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Tour of AM CVn
Narrator (April Hobart, CXC): In the middle of the twentieth century, an unusual star
was spotted in the constellation of Canes Venatici (Latin for "hunting dogs"). Years
later, astronomers determined that this object, dubbed AM Canum Venaticorum (or, AM CVn, for
short), was, in fact, two stars. These stars revolve around each other every 18 minutes,
and are predicted to generate gravitational waves - ripples in space-time predicted by
Einstein.
Today, the name AM CVn represents a class of objects where one white dwarf star is pulling
matter from a very compact companion star, such as a second white dwarf. (White dwarf
stars are dense remains of Sun-like stars that have run out of fuel and collapsed to
the size of the Earth.) The pairs of stars in AM CVn systems orbit each other extremely
rapidly, whipping around one another in an hour, and in one case as quickly as 5 five
minutes. By contrast, the fastest orbiting planet in our Solar System, Mercury, orbits
the Sun once every 88 days.
Despite being known for almost 50 years, the question has remained: where do AM CVn systems
come from? New X-ray and optical observations have begun to answer that with the discovery
of the first known systems of double stars that astronomers think will evolve into AM
CVn systems.
Observations with optical telescopes on the ground helped identify two systems, known
as J0751 and J1741, that contain two white dwarfs and determined their masses. Scientists
used Chandra to help rule out the possibility that J0751 and J1741 contained neutron stars.
A neutron star - which would disqualify it from being a possible parent to an AM CVn
system - would give off strong X-ray emission due to its magnetic field and rapid rotation.
No X-ray emission was seen from either system, thus convincing scientists that these were
going to evolve into AM CVn in the future.
As we mentioned before, AM CVn systems are of interest to scientists because they are
predicted to be sources of gravitational waves. This is important because even though such
waves have yet to be detected, many scientists and engineers are working on instruments that
should be able to detect them in the near future. This will open a significant new observational
window to
the universe.