From: revu@ellis.uchicago.edu (Sendhil Revuluri)
Subject: Physics News Update #109 (1/8)
Summary: Latest Physics News Update
Keywords: physics news interesting banana
Reply-To: revu@midway.uchicago.edu
Organization: University of Chicago
Date: Sat, 9 Jan 1993 04:00:42 GMT

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This is a "Physics News Update" distributed by Phillip Schewe of AIP
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Sendhil Revuluri (s-revuluri@uchicago.edu)
University of Chicago

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PHYSICS NEWS UPDATE
A digest of physics news items prepared by Phillip F. Schewe, AIP
Public Information
Number 109   January 8, 1993

THE TEMPERATURE OF THE UNIVERSE IS 2.726 K.  New
data from COBE's Far Infrared Absolute Spectrophotometer
(FIRAS) presented at this week's meeting of the American
Astronomical Society (AAS) in Phoenix show that the energy
spectrum of the cosmic microwave background is extremely close
to that of a perfect black body at 2.726 K.  The agreement
between the theoretical and observed spectra (consisting of
measurements at 34 different wavelengths from 0.5 to 5 mm) is 30
times better than for the FIRAS data released 3 years ago. 
FIRAS leader John Mather of NASA/Goddard (301-286-8720)
said the agreement is so good that constraints can be placed on
the amount of radiant energy in the universe (no more than 0.03%
of the total) that could have been emitted more than a year after
the big bang.  Some cosmologists have proposed that such energy
might have been released by supermassive supernovas, by black
holes, or by the decay of unstable particles.

A DENSE CLUMP OF DARK MATTER apparently lurks within
a small group of galaxies, the NGC 200 group (containing only 3
galaxies), according to scientists using the German satellite Rosat. 
The mass of the dark matter was estimated to be 10 to 30 times
that of the visible matter in the group, a ratio much higher than
was expected for such a small group of galaxies.  Dark matter
cannot be observed directly of course; rather, Rosat measured x
rays coming from a cloud of hot gas inside the group.  The
compact extent of the cloud (1.3 million light years across) and its
high temperature (10 million K) cannot be accounted for by the
constraining effects of the visible galaxies alone, but only by the
additional shepherding presence of the dark matter.  Richard
Mushotzky of NASA/Goddard, one of the scientists to report on
the Rosat results at the AAS meeting, suggested that if the density
of dark matter inferred for NGC 200 were typical of other areas
in the universe---and small galaxy groups are more common than
rich clusters (containing hundreds or thousands of galaxies) which,
ironically, seem to have a lower-than-expected amount of dark
matter---then there might be enough matter (dark plus visible)
present to brake and reverse the expansion of the universe.

A SOURCE OF INFRARED RADIATION HAS BEEN
DISCOVERED NEAR THE GALACTIC CENTER at the
location of the object called Sgr A*.  The new IR results reinforce
the idea, established by previous measurements of Sgr A* at radio,
x-ray, and gamma wavelengths, that a black hole resides at the
core of the Milky Way.  At the AAS meeting, Laird Close of the
University of Arizona (602-621-6523) presented pictures of the
galactic core at wavelengths of 1.6 and 2.2 microns made using the
2.3-m telescope at Kitt Peak.  The observations, employing
adaptive-optics techniques in the infrared for the first time, had
sufficient resolution to show that the IR source was no larger than
0.006 light years across.  Arizona astronomer Joseph Haller
presented separate IR studies of the velocities of stars as a
function of distance out from Sgr A* showing that the velocities
increased from nearly zero at a distance of 1.4 light years from Sgr
A* to a velocity of nearly 100 km/sec at a distance of 0.7 light
years. This pattern, plus the determination that there must be at
least 100 times more mass inside the 0.7-light-year distance than
can be accounted for by the observable stars alone, suggests to
Haller that there should be a 900,000-solar-mass black hole at Sgr
A*.
Newsgroups: sci.physics