Andrew Yee[_1_]
January 17th 08, 05:30 AM
Robert Naeye / Rob Gutro
Goddard Space Flight Center, Greenbelt, Md. January 2, 2008
301-286-4453/4044
PRESS RELEASE: 08-02
WHITE DWARF PULSES LIKE A PULSAR
GREENBELT, Md. -- New observations from Suzaku, a joint Japanese Aerospace
Exploration Agency (JAXA) and NASA X-ray observatory, have challenged
scientists' conventional understanding of white dwarfs. Observers had
believed white dwarfs were inert stellar corpses that slowly cool and fade
away, but the new data tell a completely different story.
At least one white dwarf, known as AE Aquarii, emits pulses of high-energy
(hard) X-rays as it whirls around on its axis. "We're seeing behavior like
the pulsar in the Crab Nebula, but we're seeing it in a white dwarf," says
Koji Mukai of NASA Goddard Space Flight Center in Greenbelt, Md. The Crab
Nebula is the shattered remnant of a massive star that ended its life in a
supernova explosion. "This is the first time such pulsar-like behavior has
ever been observed in a white dwarf." Mukai is co-author of a paper
presented at a Suzaku science conference in San Diego, Calif., in December.
White dwarfs and pulsars represent distinct classes of compact objects that
are born in the wake of stellar death. A white dwarf forms when a star
similar in mass to our sun runs out of nuclear fuel. As the outer layers
puff off into space, the core gravitationally contracts into a sphere about
the size of Earth, but with roughly the mass of our sun. The white dwarf
starts off scorching hot from the star's residual heat. But with nothing to
sustain nuclear reactions, it slowly cools over billions of years,
eventually fading to near invisibility as a black dwarf.
A pulsar is a type of neutron star, a collapsed core of an extremely massive
star that exploded in a supernova. Whereas white dwarfs have incredibly high
densities by earthly standards, neutron stars are even denser, cramming
roughly 1.3 solar masses into a city-sized sphere. Pulsars give off radio
and X-ray pulsations in lighthouse-like beams.
The discovery team, led by Yukikatsu Terada of Saitama University in Japan,
was not expecting to find a white dwarf mimicking a pulsar. Instead, the
astronomers were hoping to find out if white dwarfs could accelerate charged
subatomic particles to near-light speed, meaning they could be responsible
for many of the cosmic rays that zip through our galaxy and occasionally
strike Earth.
Some white dwarfs, including AE Aquarii, spin very rapidly and have magnetic
fields millions of times stronger than Earth's. These characteristics give
them the energy to generate cosmic rays.
To find out if this is happening, Terada and his colleagues targeted AE
Aquarii with Suzaku in October 2005 and October 2006. The white dwarf
resides in a binary system with a normal companion star. Gas from the star
spirals toward the white dwarf and heats up, giving off a glow of low-energy
(soft) X-rays. But Suzaku also detected sharp pulses of hard X-rays. After
analyzing the data, the team realized that the hard X-ray pulses match the
white dwarf's spin period of once every 33 seconds.
The hard X-ray pulsations are very similar to those of the pulsar in the
center of the Crab Nebula. In both objects, the pulses appear to be radiated
like a lighthouse beam, and a rotating magnetic field is thought to be
controlling the beam. Astronomers think that the extremely powerful magnetic
fields are trapping charged particles and then flinging them outward at
near-light speed. When the particles interact with the magnetic field, they
radiate X-rays.
"AE Aquarii seems to be a white dwarf equivalent of a pulsar," says Terada.
"Since pulsars are known to be sources of cosmic rays, this means that white
dwarfs should be quiet but numerous particle accelerators, contributing many
of the low-energy cosmic rays in our galaxy."
Launched in 2005, Suzaku is the fifth in a series of Japanese satellites
devoted to studying celestial X-ray sources. Managed by JAXA, this mission
is a collaborative effort between Japanese universities and institutions and
Goddard.
For related images to this story, please visit on the Web:
http://www.nasa.gov/centers/goddard/news/topstory/2007/whitedwarf_pulsar.html
For more information on Suzaku, please visit:
http://suzaku.gsfc.nasa.gov/
http://www.isas.jaxa.jp/e/
Goddard Space Flight Center, Greenbelt, Md. January 2, 2008
301-286-4453/4044
PRESS RELEASE: 08-02
WHITE DWARF PULSES LIKE A PULSAR
GREENBELT, Md. -- New observations from Suzaku, a joint Japanese Aerospace
Exploration Agency (JAXA) and NASA X-ray observatory, have challenged
scientists' conventional understanding of white dwarfs. Observers had
believed white dwarfs were inert stellar corpses that slowly cool and fade
away, but the new data tell a completely different story.
At least one white dwarf, known as AE Aquarii, emits pulses of high-energy
(hard) X-rays as it whirls around on its axis. "We're seeing behavior like
the pulsar in the Crab Nebula, but we're seeing it in a white dwarf," says
Koji Mukai of NASA Goddard Space Flight Center in Greenbelt, Md. The Crab
Nebula is the shattered remnant of a massive star that ended its life in a
supernova explosion. "This is the first time such pulsar-like behavior has
ever been observed in a white dwarf." Mukai is co-author of a paper
presented at a Suzaku science conference in San Diego, Calif., in December.
White dwarfs and pulsars represent distinct classes of compact objects that
are born in the wake of stellar death. A white dwarf forms when a star
similar in mass to our sun runs out of nuclear fuel. As the outer layers
puff off into space, the core gravitationally contracts into a sphere about
the size of Earth, but with roughly the mass of our sun. The white dwarf
starts off scorching hot from the star's residual heat. But with nothing to
sustain nuclear reactions, it slowly cools over billions of years,
eventually fading to near invisibility as a black dwarf.
A pulsar is a type of neutron star, a collapsed core of an extremely massive
star that exploded in a supernova. Whereas white dwarfs have incredibly high
densities by earthly standards, neutron stars are even denser, cramming
roughly 1.3 solar masses into a city-sized sphere. Pulsars give off radio
and X-ray pulsations in lighthouse-like beams.
The discovery team, led by Yukikatsu Terada of Saitama University in Japan,
was not expecting to find a white dwarf mimicking a pulsar. Instead, the
astronomers were hoping to find out if white dwarfs could accelerate charged
subatomic particles to near-light speed, meaning they could be responsible
for many of the cosmic rays that zip through our galaxy and occasionally
strike Earth.
Some white dwarfs, including AE Aquarii, spin very rapidly and have magnetic
fields millions of times stronger than Earth's. These characteristics give
them the energy to generate cosmic rays.
To find out if this is happening, Terada and his colleagues targeted AE
Aquarii with Suzaku in October 2005 and October 2006. The white dwarf
resides in a binary system with a normal companion star. Gas from the star
spirals toward the white dwarf and heats up, giving off a glow of low-energy
(soft) X-rays. But Suzaku also detected sharp pulses of hard X-rays. After
analyzing the data, the team realized that the hard X-ray pulses match the
white dwarf's spin period of once every 33 seconds.
The hard X-ray pulsations are very similar to those of the pulsar in the
center of the Crab Nebula. In both objects, the pulses appear to be radiated
like a lighthouse beam, and a rotating magnetic field is thought to be
controlling the beam. Astronomers think that the extremely powerful magnetic
fields are trapping charged particles and then flinging them outward at
near-light speed. When the particles interact with the magnetic field, they
radiate X-rays.
"AE Aquarii seems to be a white dwarf equivalent of a pulsar," says Terada.
"Since pulsars are known to be sources of cosmic rays, this means that white
dwarfs should be quiet but numerous particle accelerators, contributing many
of the low-energy cosmic rays in our galaxy."
Launched in 2005, Suzaku is the fifth in a series of Japanese satellites
devoted to studying celestial X-ray sources. Managed by JAXA, this mission
is a collaborative effort between Japanese universities and institutions and
Goddard.
For related images to this story, please visit on the Web:
http://www.nasa.gov/centers/goddard/news/topstory/2007/whitedwarf_pulsar.html
For more information on Suzaku, please visit:
http://suzaku.gsfc.nasa.gov/
http://www.isas.jaxa.jp/e/