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Space Science

Fastest (and Most Compact) Stellar Spinner Confirmed 47

Posted by Soulskill
from the getting-dizzy-now dept.
gregg writes "HM Cancri has been confirmed as a binary system of two white dwarfs orbiting each other so closely that they complete one orbit every 5.4 minutes; they are separated by a mere 8 Earth diameters. 'These are the burnt-out cinders of stars such as our Sun, and contain a highly condensed form of helium, carbon and oxygen. The two white dwarfs in HM Cancri are so close together that mass is flowing from one star to the other. HM Cancri was first noticed as an X-ray source in 1999, showing a 5.4 minutes periodicity, but for a long time it has remained unclear whether this period also indicated the actual orbital period of the system. It was so short that astronomers were reluctant to accept the possibility without solid proof. '"
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Fastest (and Most Compact) Stellar Spinner Confirmed

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  • > The two white dwarfs in HM Cancri are so close together that mass is flowing
    > from one star to the other.

    Not a unique feature of this pair. This is common in pairs that are much farther apart.

    • by AstroMatt (1594081) on Saturday March 13, 2010 @11:45AM (#31464586)
      It happens in binary main sequence stars. This is only one of 2 binary white dwarf systems that have direct impact accretion (the other is named V407 Vul). Usually the accretion stream misses the primary star, and forms an accretion disk. In these systems, the accretion stream slams into the the accreting white dwarf at a velocity of about 1% the speed of light, btw!
    • by FatdogHaiku (978357) on Saturday March 13, 2010 @11:51AM (#31464618)
      Does this mean that at some point one of them could lose so much mass that there will no longer be a stable pair? I have this vision of one of them suddenly shooting off at a tangent at a horrendous velocity like some cosmic bowling ball.
      • by frieko (855745) on Saturday March 13, 2010 @12:22PM (#31464786)
        Like this? [wikipedia.org]
        • Yup, kinda what I was thinking. Wouldn't want to be sitting at the telescope and notice a blue shifted star getting bigger and bigger...
          Thanks for the link.
      • You have a really weird way of playing bowling. Now, if you had gone with hammer throw [wikipedia.org], you would have had a much better analogy.

        • A former girlfriend almost kneecapped me one time while I was teaching her to bowl, no joke. She let go of the ball on the back swing and I had to jump to clear it.

          I don't try to teach anyone to bowl anymore.
      • Re: (Score:2, Insightful)

        by Jenming (37265)

        If you make a closed box around the two white dwarfs and move mass from one to the other you will see that the center of gravity does not change and so I would not think anything would go flying off. Rather both bodies would just move toward the center of gravity while the larger one got larger and the smaller got smaller. If they collided with some force stuff could be thrown away from the collision, but no escape velocity could be reached without another force being involved.

    • It's easy to observe, too! Mass tends to flow from my mouth to my ass, where some continues on outside the body and the rest seems to accumulate...
  • I would be so pissed if my alarmclock went ringing every 5.4 minutes! I say we nuke 'em just to be sure we will never build a colony there!
    • by Rich0 (548339)

      Well, I don't know what the masses of these stars are, but if they're high enough they'll eventually "nuke" themselves. When one star gains enough mass - either by pulling it out of the other or from the eventual collision when their orbits collapse - if that star has sufficient mass it will trigger a supernova as the core collapses into a black hole.

      • by santax (1541065)
        I am sorry my friend, although you are probably right, 'probably' just isn't good enough with my alarm-clock ringing every 5.4 minutes. We need guarantees!
      • Re:Oh my God... (Score:5, Informative)

        by mrtommyb (1534795) on Saturday March 13, 2010 @11:42AM (#31464558)
        The total mass is almost certainly less than 1.4 time the mass of the sun and therefore does not have enough total mass to create supernova and a neutron star (its nowhere near massive enough to form a black hole).
        • by SPickett (911670)
          From the last line of the article neither of us read:
          "It is thought that the white dwarf pair are reaching the end of their frenzied dance. As more gravitational waves are generated, energy is lost from the system, making them spiral closer together until they collide, possibly exploding as a type 1a supernova."
  • Proof? (Score:3, Funny)

    by Mycroft-X (11435) on Saturday March 13, 2010 @11:02AM (#31464334)

    It was so short that astronomers were reluctant to accept the possibility without solid proof.

    What about very hot, plasmatic proof?

  • Tidal bulges (Score:4, Insightful)

    by Frequency Domain (601421) on Saturday March 13, 2010 @11:06AM (#31464356)
    The artist's rendition shows two spherical bodies, but there's no way that can be correct. At the orbital velocities involved these things must have tidal bulges that make Kevin Smith look positively svelte!
    • You have to remember that a white dwarf's gravity is truly enormous and that even at the orbital velocities these dwarfs are orbiting each other, they should still be mostly spherical. At least spherical enough that an artists' rendition shouldn't be too inaccurate.

    • Re:Tidal bulges (Score:5, Informative)

      by AstroMatt (1594081) on Saturday March 13, 2010 @12:03PM (#31464692)
      The mass losing star is somewhat teardrop shaped, with the point pointing towards the other star - that's where mass flows through. It's a 3D analog of a spring-fed lake in a valley overflowing a saddle pass and flowing into the next valley. The mass flow in this system is likely helium mostly, and the rate is equivalent to about 100,000 Nimitz-class aircraft carriers per second. The impact velocity is about 1% the speed of light.
    • Re:Tidal bulges (Score:5, Informative)

      by bcrowell (177657) on Saturday March 13, 2010 @12:12PM (#31464732) Homepage

      The artist's rendition shows two spherical bodies, but there's no way that can be correct. At the orbital velocities involved these things must have tidal bulges that make Kevin Smith look positively svelte!

      You're right, the artist's conception is messed up. Here [arxiv.org] is the scientific paper. Figure 3 on p. 4 has a realistic diagram, showing one star completely filling its Roche lobe.

      Anyway, this is cool because this system is much closer and higher in frequency than the classic Hulse-Taylor [slashdot.org] binary pulsar. That means that it's radiating gravitational waves at a much higher rate.

      • Here [arxiv.org] is the scientific paper. Figure 3 on p. 4 has a realistic diagram, showing one star completely filling its Roche lobe.

        Way cool! Thanks for the link.

  • by Takeel (155086) <v32gd4r02&sneakemail,com> on Saturday March 13, 2010 @11:11AM (#31464386) Homepage Journal

    The best use for this is obviously to install it on the wheels of a stellar El Dorado.

  • And I don't care how good she is, "stellar" is just too strong of an adjective.
  • This [youtube.com] is a video of two combining neutron stars, not white dwarves, so you'll have to suspend disbelief.

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