Astronomers using the National Science Foundation’s (NSF) newly
commissioned Robert C. Byrd Green Bank Telescope (GBT) have detected
remarkably faint radio signals from an 820 year-old pulsar, making it
the youngest radio-emitting pulsar known. This discovery pushes the
boundaries of radio telescope sensitivity for discovering pulsars, and
will enable scientists to conduct observations that could lead to a
better understanding of how these stars evolve.

“Important questions about pulsars may be answered by long-term
monitoring of objects such as the one we just detected,” said Fernando
Camilo of Columbia University in New York City. “Young pulsars are
particularly rare, and being able to study such a young one at radio
wavelengths provides an outstanding opportunity to learn critical facts
about their evolution and workings.” The results of this research,
based on observations conducted on February 22-23, 2002, were accepted
for publication in the Astrophysical Journal Letters.

Scientists have long suspected that a pulsar – a rapidly spinning,
superdense neutron star – was born when a giant star ended its life in a
cataclysmic supernova explosion observed in late summer of 1181, as
suggested by Japanese and Chinese historical records. For the past 20
years, astronomers have searched this supernova remnant (3C58), located
10,000 light-years away in the constellation Cassiopeia, for the
telltale pulsations of a newly born pulsar. Late in 2001, data from
NASA’s Chandra X-ray satellite confirmed its existence, but it remained
an elusive quarry for radio telescopes.

“We believed from historical records and certainly knew from recent
X-ray observations that this star was there,” Camilo remarked, “but
despite many attempts, no one had been able to find any radio pulsations
from it because the signals are, it turns out, incredibly weak.” For
comparison, this pulsar’s radio emission is some 250 times weaker than
that from the famous pulsar in the Crab Nebula (the remnant of an
explosion in the year 1054 recorded by Chinese astronomers and possibly
also by Native Americans of the Anasazi tribe in modern-day Arizona and
New Mexico).

“Although we knew what we were looking for,” said Camilo “it took the
new Green Bank Telescope with its unmatched sensitivity – and,
importantly, location in the National Radio Quiet Zone – to make this
remarkable detection.”

A pulsar is formed when a massive star runs out of nuclear fuel and dies
in a cataclysmic explosion called a supernova. The outer layers of the
star are blown off into space, and are often seen as an expanding
remnant shell of hot gas. The core of the star, with 40 percent more
mass than our Sun, collapses under its own gravity to a sphere only
about 10 miles in diameter, composed mostly of neutrons. These densest
objects known in the Universe typically are born spinning very rapidly;
the newly detected pulsar, known as PSR J0205+6449, presently rotates 15
times every second.

The spinning neutron star has very powerful magnetic and electric fields
that accelerate electrons and other subatomic particles, causing them to
emit beams of radio waves, X-rays, and other forms of radiation. If
these beams intersect the Earth as the star rotates, we can then detect
the pulsar, as it appears to flash on-and-off, much like a lighthouse.
As the pulsar ages, it gradually slows down and loses its rotational
energy. After a few million years it is no longer powerful enough to
generate radio emission and “turns-off.”

By detecting this pulsar in the radio spectrum, astronomers may now
follow its evolution with greater ease and flexibility than with X-ray
telescopes on satellites, study the pulsar emission mechanisms, and also
characterize the dynamic interstellar medium between the Earth and the

“Finding a radio pulsar this young could be somewhat of a gold mine for
years to come,” noted Camilo. “We can very precisely measure how its
rate of rotation changes over time, potentially inferring fundamental
clues about what causes a magnetized neutron star to spin down. We also
will make valuable comparisons to the X-ray data, which may help us
determine exactly how these objects generate and emit radiation.”

The researchers also point to the fact that this discovery bodes well
for the GBT being able to study additional young pulsars that have
previously escaped detection. “By using this magnificent new telescope,
we should be able to discover other very young pulsars that we surmise
are there, but are simply too weak to detect by any other means,” said
Camilo. “Measuring the luminosity and spectrum of a large sample of
these stars will be crucial for making an accurate census of pulsars in
our Galaxy.”

The researchers used the new Berkeley-Caltech Pulsar Machine to process
the signals from the GBT and record them for later analysis.

The group led by Camilo in this investigation consists also of: Ingrid
H. Stairs (NRAO Green Bank, West Virginia); Duncan R. Lorimer, Michael
Kramer, Maura A. McLaughlin (University of Manchester, Jodrell Bank
Observatory, Cheshire, U.K.); Donald C. Backer (University of
California, Berkeley); Scott M. Ransom (McGill University, Montreal,
Canada); Bernd Klein, Richard Wielebinski, Peter Muller
(Max-Planck-Institut fur Radioastronomie, Bonn, Germany); and Zaven
Arzoumanian (Universities Space Research Association/NASA-Goddard Space
Flight Center, Greenbelt, Maryland).

The GBT is the world’s largest fully steerable radio telescope. It was
dedicated on August 25, 2000.

The National Radio Astronomy Observatory is a facility of the National
Science Foundation, operated under cooperative agreement by Associated
Universities, Inc.

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Graphic of pulsar:

Caption: “A pulsar is a rapidly spinning neutron star. It is a sphere
composed mostly of neutrons, approximately 10 miles in diameter, but
with 40 percent more mass than the Sun. A typical pulsar has a magnetic
field a trillion times stronger than the Earth’s, represented by the red
belts emanating from its surface. These fields and associated
electrical fields accelerate electrons and other subatomic particles to
nearly the speed of light, causing them to emit beams of radio waves and
other forms of radiation. As the pulsar rotates, these beams sweep
across space. If the beams intersect the Earth, the pulsar can be seen
switching ‘on’ and ‘off,’ much like a lighthouse.”

Images of the Green Bank Telescope are on: