Fraser CainOver the last 70 years, astronomers have charted the disappearance of hundreds of massive stars from the night sky. These kinds of stars should be detonating as supernovae, but instead, they've just vanished. The evidence is growing that some of these stars are imploding into black holes without a peep. A new paper charts the behavior of the star VFTS 243, a main sequence star with a black hole companion that probably suffered a complete collapse.
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.132.191403
Constraints on Neutrino Natal Kicks from Black-Hole Binary VFTS 243
The recently reported observation of VFTS 243 is the first example of a massive black-hole binary system with negligible binary interaction following black-hole formation. The black-hole mass ($\ensuremath{\approx}10{M}_{\ensuremath{\bigodot}}$) and near-circular orbit ($e\ensuremath{\approx}0.02$) of VFTS 243 suggest that the progenitor star experienced complete collapse, with energy-momentum being lost predominantly through neutrinos. VFTS 243 enables us to constrain the natal kick and neutrino-emission asymmetry during black-hole formation. At 68% confidence level, the natal kick velocity (mass decrement) is $\ensuremath{\lesssim}10\text{ }\text{ }\mathrm{km}/\mathrm{s}$ ($\ensuremath{\lesssim}1.0{M}_{\ensuremath{\bigodot}}$), with a full probability distribution that peaks when $\ensuremath{\approx}0.3{M}_{\ensuremath{\bigodot}}$ were ejected, presumably in neutrinos, and the black hole experienced a natal kick of $4\text{ }\text{ }\mathrm{km}/\mathrm{s}$. The neutrino-emission asymmetry is $\ensuremath{\lesssim}4%$, with best fit values of $\ensuremath{\sim}0--0.2%$. Such a small neutrino natal kick accompanying black-hole formation is in agreement with theoretical predictions.