Black holes
are not the only objects in the universe that spew powerful jets from their
poles. Dead, smoldering stars can emit them, too, and the jets they create
rival and might even surpass those fired by black holes, scientists find.
The
discovery, to be detailed in an upcoming issue of The Astrophysical Journal
Letters, shows that the unusual properties of black holes—like the presence
of an event horizon and the lack of an actual surface—are not required for jets
to form.
"Gravity
appears to be the key to creating these jets, not some trick of the event
horizon," said study leader Sebastian Heinz of the University of Wisconsin at Madison.
Using
NASA's Chandra X-ray Observatory, scientists spotted the jet 20,000 light-years
from Earth in Circinus X-1, a system where a spinning stellar corpse known as a
neutron
star is orbiting a normal star several times the mass of the sun. A neutron
star forms when the material left over from a supernova explosion collapses
into a dense core.
Many jets
have been found near black holes, but the Circinus
X-1 jet is the first extended X-ray jet associated with a neutron star.
Heinz and
his colleagues estimate that a surprisingly high percentage of the energy
created by material falling onto the neutron star is used to power the jet.
"In terms
of energy efficiency across the universe, this result shows that neutron stars
are near the top of the list. This jet is almost as efficient as one from a
black hole," said study team member Norbert Schulz of the Massachusetts
Institute of Technology.
The Chandra
findings also help clear up a mystery about how diffuse lobes of
radio-emitting gas around Circinus X-1 are created. The researchers found the
X-ray jets of high-energy particles spewed by the system's neutron star are
powerful enough to maintain the lobes.
"We've seen
enormous radio clouds around supermassive black holes at the centers of
galaxies," Heinz said. "What's unusual here is that this pocket-sized version,
relatively speaking, is being powered by a neutron star, not a black hole."
Heinz and
his team spotted two extended features shaped like a "V" in the Chandra
observations of Circinus X-1 that they speculate could represent the outer
walls of a wide jet. Another possibility is that the features represent two
separate, narrow jets fired at different times as the neutron star wobbles
to and fro in space like a spinning top.
If this
second scenario is correct, Circinus X-1 would have one of the longest,
narrowest jets found to date, surpassing even those discovered around black
holes.
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