Re: accretion/event horizon

From: Joseph Lazio (jlazio_at_adams.patriot.net)
Date: 01/06/05 

Date: 06 Jan 2005 09:01:49 -0500

>>>>> "s" == spiderrescue <spiderrescue@mac.com> writes:

s> just reading about the chandra observations of the event horizons
s> of xray novae. whilst reading it a question came to mind; have all
s> the previous 'observations' of black holes been based only upon the
s> observing of relative motions created by the enormous densities
s> that define black holes?

I'd phrase it as something like the following. Assuming that general
relativity is the correct description of gravity (at least on
macroscopic scales), the motions of gas or stars in the neighborhood
of certain dark objects is only consistent with those objects being
black holes.

In other words, their presence has been inferred not observed directly.

s> have we not directly seen structures of the black holes themselves
s> until this point? what about jets like m87 (?) that come to mind;
s> wouldnt we be able to discern where the event horizon would be
s> there, or are we not certain that is a black hole?

The future may be different. There are plans to use the technique of
very long baseline interferometry (VLBI) at sub-millimeter wavelengths
to image the neighborhood of the object Sgr A* at the center of the
Milky Way Galaxy. If everything works, the observations should be
able to detect the "shadow" of the black hole against its accretion
disk. See Volume 18 of GCNEWS,
<URL:http://www.aoc.nrao.edu/~gcnews/gcnews/Vol.18/gcnews.shtml>. 

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