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Formation Constraints Indicate a Black Hole Accretor in 47 Tuc X9

Church, Ross P. LU ; Strader, Jay; Davies, Melvyn B. LU and Bobrick, Alexey LU (2017) In Astrophysical Journal Letters 851(1).
Abstract

The luminous X-ray binary 47 Tuc X9 shows radio and X-ray emission consistent with a stellar-mass black hole (BH) accreting from a carbon-oxygen white dwarf. Its location, in the core of the massive globular cluster 47 Tuc, hints at a dynamical origin. We assess the stability of mass transfer from a carbon-oxygen white dwarf onto compact objects of various masses, and conclude that for mass transfer to proceed stably, the accretor must, in fact, be a BH. Such systems can form dynamically by the collision of a stellar-mass BH with a giant star. Tidal dissipation of energy in the giant's envelope leads to a bound binary with a pericenter separation less than the radius of the giant. An episode of common-envelope evolution follows, which... (More)

The luminous X-ray binary 47 Tuc X9 shows radio and X-ray emission consistent with a stellar-mass black hole (BH) accreting from a carbon-oxygen white dwarf. Its location, in the core of the massive globular cluster 47 Tuc, hints at a dynamical origin. We assess the stability of mass transfer from a carbon-oxygen white dwarf onto compact objects of various masses, and conclude that for mass transfer to proceed stably, the accretor must, in fact, be a BH. Such systems can form dynamically by the collision of a stellar-mass BH with a giant star. Tidal dissipation of energy in the giant's envelope leads to a bound binary with a pericenter separation less than the radius of the giant. An episode of common-envelope evolution follows, which ejects the giant's envelope. We find that the most likely target is a horizontal-branch star, and that a realistic quantity of subsequent dynamical hardening is required for the resulting binary to merge via gravitational wave emission. Observing one binary like 47 Tuc X9 in the Milky Way globular cluster system is consistent with the expected formation rate. The observed 6.8-day periodicity in the X-ray emission may be driven by eccentricity induced in the ultra-compact X-ray binary's orbit by a perturbing companion.

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
binaries: close, globular clusters: individual (47 Tuc), stars: black holes, X-rays: binaries
in
Astrophysical Journal Letters
volume
851
issue
1
publisher
University of Chicago Press
external identifiers
  • scopus:85039171791
  • wos:000417542100004
ISSN
2041-8205
DOI
10.3847/2041-8213/aa9aeb
language
English
LU publication?
yes
id
d97a085c-55b4-4c88-83f3-5ae6edea0236
date added to LUP
2018-01-05 10:44:59
date last changed
2018-01-16 13:29:21
@article{d97a085c-55b4-4c88-83f3-5ae6edea0236,
  abstract     = {<p>The luminous X-ray binary 47 Tuc X9 shows radio and X-ray emission consistent with a stellar-mass black hole (BH) accreting from a carbon-oxygen white dwarf. Its location, in the core of the massive globular cluster 47 Tuc, hints at a dynamical origin. We assess the stability of mass transfer from a carbon-oxygen white dwarf onto compact objects of various masses, and conclude that for mass transfer to proceed stably, the accretor must, in fact, be a BH. Such systems can form dynamically by the collision of a stellar-mass BH with a giant star. Tidal dissipation of energy in the giant's envelope leads to a bound binary with a pericenter separation less than the radius of the giant. An episode of common-envelope evolution follows, which ejects the giant's envelope. We find that the most likely target is a horizontal-branch star, and that a realistic quantity of subsequent dynamical hardening is required for the resulting binary to merge via gravitational wave emission. Observing one binary like 47 Tuc X9 in the Milky Way globular cluster system is consistent with the expected formation rate. The observed 6.8-day periodicity in the X-ray emission may be driven by eccentricity induced in the ultra-compact X-ray binary's orbit by a perturbing companion.</p>},
  articleno    = {L4},
  author       = {Church, Ross P. and Strader, Jay and Davies, Melvyn B. and Bobrick, Alexey},
  issn         = {2041-8205},
  keyword      = {binaries: close,globular clusters: individual (47 Tuc),stars: black holes,X-rays: binaries},
  language     = {eng},
  month        = {12},
  number       = {1},
  publisher    = {University of Chicago Press},
  series       = {Astrophysical Journal Letters},
  title        = {Formation Constraints Indicate a Black Hole Accretor in 47 Tuc X9},
  url          = {http://dx.doi.org/10.3847/2041-8213/aa9aeb},
  volume       = {851},
  year         = {2017},
}