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Studying the properties of neutron stars offers a unique window into the properties of nuclear
matter. Measuring neutron star masses and radii yields direct information about the interior composition
that can be compared with theoretical predictions. Studies of young radio pulsars and the remarkable
magnetar subclass have revealed that as many as one in ten neutron stars, which have descended from
normal stars, are born with magnetic fields that exceed 10 14 times that of our Sun. What sets this fraction,
and whether or not the birth of these highly magnetic neutron stars visibly alters the supernovae event, are
actively under investigation. Progress here will depend on large supernovae surveys as well as continued
radio and X-ray pulsar observations. The most rapidly rotating neutron stars appear to spin on their axes
about once every one and a half milliseconds, by accreting material from a rapidly rotating disk of matter
donated from a companion star. However, ever more sensitive radio pulsar surveys continue to find that
the maximum spin rate observed is surprisingly less than the maximum possible value, leading to the
speculative suggestion that gravitational wave emission regulates the maximum rate. This hypothesis is
testable with Advanced LIGO.
The Chemistry of the Universe
Many astrophysical processes exhibit rich chemical signatures and products. The cycle of matter
in our Galaxy proceeds from the expulsion of matter into interstellar space from dying stars, where it
undergoes chemical transformations and eventual incorporation into diffuse clouds and dense molecular
clouds. Well over 140 molecules, rich in organic material, have been detected in the interstellar medium
by radio, microwave and infrared techniques, and this is almost certainly the tip of the interstellar
chemical iceberg (Figure 2-13). Thanks to the diverse range of interstellar energy sources and
FIGURE 2‐13 Some of the many forms that carbon may take in interstellar molecules. From Ehrenfreund P. and
Charnley, S. 2000. Organic molecules in the interstellar medium, comets and meteorites: A voyage from dark
clouds to the early Earth. Credit: Pascale Ehrenfreund and Steven B. Charnley, “Organic Molecules in the
Interstellar Medium, Comets, and Meteorites: A Voyage from Dark Clouds to the Early Earth,” Annual Review of
Astronomy and Astrophysics 38, 427‐483, 2000.
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