Click here for more news
Get free e-mail news
WASHINGTON -- Astronomers studying two exploding stars, or supernovae,
have found evidence the blasts received an extra boost from newborn
black holes. The supernovae were found to emit jets of particles
traveling at more than half the speed of light.
Previously, the only catastrophic events known to produce such
high-speed jets were gamma-ray bursts, the universe's most luminous
explosions. Supernovae and the most common type of gamma-ray bursts
occur when massive stars run out of nuclear fuel and collapse. A
neutron star or black hole forms at the star's core, triggering a
massive explosion that destroys the rest of the star.
"The explosion dynamics in typical supernovae limit the speed of the
expanding matter to about three percent the speed of light,"
explained Chryssa Kouveliotou, an astrophysicst at NASA's Marshall
Space Flight Center in Huntsville, Ala., co-author of one of the new
studies. "Yet, in these new objects, we're tracking gas moving some
20 times faster than this."
The new results, published in this week's edition of the journal
Nature, used observations from several space and ground-based
observatories, including NASA's SWIFT satellite.
The astronomers discovered the ultrafast debris by studying two
supernovae at radio wavelengths using numerous facilities, including
the National Science Foundation's Very Large Array in Socorro, N.M.,
and the Robert C. Byrd Green Bank Telescope in West Virginia. One
team used the real-time operating mode of the European Very Long
Baseline Interferometry Network, an international collaboration of
radio telescopes, to rapidly analyze data.
"In every respect, these objects look like gamma-ray bursts -- except
that they produced no gamma rays," said Alicia Soderberg at the
Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.
Soderberg led a team that studied SN 2009bb, a supernova discovered in
March 2009. It exploded in the spiral galaxy NGC 3278, located about
130 million light-years away.
The other object is SN 2007gr, which was first detected in August 2007
in the spiral galaxy NGC 1058, some 35 million light-years away. The
study team, which included Kouveliotou and Alexander van der Horst, a
NASA Postdoctoral Program Fellow in Huntsville, was led by Zsolt
Paragi at the Netherlands-based Joint Institute for Very Long
Baseline Interferometry in Europe.
The researchers searched for gamma-ray signals associated with the
supernovae using archived records in the Gamma-Ray Burst Coordination
Network located at NASA's Goddard Space Flight Center in Greenbelt,
Md. The project distributes and archives observations of gamma-ray
bursts by NASA's Swift spacecraft, the Fermi Gamma-ray Space
Telescope and many others. However, no bursts coincided with the
supernovae.
Unlike typical core-collapse supernovae, the stars that produce
gamma-ray bursts possess what astronomers call a "central engine" --
likely a nascent black hole -- that drives particle jets clocked at
more than 99 percent the speed of light.
By contrast, the fastest outflows detected from SN 2009bb reached 85
percent the speed of light and SN 2007gr reached more than 60 percent
of light speed.
"These observations are the first to show some supernovae are powered
by a central engine," Soderberg said. "These new radio techniques now
give us a way to find explosions that resemble gamma-ray bursts
without relying on detections from gamma-ray satellites."
Perhaps as few as one out of every 10,000 supernovae produce gamma
rays that we detect as a gamma-ray burst. In some cases, the star's
jets may not be angled in a way to produce a detectable burst. In
others, the energy of the jets may not be enough to allow them to
overcome the overlying bulk of the star.
"We've now found evidence for the unsung crowd of supernovae -- those
with relatively dim and mildly relativistic jets that only can be
detected nearby," Kouveliotou said. "These likely represent most of
the population."
For more information, images and animation about this discovery,
visit:
http://www.nasa.gov/swiftSource:
NASA
Thursday, January 28, 2010 |
Posted in
|
Read More »
