Bizarre pulsar just gets stranger
Pastor Dale Morgan
Bizarre pulsar just gets stranger*
Science and space news on USATODAY.com
By Clara Moskowitz,
Pulsars are like cosmic lighthouses sending out sweeping beams that
blink at us across the galactic expanse. Now scientists have spotted a
wacky pulsar that doesn't behave exactly like its fellows: Instead of
circling a white dwarf star, this one orbits a sun-like star along an
oval path.
All other known pulsars that rotate as quickly as this one seem to have
picked up speed by pulling off mass from a companion star that has
reached the advanced stage of red giant, when its gaseous layers bloat
out prior to the end-stage of life as a very compact, dim, white dwarf.
"The fact that it's around a sun-like star is fascinating because if
that is the companion to this pulsar, then it certainly didn't accrete
matter from that star — it hasn't been a red giant yet," said David
Champion, an astronomer at Canada's McGill University.
To account for this odd duck, called PSR J1903+0327, scientists have
concocted a few new ideas, including the possibility that the pulsar
originated in a globular cluster with a different companion, but was
kicked out by a near-miss with another star.
"The reason why we're so excited about this is the impact it might have
on our understanding of where the pulsars that we look at are coming
from," Champion told SPACE.com. "We've never seen anything like this
before."
Champion and his colleagues detail their findings in the May 15 issue of
the journal Science.
Quite a surprise
Pulsars are thought to form when a massive star reaches the end of its
life and explodes in a supernova. The remnants of these stars sometimes
collapse into neutron stars, so-called because they are so dense that
the protons and electrons that formed the star's atoms have been
squashed into neutrons (if the original star was even more massive, it
would collapse into a black hole).
Not only is the star's matter tightly-packed after all this squashing,
but the star's magnetic field is compressed into a tiny space as well.
Scientists think this powerful field accelerates charged particles
around the star, causing them to emit radiation that is focused into a
beam by the magnetic field lines.
As these neutron stars rotate, so too do their light beams. If a neutron
star happens to be shooting out its jet in our direction, we call it a
pulsar, because we see a pulse every time the rotating beam reaches us.
Usually, pulsars slow down in their rotation over time as they lose
energy. When one attains a speed as fast as PSR J1903+0327, which
rotates every 2.15 milliseconds, scientists think it has "recycled"
itself by sucking up mass from a companion red dwarf. When this happens,
scientists usually see a quickly spinning pulsar orbiting around a white
dwarf (the end stage of a red giant) in a circular orbit (the red
giant's tidal forces stabilize the pulsar's orbit into a circle).
"This new pulsar is quite a surprise," Champion said, referring to the
new object's oblong orbit around a sun-like star.
Cozy origins
The scientists speculate that the strange pulsar may have started out in
a globular cluster, where stars are much closer to each other and
interact more often than in the rest of the galaxy. In this case, it
would have originally gone through the normal recycling process, but
lost its aged red giant companion when a younger sun-like star came
flying in and knocked it away.
Another hypothesis is that the pulsar originated in a triple star
system, but its main red giant companion was destroyed.
The team hopes further study of this unique object will help solve the
mystery and teach us more about how pulsars form.
"It's always the most unusual objects that advance our understanding the
most in these cases," Champion said.