Molecules in a Bose-Einstein condensate
1 April 2000
The presence of Rb molecules in a Bose-Einstein condensate of Rb
atoms, first created at the University of Colorado in 1995, has
been experimentally demonstrated at the University of Texas. The
two-atomic molecules (dimers) are produced when two nearby atoms
absorb a photon and then emit another one - a photo-dissociation
process which leads to an effective cooling of Rb2 molecules to
about 100 nK. With low thermal velocities making the molecules
amenable to a high-resolution spectroscopic study, they were
found to have a lifetime of 1 ms and to account for about 1% of
1 April 2000
A 10-nm free-electron UV laser has been constructed at the DESY
lab in Hamburg by the TESLA research group. Free-electron lasers
normally depend for their operation on the so-called `undulator,'
a device capable of producing radiation in the frequency range
unattainable by other means. The light emitted by electrons in
this device (due to small-amplitude oscillations perpendicular to
very nearly straight travel line) is stored in a mirrored cavity
and stimulates a coherent radiation. At wavelengths below 150 nm,
however, the cavity walls do not reflect effectively enough to
secure the light accumulation process. The TESLA experiment
involves instead a single pass of light through a very long
undulation section, a coherent synchrotron radiation resulting
from the light-electron interaction. Besides an analogous 5-nm-
wavelength laser planned for 2003, the development of a 500-GeV
linear electron accelerator with an integrated X-ray laser will
possibly benefit from the new technique.
Physics News Update, Number 473
Dark matter particles detected?
1 April 2000
Contrary to the view that the Universe is mainly made of stars,
gas, and dust, it is now well established that it is actually
dominated by the `dark matter' (or `hidden mass') of unknown
nature, which is only felt through its interaction with the
normal matter and which, in particular, forms the extended
massive halo around our galaxy. Possible candidates for dark
matter particles are the so-called "weakly interacting massive
particles" (WIMPs). Although attempts to detect dark matter
particles directly - by, say, observing recoil nuclei in the
scintillation material - are being made in many laboratories
around the world, thus far none of them has been successful due
to the extremely weak interaction involved and because of the
large number of low-energy background recoil nuclei. Yet, the
DAMA experiment at the Gran Sasso National Lab in Italy now
reports seasonal variations in the number of such recoil nuclei.
This may be due to the fact that the orbital motion of the Earth
superposes on the solar system's motion through the Milky Way
halo thus causing both the WIMP velocity in a detector and the
intensity of WIMP-nucleus interactions to vary in time over the
calendar year. The mass of the observed WIMPs is estimated to be
about 50 times that of the proton. The study is still at the
preliminary stage and alternative interpretations of the observed
seasonal variations are possible as well. Further independent
experiments will hopefully clarify the matter.
Observations of the M31 core
1 April 2000
New high-resolution images from the Chandra X-ray Observatory
revealed five point X-ray sources in the central 1' region of the
core of the galaxy M31 in the Andromeda Nebula, one of which, 1''
off the centre, is thought to be a supermassive black hole. While
the black hole in M31's core is about 3×107 times more massive than
the sun according to previous observations, this source has an
unusually soft X-ray spectrum, suggesting that the x-ray
radiation is generated when an accretion disk forms around the
black hole. A theoretical explanation of the observed spectral
feature has yet to be found. Another X-ray source, 26'' off the
centre, may be identified with a stellar mass black hole that
emits radiation as the material of a neighbouring star is
accreting onto it.
New type of quasar
1 April 2000
According to R Antonucci's 1985 unified scheme, the precise type
of the activity of a galactic nucleus depends on how the line of
sight is oriented relative to the rotation axis of the central
black hole. This idea has now been confirmed by the Chandra
observations of a galaxy whose nucleus is a powerful X-ray source
but which shows little or no quasar activity in the optical and
radio range. The Chandra team (led by A Fabian) called the new
type of galaxy a Type 2 quasar.
The Extracts from the Internet is a section of Uspekhi Fizicheskih Nauk (Physics Uspekhi) the monthly rewiew journal of the current state of the most topical problems in physics and in associated fields. The presented News is devoted to the fundamental discoveries of physics and astrophysics.
Permanent editor is Yu.N. Eroshenko.
It is compiled from a multitude of Internet sources.