Number 135, July 1, 1993 by Phillip F. Schewe and Ben Stein
DURING THE LAST THREE MINUTES before two neutron stars or two black
holes spiral in on each other and coalesce there should be a "chirp"
in which the gravitational-wave emission from the system increases in frequency
from 10 up to 1000 Hz. Since this sort of dying gasp is just what proposed
gravitational wave detectors such as LIGO (in the US) and VIRGO (in Italy)
would be looking for, scientists at Caltech and Northwestern have produced
computer simulations of waveforms from such collapsing binary systems so
that they'll be able to separate signal from noise when the time comes
(Curt Cutler et al., Physical Review Letters, 17 May 1993). The shape of
the signal may enfold more information than was previously thought. For
example, in some cases it might be possible to calculate the neutron stars'
mass, density, and composition. (Science News, 26 June 1993.)
NEUTRINO MASS AND SOLAR NEUTRINO UPDATE . At the Moriond neutrino meeting
held in February in Switzerland, the latest neutrino mass limits reported
were 8 eV for the mass of the electron antineutrino (a Livermore result)
and 7.2 eV for electron neutrinos (Mainz). Both limits were established
in tritium beta decay experiments. As for the solar neutrino problem, a
combination of results from the two gallium detector groups, SAGE (former
Soviet Union) and GALLEX (Italy), gives a measured flux value of 72 solar
neutrino units (one SNU equals 10**-36 neutrino captures per second per
detector target atom). This is still low compared to the standard solar
model prediction of 125-132 SNU. (CERN Courier, June 1993.)
RADIOACTIVE BEAMS, beams in which non-naturally-occurring isotopes with
specially tailored ratios of protons to neutrons, are helping scientists
study the extremes of nuclear stability. The inventory of stable nuclei
is usually portrayed as a zone on a plot whose axes are proton number (y
axis) and neutron number (x axis). The upper border of this zone---the
proton dripline---reflects the fact that a nucleus becomes unstable because
of Coulomb repulsion if there are too many protons. The lower border---the
neutron dripline---corresponds to the case of a nucleus having too many
neutrons, which taxes the strong interaction's ability to hold the nucleus
together. Radioactive beamlines at Michigan State, RIKEN (Japan), Louvain-la-Neuve
(Belgium), and elsewhere allow nuclear physicists to better map the driplines,
which in turn allow the study of several nuclei phenomena, such as the
formation of heavy nuclei in the high-density environment of neutron stars
or supernovae. (Science, 25 June 1993.)
EXPECTED DEVELOPMENTS AND DISCOVERIES IN ASTRONOMY over the next twenty
years include the return of humans to the Moon, a consensus on a value
for the Hubble Constant, the launch of an 8-meter orbiting optical telescope,
rock samples returned from Mars, a mission to Pluto, the observation and
study of mature planetary systems around nearby stars, and the imaging
of the surfaces of other stars. These are some of the predictions offered
by various scientists in the 20th anniversary issue of Astronomy Magazine.
Many of those asked were less certain about establishing the nature of
dark matter or unequivocally demonstrating the existence of black holes.
(Astronomy, Aug 1993.)
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