Fastest star in Milky Way propelled by a thermonuclear supernova

March 9, 2015  |   |  2 Comments
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illustration of supernova-explosion

Artist’s conception of a star (left) being ejected from a galaxy by a supernova explosion. In reality the supernova would have been faded away long before the star reached that position. (credit: ESA/Hubble, NASA)

A team of astronomers, including University of Hawaiʻi at Mānoa astronomer Eugene Magnier, used the 10-meter Keck II and Pan-STARRS1 telescopes in Hawaiʻi to find a star that breaks the galactic speed record. It travels at about 1,200 kilometers per second (about 2.7 million mph), a speed that will enable the star to escape from our Milky Way galaxy.

“At that speed, you could travel from Earth to the moon in 5 minutes,” Magnier commented.

The team showed that, unlike the half-dozen other known escaping stars, this compact star was ejected from an extremely tight binary by a thermonuclear supernova explosion. These results—“The fastest unbound star in our Galaxy ejected by a thermonuclear supernova”—were published in the March 6, 2015 issue of the journal Science.

Stars like the sun are bound to our galaxy by its gravity and orbit its center at relatively moderate velocities, tens to a few hundreds of kilometers per second. Only a few so-called hypervelocity stars are known that travel so fast that they are unbound. A close encounter with the supermassive black hole at the center of the Milky Way is usually considered the most plausible mechanism for enabling these stars to escape from the galaxy.

“By observing the sky repeatedly over several years, the Pan-STARRS1 survey lets us make a movie of the motions of the stars in the sky. That enables us to study the behaviors of extremely rare and weird stars like US708,” Magnier explained.

Read the Institute for Astronomy news release for more on the US708 discovery.

Animation of the mass-transfer phase to a white dwarf followed by a double-detonation supernova that leads to the ejection of US708 from the galaxy. (credit: NASA, ESA and P. Ruiz-Lapuente, cut and colored by S. Geier)

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Category: Research

Comments (2)

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  1. Mr. Raymond Kenneth Petry says:

    That was ‘one’ confused report—
    1. The IFA captioned it a “double detonation” (but no explanation why);
    2. All supernovae we know-about are ‘thermonuclear’ (beyond neutrinos);
    3. Categorically ‘thermonuclear’ implicates the impulse given its core.
    (And cores are considered stars too, e.g. ‘neutron stars’.)
    —Ray.

  2. Eugene Magnier says:

    Thanks for the comment. You are right about point (1): we did not really explain the double-detonation in the caption. In such a supernova, an Oxygen/Carbon white dwarf accumulates Hydrogen and Helium from a donor star (in this case, the star destined to become US708). When enough H/He accumulate on the surface of the white dwarf, they can spontaneously ignite in a fusion reaction. The heat and pressure from that reaction can then trigger a fusion reaction in the O/C white dwarf, resulting in the full-scale supernova (Type Ia).

    As for your points 2 & 3, it is typical in astronomy to refer to the “Type Ia” or white-dwarf supernova, like I described above, as “thermonuclear” because the reaction is driven and sustained by the high temperatures (of the H/He reaction and the radioactive decay of the nickel by products). The other kind of supernova, in which massive star explodes, is called a core-collapse supernova, not a thermonuclear supernova. In the core collapse case, the supernova explosion is not driven by high temperatures, but instead by gravity. So, in this case, the supernova that disrupted the system and resulted in the high velocity of US708 was a thermonuclear, not a core-collapse supernova.

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