it encounters a massive object between the galaxy and us. These gravitational lenses often allow astronomers to peer much further back into the early universe than they would normally be able to. The massive objects that create the lenses are usually huge clusters of massive galaxies. "We typically see the gravitational lens create a series of bright arcs or spots around a galaxy cluster. What we are observing here is a similar effect but on much smaller scale, happening only around a single but very massive galaxy," says Kneib. |
 An Einstein ring can be seen in this image from the COSMOS project. An Einstein ring is a complete circle image of a background galaxy, which is formed when the background galaxy, a massive, foreground galaxy, and the Hubble Space Telescope are all aligned perfectly. NASA/ESA/C. Faure/J.P. Kneib [View Larger Image] Hubble astronomers went through a unique process to identify these incredible natural lenses. First, possible galaxies were identified from a galaxy catalog, comprising more than two million galaxies. "We then had to look through each individual COSMOS image by eye and identify any potential strong gravitational lenses," says Faure. Finally, checks were made to see if the foreground galaxy and the lensed galaxy were really different or just one galaxy with an odd shape. "With this sample of gravitational systems identified by the human eye, we now plan use the sample of lenses to train robot software to find more of these lenses across the entire Hubble image archive, and we may find even more strong lensing systems in the COSMOS field," adds Kneib. The new results confirm that the universe is filled with gravitational lensing systems. Extrapolating these new findings to the whole sky, predicts no less than half a million similar lenses in total. The future prospects for finding more of these systems are thus excellent. The study of these gravitational lenses will give astronomers a first-rate opportunity to probe the dark matter distribution around galactic lenses. Once astronomers find even larger numbers of these smaller, stronger lenses they can be used to create a census of galaxy masses in the universe to test the predictions of cosmological models. |
Filed under: Astronomy
 This artist's concept illustrates the idea that rocky, terrestrial worlds like the inner planets in our solar system, may be plentiful and diverse in the universe. Credit: NASA/JPL-Caltech |
Meyer is presenting the findings at the annual meeting of the American Association for the Advancement of Science in Boston. The results appear in the Feb. 1 issue of Astrophysical Journal Letters.
The astronomers used Spitzer to survey six sets of stars, grouped depending on their age, with masses comparable to our sun. The sun is about 4.6 billion years old. "We wanted to study the evolution of the gas and dust around stars similar to the sun and compare the results with what we think the solar system looked like at earlier stages during its evolution," Meyer said.
The Spitzer telescope does not detect planets directly. Instead it detects dust the rubble left over from collisions as planets form at a range of infrared wavelengths. The hottest dust is detected at the shortest wavelengths, between 3.6 microns and 8 microns. Cool dust is detected at the longest wavelengths, between 70 microns and 160 microns. Warm dust can be traced at 24-micron wavelengths. Because dust closer to the star is hotter than dust farther from the star, the "warm" dust likely traces material orbiting the star at distances comparable to the distance between Earth and Jupiter.
"We found that about 10 to 20 percent of the stars in each of the four youngest age groups shows 24-micron emission due to dust," Meyer said. "But we don't often see warm dust around stars older than 300 million years. The frequency just drops off.
"That's comparable to the time scales thought to span the formation and dynamical evolution of our own solar system," he added. "Theoretical models and meteoritic data suggest that Earth formed over 10 to 50 million years from collisions between smaller bodies."
In a separate study, Thayne Currie and Scott Kenyon of the Smithsonian Astrophysical Observatory, Cambridge, Mass., and their colleagues also found evidence of dust from terrestrial planet formation around stars from 10 to 30 million years old. "These observations suggest that whatever led to the formation of Earth could be occurring around many stars between three million and 300 million years old," Meyer said.
Kenyon and Ben Bromley of the University of Utah, Salt Lake City, have developed planet formation models that provide a plausible scenario. Their models predict warm dust would be detected at 24-micron wavelengths as small rocky bodies collide and merge. "Our work suggests that the warm dust Meyer and colleagues detect is a natural outcome of rocky planet formation. We predict a higher frequency of dust emission for the younger stars, just as Spitzer observes," said Kenyon.
The numbers on how many stars form planets are ambiguous because there's more than one way to interpret the Spitzer data, Meyer said. The warm-dust emission that Spitzer observed around 20 percent of the youngest cohort of stars could persist as the stars age. That is, the warm dust generated by collisions around stars three to 10 million years old could carry over and show up as warm dust emission seen around stars in the 10- to 30- million-year-old range and so on. Interpreting the data this way, about one out of five sun-like stars is potentially planet-forming, Meyer said.
There's another way to interpret the data. "An optimistic scenario would suggest that the biggest, most massive disks would undergo the runaway collision process first and assemble their planets quickly. That's what we could be seeing in the youngest stars. Their disks live hard and die young, shining brightly early on, then fading," Meyer said. "However, smaller, less massive disks will light up later. Planet formation in this case is delayed because there are fewer particles to collide with each other."
If this is correct and the most massive disks form their planets first and the wimpiest disks take 10 to 100 times longer, then up to 62 percent of the surveyed stars have formed, or may be forming, planets. "The correct answer probably lies somewhere between the pessimistic case of less than 20 percent and optimistic case of more than 60 percent," Meyer said.
The next critical test of the assertion that terrestrial planets like Earth could be common around stars like the sun will come next year with the launch of NASA's Kepler mission.
Meyer's 13 co-authors include John Carpenter of the California Institute of Technology in Pasadena. NASA's Jet Propulsion Laboratory in Pasadena manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at Caltech. Caltech manages JPL for NASA.
Posted by:
Lucimary Vargas
Além Paraíba-MG-Brasil
observatorio.monoceros@gmail.com
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"We're very confident that we hit the satellite," said Marine Gen. James Cartwright, vice chairman of the Joint Chiefs of Staff. "We also have a high degree of confidence that we got the tank."
The SM-3 tactical missile, a modified component of the Aegis sea-based missile defense system, was aiming for a fuel tank embedded inside the craft's structure to release an estimated 1,000 pounds of corrosive hydrazine propellant.
Cartwright said he's about 80 to 90 percent sure the missile hit the fuel tank, based on data from a suite of optical, infrared and radar sensors derived from the national missile defense system.
A tracking camera aboard an aircraft flying over the Pacific captured dramatic images of the intercept, showing the moment of impact and a cloud of debris left behind after the collision.
"We have a fireball, and given that there's no fuel, that would indicate that that's the hydrazine fire. We have a vapor cloud that formed. That again would be likely to be the hydrazine. We also have some spectral analysis from airborne platforms that indicate the presence of hydrazine after the intercept. So again that would indicate to us that the hydrazine vented overboard in some quantity and we're starting to see that in space," Cartwright said.
Detailed results of the unprecedented strike must be confirmed through additional analysis before military officials will draw any more conclusions. That analysis is expected to take a day or two to complete.
"We're trying to pull all these pieces together and make sure that we're not stringing facts together erroneously," Cartwright said.
The SM-3 missile launched from the USS Lake Erie stationed northwest of Hawaii at 10:26 p.m. EST Wednesday. High seas in the Pacific Ocean threatened to preclude an attempt early in the day, but Navy ships reported acceptable conditions once they arrived at the launch site.
Based on recommendations from senior military commanders, Defense Secretary Robert Gates ordered the Navy to take advantage of the Wednesday's opportunity. An incoming weather system could have thwarted launch attempts in subsequent days.
A control center at Vandenberg Air Force Base in California confirmed the missile successfully crashed into the orbiting spacecraft at an altitude of 153 miles, Pentagon officials said.
Lacking a warhead, the interceptor relied on hitting the satellite with a combined relative velocity of about 22,000 miles per hour. The energy of the impact was enough to destroy the spacecraft, which was lost almost immediately after its December 2006 launch.
"This was uncharted territory," Cartwright said. "The technical degree of difficulty was significant here."
Initial radar data indicates the dead satellite broke into fragments no larger than a football, Cartwright reported.
"At the point of intercept last night, there were a few cheers from people who have spent many days working on this project," he said.
Infrared sensors detected numerous objects streaking through the atmosphere, but no sizable pieces of debris have reached the ground. Officials expected a large percentage of the debris to re-enter within the first few hours after the satellite's destruction.
A group of amateur astronomers in Prince George, British Columbia, observed more than a dozen visible debris trails crossing the sky less than 15 minutes after the impact, according to message distributed by the Royal Astronomical Society of Canada.
The targeted satellite's orbit would have taken it northeast across the Pacific Ocean and over Canada in the minutes following the strike.
The mission took only a few minutes to complete but more than a month to plan, according to senior military personnel.
The 5,000-pound satellite – called USA 193 in the military's spacecraft naming system – was about the size of a school bus, defense officials say. USA 193 was operated by the National Reconnaissance Office, the federal agency responsible for fielding spy satellites.
Officials don't know why the experimental satellite died because engineers are not able to communicate with it.
"A smoking gun on exactly why (the satellite failed) is something that has eluded us to date, just because we can't get any diagnostics to tell us what's going on," Cartwright said. "It didn't respond to us."
Because the craft failed so soon after launch, nearly all of its hydrazine maneuvering fuel remained on-board. The corrosive propellant had likely frozen during its 14-month stay in space, and military officials say the frozen tank would have survived a fiery uncontrolled entry into the atmosphere and made it to the ground.
Without control of the satellite, military leaders watched as drag from the thin outer reaches of the atmosphere gradually lowered the craft's orbit. The satellite's orbit fell by an average of more than 60 miles between its launch and this month, a rate that would have led to its natural decay by sometime next month, according to analysis by international hobbyists that observe spacecraft orbiting the planet.
Aerospace industry analysts predicted the hydrazine could be dispersed in an area about the size of two football fields, although the tank would have most likely landed in the ocean or an unpopulated area.
But hydrazine could be deadly to humans if they are exposed to heavy concentrations of the rocket fuel.
"You have to treat this as if it's going to hurt someone," Cartwright said. "If you can mitigate the threat, then you should take action if you have the opportunity."
Engineers estimated up to 2,800 pounds of debris could have made it to Earth if left intact. The satellite also carried sensitive experimental reconnaissance equipment, according to reports.
Some experts said the Pentagon's actions could be driven by the potential of classified technology falling into the wrong hands should the spacecraft come down on land.
"The hydrazine was unique here, not the size of the mass, not the reentry, not the classified nature," Cartwright said. "It was the hydrazine that drove this."
Officials began planning a possible strike in January, and President Bush gave the go-ahead to shoot down the satellite earlier this month.
"You want to reach out to each one of those people that probably gave up their weekends and nights to get this done in 30 days and put it together," Cartwright said.
The Missile Defense Agency added special instrumentation to beam telemetry from the missile to control centers, giving engineers additional insight into the mission. Other changes included tweaking software to allow the interceptor, originally designed to fend off short- and medium-range missiles, to reach a satellite in orbit.
"It's not something that we would be entering into the service in some standard way," Cartwright said. "This is a one-time type of event."
The launch also used a network of sensors used by the missile defense system to detect incoming ballistic missiles. The sensors included airborne detectors, ground radars and telescopes in Hawaii, tracking stations on ships, and satellite-based infrared instruments on the military's early warning satellites, a senior military official said on background.
The use of multiple tiers of the missile defense system in Wednesday's space shot proves it works, Secretary Gates said.
"Completely a side benefit of yesterday's action was to underscore the money that the Congress has been voting for this has resulted in a very real capability," Gates said.
Wednesday's intercept was the first time the U.S. military destroyed an orbiting satellite since 1985, when an air-launched missile struck a beleaguered solar observatory. China garnered international criticism last year when it conducted an unannounced test of an anti-satellite, or ASAT, weapon against one of its own weather satellites.
Military leaders drew distinctions between that test and Wednesday's mission. The concern that compelled the Pentagon's decision was public safety, Cartwright said.
"We did that in the 1980s. We understand ASAT. There's no reason to go back and reprove what we've already done," he said.
Government officials also informed foreign governments a week before the test. The Pentagon worked closely with the State Department to begin diplomatic efforts, according to Ambassador James Jeffrey, President Bush's deputy national security advisor.
Agencies are following a U.N. treaty that calls for member states to inform other countries about space activities of potential concern, Jeffrey said.
"What we've tried to do from the beginning was be as open as possible about the intention," said Navy Adm. Mike Mullen, chairman of the Joint Chiefs of Staff.
Senior military leaders say the strike can serve as a model of openness to China and other countries conducting similar operations.
"The Chinese did not do that when they launched their anti-satellite test," said Navy Adm. Timothy Keating, commander of U.S. Pacific Command. "We hope there are some lessons that become apparent to them."
China's test last year created more than 2,000 pieces of space junk, most of which is still in orbit and could pose a risk to other spacecraft.
"The Chinese ASAT test was conducted against a satellite in a circular orbit at around 850 kilometers of altitude," said Mike Griffin, NASA administrator, during a press conference last week. "So the debris that was generated could go (through) a very large swath of Earth orbital space and will be up for decades."
Most of the chunks generated from Wednesday's intercept were expected to be down within hours and days.
"That's an enormous difference to spacefaring nations," Griffin said.
 This Chandra image shows the supernova Kes 75. The pulsar is in the center of the blue area at the top. NASA/CXC/M. Gonzalez/F. Gavriil/P. Slane [View Larger Image] Observations from NASA's Rossi X-ray Timing Explorer (RXTE) have revealed that the youngest known pulsing neutron star has thrown a temper tantrum. The collapsed star occasionally unleashes powerful bursts of X-rays, which are forcing astronomers to rethink the life cycle of neutron stars. "We are watching one type of neutron star literally change into another right before our very eyes. This is a long-sought missing link between different types of pulsars," says Fotis Gavriil of NASA's Goddard Space Flight Center and the lead author of the paper. A neutron star forms when a massive star explodes as a supernova, leaving behind an ultradense core. Most known neutron stars emit regular pulsations that are powered by rapid spins. Astronomers have found nearly 1,800 of these so-called pulsars in our galaxy. Pulsars have incredibly strong magnetic fields by Earthly standards, but a dozen of them. Slow rotators known as magnetars actually derive their energy from incredibly powerful magnetic fields, the strongest known in the universe. These fields can stress the neutron star's solid crust past the breaking point, triggering starquakes that snap magnetic-field lines, producing violent and sporadic X-ray bursts. But what is the evolutionary relationship between pulsars and magnetars? Astronomers would like to know if magnetars represent a rare class of pulsars, or if some or all pulsars go through a magnetar phase during their life cycles. Gavriil and his colleagues have found an important clue by examining archival RXTE data of a young neutron star, known as PSR J1846-0258 for its sky coordinates in the constellation Aquila. Previously, astronomers had classified PSR J1846 as a normal pulsar because of its fast spin (3.1 times per second) and pulsar-like spectrum. But RXTE caught four magnetar-like X-ray bursts on May 31, 2006, and another on July 27, 2006. Although none of these events lasted longer than 0.14 second, they all packed the wallop of at least 75,000 Suns. |
 These images from NASA's Chandra X-ray Observatory show the pulsar in Kes 75 in October 2000 (left) and June 2006 (right). The pulsar clearly brightened in X-rays after giving off powerful outbursts earlier in 2006. NASA/CXC/M. Gonzalez/F. Gavriil/P. Slane [View Larger Image] "Young, fast-spinning pulsars were not thought to have enough magnetic energy to generate such powerful bursts," says coauthor Marjorie Gonzalez, who worked on this paper at McGill University in Montreal, Canada. "Here's a normal pulsar that's acting like a magnetar." Observations from NASA's Chandra X-ray Observatory also provided key information. Chandra observed the neutron star in October 2000 and again in June 2006, around the time of the bursts. Chandra showed the object had brightened in X-rays, confirming that the bursts were from the pulsar, and that its spectrum had changed to become more magnetar-like. Astronomers know that PSR J1846 is very young for several reasons. First, it resides inside a supernova remnant known as Kes 75, an indicator that it hasn't had time to wander from its birthplace. Second, based on the rapidity that its spin rate is slowing down, astronomers calculate that it can be no older than 884 years, an infant on the cosmic timescale. Magnetars are thought to be about 10,000 years old, whereas most pulsars are thought to be considerably older. The fact that PSR J1846's spin rate is slowing down relatively fast also means that it has a strong magnetic field that is breaking the rotation. The implied magnetic field is trillions of times stronger than Earth's field, but it's 10 to 100 times weaker than typical magnetar field strengths. Coauthor Victoria Kaspi of McGill University notes, "PSR J1846's actual magnetic field could be much stronger than the measured amount, suggesting that many young neutron stars classified as pulsars might actually be magnetars in disguise, and that the true strength of their magnetic field only reveals itself over thousands of years as they ramp up in activity." |
"Failure to act now to regulate space to protect property and human life would be pure folly." - Tommaso Sgobba.Other scientists agree with Sgobba, recommending that future missions in to space abide by some strict codes of practice (possibly more strict than those imposed on international civil aviation) to drastically cut the rate of orbital littering by the 20 countries currently able to send stuff into space.
Filed under: Earth Observation, Satellites, Space Flight
Filed under: Astronomy
"This new knowledge is crucial for us to understand the history and evolution of the cosmos […] Such a tool will also enable us to glimpse a little more of the nature of dark matter." - Ludovic Van Waerbeke, Assistant Professor, Department of Physics and Astronomy, UBCSource: UBC Press Release
Filed under: Dark Matter, Observing
Filed under: Astronomy
"If the hypothesis analyzed in this paper is correct, modern methods aimed at averting the asteroid danger appear to be inefficient. This is related to the fact that their main idea is revealing big meteors and asteroids with dangerous orbits and, then, monitoring these bodies. However, if the main danger consists in abrupt changes of asteroidal orbits (because of scattering on a PBH), revealing potentially dangerous bodies is hardly possible."
In old data archived from NASA's Chandra X-ray Observatory, Rasmus Voss (Max Planck Institute for Extraterrestrial Physics, Germany) and Gijs Nelemans (Radboud University, the Netherlands) found an X-ray source at the location where a Type Ia supernova, SN 2007on, later blew up. The supernova was discovered on November 5, 2007, in the outer edge of NGC 1404, an elliptical galaxy some 65 million light-years away in the southern constellation Fornax.
If the X-ray source was indeed the supernova's progenitor, notes Nelemans, this would support the theory that Type Ia explosions occur in binary-star systems where matter from a normal star streams onto a white-dwarf companion. The nuclear fusion of the freshly arrived material on the dwarf's surface would produce strong X-rays.
If such a feasting white dwarf grows heftier than 1.39 solar masses (the "Chandrasekhar limit"), it can't hold itself up against its own gravity anymore, and it starts to collapse inward. Within moments the temperature and pressure at its center become so great that the entire star explodes in a runaway thermonuclear reaction — as a distinctive, Type Ia supernova.
Because all white dwarfs have the same mass when they reach this tipping point, astrophysicists expect all Type Ia's (of a given subtype) to have the same luminosity. Therefore, cosmologists believe they can use Type Ia's as accurate "standard candles" to measure the distances of remote galaxies independently of redshift. By comparing the supernova distances to the redshifts of the host galaxies, astronomers can chart the history of the universe's changing expansion rate. In 1998 such studies led to the discovery that the expansion is speeding up, presumably due to some kind of "dark energy" pervading space.
Two Ways to Collapse
But no one knows for sure whether Type Ia supernovas really arise from a white dwarf accreting matter slowly from a normal star. Another possibility is that the blasts result from the merger of two white dwarfs in a close binary system spiraling together. A better understanding of the nature of Type Ia progenitors might help firm up the cosmological supernova data.
There's a key difference between the two scenarios. In the slow-accretion version, matter falling onto the white dwarf makes it shine brightly in X-rays. In the two-white-dwarfs version, no matter is exchanged beforehand and the system is essentially X-ray dark.
Pinpointing the Site. . . Maybe
Voss and Nelemans published their discovery of the possible X-ray progenitor of SN 2007on in the February 14th issue of Nature. It seemed to settle the question in favor of the standard, slow-accretion model.
However, after their paper was accepted for publication in mid-December, nagging doubts about the apparent association have surfaced.
In particular, more precise measurements of the supernova's position with telescopes run by the European Southern Observatory in Chile, including the Very Large Telescope at Cerro Paranal, reveal a small offset from the Chandra X-ray source's position. The discrepancy is barely more than one arcsecond, but that's enough to mean the X-ray source and the supernova had nothing whatever to do with each other — if in fact the X-ray position is as accurate as Chandra's operators believed.
Probably it is. Only a few X-ray photons were detected in the four-year-old Chandra observation, but that's enough that the probability of the X-ray source really being the supernova progenitor is now estimated to be no more than 1 percent, says Nelemans.
On the other hand, given the rarity of similar X-ray sources, the probability of a chance alignment is also less than 1 percent! "One way or the other, we have come across a very improbable event," says Nelemans.
Future observations should settle the issue. If the X-ray source was indeed what blew up later, it should now be gone. Voss and Nelemans are applying for Chandra time later this year to check.
Meanwhile, they are on the hunt for X-ray progenitors of other Type Ia events.
Posted by:
Lucimary Vargas
Além Paraíba-MG-Brasil
observatorio.monoceros@gmail.com
