Largest Yellow Star Ever Found, 1300 Times The Sun's Diameter

Credit: ESO/Digitized Sky Survey 2

Using ESO's Very Large Telescope Interferometer (VLTI), Olivier Chesneau (Observatoire de la Côte d'Azur, Nice, France) and an international team of collaborators have found that the yellow hypergiant star HR 5171 A[1] is absolutely huge — 1300 times the diameter of the Sun and much bigger than was expected [2].  This makes it the largest yellow star known. It is also in the top ten of the largest stars known — 50% larger than the famous red supergiant Betelgeuse — and about one million times brighter than the Sun. HR 5171, the brightest star just below the centre of this wide-field image, is a yellow hypergiant, a very rare type of stars with only a dozen known in our galaxy. Its size is over 1,300 times that of the Sun -- one of the 10 largest stars found so far. Observations with ESO's Very Large Telescope Interferometer have shown that it is actually a double star, with the companion in contact with the main star. "The new observations also showed that this star has a very close binary partner, which was a real surprise," says Chesneau. "The two stars are so close that they touch and the whole system resembles a gigantic peanut." The astronomers made use of a technique called interferometry to combine the light collected from multipleindividual telescopes, effectively creating a giant telescope up to 140 metres in size. The new results prompted the team to thoroughly investigate older observations of the star spanning more than sixty years, to see how it had behaved in the past [3]. This artist’s impression shows the yellow hypergiant star HR 5171. This is a very rare type of star with only a dozen known in our galaxy. Its size is over 1300 times that of our Sun — one of the largest ten stars found so far. Observations with ESO’s Very Large Telescope Interferometer have shown that it is actually a double star, with the

Credit: ESO

companion in contact with the main star. Yellow hypergiants are very rare, with only a dozen or so known in our galaxy — the best-known example being Rho Cassiopeiae. They are among the biggest and brightest stars known and are at a stage of their lives when they are unstable and changing rapidly. Due to this instability, yellow hypergiants also expel material outwards, forming a large, extended atmosphere around the star. This artist’s animation shows the yellow hypergiant star HR 5171. This is a very rare type of star and only a dozen are known in our galaxy. Its size is over 1300 times that of the Sun — one of the ten biggest stars found so far. Observations with ESO’s Very Large Telescope Interferometer have shown

(Credit: ESO)

that it is actually a double star, with the companion in contact with the main star.Despite its great distance of nearly 12 000 light-years from Earth, the object can just about be seen with the naked eye [4] by the keen-sighted. HR 5171 A has been found to be getting bigger over the last 40 years, cooling as it grows, and its evolution has now been caught in action. Only a few stars are caught in this very brief phase, where they undergo a dramatic change in temperature as they rapidly evolve. By analysing data on the star's varying brightness, using observations from other observatories, the astronomers confirmed the object to be an eclipsing binary system where the smaller component passes in front and behind the larger one as it orbits. In this case HR 5171 A is orbited by its companion star every 1300 days. The smaller companion is only slightly hotter than HR 5171 A's surface temperature of 5000 degrees Celsius. Chesneau concludes "The companion we have found is very significantas it can have an influence on the fate of HR 5171 A, for example, stripping off its outer layers and modifying its evolution." This new discovery highlights the importance of studying these huge and short-lived yellow hypergiants, and could provide a means of understanding the evolutionary processes of massive stars in general. This zoom sequence takes us from a wide view of the spectacular southern Milky Way into a closeup view of one of its biggest and rarest stars — the yellow hypergiant star HR 5171. This monster stars has a radius over 1300 times that of the Sun — it is one of the largest ten stars found so far. Observations with ESO’s Very Large Telescope Interferometer have shown that it is actually a double star, with the companion in contact with the main star. Credit: ESO/Nick Risinger (skysurvey.org)/Digitized Sky Survey 2. Music: movetwo, Contacts and sources: Richard Hook, Source: Article

Read More........→September 26, 2014

Extreme Power of Black Hole Revealed

Astronomers have used NASA's Chandra X-ray Observatory and a suite of other telescopes to reveal one of the most powerful black holes known. The black hole has created enormous structures in the hot gas surrounding it and prevented trillions of stars from forming
The black hole is in a galaxy cluster named RX J1532.9+3021 (RX J1532 for short), located about 3.9 billion light years from Earth. The image here is a composite of X-ray data from Chandra revealing hot gas in the cluster in purple and optical data from the Hubble Space Telescope showing galaxies in yellow. The cluster is very bright in X-rays implying that it is extremely massive, with a mass about a quadrillion - a thousand trillion - times that of the sun. At the center of the cluster is a large elliptical galaxy containing the supermassive black hole. The large amount of hot gas near the center of the cluster presents a puzzle. Hot gas glowing with X-rays should cool, and the dense gas in the center of the cluster should cool the fastest. The pressure in this cool central gas is then expected to drop, causing gas further out to sink in towards the galaxy, forming trillions of stars along the way. However, astronomers have found no such evidence for this burst of stars forming at the center of this cluster. This problem has been noted in many galaxy clusters but RX J1532 is an extreme case, where the cooling of gas should be especially dramatic because of the high density of gas near

Artist's view of the Chandra X-ray Observatory

the center. Out of the thousands of clusters known to date, less than a dozen are as  extreme as RX J1532. The Phoenix Cluster is the most extreme, where, conversely, large numbers of stars have been observed to be forming. What is stopping large numbers of stars from forming in RX J1532? Images from the Chandra X-ray Observatory and the NSF's Karl G. Jansky Very Large Array (VLA) have provided an answer to this question. The X-ray image shows two large cavities in the hot gas on either side of the central galaxy. The Chandra image has been specially processed to emphasize the cavities. Both cavities are aligned with jets seen in radio images from the VLA. The location of the supermassive black hole between the cavities is strong evidence that the supersonic jets generated by the black hole have drilled into the hot gas and pushed it aside, forming the cavities. Shock fronts - akin to sonic booms - caused by the expanding cavities and the release of energy by sound waves reverberating through the hot gas provide a source of heat that prevents most of the gas from cooling and forming new stars. The cavities are each about 100,000 light years across, roughly equal to the width of the Milky Way galaxy. The power needed to generate them is among the largest known in galaxy clusters. For example, the power is almost 10 times greater than required to create the well-known cavities in Perseus. Although the energy to power the jets must have been generated by matter falling toward the black hole, no X-ray emission has been detected from infalling material. This result can be explained if the black hole is "ultramassive" rather than supermassive, with a mass more than 10 billion times that of the sun. Such a black hole should be able to produce powerful jets without consuming large amounts of mass, resulting in very little radiation from material falling inwards. Another possible explanation is that the black hole has a mass only about a billion times that of the sun but is spinning extremely rapidly. Such a black hole can produce more powerful jets than a slowly spinning black hole when consuming the same amount of matter. In both explanations the black hole is extremely massive. A more distant cavity is also seen at a different angle with respect to the jets, along a north-south direction. This cavity is likely to have been produced by a jet from a much older outburst from the black hole. This raises the question of why this cavity is no longer aligned with the jets. There are two possible explanations. Either large-scale motion of the gas in the cluster has pushed it to the side or the black hole is precessing, that is, wobbling like a spinning top. A paper describing this work was published in the November 10th, 2013 issue of The Astrophysical Journal and is available online (http://arxiv.org/abs/1306.0907). The first author is Julie Hlavacek-Larrondo from Stanford University. The Hubble data used in this analysis were from the Cluster Lensing and Supernova survey, led by Marc Postman from Space Telescope Science Institute: http://www.stsci.edu/~postman/CLASH/Home.html, NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Mass., controls Chandra's science and flight operations. For more information about Chandra X-ray Observatory, visit: http://www.nasa.gov/mission_pages/chandra/main/, Chandra on Flickr: http://www.flickr.com/photos/nasamarshall/sets/72157606205297786/, Images, Text, Credits: X-ray: NASA/CXC/Stanford/J.Hlavacek-Larrondo et al, Optical: NASA/ESA/STScI/M.Postman & CLASH team.Greetings, Orbiter.ch, Source: Orbiter.ch Space News

Read More........→March 19, 2014

‘Death Stars’ In Orion Blast Planets Before They Form

Credit: NRAO/AUI/NSF; B. Saxton

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. This artist's concept shows two proplyds, or protostars, around a massive O-type star. The nearer proplyd is having its planet-forming dust and gas blasted away by the radiation from the star. The farther proplyd is able to retain its planet-making potential. 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. Fly-in to the Orion Nebula where ALMA reveals massive stars blasting away planet-forming dust-gas around young protoplanetary disks. 

Narration: Dr. Rita K. Mann; Video and Images Courtesy of Brian Kent, NRAO/AUI/NSF; Model from Brian Abbot (AMNH/Hayden); Data from Hillenbrand, L., 1997, AJ, 113, 1733; Bill Saxton, NRAO/AUI/NSF; NASA/ESA, M. Robberto (Space Telescope Science Institute/ESA) and the Hubble Space Telscope Orion Treasury Project Team; NASA/ESA Hubble Space Telescope Bally et al.; Smith et al.; NASA, C.R. O'Dell and S.K. Wong (Rice University) 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 Hawaii, 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 Hawaii; 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. ALMA, an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA. Contacts and sources: Charles Blue, National Radio Astronomy Observatory, Source: Article

Read More........→March 16, 2014

Herschel Discovers Water Vapor Around Dwarf Planet Ceres

Dwarf planet Ceres is located in the main asteroid belt, between the orbits of Mars and Jupiter, as illustrated in this artist's conception. Observations by the Herschel space observatory between 2011 and 2013 find that the dwarf planet has a thin water vapor atmosphere. This is the first unambiguous detection of water vapor around anobject in the asteroid belt. Illustration credit: ESA/ATG medialab, Note: For more information, see PIA17831: Water Detection on Ceres, Herschel Telescope Detects Water on Dwarf Planet and Herschel Discovers Water Vapor Around Dwarf Planet Ceres. Source: Article

Read More........→January 25, 2014

Binary-Star Formation Theory Boosted By New Study

Credit: Bill Saxton, NRAO/AUI/NSF

Using the new capabilities of the upgraded Karl G. Jansky Very Large Array (VLA), scientists have discovered previously-unseen binary companions to a pair of very young protostars. The discovery gives strong support for one of the competing explanations for how double-star systems form. Astronomers know that about half of all Sun-like stars are members of double or multiple-star systems, but have debated over how such systems are formed. Binary star formation through disk fragmentation starts (left) with a young star surrounded by a rotating disk of gas and dust. The disk fragments under its own gravity, with a second star forming within the disk (center), surrounded by its own disk. At right, the two stars form an orbiting pair. 100 Astronomical Units (AU) is roughly the diameter of our Solar System. "The only way to resolve the debate is to observe very young stellar systems and catch them in the act of formation," said John Tobin, of the National Radio Astronomy Observatory (NRAO). "That's what we've done with the stars we observed, and we got valuable new clues from them," he added. Their new clues support the idea that double-star systems form when a disk of gas and dust whirling around one young star fragments, forming another new star in orbit with the first. Young stars that still are gathering matter from their surroundings form such disks, along with jet-like outflows rapidly propelling material in narrow beams perpendicular to the disk. When Tobin and an international team of astronomers studied gas-enshrouded young stars roughly 1,000 light-years from Earth, they found that two had previously-unseen companions in the plane where their disks would be expected, perpendicular to the direction of the outflows from the systems. One of the systems also clearly had a disk surrounding both young stars. "This fits the theoretical model of companions forming from fragmentation in the disk," Tobin said. "This configuration would not be required by alternative explanations," he added. The new observations add to a growing body of evidence supporting the disk-fragmentation idea. In 2006, a different VLA observing team found an orbiting pair of young stars, each of which was surrounded by a disk of material. The two disks, they found, were aligned with each other in the same plane. Last year, Tobin and his colleagues found a large circumstellar disk forming around a protostar in the initial phases of star formation. This showed that disks are present early in the star formation process, a necessity for binary pairs to form through disk fragmentation. "Our new findings, combined with the earlier data, make disk fragmentation the strongest explanation for how close multiple star systems are formed," said Leslie Looney of NRAO and the University of Illinois. "The increased sensitivity of the VLA, produced by a decade-long upgrade project completed in 2012, made the new discovery possible," Claire Chandler of NRAO said. The new capability was particularly valuable at the VLA's highest frequency band, from 40-50 GHz, where dust in the disks surrounding young stars emits radio waves. The astronomers observed the young stars during 2012 with the VLA and with the Combined Array for Research in Millimeter-wave Astronomy (CARMA) in California. Tobin, Chandler, and Looney were part of a research team of astronomers from the U.S., Mexico, and the Netherlands. The scientists published their findings in the Astrophysical Journal. Contacts and sources: Dave Finley, National Radio Astronomy Observatory, The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc. Source: Article

Read More........→January 07, 2014