The Pulsar Phoenix
|This artist's animation depicts the explosive death of a massive star, followed by the creation of a disk made up of the star's ashes. NASA's Spitzer Space Telescope was able to see the warm glow of such a dusty disk using its heat-seeking infrared vision. Astronomers believe planets might form in this dead star's disk, like the mythical Phoenix rising up out of the ashes. Animation credit: NASA/JPL-Caltech
NASA's Spitzer Space Telescope has uncovered new evidence that planets might rise up out of a dead star's ashes.
Spitzer surveyed the scene around a pulsar, the remnant of an exploded star. The infrared telescope 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.
"We're amazed that the planet-formation process seems to be so universal," said Deepto Chakrabarty of the Massachusetts Institute of Technology in Cambridge, 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 formed," he added.
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.
|This false-color image from three of NASA's Great Observatories provides one example of a star that died in a fiery supernova blast. Called Cassiopeia A, this supernova remnant is located 10,000 light-years away in the constellation Cassiopeia. At the center of this orb, visible only as a tiny turquoise dot, is the leftover corpse of the now-dead star, called a neutron star. The multi-hued shell outside the neutron star is the rest of the original star's scattered remains. Image credit: NASA/JPL-Caltech/Steward Observatory
The finding also 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 Cassiopeia constellation. 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.
|This artist's concept depicts the pulsar planet system discovered by Aleksander Wolszczan in 1992. Wolszczan used the Arecibo radio telescope in Puerto Rico to find three planets - the first of any kind ever found outside our solar system - circling a pulsar called PSR B1257+12. Pulsars are rapidly rotating neutron stars, which are the collapsed cores of exploded massive stars. They spin and pulse with radiation, much like a lighthouse beacon. Here, the pulsar's twisted magnetic fields are highlighted by the blue glow.
Image credit: NASA/JPL-Caltech
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 said.
Pulsar planets would be bathed in intense radiation and would be quite different from those in our solar system. "These planets must be among the least hospitable places in the galaxy for the formation of life," said Charles Beichman, an astronomer at NASA's Jet Propulsion Laboratory and the California Institute of Technology, both in Pasadena, Calif. "While you could be close enough to your pulsar to have the temperature at the surface of a pulsar planet be ok, the elements of life -- especially water and the lighter elements -- are likely to be absent, thrown off in the supernova explosion, or indeed in the case of hydrogen, most of it already burned up in the stellar furnace in the star before it exploded."
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