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  • richardmitnick 1:14 pm on February 3, 2017 Permalink | Reply
    Tags: Asteroid 2010 TK7, , , Astronomy Now, ,   

    From Astronomy Now: “NASA’s OSIRIS-REx probe moonlights as asteroid sleuth” 

    Astronomy Now bloc

    Astronomy Now

    1 February 2017
    Stephen Clark

    NASA OSIRIS-REx Spacecraft
    NASA OSIRIS-REx Spacecraft

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    The OSIRIS-REx spacecraft will undertake a search for Earth-Trojan asteroids while on its outbound journey to the asteroid Bennu. Earth Trojans are asteroids that share an orbit with Earth while remaining near a stable point 60 degrees in front of or behind the planet. Credit: University of Arizona/Heather Roper

    On course to collect specimens from asteroid Bennu after its launch last year, NASA’s OSIRIS-REx spacecraft will search this month for objects sharing an orbit with Earth, a bonus science opportunity to locate possible fragments of the primordial building blocks that formed our home planet.

    The long-range observations begin Feb. 9 and run through Feb. 20, using one of the probe’s cameras to look for asteroids embedded in swarms scientists believe lurk ahead of and behind Earth in its orbit around the Sun.

    Named Earth-Trojans, the objects likely group in clouds at Sun-Earth Lagrange points, where the combined pull of gravity from the bodies would allow asteroids to orbit in lock-step with Earth. The so-called L4 and L5 Lagrange points lead and follow Earth by 60 degrees in its path around the Sun.

    LaGrange Points map. NASA
    LaGrange Points map. NASA

    The same positions in front of and behind Jupiter harbour thousands of Trojan asteroids, and smaller Trojan swarms have been discovered near Venus, Mars, Uranus and Neptune.

    It turns out OSIRIS-REx is about to pass through the Sun-Earth L4 Lagrange point, and managers decided to scan the region where Earth-Trojans might be located to see what the spacecraft can find.

    Now located nearly 74 million miles (119 million kilometres) from Earth, OSIRIS-REx is on a seven year-journey to asteroid Bennu and back, charged with gathering rock samples from the mountain-sized object and delivering them to scientists for examination inside laboratories on the ground.

    Since its launch Sept. 8, 2016, OSIRIS-REx has switched on all of its science instruments and performed a major course correction maneuver to aim for a flyby of Earth this Sept. 22. Earth’s gravity will slingshot the spacecraft toward Bennu.

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    A rendering of Bennu, the target asteroid of the UA-led OSIRIS-REx mission. Bringing back a sample from Bennu will help scientists better understand how the solar system, including Earth, was formed. No image credit.

    The Dec. 28 burn changed OSIRIS-REx’s speed by 964 mph (431 metres per second) and consumed a quarter of the probe’s propellant supply. The maneuver was the largest of the mission until the Lockheed Martin-built spacecraft’s arrival burn at Bennu in August 2018.

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    Artist’s concept of the OSIRIS-REx spacecraft’s deep space maneuver. Credit: NASA

    Another small “clean-up” thruster firing Jan. 18 further tweaked OSIRIS-REx’s trajectory, and the spacecraft switched over to its high-power antenna Jan. 25 to beam data back to Earth at faster rates.

    The milestones clear the way for the mission’s first science campaign next week.

    “The Earth-Trojan asteroid search provides a substantial advantage to the OSIRIS-REx mission,” said Dante Lauretta, OSIRIS-REx principal investigator from the University of Arizona in Tucson. “Not only do we have the opportunity to discover new members of an asteroid class, but more importantly, we are practicing critical mission operations in advance of our arrival at Bennu, which ultimately reduces mission risk.”

    Only one of the elusive Earth-Trojans has been detected to date.

    Astronomers using NASA’s WISE infrared telescope confirmed the discovery of an asteroid in 2011 that fit the definition of an Earth-Trojan.

    NASA/WISE Telescope
    NASA/WISE Telescope

    Asteroid 2010 TK7 is about 1,000 feet (300 metres) in diameter, and experts predict its extreme orbit, which takes it far above and below the plane of the planets, will be stable for at least the next several thousand years.

    3
    Scientists consider 2010 TK7 an outlier of a large group of asteroids sharing Earth’s orbit, some of which may have been there since the solar system formed more than 4.5 billion years ago.
    The University of Western Ontario and CFHT

    “The orbital motion of 2010 TK7 is chaotic and unstable on billion-year timescales, and it is unlikely to be a remnant from the formation of the Earth,” Lauretta wrote in a blog post describing the upcoming observing campaign. “The existence and size of a primordial population of Earth-Trojans (genuine remnants of the building blocks of our planet) are not well constrained and represents a significant gap in our inventory of small bodies in near-Earth space.”

    Earth-Trojans are difficult to find from the ground because they are usually in daylight, and the WISE spacecraft orbiting Earth detected 2010 TK7 because its unique orbit oscillates farther from the sun’s position in the sky than most members of the group.

    Current ground-based surveys are only sensitive to Earth-Trojan asteroids bigger than about 3,000 feet, or approximately 1 kilometre, said Carl Hergenrother, an OSIRIS-REx staff scientist at the University of Arizona.

    4
    This artist’s concept illustrates the first known Earth-Trojan asteroid, discovered by NEOWISE, the asteroid-hunting portion of NASA’s WISE mission. The asteroid is shown in gray and its extreme orbit is shown in green. Earth’s orbit around the sun is indicated by blue dots. The objects are not drawn to scale. Credit: Paul Wiegert, University of Western Ontario, Canada

    By mid-February, OSIRIS-REx will be “an ideal spot to undertake a survey,” Lauretta wrote.

    Between Feb. 9 and Feb. 20, the spacecraft’s mapping camera will take 145 pictures per day of the volume of space where Earth-Trojans are expected to reside, according to Lauretta.

    “It’s a big cloud, and there should be material there,” Hergenrother said at a Jan. 12 meeting of NASA’s Small Bodies Assessment Group. “We should be able to detect stuff down to 100 metres (330 feet), and possibly even smaller, depending on the performance of our cameas, and the albedo (reflectivity).

    “If we don’t find anything, it either means there’s a lot less objects out there than we were thinking, or they’re a lot smaller,” Hergenrother said.

    While Lauretta said there is a scientific motivation for the Earth-Trojan search, the top reason for the campaign is to practice techniques the OSIRIS-REx science team plans to employ once the spacecraft arrives at Bennu.

    On approach to Bennu, the probe’s cameras will look near the asteroid to hunt for tiny miniature moons as small as 4 inches (10 centimetres). Navigators want to know the location of any debris around Bennu to prevent a crash with the spacecraft.

    Jupiter and several large distant asteroids will be imaged by OSIRIS-REx’s camera when it scans for Earth-Trojans. The images will help the ground team rehearse the complex real-time in-space navigation the mission requires during the rendezvous with Bennu, along with the identification of moving targets mimicking the behaviour of potential mini-moons surrounding the asteroid.

    Although the scientific objectives are secondary, Lauretta said his team is excited about the prospect of making a discovery so early in the mission.

    “We’ll clearly be able to set an upper limit on what’s out there because we know what we could detect if it was there,” Lauretta said at the Jan. 12 science meeting.

    OSIRIS-REx could also discover an asteroid from another family that just happens to pass through the camera’s field-of-view, Lauretta said. But scientists will pin down the orbit of any object OSIRIS-REx detects, and an Earth-Trojan asteroid locked in a stable orbit could be evidence of a larger cloud of mini-worlds hidden from view.

    “Is this dynamically stable? Could it be a primordial Earth object?” Lauretta asked, posing questions scientists will have if OSIRIS-REx finds anything starting next week. “That would be the most fascinating thing that we could discover.”

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  • richardmitnick 10:50 am on November 8, 2016 Permalink | Reply
    Tags: , Astronomy Now, , , ,   

    From Astronomy Now: “Breakthrough Listen searches new-found nearby planet Proxima b for signs of ET” 

    Astronomy Now bloc

    Astronomy Now

    8 November 2016
    No writer credit found

    1
    The 64-metre-wide Parkes Radio Telescope in New South Wales, Australia is affectionately known as “The Dish.” It played an iconic role in receiving the first deliberate transmissions from the surface of another world, as the astronauts of Apollo 11 set foot on our Moon. Now, Parkes joins once again in expanding human horizons as we search for the answer to one of our oldest questions: Are we alone? Image credit: Parkes Radio Telescope © 2005 Shaun Amy.

    Breakthrough Listen, the 10-year, $100-million astronomical search for intelligent life beyond Earth launched in 2015 by Internet entrepreneur Yuri Milner and Stephen Hawking, today announced its first observations using the Parkes Radio Telescope in New South Wales, Australia.

    Parkes joins the Green Bank Telescope (GBT) in West Virginia, USA, and the Automated Planet Finder (APF) at Lick Observatory in California, USA, in their ongoing surveys to determine whether civilisations elsewhere have developed technologies similar to our own.

    gbo-logo
    GBO radio telescope, West Virginia, USA
    GBO radio telescope, West Virginia, USA

    Lick Automated Planet Finder telescope, Mount Hamilton, CA, USA
    Lick Automated Planet Finder telescope, Mount Hamilton, CA, USA

    Parkes radio telescope is part of the Australia Telescope National Facility, owned and managed by Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO).

    Drawing on over nine months of experience in operation of the dedicated Breakthrough Listen instrument at GBT, a team of scientists and engineers from the University of California, Berkeley’s SETI Research Center (BSRC) deployed similar hardware at Parkes, bringing Breakthrough Listen’s unprecedented search tools to a wide range of sky inaccessible from the GBT. The Southern Hemisphere sky is rich with targets, including the centre of our own Milky Way galaxy, large swaths of the galactic plane, and numerous other galaxies in the nearby universe.

    “The Dish” at Parkes played an iconic role in receiving the first deliberate transmissions from the surface of another world, as the astronauts of Apollo 11 set foot on our Moon. Now, Parkes joins once again in expanding human horizons as we search for the answer to one of our oldest questions: Are we alone?

    “The Parkes Radio Telescope is a superb instrument, with a rich history,” said Pete Worden, Chairman of Breakthrough Prize Foundation and Executive Director of the Breakthrough Initiatives. “We’re very pleased to be collaborating with CSIRO to take Listen to the next level.”

    With its new combined all-sky range, superb telescope sensitivity and computing capacity, Breakthrough Listen is the most powerful, comprehensive, and intensive scientific search ever undertaken for signs of intelligent life beyond Earth.

    Moreover, this expansion of Breakthrough Listen’s range follows the announcement on 12 October that it will be joining forces with the new FAST telescope — the world’s largest filled-aperture radio receiver — to coordinate their searches for artificial signals. The two programs will exchange observing plans, search methods and data, including the rapid sharing of promising new signals for additional observation and analysis. The partnership represents a major step toward establishing a fully connected, global search for intelligent life in the universe.

    “The addition of Parkes is an important milestone,” said Yuri Milner, founder of the Breakthrough Initiatives, which include Breakthrough Listen. “These major instruments are the ears of planet Earth, and now they are listening for signs of other civilisations.”

    First light focused on exo-Earth

    After 14 days of commissioning and test observations, first light for Breakthrough Listen at Parkes was achieved on 7 November, with an observation of the newly-discovered Earth-size planet orbiting the nearest star to the Sun. Proxima Centauri, a red dwarf star 4.2 light-years from Earth, is now known to have a planet (“Proxima b”) within its habitable zone — the region where water could exist in liquid form on the planet’s surface. Such “exo-Earths” (habitable zone exoplanets) are among the primary targets for Breakthrough Listen.

    Centauris Alpha Beta Proxima 27, February 2012. Skatebiker
    Centauris Alpha Beta Proxima 27, February 2012. Skatebiker

    “The chances of any particular planet hosting intelligent life-forms are probably minuscule,” said Andrew Siemion, director of UC Berkeley SETI Research Center. “But once we knew there was a planet right next door, we had to ask the question, and it was a fitting first observation for Parkes. To find a civilisation just 4.2 light-years away would change everything.”

    As the closest known exoplanet, Proxima b is also the current primary target for Breakthrough Listen’s sister initiative, Breakthrough Starshot, which is developing the technology to send gram-scale spacecraft to the nearest stars.

    “Parkes is one of the most highly cited radio telescopes in the world, with a long list of achievements to its credit, including the discovery of the first ‘fast radio burst.’ Parkes’ unique view of the southern sky, and cutting-edge instrumentation, means we have a great opportunity to contribute to the search for extra-terrestrial life,” said Douglas Bock, Director of CSIRO Astronomy and Space Science.

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  • richardmitnick 9:18 am on November 6, 2016 Permalink | Reply
    Tags: , Astronomy Now, , , Very Long Baseline Array (VLBA)   

    From Astronomy Now: “Galactic merger exposes supermassive black hole” 

    Astronomy Now bloc

    Astronomy Now

    4 November 2016
    No writer credit found

    1
    This NASA/ESA Hubble Space Telescope image of galaxy cluster ZwCl 8193 reveals the core of the giant galaxy 2MASX 17171926+4226571, the smaller galaxy and a trail of debris. The position of the giant galaxy’s core is marked by the white ‘+’ and optical identification of B3 1715+425 is enclosed by a white circle centred on its Hubble position. Image credit: J.J. Condon et al. / NASA / ESA / Hubble / NSF / VLBA.

    Astronomers using the super-sharp radio vision of the National Science Foundation’s Very Long Baseline Array (VLBA) have found the shredded remains of a galaxy that passed through a larger galaxy, leaving only the smaller galaxy’s nearly-naked supermassive black hole to emerge and speed away at more than 2,000 miles per second.

    NRAO VLBA
    NRAO/VLBA

    The galaxies are part of a cluster of galaxies more than 2 billion light-years from Earth. The close encounter, millions of years ago, stripped the smaller galaxy of nearly all its stars and gas. What remains is its black hole and a small galactic remnant only about 3,000 light-years across. For comparison, our Milky Way Galaxy is approximately 100,000 light-years across.

    The discovery was made as part of a program to detect supermassive black holes, millions or billions of times more massive than the Sun, that are not at the centres of galaxies. Supermassive black holes reside at the centres of most galaxies.

    Sag A*  NASA Chandra X-Ray Observatory 23 July 2014, the supermassive black hole at the center of the Milky Way
    Sag A* NASA Chandra X-Ray Observatory 23 July 2014, the supermassive black hole at the center of the Milky Way

    Large galaxies are thought to grow by devouring smaller companions. In such cases, the black holes of both are expected to orbit each other, eventually merging.

    “We were looking for orbiting pairs of supermassive black holes, with one offset from the centre of a galaxy, as telltale evidence of a previous galaxy merger,” said James Condon, of the National Radio Astronomy Observatory. “Instead, we found this black hole fleeing from the larger galaxy and leaving a trail of debris behind it,” he added.

    “We’ve not seen anything like this before,” Condon said.

    The astronomers began their quest by using the VLBA to make very high-resolution images of more than 1,200 galaxies, previously identified by large-scale sky surveys done with infrared and radio telescopes. Their VLBA observations showed that the supermassive black holes of nearly all these galaxies were at the centres of the galaxies.

    However, one object, in a cluster of galaxies called ZwCl 8193, did not fit that pattern. Further studies showed that this object, called B3 1715+425, is a supermassive black hole surrounded by a galaxy much smaller and fainter than would be expected. In addition, this object is speeding away from the core of a much larger galaxy, leaving a wake of ionised gas behind it.

    The scientists concluded that B3 1715+425 is what has remained of a galaxy that passed through the larger galaxy and had most of its stars and gas stripped away by the encounter — a “nearly naked” supermassive black hole.

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    Depiction on B3 1715+425

    The speeding remnant, the scientists said, probably will lose more mass and cease forming new stars.

    “In a billion years or so, it probably will be invisible,” Condon said. That means, he pointed out, that there could be many more such objects left over from earlier galactic encounters that astronomers can’t detect.

    The scientists will keep looking, however. They’re observing more objects, in a long-term project with the VLBA. Since their project is not time-critical, Condon explained, they use “filler time” when the telescope is not in use for other observations.

    “The data we get from the VLBA is very high quality. We get the positions of the supermassive black holes to extremely good precision. Our limiting factor is the precision of the galaxy positions seen at other wavelengths that we use for comparison,” Condon said. With new optical telescopes that will come on line in future years, such as the Large Synoptic Survey Telescope (LSST), he said, they will then have improved images that can be compared with the VLBA images.

    LSST/Camera, built at SLAC
    LSST/Camera, built at SLAC
    LSST Interior
    LSST telescope, currently under construction at Cerro Pachón Chile
    LSST telescope, currently under construction at Cerro Pachón Chile

    They hope that this will allow them to discover more objects like B3 1714+425.

    “And also maybe some of the binary supermassive black holes we originally sought,” he said.

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  • richardmitnick 2:33 pm on September 20, 2016 Permalink | Reply
    Tags: , Astronomy Now, , Researchers now know why some minor planets have rings   

    From Astronomy Now: “Origin of minor planets’ rings revealed” 

    Astronomy Now bloc

    Astronomy Now

    19 September 2016
    No writer credit found

    1
    Chariklo is currently the largest known centaur, with an estimated diameter of about 250 kilometres (160 miles). It is a minor planet (possibly a dwarf planet) orbiting the Sun between Saturn and Uranus, grazing the latter’s orbit. Chiron is likely to be the second largest centaur with a diameter of 220 kilometres (140 miles). In 2014, stellar occultation observations revealed that rings exist around Chariklo. Soon after this, scientists discovered that rings likely exist around Chiron, but the origin of the rings around these minor planets remained a mystery. This artist’s impression shows a close-up of what the rings around Chariklo might look like. Image credit: ESO/L. Calçada/M. Kornmesser/Nick Risinger.

    A team of researchers has clarified the origin of the rings recently discovered around two minor planets known as centaurs, and their results suggest the existence of rings around other centaurs. These findings were published on 29 August in Astrophysical Journal Letters.

    The lead author of the paper is Ryuki Hyodo (Kobe University Department of Planetology, Graduate School of Science), and co-authors are Professor Sébastien Charnoz (Institute de Physique du Globe/Université Paris Diderot), Project Associate Professor Hidenori Genda (Earth-Life Science Institute, Tokyo Institute of Technology), and Professor Keiji Ohtsuki (Kobe University Department of Planetology, Graduate School of Science).

    Centaurs are minor planets that orbit between Jupiter and Neptune, their current or past orbits crossing those of the giant planets. It is estimated that there are around 44,000 centaurs with diameters larger than one kilometre.

    Until recently it was thought that the four giants such as Saturn and Jupiter were the only ringed celestial bodies within our solar system. However, in 2014 observations of stellar occultation (an event that occurs when light from a star is blocked from the observer by a celestial body) by multiple telescopes revealed that rings exist around the centaur 10199 Chariklo. Soon after this, scientists discovered that rings likely exist around another centaur, 2060 Chiron, but the origin of the rings around these minor planets remained a mystery.

    The team began by estimating the probability that these centaurs passed close enough to the giant planets to be destroyed by their tidal pull. Their results showed that approximately 10 percent of centaurs would experience that level of close encounter. Next, they used computer simulations to investigate the disruption caused by tidal pull when the centaurs passed close by the giant planets. The outcome of such encounters was found to vary depending on parameters such as the initial spin of the passing centaur, the size of its core, and the distance of its closest approach to a giant planet. They found that if the passing centaur is differentiated and has a silicate core covered by an icy mantle, fragments of the partially-destroyed centaur will often spread out around the largest remnant body in a disc shape, from which rings are expected to form.

    The results of their simulations suggest that the existence of rings around centaurs would be much more common than previously thought. It is highly likely that other centaurs with rings and/or small moons exist, awaiting discovery by future observations.

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  • richardmitnick 11:09 am on August 7, 2016 Permalink | Reply
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    From Astronomy Now: “Do black holes have a back door?” 

    Astronomy Now bloc

    Astronomy Now

    6 August 2016
    No writer credit found

    1
    In the 2014 science fiction film Interstellar, a group of astronauts traverse a wormhole near a black hole called Gargantua. A recent study by researchers at the Institute of Corpuscular Physics in Valencia suggests that matter might indeed survive its foray into these space objects and come out the other side. Illustration: A realistic accretion disc gravitationally lensed by a rotating black hole. Credit: Double Negative artists/DNGR/TM & © Warner Bros. Entertainment Inc./ Creative Commons (CC BY-NC-ND 3.0) license.

    One of the biggest problems when studying black holes is that the laws of physics as we know them cease to apply in their deepest regions. Large quantities of matter and energy concentrate in an infinitely small space, the gravitational singularity, where space-time curves towards infinity and all matter is destroyed. Or is it?

    A recent study by researchers at the Institute of Corpuscular Physics (IFIC, CSIC-UV) in Valencia suggests that matter might in fact survive its foray into these space objects and come out the other side.

    Published in the journal Classical and Quantum Gravity, the Valencian physicists propose considering the singularity as if it were an imperfection in the geometric structure of space-time. And by doing so they resolve the problem of the infinite, space-deforming gravitational pull.

    “Black holes are a theoretical laboratory for trying out new ideas about gravity,” says Gonzalo Olmo, a Ramón y Cajal grant researcher at the Universitat de València (University of Valencia, UV). Alongside Diego Rubiera, from the University of Lisbon, and Antonio Sánchez, PhD student also at the UV, Olmo’s research sees him analysing black holes using theories besides general relativity (GR).

    Specifically, in this work he has applied geometric structures similar to those of a crystal or graphene layer, not typically used to describe black holes, since these geometries better match what happens inside a black hole: “Just as crystals have imperfections in their microscopic structure, the central region of a black hole can be interpreted as an anomaly in spacetime, which requires new geometric elements in order to be able to describe them more precisely. We explored all possible options, taking inspiration from facts observed in nature.”

    Using these new geometries, the researchers obtained a description of black holes whereby the centre point becomes a very small spherical surface. This surface is interpreted as the existence of a wormhole within the black hole. “Our theory naturally resolves several problems in the interpretation of electrically-charged black holes,” Olmo explains. “In the first instance we resolve the problem of the singularity, since there is a door at the centre of the black hole, the wormhole, through which space and time can continue.”

    This study is based on one of the simplest known types of black hole, rotationless and electrically-charged. The wormhole predicted by the equations is smaller than an atomic nucleus, but gets bigger the bigger the charge stored in the black hole. So, a hypothetical traveller entering a black hole of this kind would be stretched to the extreme, or “spaghettified,” and would be able to enter the wormhole. Upon exiting they would be compacted back to their normal size.

    Seen from outside, these forces of stretching and compaction would seem infinite, but the traveller himself, living it first-hand, would experience only extremely intense, and not infinite, forces. It is unlikely that the star of Interstellar would survive a journey like this, but the model proposed by IFIC researchers posits that matter would not be lost inside the singularity, but rather would be expelled out the other side through the wormhole at its centre to another region of the universe.

    Another problem that this interpretation resolves, according to Olmo, is the need to use exotic energy sources to generate wormholes. In Einstein’s theory of gravity, these “doors” only appear in the presence of matter with unusual properties (a negative energy pressure or density), something which has never been observed. “In our theory, the wormhole appears out of ordinary matter and energy, such as an electric field” (Olmo).

    The interest in wormholes for theoretical physics goes beyond generating tunnels or doors in spacetime to connect two points in the universe. They would also help explain phenomena such as quantum entanglement or the nature of elementary particles. Thanks to this new interpretation, the existence of these objects could be closer to science than fiction.

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  • richardmitnick 3:59 pm on August 2, 2016 Permalink | Reply
    Tags: , Astronomy Now, , MIlky Way voids   

    From Astronomy Now: “A giant stellar void in the Milky Way” 

    Astronomy Now bloc

    Astronomy Now

    2 August 2016
    No writer credit found

    Milky Way NASA/JPL-Caltech /ESO R. Hurt
    Milky Way NASA/JPL-Caltech /ESO R. Hurt

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    An artist’s impression of the implied distribution of young stars, represented here by Cepheids shown as blue stars, plotted on the background of a drawing of the Milky Way. With the exception of a small clump in the galactic centre, the central 8,000 light-years appear to have very few Cepheids, and hence very few young stars. Illustration credit: University of Tokyo.

    A major revision is required in our understanding of our Milky Way Galaxy according to an international team led by Prof. Noriyuki Matsunaga of the University of Tokyo. The Japanese, South African and Italian astronomers find that there is a huge region around the centre of our own galaxy which is devoid of young stars. The team publish their work in a paper in Monthly Notices of the Royal Astronomical Society.

    The Milky Way is a spiral galaxy containing many billions of stars, with our Sun about 26,000 light-years from its centre. Measuring the distribution of these stars is crucial to our understanding of how our galaxy formed and evolved. Pulsating stars called Cepheids are ideal for this. They are much younger (between 10 and 300 million years old) than our Sun (4.6 billion years old) and they pulsate in brightness in a regular cycle. The length of this cycle is related to the luminosity of the Cepheid, so if astronomers monitor them they can establish how bright the star really is, compare it with what we see from Earth, and work out its distance.

    2
    An artist’s illustration of the Milky Way, the galaxy we live in, showing the locations of the newly discovered Cepheid stars marked by yellow dots. The previously known objects, located around the Sun (marked by a red cross), are indicated by small white dots. The central green circle around the core of the galaxy marks the location of the ‘Cepheid desert.’ Illustration credit: University of Tokyo.

    Despite this, finding Cepheids in the inner Milky Way is difficult, as the galaxy is full of interstellar dust which blocks out light and hides many stars from view. Matsunaga’s team compensated for this, with an analysis of near-infrared observations made with the IRSF 1.4-metre Japanese-South African telescope located at Sutherland, South Africa. To their surprise they found hardly any Cepheids in a huge region stretching for thousands of light-years from the core of the galaxy.

    Noriyuki Matsunaga explains: “We already found some time ago that there are Cepheids in the central heart of our Milky Way (in a region about 150 light-years in radius). Now we find that outside this there is a huge Cepheid desert extending out to 8,000 light-years from the centre.”

    This suggests that a large part of our galaxy, called the extreme inner disc, has no young stars. Co-author Michael Feast notes: “Our conclusions are contrary to other recent work, but in line with the work of radio astronomers who see no new stars being born in this desert.”

    Another author, Giuseppe Bono, points out: “The current results indicate that there has been no significant star formation in this large region over hundreds of millions years. The movement and the chemical composition of the new Cepheids are helping us to better understand the formation and evolution of the Milky Way.”

    Cepheids have more typically been used to measure the distances of objects in the distant universe, and the new work is an example instead of the same technique revealing the structure of our own Milky Way.

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  • richardmitnick 10:11 am on May 1, 2016 Permalink | Reply
    Tags: , Astronomy Now, , NGC 339   

    From Astronomy Now: “Hubble sees a glittering sphere of stars in the Small Magellanic Cloud” 

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    Astronomy Now

    25 April 2016

    1
    DSS image of region near globular cluster NGC 339, in the Small Magellanic Cloud

    This NASA/ESA Hubble Space Telescope image reveals the simple beauty of NGC 339, a massive intermediate age star cluster in the southern constellation of Tucana (The Toucan).

    NASA/ESA Hubble Telescope
    NASA/ESA Hubble Telescope

    NGC 339 is part of the Small Magellanic Cloud (SMC), a dwarf galaxy that lies around 200,000 light-years away from us.

    Small Magellanic Cloud. NASA/ESA Hubble and Digitized Sky Survey 2
    Small Magellanic Cloud. NASA/ESA Hubble and ESO/Digitized Sky Survey 2

    Along with our own galaxy, the Milky Way, the SMC is one of a collection of neighbouring galaxies known as the Local Group.

    Local Group. Andrew Z. Colvin 3 March 2011
    Local Group. Andrew Z. Colvin 3 March 2011

    By measuring the brightnesses and colours of the stars of NGC 339, astronomers were able to estimate the overall age of the cluster — a method that places NGC 339 at around 6.5 billion years old. This makes it only half the age of the more common globular clusters. The relationship between massive intermediate age star clusters, such as NGC 339, and the true globular clusters is not yet fully understood. So far, none of these type of clusters has been found in the Milky Way.

    In this very detailed image, it is also possible to see a number of galaxies. They appear as fuzzy, extended blobs, contrasting with the sharp stars that make up NGC 339. Most obvious here are two elliptical galaxies, one towards the top left of the image and another in the centre right. These galaxies are not associated with NGC 339 but lie far in the background, across the vast expanse of the cosmos.

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  • richardmitnick 9:42 am on April 7, 2016 Permalink | Reply
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    From Astronomy Now: “The ‘topsy turvy’ ocean circulation of saline exoplanets” 

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    Astronomy Now

    5 April 2016
    No writer credit found

    1
    An artist’s impression of an ocean-bearing super-Earth. Image credit: NASA / Ames / JPL-Caltech.

    The salt levels of oceans on distant Earth-like planets could have a major effect on their climates — according to new research from the Centre for Ocean and Atmospheric Sciences at the University of East Anglia.

    A study just published reveals that the circulation in extremely salty or fresh water extra-terrestrial seas would influence their temperatures — and could in fact make for more habitable conditions for alien life.

    Until recently, computer simulations of habitable climates on Earth-like planets have mainly focused on their atmospheres. But studying their oceans is vital for understanding climate stability and habitability — as on our own Earth.

    Not only this, but until now, researchers had not considered that the seas on distant Earth-like planets might not be quite like ours — they might be significantly more or less salty than the oceans on Earth.

    Prof. David Stevens, from UEA’s School of Mathematics, said: “The number of planets being discovered outside our solar system is rapidly increasing. Our research helps to answer whether or not these planets could sustain alien life.

    “We think that many planets may be uninhabitable because they are either too close or too far from their sun. A planet’s habitable zone is based on its distance from the sun and temperatures at which it is possible for the planet to have liquid water.

    “Oceans play a vital role in sustaining life and also have an immense capacity to control climate. But previous studies on ocean circulation on other planets have made the assumption that fundamental ocean properties — such as the salinity and depth of water — would be similar to that on Earth.

    “We wanted to find out what might be happening on other planets which might appear superficially similar to Earth, but where conditions such as salinity are radically different to our own planet.”

    The research team used computer models of ocean circulation on exoplanets to see what would happen when their oceans had different salinity levels to Earth. They considered oceans with very low salinity (similar to freshwater), salinity similar to the average value of Earth’s oceans, and high salinity (similar levels to the Dead Sea).

    Dr. Manoj Joshi, from UEA’s School of Environmental Sciences, said: “On Earth, we have a circulation where warm water moves towards the poles at the surface, before being cooled, then sinking at high latitudes and travelling towards the equator at depth.

    “Our research shows that oceans on other planets with a much higher salinity could circulate in the opposite direction — with polar water flowing towards the equator at the surface, sinking in the tropics and travelling back towards the poles at depth. We also found a similar pattern emerging for freshwater oceans.

    “These circulation patterns are the opposite of what happens on Earth, and would result in a dramatic warming in the polar regions.

    “Such a circulation scenario might extend the planet’s range of habitability.”

    Jodie Cullum, from UEA’s School of Mathematics, said: “Of course, on any given exoplanet, many other properties are likely to differ from their Earth-like values, some of which may also have a significant influence on ocean circulation — such as tidal forces, planetary rotation, ocean depth and the location of continents.

    “But this is important work which will help us better-understand the habitability of distant planets in more accurate detail than ever before.”

    Science paper
    Importance of ocean salinity for climate and habitability
    Science team
    Jodie Cullum,a,b,1, David P. Stevensa,b, and Manoj M. Joshia,c

    Author Affiliations
    a Centre for Ocean and Atmospheric Sciences, University of East Anglia, Norfolk NR4 7TJ, United Kingdom;
    b School of Mathematics, University of East Anglia, Norfolk NR4 7TJ, United Kingdom;
    c School of Environmental Sciences, University of East Anglia, Norfolk NR4 7TJ, United Kingdom

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  • richardmitnick 7:57 am on March 26, 2016 Permalink | Reply
    Tags: , Astronomy Now, , ,   

    From Astronomy Now: “Magnetar could have boosted explosion of extremely bright supernova” 

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    Astronomy Now

    25 March 2016
    No writer credit found

    1
    Artist’s impression of a magnetar boosting a super-luminous supernova and gamma-ray burst. Image credit: Kavli IPMU.

    Calculations by scientists have found highly magnetised, rapidly spinning neutron stars called magnetars could explain the energy source behind two extremely unusual stellar explosions.

    Stellar explosions known as supernovae usually shine a billion times brighter than the Sun. Super-luminous supernovae [hypernovae] (SLSNe) are a relatively new and rare class of stellar explosions, 10 to 100 times brighter than normal supernovae. But the energy source of their super-luminosity, and explosion mechanisms are a mystery and remain controversial amongst scientists.

    A group of researchers led by Melina Bersten, an Instituto de Astrofisica de La Plata researcher and affiliate member of Kavli IPMU, and including Kavli IPMU Principal Investigator Ken’ichi Nomoto, tested a model that suggests that the energy to power the luminosity of two recently discovered SLSNe, SN 2011kl and ASASSN-15lh, is mainly due to the rotational energy lost by a newly born magnetar.

    “These supernovae can be found in very distant universe, thus possibly informing us the properties of the first stars of the universe,” said Nomoto.

    2
    The yellow-orange host galaxy (left) before the supernova, and afterwards (right) when the ASASSN-15lh supernova’s blue light outshines its host galaxy. Image credit: The Dark Energy Survey / B. Shappee / ASAS-SN team.

    Dark Energy Icon
    Dark Energy Camera. Built at FNAL
    NOAO/CTIO Victor M Blanco 4m Telescope
    Dark Energy Survey, Dark Energy Camera. Built at FNAL, NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam

    Interestingly, both explosions were found to be extreme cases of SLSNe. First, SN 2011kl was discovered in 2011 and is the first supernovae to have an ultra long gamma-ray burst that lasted several hours, whereas typical long-duration gamma-ray bursts fade in a matter of minutes. The second, ASASSN-15lh, was discovered in 2015 and is possibly the most luminous and powerful explosion ever seen, more than 500 times brighter than normal supernovae. For more than a month its luminosity was 20 times brighter than the whole Milky Way galaxy.

    The team performed numerical hydrodynamical calculations to explore the magnetar hypothesis, and found both SLSNe could be understood in the framework of magnetar-powered supernovae. In particular, for ASASSN-15lh, they were able to find a magnetar source with physically allowed properties of magnetic field strength and rotation period. The solution avoided the prohibited realm of neutron star spins that would cause the object to breakup due to centrifugal forces.

    3
    Light curves of ASASSN-15lh and SN 2011kl compared with normal supernovae SN 1999em and SN 1987A. Image credit: Bersten et al.

    “These two extreme super-luminous supernovae put to the test our knowledge of stellar explosions,” said Bersten.

    To confirm the team’s calculations, further observations would need to be carried out when the material ejected by the supernova is expected to become thin. The most powerful telescopes, including the NASA/ESA Hubble Space Telescope, will be required for this purpose. If correct, these observations will allow scientists to probe the inner part of an exploding object, and provide new insight on its origin, and evolution of stars in the Universe.

    NASA/ESA Hubble Telescope
    NASA/ESA Hubble Telescope

    The group’s paper was recently published in The Astrophysical Journal Letters.

    Science team:
    Melina C. Bersten, Omar G. Benvenuto, Mariana Orellana, and Ken’ichi Nomoto

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  • richardmitnick 7:33 am on March 26, 2016 Permalink | Reply
    Tags: A new way to determine the age of stars?, , Astronomy Now,   

    From Astronomy Now: “A new way to determine the age of stars?” 

    Astronomy Now bloc

    Astronomy Now

    24 March 2016
    No writer credit found

    Globular star cluster Terzan 1, taken by Hubble. Image credit: NASA & ESA
    Globular star cluster Terzan 1, taken by Hubble. Image credit: NASA & ESA

    NASA/ESA Hubble Telescope
    NASA/ESA Hubble Telescope

    Researchers have developed a new conceptual framework for understanding how stars similar to our Sun evolve. Their framework helps explain how the rotation of stars, their emission of X-rays, and the intensity of their stellar winds vary with time. According to first author Eric Blackman, professor of physics and astronomy at the University of Rochester, the work could also “ultimately help to determine the age of stars more precisely than is currently possible.”

    In a paper published today in Monthly Notices of the Royal Astronomical Society, the researchers describe how they have corroborated known, observable data for the activity of Sun-like stars with fundamental astrophysics theory. By looking at the physics behind the speeding up or slowing down of a star’s rotation, its X-ray activity, and magnetic field generation, Blackman says the research is a “first attempt to build a comprehensive model for the activity evolution of these stars.”

    Using our Sun as the calibration point, the model most accurately describes the likely behaviour of the Sun in the past, and how it would be expected to behave in the future. But Blackman adds that there are many stars of similar mass and radius, and so the model is a good starting point for predictions for these stars.

    “Our model shows that stars younger than our Sun can vary quite significantly in the intensity of their X-ray emission and mass loss,” said Blackman. “But there is a convergence in the activity of the stars after a certain age, so you could say that our Sun is very typical for stars of its mass, radius, and its age. They get more predictable as they age.”

    “We’re not yet at the point where we can accurately predict a star’s precise age, because there are simplifying assumptions that go into the model,” said Blackman. “But in principle, by extending the work to relax some of these assumptions we could predict the age of for a wide range of stars based on their X-ray luminosity.”

    At the moment, empirically determining the age of stars is most easily accomplished if a star is among a cluster of stars, from whose mutual properties astronomers can estimate the age. Blackman explains that its age can then be estimated “to an accuracy not better than a factor of 25 percent of its actual age, which is typically billions of years.” The problem is worse for “field stars,” alone in space such that the cluster method of dating cannot be used. For these stars, astronomers have turned to gyrochronology and “activity” ageing — empirically ageing the stars based the fact that older stars of known age rotate more slowly and have lower X-ray luminosities than younger stars.

    “Over the past few decades astronomers have been able to empirically measure these trends in rotation and magnetic activity for stars like the Sun, but Eric and his collaborators are trying to devise a comprehensive theoretical interpretation,” said Eric Mamajek, professor of physics and astronomy at the University of Rochester and one of the astronomers leading the development of empirical methods for determining a tar’s age. “Ultimately this should lead to improved constraints on the evolution of rotation and activity in Sun-like stars, and better constraints on how the magnetic properties of our Sun have changed over the course of its main sequence life.”

    And this is where the model developed by Blackman and his coauthor James E. Owen is important: it provides a physics explanation for how stellar rotation, activity, magnetic field, and mass loss all mutually evolve with age.

    “Only by tackling the entire problem of how stellar rotation, X-ray activity, magnetic field and mass-loss mutually affect each other could we build a complete picture,” said Owen, a NASA Hubble fellow at the Institute for Advanced Study, Princeton. “We find these processes to be strongly intertwined, and the majority of previous approaches had only considered the evolution of one or two processes together, not the complete problem.”

    See the full article here .

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