Questions concerning hypervelocity stars

Hey everybody, I'm new here and what better way to start then jump right in!! I have a few questions concerning hypervelocity stars for a sci fi book that I want to write.

First of all, what is the agreed upon "average" speed of a hypervelocity star? I have done a bit of googling, but I have seen a lot of different numbers. Would 1000km/s be about right?

Secondly, I have read that some hypervelocity stars are thought to have originated in the Magellanic Clouds. Which one would be more likely to produce hypervelocity stars? The LMC or the SMC?

Thirdly and finally, given the speed and the distance of the LMC/SMC, how long would it take a hypervelocity star to reach Earth? I know this would never happen, but keep in mind it's just for a sci fi novel :P

Thank you all for your help and I look forward to being a member of these forums Merry Christmas!!!

Travito

Travito wrote:
Hey everybody, I'm new here and what better way to start then jump
right in!! I have a few questions concerning hypervelocity stars for
a sci fi book that I want to write.

First of all, what is the agreed upon "average" speed of a
hypervelocity star? I have done a bit of googling, but I have seen a
lot of different numbers. Would 1000km/s be about right?

1000 km/s is the right order of magnitude, yes.


Secondly, I have read that some hypervelocity stars are thought to
have originated in the Magellanic Clouds. Which one would be more
likely to produce hypervelocity stars? The LMC or the SMC?

Of all the known HVSs, AFAIK only one is proposed to come from the LMC, and
this may be doubtful. All the others are moving directly away from the
Milky Way's galactic core. Neither cloud should produce HVS and the
proposed mechanism specifically requires a binary system that has a close
encounter with the galactic centre's black hole (maybe the LMC has a core
BH, probably much smaller than the one in our galaxy). If one of these
originates in the LMC it would require a similar black hole to produce the
high speed from a binary star encounter.

Thirdly and finally, given the speed and the distance of the LMC/SMC,
how long would it take a hypervelocity star to reach Earth? I know
this would never happen, but keep in mind it's just for a sci fi
novel :P

A good approximation for such questions is "one km/sec is one
parsec/megayear". So a speed of 1000 km/sec is 1000 pc/10^6 yr. Distance
(from the Sun) is around 55000 pc for the LMC, so it would take 55 million
years to get here. This doesn't sound like a dramatic plot device, but
YMMV.

Thank you all for your help and I look forward to being a member of
these forums Merry Christmas!!!

Travito

--
Mike Dworetsky

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