An artist’s imagination of a kilonova. (Dana Berry, SkyWorks Digital, Inc.) |
In the world of
astrophysics, Aug. 17, 2017, was a red-letter day. “This is a game-changer for
astrophysics,” said UC Santa Barbara faculty member Andy Howell, who leads the
supernova group at the Las Cumbres Observatory (LCO). “A hundred years after
Einstein theorized gravitational waves, we’ve seen them and traced them back to
their source to find an explosion with new physics of the kind we’ve only
dreamed about.”
First, NASA’s
orbiting Fermi satellite identified a burst of high-energy gamma rays. Then, in
the minute leading up to the Fermi burst, scientists noticed microscopic
distortions in space caused by gravitational waves passing through the Earth.
When they combined the data from the two Laser Interferometer
Gravitational-Wave Observatory (LIGO) facilities in Hanford, Washington, and
Livingston, Louisiana, with the data from the Virgo detector in Italy, they
realized they could localize the disturbance to a relatively small region of
the sky — only about 150 times the size of the full moon — near the
constellation Hydra.
Astronomers at
Las Cumbres Observatory (LCO) in Santa Barbara activated their robotic network
of 20 telescopes around the world and were one of six teams to co-discover a
new source of light in that region and localize it to the galaxy NGC 4993, only
about 130 million light years away.
“Such a
gravitational wave signal had never been seen before but was unmistakably
generated by two neutron stars spiraling together,” explained Iair Arcavi, a
NASA Einstein postdoctoral fellow in UC Santa Barbara’s Department of Physics
and leader of the LCO follow-up effort. The resultant study appears in the
journal Nature.
The outburst
that occurs right after two neutron stars merge is called a kilonova, a
phenomenon that had long been theorized though never conclusively observed —
until now.
Unlike
traditional ground-based facilities with single telescopes, the LCO network
could observe the phenomenon every few hours for five consecutive days. During
that time, the light from the explosion dimmed by a factor of 20, fading at an
unprecedented rate for something so luminous.
“This marks the
first time in history that an astronomical phenomenon has been first sensed
through gravitational waves and then seen with telescopes,” Arcavi said. “For
years, we’ve heard theorists predict how a kilonova should look. I couldn’t
believe we were finally seeing one for the first time.”
Kilonovae are
thought to be the primary source of all the elements heavier than iron in the
universe. For example, most of the gold on Earth may have been created in a
kilonova. The name originates from the prediction that a kilonova would be a
thousand times brighter than a nova, though dimmer than a supernova.
“We know now
that one reason they had been so elusive is that they fade too quickly for
conventional astronomical facilities to detect,” Arcavi said.
“Thanks to
knowing where to look and then having telescopes networked together all around
the world, we were able to watch this new type of cosmic explosion rise and
fade in real time,” said co-author Curtis McCully, a postdoctoral researcher at
LCO and in the UCSB Department of Physics.
“This is a
remarkable story of the advent of gravitational wave astronomy combined with
robotic internet-based optical astronomy.”
LCO astronomers
also used their and other facilities around the world, including the 8-meter
Gemini telescope in Chile, to split the light of the kilonova into its
chromatic components: a rainbow. McCully led this study, which appears in The
Astrophysical Journal Letters.
“We found that
only a tiny amount of material was ejected in the explosion —only about 1
percent of the total matter in the system,” he noted. “The material was also
flung out at an extraordinary speed, as much as 30 percent of the speed of
light.”
The LCO group
also contributed to a third study measuring the Hubble constant, which
characterizes the expansion rate of the universe. That research used the
inspiraling neutron stars as “standard sirens” to determine their distance from
Earth and compared that distance to the redshift, or how much light has been
stretched by the expansion of the universe. That study appears in the journal
Nature.
Via DailyGalaxy
Facinating .
ReplyDelete