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April
5, 2006: NASA's Spitzer Space Telescope has uncovered
new evidence that planets might rise up out of a dead star's
ashes.
The
infrared telescope surveyed the scene around a pulsar, the
remnant of an exploded star, and found a surrounding disk
made up of debris shot out during the star's death throes.
The dusty rubble in this disk might ultimately stick together
to form planets.
This
is the first time scientists have detected planet-building
materials around a star that died in a fiery blast.
![see caption](images/pulsarplanets/ssc2006-10b_small_strip.jpg)
Above:
An artist's concept of a planet-forming disk around pulsar
4U 0142+61. [Movie]
The
paper on the Spitzer finding appears in the April 6 issue
of Nature. Other authors of the paper are lead author Zhongxiang
Wang and co-author David Kaplan, both of the Massachusetts
Institute of Technology.
"We're
amazed that the planet-formation process seems to be so universal,"
says Deepto Chakrabarty of the Massachusetts Institute of
Technology, principal investigator of the new research. "Pulsars
emit a tremendous amount of high energy radiation, yet within
this harsh environment we have a disk that looks a lot like
those around young stars where planets are [being born]."
The
finding represents the missing piece in a puzzle that arose
in 1992, when Aleksander Wolszczan of Pennsylvania State University
found three planets circling a pulsar called PSR B1257+12.
Those pulsar planets, two the size of Earth, were the first
planets of any type ever discovered outside our solar system.
Astronomers have since found indirect evidence the pulsar
planets were born out of a dusty debris disk, but nobody had
directly detected this kind of disk until now.
The
pulsar observed by Spitzer, named 4U 0142+61, is 13,000 light-years
away in the constellation Cassiopeia. It was once a large,
bright star with a mass between 10 and 20 times that of our
sun. The star probably survived for about 10 million years,
until it collapsed under its own weight about 100,000 years
ago and blasted apart in a supernova explosion.
Some of the debris,
or "fallback," from that explosion eventually settled
into a disk orbiting the shrunken remains of the star, or
pulsar. Spitzer was able to spot the warm glow of the dusty
disk with its heat-seeking infrared "eyes." The
disk orbits at a distance of about 1 million miles and probably
contains about 10 Earth-masses of material.
Pulsars
are a class of supernova remnants, called neutron stars, which
are incredibly dense. They have masses about 1.4 times that
of the sun squeezed into bodies only 10 miles wide. One teaspoon
of a neutron star would weigh about 2 billion tons. Pulsar
4U 0142+61 is an X-ray pulsar, meaning that it spins and pulses
with X-ray radiation.
Right:
Planets around pulsars are bathed in intense radiation. "These
planets must be among the least hospitable places in the galaxy
for the formation of life," says Charles Beichman, an
astronomer at JPL. [More]
Any planets around
the stars that gave rise to pulsars would have been incinerated
when the stars blew up. The pulsar disk discovered by Spitzer
might represent the first step in the formation of a new,
more exotic type of planetary system, similar to the one found
by Wolszczan in 1992.
"I
find it very exciting to see direct evidence that the debris
around a pulsar is capable of forming itself into a disk.
This might be the beginning of a second generation of planets,"
Wolszczan says.
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Source: NASA
Press release | Production Editor:
Dr. Tony Phillips | Credit: Science@NASA
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