IP: Spinning Black Hole

[David Farber <dave@farber.net>]

>From: "PAUL JULIEN" <p.julien@worldnet.att.net>
>To: <farber@cis.upenn.edu>
>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.ht
>m  ,
>
>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.ht
>m



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