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Tim Kendall's Extreme Astrophysics

A new route for the formation of black hole binaries and a prediction for their mass distribution

15 Feb 2016, 15:28 UTC
A new route for the formation of black hole binaries and a prediction for their mass distribution
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In a new Oxford University press release astronomers have revealed an evolutionary route to the formation of stellar-mass black hole binaries such as the one recently seen by Advanced LIGO. While the observed mass deficit of three solar masses exactly fitted Einstein’s predictions, the actual masses, around 30 MSun each, are unexpectedly large. However, tidally induced internal mixing often occurs in massive close binary stars, and careful modelling of this process has revealed new insights into exactly how this affects the masses of the final black holes:

One complication to theories around the formation of tight pairs of compact stars stems from the fact that stars are generally thought to expand when they age. This new theory avoids such an expansion by invoking a mechanism that keeps the interior of very close and sufficiently massive stars completely chemically mixed. The reason for this is that tidal forces keep the stars in bound rotation – that is, they continue to show the same side to each other, similar to how the same side of the Moon always faces the Earth. The fast orbital motion involved in this process leads to extremely rapid rotation of the stars, which triggers internal chemical mixing ...

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