* Original: FROM..... Dave Farber


From: "PAUL JULIEN"
Subject: Spinning Black Hole
Date: Thu, 10 May 2001 18:03:54 -0400
X-Mailer: Microsoft Outlook Express 5.00.2615.200

Dave:

Evidence for a black hole spinning at 450 Hz.  APS = American Physical
Society. Nice graphics and explanation on the link

http://www.gsfc.nasa.gov/GSFC/SpaceSci/structure/spinningbh/spinningbhpix.htm
,

the link given in the text.  You have to try to imagine an object about the
size of Long Island, but with a mass of about 2 millions earths, spinning
at 450 revolutions/sec.   And this is a "micro-blackhole", not a big one.

Paul Julien
Rutherford NJ

*


PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 538  May 7, 2001   by Phillip F. Schewe, Ben Stein, and
James Riordon

THE FIRST DIRECT EVIDENCE OF BLACK HOLE ROTATION arrives in the form of the
telltale dimming of x rays coming from a microquasar about 10,000 light
years from Earth. The object in question, GRO J1655-40, consists of a black
hole devouring a nearby normal-star companion.  The pillage is not
direct.  Instead matter from the star collects on an accretion disk
orbiting the black hole before taking the final plunge through the event
horizon.  This jumping-off platform is so hot that matter there glows at
x-ray wavelengths.  Seeing this glow and measuring how the glow changes
over short time intervals requires the use of a special telescope the Rossi
X Ray Timing Explorer (RXTE), which takes snapshots at a rate of 1000 per
second.  A common type of x- ray modulation seen in x-ray binary systems,
called a quasi-periodic oscillation (QPO), is thought to occur because the
hottest x-ray emitting part of the disk, in its swift orbit around the
black hole, is periodically occluded by the black hole itself.  The
gravitational fields at work are enormous after all, the inner edge of the
accretion disk is only tens of kilometers or so  from a black hole of about
7 solar masses.  The specific orbital radius can be deduced from the laws
of general relativity which predict a fixed "innermost stable orbit" for
matter circling a black hole.  In this case the predicted orbit is about 64
km.  Many theorists believe, however, that a black hole that spins would
have a much smaller event horizon and this would permit orbiting matter to
attain a much tighter innermost stable position, and a correspondingly
faster orbital rate.  At last week's APS meeting in Washington DC, Tod
Strohmayer of the Goddard Space Flight Center (301-286-1256) reported a
previously undiscovered QPO pattern in x rays from GRO J16550-40. The
frequency of this QPO, 450 Hz, is the highest ever seen for x rays coming
from a black hole system, implying an orbital radius of only 49 km a value
consistent, Strohmayer says, with a spinning black hole.  (Preprint on Los
Alamos server: astro- ph/0104487); video at
http://www.gsfc.nasa.gov/GSFC/SpaceSci/structure/spinningbh/spinningbhpix.htm