tems in which the X-ray emission is strongly
beamed, however, and if the beaming axis
is perpendicular to the orbital plane, then
that would increase the ULX’s chance of being observed in such an apparently unlikely
orientation.
Even so, it would be bold to invoke observationally-disfavored beaming to argue that a
system has a reasonable probability of containing an IMBH, given that beaming was first
applied in this context to avoid the need for
IMBHs. Taken at face value, then, the system
is unlikely to be sufficiently face-on to contain an IMBH. Much of the ULX community
will not be surprised by that broad conclusion; the idea that most ULXs contain stellarmass black holes has gradually become the
dominant position. Nonetheless, the Gemini
data are the most direct observations supporting that conclusion.
More unexpected is our finding that the
black hole in M101 ULX-1 can sustain such
a high luminosity from wind accretion. Capture of material from a stellar wind is typically associated with fairly low-luminosity
accretion, but M101 ULX-1 demonstrates
that sometimes wind capture can be extremely efficient. This unlooked-for result
might be as important as the mass measurement itself.
References:
Gladstone, J.C., Roberts, T.P., and Done, C., “The
Ultraluminous State,” Monthly Notices of the Royal
Astronomical Society, 397: 1836, 2009
Liu, J.-F., et al., “Puzzling Accretion onto a Black
Hole in the Ultraluminous X-ray Source M 101
ULX-1,” Nature, 503: 500, 2013
Pakull, M., and Mirioni, L., “Bubble Nebulae
around Ultraluminous X-Ray Sources,” Revista
Mexicana de Astronomía y Astrofísica (Serie de
Conferencias) ,15: 197-199, 2003
Webb, N., et al., “Radio Detections During Two
State Transitions of the Intermediate-Mass Black
Hole HLX-1,” Science, 337: 554, 2012
Figures 2 and 3 reprinted by permission of Macmillan Publishers, Ltd: Nature, doi:10.1038/nature12762, copyright 2013.
Both authors work in the Beijing headquarters of
the National Astronomical Observatories of the
Chinese Academy of Sciences.
Stephen Justham is a Research Fellow and can be
contacted at: [email protected]
Jifeng Liu is a Bairen Professor and can be contacted at: [email protected]
Whatever the final scientific impact that
these results produce on our understanding
of black holes and their accretion, we marvel
that it is possible to measure the motion of
a star orbiting a black hole in M101 — some
20 million light-years away — and thereby
to constrain the mass of that black hole.
Acknowledgements:
J.-F.L. and S.J. thank the other authors of the
associated journal article: Joel Bregman, Yu
Bai, and Paul Crowther. We also thank the Chinese Academy of Sciences and National Science Foundation of China for support during
this work.
January2014 2013 Year in Review
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