Hubble's Universe Unfiltered

  • November 1, 2010

    Episode 14: A Runaway Star

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    In order to get observing time on Hubble, an astronomer needs a well thought-out plan of exactly what to observe and the science that may be learned. However, the universe is continually surprising us by providing unanticipated results. When a survey of a star-forming region found a star 90 times as massive as the Sun, located hundreds of light-years from its home, and speeding by at a quarter of a million miles per hour — well, that's a surprise that's worth investigating a bit further.

    • This story derives from results of the Cosmic Origins Spectrograph instrument on Hubble. While Hubble is famous for its awe-inspiring pictures, astronomers learn just as much from examining Hubble's spectral observations, especially in the ultraviolet region not observable from the ground.

      Ultraviolet light has shorter wavelengths and higher energies than the visible light seen by our eyes. Very massive stars produce higher energy emission, which has important spectral features to study in the ultraviolet region. You may not see spectra on the covers of magazines, but many of Hubble's most important results are based on these detailed graphs of emission versus wavelelength.

    • The Large Magellanic Cloud is one of the great wonders of the night sky. It is, however, located at 70 degrees south of the celestial equator and is only viewable by those in the southern hemisphere. Conversely, the stars of the Big Dipper are located about 55 degrees north of the celestial equator and are best viewed from the northern hemisphere.

      Although bearing the name of the explorer Magellan, this small galaxy has been a spectacular sight for anyone who has ever lived "down under." I hope to be able to travel there and see it myself one day. Even more spectacular would be the view from the stars of the LMC, looking back at our Milky Way Galaxy.

    • It has always struck me as a little strange that the largest star-forming region in our Local Group of galaxies, 30 Doradus, would be found in a dwarf galaxy. One would expect that the larger galaxies, like Andromeda, Triangulum, or the Milky Way, would have much more gas and dust available to make larger star-forming regions. The fact that a dwarf galaxy can make a huge star factory shows that size alone is not the determining factor. The creation of a star-forming region is also guided by the motions of the gas and dust, as well as the time available for it to collect into a vast cloud. In that sense, perhaps the calmer environment of a dwarf galaxy makes for the best place to harbor a giant starbirth cloud.

    • The orbits of planets and stars are governed by gravity, and one thinks of them as being fully predictable. In truth, that's not always the case. For two objects orbiting one another, like the Sun and Earth, the equations have an exact solution. However, add in a third object, like the Moon, and the problem becomes much, much harder. Isaac Newton recognized this difficulty in his "Principia," the same book in which he introduced the mathematics of gravity. While the "three-body problem" has a number of special cases that provide analytic solutions, the general problem is best solved by using computers to integrate the orbits. Sometimes, those orbits can be unstable and greatly disrupt the system. Even more complicated are the orbits of all the stars in a star cluster. Such calculations are known as "N-body" problems, where "N" represents a large number — thousands to millions in the case of star clusters.

    Image notes

    Large and Small Magellanic Clouds
    Credit and Copyright: Akira Fujii/David Malin Images

    Large Magellanic Cloud from the Anglo-Australian Observatory
    Credit: David Malin
    Copyright: Australian Astronomical Observatory

    30 Doradus from Star Shadows Remote Observatory
    Credit and Copyright: Harvey/Star Shadows Remote Observatory

    30 Doradus from ESO
    Credit: ESO, J. Alves (Calar Alto, Spain), and B. Vandame and Y. Beletski (ESO)
    Acknowledgment: B. Fosbury (ST-ECF)

    Visible-light Spectrum Diagram
    Credit: Philip Ronan

    Spectrum of the Sun
    Credit: N.A.Sharp, NOAO/NSO/Kitt Peak FTS/AURA/NSF

    Ultraviolet Spectra of 30 Dor #016 and HDE 269810
    Credit: NASA, ESA, and C. Evans, et al. (from The Astrophysical Journal, vol. 715, p. L74, 2010)

    30 Dor #016 from Hubble and ESO
    Credit: NASA, ESA, J. Walsh (ST-ECF), and ESO
    Acknowledgment: Z. Levay (STScI)

    Three Stars and Gravitational Ejection Diagrams
    Credit: NASA, ESA, and A. Feild (STScI)