Starburst Gives Earth an Energy Bath
First recorded radiation from a star outside the solar system affected our atmosphere, adding to evidence of 'magnetars.'
For a few moments last month, an immense burst of radiation from beyond our solar system bathed the night side of Earth with an intensity matching the sun's.
The outburst from a bizarre type of star 20,000 light-years away disrupted satellites and radio communications, representing the first time researchers have seen radiation from outside the solar system significantly affect Earth's upper atmosphere.
"It was as if night was briefly turned into day in the ionosphere," says Umran Inan, a professor of electrical engineering at Stanford University in California and the head of a team that monitored the atmospheric disturbance.
If it could have been tapped, the outburst's energy would meet humanity's needs for billions of years.
The event also provided what researchers say is the most convincing evidence yet for the existence of magnetars, rotating remnants of collapsed stars with enormous magnetic fields.
Researchers discussed the burst, which occurred Aug. 27, during a briefing this week at the National Aeronautics and Space Administration headquarters in Washington.
The culprit, astronomers say, is a neutron star in the constellation Aquila, which for years has been emitting pulses of gamma rays. Neutron stars form after the explosion and collapse of stars at least 10 times as massive as the sun. Once the collapse ends, all that remains of the star's core is a rotating body 12 miles across made of fluid neutrons surrounded by a mile-thick iron crust.
For all its strength, however, the crust becomes unstable in the face of the neutron star's enormous magnetic field. When the field shifts, it tears at the crust, generating star quakes that can crack the surface and cause powerful bursts of gamma rays. Because the neutron star is rotating, the periodic outbursts generally appear as repeating pulses of gamma radiation in space-based detectors, leading astronomers to call them soft gamma-ray repeaters.
The notion that the pulses resulted from the interaction of the magnetic fields with the crust was proposed in 1992 by University of Texas astrophysicist Robert Duncan, who dubbed the objects magnetars.
Hold onto your keys
Researchers estimate that the gamma-ray repeater responsible for August's outburst hosts a magnetic field 800 trillion times stronger than Earth's and 100 times stronger than any other known field in the universe.
A field that strong would "pull the keys out of your pocket from a distance half way to the moon," Dr. Duncan says.
So far, astronomers have detected only four of these soft gamma-ray repeaters. But Chryssa Kouveliotou, who led one team that detected the August outburst, says if the magnetar theory stands up, the Milky Way may hold up to 100 million inactive magnetars.
The object responsible for August's outburst, however, was anything but inactive. The radiation reaching our solar system affected detectors in at least seven spacecraft from Earth orbit to Jupiter, pushing readings off the top of the scale in some cases and triggering emergency shutdown circuits in two.
Dr. Kouveliotou, an astrophysicist with NASA's Marshall Space Flight Center in Huntsville, Ala., adds that magnetars seem to hold the key to a number of mysteries shrouding the evolution of stars. Magnetars may spend their first 10,000 years as soft gamma-ray repeaters. As they age, their rotation slows and they become X-ray pulsars, which emit X-rays for another 30,000 years. Then "they fade to black and drift for eternity through the heavens." This may help explain why some supernova remnants seem devoid of pulsars, she adds. "Their lights may have gone out sooner than we expected."
The magnetar explanation received additional support from radio-telescope observations of the outburst's afterglow. Theorists predicted that a star quake would eject large numbers of subatomic particles that travel at near light speed and emit short-lived radio signals.
"Where there's smoke, there's fire, and we've seen the smoke," says Dale Frail, the astronomer who discovered the signature using the Very Large Array radio telescope near Socorro, N.M.