[seminar] Astro Journal Club on 22 April

[Oskari Miettinen]

Dear all,

The Astro Journal Club will be held on Wednesday at 10:15 in the seminar
room F-201 of the Physics Department. This time we will discuss about the
event horizon of M87*.

Presenter: Oskari Miettinen
Paper title: The Event Horizon of M87
Authors: Broderick, A. E., Narayan, R., Kormendy, J., et al.

Summary:
The 6 billion solar mass supermassive black hole at the center of the
giant elliptical galaxy M87 powers a relativistic jet. Observations at
millimeter wavelengths with the Event Horizon Telescope have localized the
emission from the base of this jet to angular scales comparable to the
putative black hole horizon. The jet might be powered directly by an
accretion disk or by electromagnetic extraction of the rotational energy
of the black hole. However, even the latter mechanism requires a confining
thick accretion disk to maintain the required magnetic flux near the black
hole. Therefore, regardless of the jet mechanism, the observed jet power
in M87 implies a certain minimum mass accretion rate. If the central
compact object in M87 were not a black hole but had a surface, this
accretion would result in considerable thermal near-infrared and optical
emission from the surface. Current flux limits on the nucleus of M87
strongly constrain any such surface emission. This rules out the presence
of a surface and thereby provides indirect evidence for an event horizon.

Link to the paper: http://adsabs.harvard.edu/abs/2015arXiv150303873B

Hope to see you all on Wednesday!

Best wishes,
Oskari