4
$\begingroup$

The Hills mechanism postulates that when a stellar binary system is perturbed by a supermassive black hole (SMBH), the tidal forces at play result in the capture of one star while simultaneously ejecting the other.

My question is as follows: Why does one star become captured while the other is ejected? Is it not possible for the SMBH to capture both stars and maintain the binary system within its orbit, or alternatively, eject the entire binary system?

Improve this question
$\endgroup$
5
  • $\begingroup$ Reading the original paper "Hyper-velocity and tidal stars from binaries disrupted by a massive Galactic black hole", it appears that the result was based on computer simulations. To quote: "It is thus energetically possible for the encounter to dissolve the binary, but in almost every case the encounter left behind either the original binary or one in which the black hole had replaced one star". Note the "in almost every case" case bit. $\endgroup$
    – Martin C.
    Commented Oct 20, 2023 at 11:16
  • $\begingroup$ So, there isn't an explanation for how this occurs, such as a model or equation? From what I gather, all three cases are possible, but their likelihood is determined based on observations. But then, how would one theorize what would happen when an arbitrary binary star enters the tidal influence of a black hole? $\endgroup$
    – RKerr
    Commented Oct 20, 2023 at 11:44
  • $\begingroup$ Well, the simulations are certainly based on equations! The paper specifies that the Newtonian (i.e. not GR) equations of motions were used, and solved with 'the Shampine-Gordorn variable-order, variable-step-size integrator'. There are also several nice graphs indicating the probability of an exchange as a function of the dimensionless closest approach parameter, for certain fixed masses of the three objects. These probabilities are based on numerical simulations. $\endgroup$
    – Martin C.
    Commented Oct 20, 2023 at 12:45
  • $\begingroup$ I suggest you read the paper - it is short and not particularly dense. $\endgroup$
    – Martin C.
    Commented Oct 20, 2023 at 12:46
  • $\begingroup$ I am not aware of nice analytical results, but that doesn't mean they don't exist. This is basically a variant of the 3-body problem. $\endgroup$
    – Martin C.
    Commented Oct 20, 2023 at 12:47

0

Reset to default