If the star (S5-HVS1) has been accelerated to 1,700 km/s by a close encounter with the super massive black hole at the centre of our galaxy (Sagittarius A*) what would happen to any planets orbiting this star?

Would they have been stripped off by the massive acceleration or could any conceivably still be in orbit?

Presumably any orbiting bodies would be significantly perturbed!?

see https://www.sciencealert.com/our-bossy-black-hole-kicked-out-a-star-and-it-s-shooting-through-the-galaxy-insanely-fast

  • $\begingroup$ Whatever accelerating forces happen will happen to the planets as well as the star, unless a planet effectively hits the Roche Limit of the system. Not sure what you're asking here. $\endgroup$ – Carl Witthoft Nov 13 '19 at 18:11

According to Ginsburg, Loeb & Wegner (2012) "Hypervelocity planets and transits around hypervelocity stars", planet-hosting hypervelocity stars could form from the disruption of a stellar binary by a massive black hole, and the probability that the planet remains bound to the hypervelocity star is fairly high for suitable initial conditions.

In their simulations, this required initial planetary separations of 0.02–0.05 AU. The star S5-HVS1 is described in Koposov et al. (2019) "The Great Escape: Discovery of a nearby 1700 km/s star ejected from the Milky Way by Sgr A*" as a 2.35 solar mass A-type star. Planets around similar stars include ultra-hot Jupiters such as KELT-9b, which may at first appear promising.

The initial binary separation is another matter. The systems Ginsburg et al. investigated had binary separations in the range 0.05–0.5 AU. For the S-type planetary systems considered (the planet orbiting one of the stars as a satellite), this is a much smaller separation than any known planet-hosting binary: the planets known in such systems are in circumbinary systems which the paper does not explore.

It's therefore unclear whether the kind of progenitor system required would be capable of forming planets in the first place.

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  • $\begingroup$ Thanks @antispinwards for the interesting info. Intelligent life would certainly have a odd view of the universe if it were to evolve on a planet around S5-HVS1 ! Admittedly this seems highly unlikey! $\endgroup$ – MiguelH Nov 14 '19 at 9:17

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