About three times a second, a 10, 000-year-old stellar
corpse sweeps a beam of gamma-rays toward Earth. Discovered by NASA's
Fermi Gamma-ray Space Telescope, the object, called a pulsar, is the
first one known that only "blinks" in gamma rays.
"This is the first example of a new class of pulsars that will give us
fundamental insights into how these collapsed stars work, " said
Stanford University's Peter Michelson, principal investigator for
Fermi's Large Area Telescope in Palo Alto, Calif.
The gamma-ray-only pulsar lies within a supernova remnant known as CTA
1, which is located about 4, 600 light-years away in the constellation
Cepheus. Its lighthouse-like beam sweeps Earth's way every 316.86
milliseconds. The pulsar, which formed about 10, 000 years ago, emits
1, 000 times the energy of our sun.
A pulsar is a rapidly spinning neutron star, the crushed core left
behind when a massive sun explodes. Astronomers have cataloged nearly
1, 800 pulsars. Although most were found through their pulses at radio
wavelengths, some of these objects also beam energy in other forms,
including visible light and X-rays. However, the source in CTA 1 only
pulses at gamma-ray energies.
"We think the region that emits the pulsed gamma rays is broader than
that responsible for pulses of lower-energy radiation, " explained
team member Alice Harding at NASA's Goddard Space Flight Center in
Greenbelt, Md. "The radio beam probably never swings toward Earth, so
we never see it. But the wider gamma-ray beam does sweep our way."
Scientists think CTA 1 is only the first of a large population of
similar objects.
"The Large Area Telescope provides us with a unique probe of the
galaxy's pulsar population, revealing objects we would not otherwise
even know exist, " says Fermi project scientist Steve Ritz, also at
Goddard.
The pulsar in CTA 1 is not located at the center of the remnant's
expanding gaseous shell. Supernova explosions can be asymmetrical,
often imparting a "kick" that sends the neutron star careening
through space. Based on the remnant's age and the pulsar's distance
from its center, astronomers believe the neutron star is moving at
about a million miles per hour -- a typical speed.
Fermi's Large Area Telescope scans the entire sky every three hours
and detects photons with energies ranging from 20 million to more
than 300 billion times the energy of visible light. The instrument
sees about one gamma ray every minute from CTA 1, enough for
scientists to piece together the neutron star's pulsing behavior, its
rotation period, and the rate at which it is slowing down.
A pulsar's beams arise because neutron stars possess intense magnetic
fields and rotate rapidly. Charged particles stream outward from the
star's magnetic poles at nearly the speed of light to create the
gamma-ray beams Fermi sees. Because the beams are powered by the
neutron star's rotation, they gradually slow the pulsar's spin. In
the case of CTA 1, the rotation period is increasing by about one
second every 87, 000 years.
"This observation shows the power of the Large Area Telescope, "
Michelson said. "It is so sensitive that we can now discover new
types of objects just by observing their gamma-ray emissions."
NASA's Fermi Gamma-ray Space Telescope is an astrophysics and particle
physics partnership, developed in collaboration with the U.S.
Department of Energy, along with important contributions from
academic institutions and partners in France, Germany, Italy, Japan,
Sweden, and the U.S.
A paper about the new pulsar appears in the Oct. 16 edition of Science
Express. For images and animations associated with this release,
visit: http://www.nasa.gov/fermi
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