Number 256, January 26, 1996 by Phillip F. Schewe and Ben Stein
MACHOS MAY MAKE UP A CONSIDERABLE FRACTION OF DARK MATTER in our galaxy's
halo, a new study shows. Last year the MACHO (massive compact halo object)
collaboration announced the observation of three events in which the light
from a star in the Large Magellanic Cloud brightened as a result of gravitational
microlensing by a nonluminous object lying in the galactic halo along our
line of sight. At last week's meeting of the American Astronomical Society
in San Antonio, David Bennett of Livermore announced that the MACHO team
has now recorded seven events. Since their report last year, the team has
improved the sensitivity of its detection process, both of lighter halo
objects (down to 10**-6 solar masses) and heavier objects (1 solar mass).
The greater mass sensitivity was decisive: the seven events appear to correspond
to white dwarfs in the range 0.1 to 1.0 solar masses. The MACHO group finds
these needles in a haystack by taking pictures of the 9 million stars every
night and looking for telltale light enhancements. The event sample is
not very large, but the researchers are so confident of their events that
they use the number to estimate a value of at least 50% as the likely contribution
of MACHOs to the dark matter believed to be lurking in the halo.
SPACEBORNE PARTICLE PHYSICS . Major new accelerators in the U.S. are
too costly, so some particle physicists hope to shift their operations
into space. SLAC has proposed building the $100- million Gamma Large Array
Space Telescope (GLAST), which would view gamma rays with stacks of silicon
microstrip detectors, some 50-100 times more sensitive than the detectors
used in the present Gamma Ray Observatory. Meanwhile, Sam Ting of MIT plans
to build to the Alpha Magnetic Spectrometer (AMS), a $20-million device
to be mounted on Space Station Alpha. AMS would use a powerful permanent
magnet to sort antiparticles from particles, the goal being to search for
antimatter in the universe and for the decay of dark matter particles (Science,
12 January 1996.)
THE FIRMEST EVIDENCE YET FOR D-WAVE SUPERCONDUCTIVITY has been found
by an IBM-Watson team (contact John Kirtley, kirtley@watson.ibm.com). Studying
small rings of a thallium-barium-copper-oxide superconductor, the team
indirectly detected phase shifts in the electron pairs which travel through
this high-temperature superconducting material without electrical resistance.
Such phase shifts are not possible in the "s- wave" electron
pairs (pairs with no relative angular momentum) that operate in low-temperature
superconductors. Previous studies of yttrium-barium-copper-oxide superconductors
suggested the presence of phase shifts, but effects owing to the peculiarities
of those complex materials could not be ruled out. (D. Tsuei et al., Science,
19 January 1996.)
13,285 PHYSICS GRADUATE STUDENTS IN THE U.S. IN 1994 . A new report by
the American Institute of Physics offers this profile: 15% were women (up
from 5% in 1970); the average time taken to earn a PhD was 6.5 years (5.3
years in 1970); condensed matter was the largest area of study (25%); 45%
were not U.S. citizens (China accounted for 30% of these); among U.S. physics
graduate students 90% were white, 5% Asian, 2% Hispanic, and 2% African
American. (Contact Patrick Mulvey at AIP, 301-209- 3070.)
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