'Death stars' in Orion blast planets before they even form
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March 10, 2014 Source: National Radio Astronomy Observatory Summary: Astronomers have studied the often deadly relationship between highly luminous O-type stars and nearby protostars in the Orion Nebula. Their data reveal that protostars within 0.1 light-years (about 600 billion miles) of an O-type star are doomed to have their cocoons of dust and gas stripped away in just a few millions years, much faster than planets are able to form.The Orion Nebula is home to hundreds of young stars and even younger protostars known as proplyds. Many of these nascent systems will go on to develop planets, while others will have their planet-forming dust and gas blasted away by the fierce ultraviolet radiation emitted by massive O-type stars that lurk nearby. A team of astronomers from Canada and the United States has used the Atacama Large Millimeter/submillimeter Array (ALMA) to study the often deadly relationship between highly luminous O-type stars and nearby protostars in the Orion Nebula. Their data reveal that protostars within 0.1 light-years (about 600 billion miles) of an O-type star are doomed to have their cocoons of dust and gas stripped away in just a few millions years, much faster than planets are able to form. "O-type stars, which are really monsters compared to our Sun, emit tremendous amounts of ultraviolet radiation and this can play havoc during the development of young planetary systems," remarked Rita Mann, an astronomer with the National Research Council of Canada in Victoria, and lead author on a paper in the Astrophysical Journal. "Using ALMA, we looked at dozens of embryonic stars with planet-forming potential and, for the first time, found clear indications where protoplanetary disks simply vanished under the intense glow of a neighboring massive star." Many, if not all, Sun-like stars are born in crowded stellar nurseries similar to the Orion Nebula. Over the course of just a few million years, grains of dust and reservoirs of gas combine into larger, denser bodies. Left relatively undisturbed, these systems will eventually evolve into fully fledged star systems, with planets -- large and small -- and ultimately drift away to become part of the galactic stellar population. Astronomers believe that massive yet short-lived stars in and around large interstellar clouds are essential for this ongoing process of star formation. At the end of their lives, massive stars explode as supernovas, seeding the surrounding area with dust and heavy elements that will get taken up in the next generation of stars. These explosions also provide the kick necessary to initiate a new round of star and planet formation. But while they still shine bright, these larger stars can be downright deadly to planets if an embryonic solar systems strays too close. "Massive stars are hot and hundreds of times more luminous than our Sun," said James Di Francesco, also with the National Research Council of Canada. "Their energetic photons can quickly deplete a nearby protoplanetary disk by heating up its gas, breaking it up, and sweeping it away." Earlier observations with the Hubble Space Telescope revealed striking images of proplyds in Orion. Many had taken on tear-drop shapes, with their dust and gas trailing away from a nearby massive star. These optical images, however, couldn't reveal anything about the amount of dust that was present or how the dust and gas concentrations changed in relation to massive stars. The new ALMA observations detected these and other never-before-imaged proplyds, essentially doubling the number of protoplanetary disks discovered in that region. ALMA also could see past their surface appearance, peering deep inside to actually measure how much mass was in the proplyds. Combining these studies with previous observations from the Submillimeter Array (SMA) in Hawai'i, the researchers found that any protostar within the extreme-UV envelope of a massive star would have much of its disk of material destroyed in very short order. Proplyds in these close-in regions retained only a fraction (one half or less) of the mass necessary to create one Jupiter-size planet. Beyond the 0.1 light-year radius, in the far-UV dominated region, the researchers observed a wide range of disk masses containing anywhere for one to 80 times the mass of Jupiter. This is similar to the amount of dust found in low-mass star forming regions. "Taken together, our investigations with ALMA suggest that extreme UV regions are not just inhospitable, but they're downright hazardous for planet formation. With enough distance, however, it's possible to find a much more congenial environment," said Mann. "This work is really the tip of the iceberg of what will come out of ALMA; we hope to eventually learn how common solar systems like our own are." Other researchers involved in this project include Doug Johnstone, National Research Council of Canada; Sean M. Andrews, Harvard-Smithsonian Center for Astrophysics; Jonathan P. Williams, University of Hawai'i; John Bally, University of Colorado; Luca Ricci, California Institute of Technology; A. Meredith Hughes, Wesleyan University, and Brenda C. Matthews, National Research Council of Canada. Story Source: The above story is based on materials provided by National Radio Astronomy Observatory. Note: Materials may be edited for content and length. |
Possible evidence for dark matter particle presented at UCLA physics symposium
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March 10, 2014 Source: University of California, Los Angeles Summary: Dark matter, the mysterious substance estimated to make up approximately more than one-quarter of the mass of the universe, is crucial to the formation of galaxies, stars and even life but has so far eluded direct observation. At a recent UCLA symposium attended by 190 scientists from around the world, physicists presented several analyses that participants interpreted to imply the existence of a dark matter particle. The likely mass would be approximately 30 billion electron-volts, said the symposium's organizer.Dark matter, the mysterious substance estimated to make up approximately more than one-quarter of the mass of the universe, is crucial to the formation of galaxies, stars and even life but has so far eluded direct observation. At a recent UCLA symposium attended by 190 scientists from around the world, physicists presented several analyses that participants interpreted to imply the existence of a dark matter particle. The likely mass would be approximately 30 billion electron-volts, said the symposium's organizer, David Cline, a professor of physics in the UCLA College of Letters and Science and one of the world's experts on dark matter. The physicists at the Feb. 26-28 event were in agreement that "there seems to be an excess in the available data that could be due to dark matter," Cline said. "At this symposium, it was obvious that excitement is building in the fields of dark matter theory and, especially, detection," said Cline, who noted that there are several ways dark matter can be observed and that all were discussed at the UCLA meeting. "Because dark matter makes up the bulk of the mass of galaxies and is fundamental in the formation of galaxies and stars, it is essential to the origin of life in the universe and on Earth," Cline said. The first evidence for dark matter was discovered in 1933 using the Mt. Wilson telescope outside of Los Angeles. More recently, various theoretical models and detector improvements have made it possible to search for dark matter particles at extremely sensitive levels -- some of the most sensitive measurements made by any scientists in the world. One search technique involves using the vast amount of dark matter in our galaxy. The NASA Fermi Satellite Telescope, an international collaboration involving NASA, the Goddard Space Flight Center and the SLAC National Accelerator Laboratory, searches for gamma rays -- very high-energy light particles -- from this dark matter. There are models of dark matter that would allow a signal in the galactic dark matter consistent with the claims at the meeting and provide a small interaction consistent with the "null results" in the direct dark matter searches all over the world. Much larger direct dark matter detectors are being planned in the U.S., Italy, Canada and China (including Xenon 3 Ton, LUX-ZEPLIN 7 Ton and DarkSide, which will weigh five tons). These larger detectors potentially could see a dark matter signal in the next few years, Cline said. Dark matter is widely thought to be a kind of massive elementary particle that interacts weakly with ordinary matter. Physicists refer to these particles as WIMPS, for weakly interacting massive particles, and think they originated from the Big Bang. WIMPs are thought to be streaming constantly through the solar system and Earth. Another search method is to look for an interaction of a WIMP with xenon or argon nuclei and others (like germanium) in very low-background laboratories deep underground in Italy, the U.S., Canada, China and other countries. While these experiments have seen no signal of a WIMP above 30 billion electron volts, "there is no incompatibility with the interesting excess in the FERMI data," Cline said. The discovery of the Higgs boson, which won the 2013 Nobel Prize in physics, plays a role in the search for dark matter, Cline said, adding that this topic was discussed in detail at the meeting. Dark matter, he said, could consist of axions, WIMPs or sterile neutrinos, all of which were discussed at the symposium. The UCLA dark matter symposium is convened every two years; this was the 11th such meeting. Cline said he and his colleagues hope to clarify the dark matter puzzle at the 2016 symposium. See more on last week's conference: https://hepconf.physics.ucla.edu/dm14 It was at this same dark matter symposium in 1998 that two groups of scientists reported that the universe is accelerating, as well as expanding, a finding Cline described as "one of the greatest discoveries in the history of science." Story Source: The above story is based on materials provided by University of California, Los Angeles. Note: Materials may be edited for content and length. |
Mystery of planet-forming disks explained by magnetism
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March 7, 2014 Source: NASA/Jet Propulsion Laboratory Summary: Astronomers say that magnetic storms in the gas orbiting young stars may explain a mystery that has persisted since before 2006. Researchers using NASA's Spitzer Space Telescope to study developing stars have had a hard time figuring out why the stars give off more infrared light than expected. The planet-forming disks that circle the young stars are heated by starlight and glow with infrared light, but Spitzer detected additional infrared light coming from an unknown source.Astronomers say that magnetic storms in the gas orbiting young stars may explain a mystery that has persisted since before 2006. Researchers using NASA's Spitzer Space Telescope to study developing stars have had a hard time figuring out why the stars give off more infrared light than expected. The planet-forming disks that circle the young stars are heated by starlight and glow with infrared light, but Spitzer detected additional infrared light coming from an unknown source. A new theory, based on three-dimensional models of planet-forming disks, suggests the answer: Gas and dust suspended above the disks on gigantic magnetic loops like those seen on the sun absorb the starlight and glow with infrared light. "If you could somehow stand on one of these planet-forming disks and look at the star in the center through the disk atmosphere, you would see what looks like a sunset," said Neal Turner of NASA's Jet Propulsion Laboratory, Pasadena, Calif. The new models better describe how planet-forming material around stars is stirred up, making its way into future planets, asteroids and comets. While the idea of magnetic atmospheres on planet-forming disks is not new, this is the first time they have been linked to the mystery of the observed excess infrared light. According to Turner and colleagues, the magnetic atmospheres are similar to what takes place on the surface of our sun, where moving magnetic field lines spur tremendous solar prominences to flare up in big loops. Stars are born out of collapsing pockets in enormous clouds of gas and dust, rotating as they shrink down under the pull of gravity. As a star grows in size, more material rains down toward it from the cloud, and the rotation flattens this material out into a turbulent disk. Ultimately, planets clump together out of the disk material. In the 1980s, the Infrared Astronomical Satellite mission, a joint project that included NASA, began finding more infrared light than expected around young stars. Using data from other telescopes, astronomers pieced together the presence of dusty disks of planet-forming material. But eventually it became clear the disks alone weren't enough to account for the extra infrared light -- especially in the case of stars a few times the mass of the sun. One theory introduced the idea that instead of a disk, the stars were surrounded by a giant dusty halo, which intercepted the star's visible light and re-radiated it at infrared wavelengths. Then, recent observations from ground-based telescopes suggested that both a disk and a halo were needed. Finally, three-dimensional computer modeling of the turbulence in the disks showed the disks ought to have fuzzy surfaces, with layers of low-density gas supported by magnetic fields, similar to the way solar prominences are supported by the sun's magnetic field. The new work brings these pieces together by calculating how the starlight falls across the disk and its fuzzy atmosphere. The result is that the atmosphere absorbs and re-radiates enough to account for all the extra infrared light. "The starlight-intercepting material lies not in a halo, and not in a traditional disk either, but in a disk atmosphere supported by magnetic fields," said Turner. "Such magnetized atmospheres were predicted to form as the disk drives gas inward to crash onto the growing star." Over the next few years, astronomers will further test these ideas about the structure of the disk atmospheres by using giant ground-based telescopes linked together as interferometers. An interferometer combines and processes data from multiple telescopes to show details finer than each telescope can see alone. Spectra of the turbulent gas in the disks will also come from NASA's SOFIA telescope, the Atacama Large Millimeter/submillimeter Array (ALMA) telescope in Chile, and from NASA's James Webb Space Telescope after its launch in 2018. JPL manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Spacecraft operations are based at Lockheed Martin Space Systems Company, Littleton, Colo. Data are archived at the Infrared Science Archive housed at the Infrared Processing and Analysis Center at Caltech. Caltech manages JPL for NASA. For more information about Spitzer, visit http://spitzer.caltech.edu and http://www.nasa.gov/spitzer . Story Source: The above story is based on materials provided by NASA/Jet Propulsion Laboratory.Note: Materials may be edited for content and length. |
Weirdness in cosmic web of the universe: Faint strings of galaxies in 'empty' space arranged in way never before seen
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March 10, 2014 Source: International Centre for Radio Astronomy Research (ICRAR) Summary: Australian astronomers have shown galaxies in the vast empty regions of the universe are actually aligned into delicate strings, according to new research. Using data from the Galaxy and Mass Assembly (GAMA) survey, the astronomers found that the small number of galaxies inside these voids are arranged in a new way never seen before.Australian astronomers have shown galaxies in the vast empty regions of the Universe are actually aligned into delicate strings, according to research published today in the Monthly Notices of the Royal Astronomical Society. A team of astronomers based at The University of Western Australia node of the International Centre for Radio Astronomy Research (ICRAR) has found short strings of faint galaxies in what were previously thought to be extremely empty parts of space. The Universe is full of vast collections of galaxies that are arranged into an intricate web of clusters and nodes connected by long strings. This remarkably organized structure is often called the 'cosmic web', with busy intersections of galaxies surrounding vast spaces, empty of anything visible to us on Earth. "The spaces in the cosmic web are thought to be staggeringly empty," said Dr Mehmet Alpaslan, who led the research. "They might contain just one or two galaxies, as opposed to the hundreds that are found in big clusters." These huge, empty regions are called voids, and for years, astronomers have been trying to understand the small population of galaxies that inhabit them. Using data from the Galaxy and Mass Assembly (GAMA) survey, Alpaslan and his colleagues found that the small number of galaxies inside these voids are arranged in a new way never seen before. "We found small strings composed of just a few galaxies penetrating into the voids, a completely new type of structure that we've called 'tendrils'," said Alpaslan. To discover tendrils, the GAMA team created the largest ever galaxy census of the southern skies using observations from the Anglo-Australian Telescope in NSW, Australia. "Our new catalogue has looked deeper into space and mapped each patch of sky up to ten times to make sure it's as thorough as possible," said Dr Aaron Robotham from The University of Western Australia node of ICRAR. "We weren't sure what we'd find when we looked at voids in detail, but it was amazing to find so many of these tendrils lurking in regions that have previously been classified as empty," said Robotham. "This means that voids might be much smaller than we previously thought, and that galaxies that were previously thought to be in a void might just be part of a tendril," said Alpaslan. The GAMA team plan to catalogue more tendrils for further study as their detailed map of the Universe expands. Story Source: The above story is based on materials provided by International Centre for Radio Astronomy Research (ICRAR). Note: Materials may be edited for content and length. |