23 research outputs found
The same frequency of planets inside and outside open clusters of stars
Most stars and their planets form in open clusters. Over 95 per cent of such
clusters have stellar densities too low (less than a hundred stars per cubic
parsec) to withstand internal and external dynamical stresses and fall apart
within a few hundred million years. Older open clusters have survived by virtue
of being richer and denser in stars (1,000 to 10,000 per cubic parsec) when
they formed. Such clusters represent a stellar environment very different from
the birthplace of the Sun and other planet-hosting field stars. So far more
than 800 planets have been found around Sun-like stars in the field. The field
planets are usually the size of Neptune or smaller. In contrast, only four
planets have been found orbiting stars in open clusters, all with masses
similar to or greater than that of Jupiter. Here we report observations of the
transits of two Sun-like stars by planets smaller than Neptune in the
billion-year-old open cluster NGC6811. This demonstrates that small planets can
form and survive in a dense cluster environment, and implies that the frequency
and properties of planets in open clusters are consistent with those of planets
around field stars in the Galaxy.Comment: 18 pages, 6 figures, 1 table (main text + supplementary information
Relativistic Binaries in Globular Clusters
Galactic globular clusters are old, dense star systems typically containing
10\super{4}--10\super{7} stars. As an old population of stars, globular
clusters contain many collapsed and degenerate objects. As a dense population
of stars, globular clusters are the scene of many interesting close dynamical
interactions between stars. These dynamical interactions can alter the
evolution of individual stars and can produce tight binary systems containing
one or two compact objects. In this review, we discuss theoretical models of
globular cluster evolution and binary evolution, techniques for simulating this
evolution that leads to relativistic binaries, and current and possible future
observational evidence for this population. Our discussion of globular cluster
evolution will focus on the processes that boost the production of hard binary
systems and the subsequent interaction of these binaries that can alter the
properties of both bodies and can lead to exotic objects. Direct {\it N}-body
integrations and Fokker--Planck simulations of the evolution of globular
clusters that incorporate tidal interactions and lead to predictions of
relativistic binary populations are also discussed. We discuss the current
observational evidence for cataclysmic variables, millisecond pulsars, and
low-mass X-ray binaries as well as possible future detection of relativistic
binaries with gravitational radiation.Comment: 88 pages, 13 figures. Submitted update of Living Reviews articl
The use of commercial alcohol products to sterilize bones prior to DNA sampling
In disaster situations it is not always possible to maintain an adequate supply of standard equipment and sterilizing solutions. We have compared bone samples from cadavers cleaned in commercial white alcohol to samples from the same individuals cleaned with 95% surgical spirit. We have found that it is possible to use a commercial, white spirit to clean specimens taken from human cadavers femoral diaphysis collected for DNA analysis.Carl Winskog, Helena Nilsson, Kerstin Montelius and Bertil Lindblo