Astronomers examined the remnants of a stellar explosion with NASA’s Chandra
X-ray Observatory and discovered one of the youngest known pulsars. The
properties of this pulsar, a neutron star rotating 15 times a second, will
enable scientists to better understand how neutron stars are formed in the
seconds just before a supernova explosion, and how they pump energy into the
space around them for thousands of years after the explosion.
A team led by Stephen Murray of the Harvard-Smithsonian Center for
Astrophysics in Cambridge, MA studied 3C58, the remains of a supernova
observed on Earth in 1181 AD in the constellation Cassiopeia. In addition
to a pulsating central source they observed an extended X-ray source
surrounding the pulsar thought to be produced by a cloud of high-energy
particles about 20 light years across.
These results were presented at the “Two Years of Science with Chandra”
symposium in Washington, D.C. According to Murray, “Our discovery shows
that all pulsars are not born equal. This pulsar is about the same age as
the Crab Nebula pulsar, but there is little family resemblance.”
Murray explained that the 3C 58 pulsar, which is now rotating at about half
the rate of the Crab pulsar, is rotating almost as fast as it was when it
was formed.
In contrast, the Crab pulsar was formed spinning much more rapidly and has
slowed to about half its initial speed. Conventional theory has assumed that
all pulsars were like the Crab, born with rapid rotation and then have spun
down considerably. The observations of 3C58, along with Chandra observations
by another group of scientists of a pulsar associated with the supernova of
386 AD have cast doubt on that assumption, however.
Furthermore, the X-ray power of 3C58 and its surrounding nebula are 20,000
and 1,000 times weaker than the Crab pulsar and its surrounding nebula
respectively. One possibility for the low power of 3C58 is that the energy
flow from its pulsar is primarily in the form of electromagnetic fields, so
the energy is transported to much greater distances from the pulsar, where
it has yet to be detected. Another possibility is that the association of
3C58 with the supernova of 1181 AD is spurious, in which case 3C58 would
be much older. In view of the lack of other radio and X-ray sources that
could be the remnant of Supernova 1181 AD, this is considered unlikely.
The team also used X-ray data taken by NASA’s Rossi X-ray Timing Explorer
satellite in 1997 to confirm the existence of the pulsar and to measure
its present slow-down rate. The Chandra observations were made on November
30, 1999, and December 23, 2000, using the High Resolution Camera (HRC),
which was built by the Smithsonian Astrophysical Observatory in Cambridge,
Mass. under the direction of Stephen Murray.
NASA’s Marshall Space Flight Center, Huntsville, Ala., manages the Chandra
program for the Office of Space Science, Washington, D.C. TRW, Inc.,
Redondo Beach, Calif., is the prime contractor for the spacecraft. The
Smithsonian’s Chandra X-ray Center controls science and flight operations
from Cambridge, Mass.
Images associated with this release are available on the World Wide Web at:
AND
IMAGE CAPTION:
[http://www1.msfc.nasa.gov/NEWSROOM/news/photos/2001/photos01-301.htm]
Chandra’s image of 3C58, the remains of a supernova observed on Earth in
1181 AD, shows a rapidly rotating neutron star embedded in a cloud of high
energy particles. The data revealed that the neutron star, or pulsar, is
rotating about 15 times a second, and is slowing down at the rate of about
10 microseconds per year.
A comparison of the rate at which the pulsar is slowing down and its age
indicate that the 3C58 pulsar, one of the youngest known pulsars, is rotating
just about as fast now as when it was formed. This is in contrast to the Crab
pulsar, which was formed spinning much more rapidly and has slowed to about
half its initial speed. Furthermore, the total X-ray luminosity of the 3C58
pulsar and its surrounding nebula is a thousand times weaker than that of
the Crab and its surrounding nebula.
Scientists hope that further study of the similarities and differences in
the behavior of these two pulsars, which are approximately the same ages,
will shed light on the process by which they are formed, and how they pump
energy into space for thousands of years after the explosion.
Credit: NASA/CXC/SAO/S. Murray et al.
