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How Do Binary Dwarf/Neutron Stars get so close?

  1. Dec 11, 2015 #1
    I am a little puzzled with how there is a White Dwarf Binary of Five Minutes. How do they get so close?
  2. jcsd
  3. Dec 11, 2015 #2
    It's more than likely that the two stars originally were more distant from each other and orbiting more slowly.
    Over a very long they have become closer, and so would need to orbit faster so that orbit is maintained.
    Remember white dwarfs are very small and dense, so they could get very close together without actually colliding or merging.
    Maybe this pair have settled into this small orbit and will stay that way for a long time, then again in the long run it's possible they will end up merging.
    The result would probably be a neutron star, or possibly a black hole, and likely there would be a supernova event just before that.

    If the original stars already are neutron stars, these are even smaller and denser then white dwarfs, and a binary pair could likely orbit even more rapidly before merging, (or exploding), could be in the region of seconds.
  4. Dec 11, 2015 #3
    Interesting. That's very good. Though I didn't think they would naturally get so close from just evolution.

    I used to believe it was from a close binary in which one star is a white dwarf, and the other is a main-sequence. They orbit really close together, almost as a W Ursae Majoris variable. When the main sequence evolves, it envelops the white dwarf in it's expanding envelope, causing a friction dynamic to slow the white dwarf, while increasing it's mass. This leads for them to get closer and by the time the planetary nebula is ejected. In the end(if a type Ia Supernova doesn't occur) a close binary is left over. Like how Henize 2-428 probably was.

    Very interesting.
  5. Dec 11, 2015 #4


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    In the case of close binary stars, we have learned orbital decay can be driven via emission of gravitational radiation. In the Hulse-Taylor study they were able to accurately acount for the decrease in orbital period of the system PSR B1913+16 over time via this mechanism. This does not, however, explain how the stars get close enough in the first place for gravitational radiation to become a driver for orbital decay. The principal mechanism for orbital decay of binary systems besides gravitational radiation is magnetized stellar winds which bleeds the system of angular momentum and energy causing the orbital period to slowly decline.
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