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  • richardmitnick 2:22 pm on May 12, 2018 Permalink | Reply
    Tags: , , , , , , Harvard Smithsonian Center for Astrophysics, ,   

    From Harvard-Smithsonian Center for Astrophysics via EarthSky: “What’s a safe distance between us and a supernova?” 

    Harvard Smithsonian Center for Astrophysics


    From Harvard-Smithsonian Center for Astrophysics

    EarthSky

    May 11, 2018

    And how many potentially exploding stars are located within the unsafe distance?

    A supernova is a star explosion – destructive on a scale almost beyond human imagining. If our sun exploded as a supernova, the resulting shock wave probably wouldn’t destroy the whole Earth, but the side of Earth facing the sun would boil away. Scientists estimate that the planet as a whole would increase in temperature to roughly 15 times hotter than our normal sun’s surface. What’s more, Earth wouldn’t stay put in orbit. The sudden decrease in the sun’s mass might free the planet to wander off into space. Clearly, the sun’s distance – 8 light-minutes away – isn’t safe. Fortunately, our sun isn’t the sort of star destined to explode as a supernova. But other stars, beyond our solar system, will. What is the closest safe distance? Scientific literature cites 50 to 100 light-years as the closest safe distance between Earth and a supernova.

    2
    Image of remnant of SN 1987A as seen at optical wavelengths with the Hubble Space Telescope in 2011.

    NASA/ESA Hubble Telescope

    This supernova was the closest in centuries, and it was visible to the eye alone. It was located on the outskirts of the Tarantula Nebula in the Large Magellanic Cloud, a satellite galaxy to our Milky Way. It was located approximately 168,000 light-years from Earth. Image via NASA, ESA, and P. Challis (Harvard-Smithsonian Center for Astrophysics).

    What would happen if a supernova exploded near Earth? Let’s consider the explosion of a star besides our sun, but still at an unsafe distance. Say, the supernova is 30 light-years away. Dr. Mark Reid, a senior astronomer at the Harvard-Smithsonian Center for Astrophysics, has said:

    “… were a supernova to go off within about 30 light-years of us, that would lead to major effects on the Earth, possibly mass extinctions. X-rays and more energetic gamma-rays from the supernova could destroy the ozone layer that protects us from solar ultraviolet rays. It also could ionize nitrogen and oxygen in the atmosphere, leading to the formation of large amounts of smog-like nitrous oxide in the atmosphere.”

    What’s more, if a supernova exploded within 30 light-years, phytoplankton and reef communities would be particularly affected. Such an event would severely deplete the base of the ocean food chain.

    Suppose the explosion were slightly more distant. An explosion of a nearby star might leave Earth and its surface and ocean life relatively intact. But any relatively nearby explosion would still shower us with gamma rays and other high-energy radiation. This radiation could cause mutations in earthly life. Also, the radiation from a nearby supernova could change our climate.

    No supernova has been known to erupt at this close distance in the known history of humankind. The most recent supernova visible to the eye was Supernova 1987A, in the year 1987. It was approximately 168,000 light-years away.

    Before that, the last supernova visible to the eye was was documented by Johannes Kepler in 1604. At about 20,000 light-years, it shone more brightly than any star in the night sky. It was even visible in daylight! But it didn’t cause earthly effects, as far as we know.

    How many potential supernovae are located closer to us than 50 to 100 light-years? The answer depends on the kind of supernova.

    A Type II supernova is an aging massive star that collapses. There are no stars massive enough to do this located within 50 light-years of Earth.

    But there are also Type I supernovae – caused by the collapse of a small faint white dwarf star. These stars are dim and hard to find, so we can’t be sure just how many are around. There are probably a few hundred of these stars within 50 light-years.

    The star IK Pegasi B is the nearest known supernova progenitor candidate. It’s part of a binary star system, located about 150 light-years from our sun and solar system.

    3
    Relative dimensions of IK Pegasi A (left), IK Pegasi B (lower center) and our sun (right). The smallest star here is the nearest known supernova progenitor candidate, at 150 light-years away. Image via RJHall on Wikimedia Commons.

    The main star in the system – IK Pegasi A – is an ordinary main sequence star, not unlike our sun. The potential Type I supernova is the other star – IK Pegasi B – a massive white dwarf that’s extremely small and dense. When the A star begins to evolve into a red giant, it’s expected to grow to a radius where the white dwarf can accrete, or take on, matter from A’s expanded gaseous envelope. When the B star gets massive enough, it might collapse on itself, in the process exploding as a supernova.

    What about Betelgeuse? Another star often mentioned in the supernova story is Betelgeuse, one of the brightest stars in our sky, part of the famous constellation Orion. Betelgeuse is a supergiant star. It is intrinsically very brilliant.

    RIGEL-BETELGEUSE-ANTARES Digital image ©Michael Carroll

    Such brilliance comes at a price, however. Betelgeuse is one of the most famous stars in the sky because it’s due to explode someday. Betelgeuse’s enormous energy requires that the fuel be expended quickly (relatively, that is), and in fact Betelgeuse is now near the end of its lifetime. Someday soon (astronomically speaking), it will run out of fuel, collapse under its own weight, and then rebound in a spectacular Type II supernova explosion. When this happens, Betelgeuse will brighten enormously for a few weeks or months, perhaps as bright as the full moon and visible in broad daylight.

    When will it happen? Probably not in our lifetimes, but no one really knows. It could be tomorrow or a million years in the future. When it does happen, any beings on Earth will witness a spectacular event in the night sky, but earthly life won’t be harmed. That’s because Betelgeuse is 430 light-years away.

    How often do supernovae erupt in our galaxy? No one knows. Scientists have speculated that the high-energy radiation from supernovae has already caused mutations in earthly species, maybe even human beings.

    One estimate suggests there might be one dangerous supernova event in Earth’s vicinity every 15 million years. Another says that, on average, a supernova explosion occurs within 10 parsecs (33 light-years) of the Earth every 240 million years. So you see we really don’t know. But you can contrast those numbers to the few million years humans are thought to have existed on the planet – and four-and-a-half billion years for the age of Earth itself.

    And, if you do that, you’ll see that a supernova is certain to occur near Earth – but probably not in the foreseeable future of humanity.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

     
  • richardmitnick 3:36 pm on May 1, 2018 Permalink | Reply
    Tags: , , , , , , , Greenland Telescpe achieves "first light" and more, Harvard Smithsonian Center for Astrophysics,   

    From Harvard Smithsonian Center for Astrophysics: “Greenland Telescope Opens New Era of Arctic Astronomy” 

    Harvard Smithsonian Center for Astrophysics


    Center For Astrophysics

    May 1, 2018

    Megan Watzke
    Harvard-Smithsonian Center for Astrophysics
    +1 617-496-7998
    mwatzke@cfa.harvard.edu

    Peter Edmonds
    Harvard-Smithsonian Center for Astrophysics
    +1 617-571-7279
    pedmonds@cfa.harvard.edu

    NSF CfA Greenland telescope

    NSF CfA Greenland telescope

    To study the most extreme objects in the Universe, astronomers sometimes have to go to some extreme places themselves. Over the past several months, a team of scientists has braved cold temperatures to put the finishing touches on a new telescope in Greenland. [This is a major gain for astronomy in the Northern Hemisphere, which sometimes seems to be less productive than the astronomical assets in the Southern Hemsphere.]

    Taking advantage of excellent atmospheric conditions, the Greenland Telescope is designed to detect radio waves from stars, galaxies and black holes. One of its primary goals is to join the Event Horizon Telescope (EHT), a global array of radio dishes that are linked together to make the first image of a supermassive black hole.

    Event Horizon Telescope Array

    Arizona Radio Observatory
    Arizona Radio Observatory/Submillimeter-wave Astronomy (ARO/SMT)

    ESO/APEX
    Atacama Pathfinder EXperiment

    CARMA Array no longer in service
    Combined Array for Research in Millimeter-wave Astronomy (CARMA)

    Atacama Submillimeter Telescope Experiment (ASTE)
    Atacama Submillimeter Telescope Experiment (ASTE)

    Caltech Submillimeter Observatory
    Caltech Submillimeter Observatory (CSO)

    IRAM NOEMA interferometer
    Institut de Radioastronomie Millimetrique (IRAM) 30m

    James Clerk Maxwell Telescope interior, Mauna Kea, Hawaii, USA
    James Clerk Maxwell Telescope interior, Mauna Kea, Hawaii, USA

    Large Millimeter Telescope Alfonso Serrano
    Large Millimeter Telescope Alfonso Serrano

    CfA Submillimeter Array Hawaii SAO
    Submillimeter Array Hawaii SAO

    ESO/NRAO/NAOJ ALMA Array
    ESO/NRAO/NAOJ ALMA Array, Chile

    South Pole Telescope SPTPOL
    South Pole Telescope SPTPOL

    Future Array/Telescopes

    Plateau de Bure interferometer
    Plateau de Bure interferometer

    NSF CfA Greenland telescope

    The Greenland Telescope has recently achieved two important milestones, its “first light” and the successful synchronization with data from another radio telescope. With this, the Greenland Telescope is ready to help scientists explore some of the Universe’s deepest mysteries.

    “We can officially announce that we are open for business to explore the cosmos from Greenland,” said Timothy Norton of the Harvard-Smithsonian Center for Astrophysics (CfA) and Senior Project Manager for the telescope. “It’s an exciting day for everyone who has worked so hard to make this happen.”

    In December 2017, astronomers were able to successfully detect radio emission from the Moon using the Greenland Telescope, an event astronomers refer to as “first light.” Then in early 2018, scientists combined data from the Greenland Telescope’s observations of a quasar with data from the Atacama Large Millimeter/submillimeter Array, or ALMA.

    ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres

    The data from the Greenland Telescope and ALMA were synchronized so that they acted like two points on a radio dish equal in size to the separation of the two observing sites, an achievement that is called “finding fringes.”

    “This represents a major step in integrating the telescope into a larger, global network of radio telescopes,” said Nimesh Patel of CfA. “Finding fringes tells us that the Greenland Telescope is working as we hoped and planned.”

    The Greenland Telescope is a 12-meter radio antenna that was originally built as a prototype for ALMA. Once ALMA was operational in Chile, the telescope was repurposed to Greenland to take advantage of the near-ideal conditions of the Arctic to study the Universe at specific radio frequencies.

    The Greenland location also allows interferometry with the Submillimeter Array in Hawaii, ALMA and other radio dishes, to become a part of the northernmost component of the EHT. This extends the baseline of this array in the north-south direction to about 12,000 km (about 7,500 miles).

    CfA Submillimeter Array Mauna Kea, Hawaii, USA, Altitude 4,080 m (13,390 ft)

    “The EHT essentially turns the entire globe into one giant radio telescope, and the farther apart radio dishes in the array are, the sharper the images the EHT can make,” said Sheperd Doeleman of the CfA and leader of the EHT project. “The Greenland Telescope will help us obtain the best possible image of a supermassive black hole outside our galaxy.”

    The Greenland Telescope joined the EHT observing campaign in the middle of April 2018 to observe the supermassive black hole at the center of the galaxy M87. This supermassive black hole and the one in our galaxy are the two primary targets for the EHT, because the apparent sizes of their event horizons are larger than for any other black hole. Nevertheless exquisite telescope resolution is required, equivalent to reading a newspaper on the Moon. This capability is about a thousand times better than what the best optical telescopes in the world can achieve.

    Scientists plan to use these observations to help test Einstein’s theory of General Relativity in environments where extreme gravity exists, and probe the physics around black holes with unprecedented detail.

    In 2011, NSF, the Associated Universities, Inc. (AUI)/National Radio Astronomy Observatory (NRAO) awarded the antenna to the Smithsonian Astrophysical Observatory (SAO) for relocation to Greenland. SAO’s project partner, the Academia Sinica Institute of Astronomy & Astrophysics (ASIAA) of Taiwan, led the effort to refurbish and rebuild the antenna to prepare it for the cold climate of Greenland’s ice sheet. In 2016, the telescope was shipped to the Thule Air Base, Greenland, 750 miles inside the Arctic Circle, where it was reassembled at this sea-level coastal site. A future site is under consideration a the summit of the Greenland ice sheet where we will be able to take advantage of lower water vapor in the atmosphere overhead and achieve even better resolution at the higher operating frequencies.

    More information on the Greenland Telescope can be found at https://www.cfa.harvard.edu/greenland12m/

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

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

     
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