Kavli Affiliate: Anna Frebel
| First 5 Authors: Kevin B. Burdge, Kareem El-Badry, Erin Kara, Claude Canizares, Deepto Chakrabarty
| Summary:
Evidence suggests that when compact objects such as black holes and neutron
stars form, they may receive a “natal kick,” where the stellar remnant gains
momentum. Observational evidence for neutron star kicks is substantial, yet
limited for black hole natal kicks, and some proposed black hole formation
scenarios result in very small kicks. Here, we report the discovery that the
canonical black hole low-mass X-ray binary V404 Cygni is part of a wide
hierarchical triple with a tertiary companion at least 3500 astronomical units
away from the inner binary. Given the orbital configuration, the black hole
likely received a sub-5 kilometer per second kick to have avoided unbinding the
tertiary. This discovery reveals that at least some black holes form with
nearly no natal kick. Furthermore, the tertiary in this system lends credence
to evolutionary models of low-mass X-ray binaries involving a hierarchical
triple structure. Remarkably, the tertiary is evolved, indicating that the
system formed 3-5 billion years ago, and that the black hole has removed at
least half a solar mass of matter from its evolved secondary companion. During
the event in which the black hole formed, it is likely that at least half of
the mass of the black hole progenitor collapsed into the black hole; it may
even have undergone a complete implosion, enabling the tertiary to remain
loosely bound.
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