PHYSICS NEWS UPDATE A digest of physics news items prepared by Phillip F. Schewe, AIP Publ

PHYSICS NEWS UPDATE
A digest of physics news items prepared by Phillip F. Schewe, AIP
Public Information
Number 160  January 14, 1994

A REJUVENATED HUBBLE SPACE TELESCOPE can now do
what it was built to do---glimpse faint objects 12 billion light years
away as well as provide unprecedentedly sharp views of nearer
objects such as individual stars in certain galaxies.  This is essential
since to better establish the existence of black holes it is necessary to
observe the motions and not just the density of stars near the
hypothetical black hole.  Also the observation of single Cepheid
variable stars in galaxies 50 to 100 million light years away will
improve the calculation of astrophysical distances and consequently
the determination of the Hubble constant.  Hubble scientists spoke at
this week's meeting of the American Astronomical Society (AAS) in
Virginia. They recounted the flawless repair mission carried out in
December by Space Shuttle astronauts, including the installation of a
corrective-optics package for the main mirror and a new wide field
planetary camera and showed "before" and "after" pictures of various
celestial objects, thus showcasing Hubble's crisp new vision.  Optical
tests are nearly complete, after which scientific observations will
resume.

GALAXY M81 LACKS DARK MATTER.  The very idea of dark
matter arose partly to explain the velocity profile of matter swirling
around spiral galaxies.  In many such galaxies the velocity of objects
(determined by the doppler shift of their light emissions) seemed to
be nearly constant as a function of the distance out from the center of
the galaxy.  Such a distribution would not occur, many scientists
believed, unless a considerable amount of nonluminous matter were
present in or near the galaxy.  But new measurements of the neutral
hydrogen in galaxy M81, made with the Very Large Array radio
telescope, indicate that the velocity of hydrogen falls off with radial
distance from the galactic center, a distribution suggesting a lack of
dark matter.  David Adler of the National Radio Astronomical
Observatory and David Westpfahl of the New Mexico Institute of
Mining and Technology said that these results, announced at the AAS
meeting, demonstrated that dark matter is not distributed in uniform
amounts among galaxies.

GAMMA-RAY FLASHES IN EARTH'S ATMOSPHERE have been
observed by the Compton Gamma Ray Observatory (GRO), according
to Neil Gehrels of NASA Goddard, who spoke at the AAS meeting.
The GRO looks for gammas from across the sky out to the furthest
corners of the universe; scientists had not expected to see them at our
home planet, Gehrels said.  He suggested that the flashes might be
occurring over intense storms and may result from upward-going
lightning.

THE SOLAR CHROMOSPHERE IS COLDER than we thought.  The
chromosphere is the region between the photosphere (the sun's
surface, at a temperature of about 6000 K) and the corona (whose
temperature is 1 million K or more).  Previously scientists had
figured that the chromosphere temperature was relatively cool---an
estimated 4300 K at an altitude of 500 km above the sun's surface---
but new measurements made at Kitt Peak show that the chromosphere
is colder than this.  High-resolution infrared observations of carbon
monoxide molecules at the limb of the sun provide a new minimum
temperature of 3500 K which, furthermore, seems to occur at a
higher altitude, 1100 km.  Robert Noyes of Harvard Smithsonian says
that carbon monoxide clouds may be a transitory phenomenon in the
solar atmosphere.  (Science, 7 Jan. 1994, Science News, 8 Jan.)