A supernova discovered Wednesday, August 24, 2011, is closer to Earth—approximately
21 million light-years away—than any other of its kind in a generation.
Astronomers believe they caught the supernova within hours of its explosion, a
rare feat made possible with a specialized survey telescope and computational
tools.
The finding of such a supernova so early and so close has energized the
astronomical community as they are scrambling to observe it with as many
telescopes as possible, including the Hubble Space Telescope.
Joshua Bloom, assistant professor of astronomy at the University
of California, Berkeley, called it “the supernova of a
generation.” Astronomers at Lawrence Berkeley National Laboratory (Berkeley
Lab) and UC Berkeley, who made the discovery, predict that it will be a target
for research for the next decade, making it one of the most-studied supernova
in history.
The supernova, dubbed PTF 11kly, occurred in the Pinwheel Galaxy, located in
the Big Dipper, otherwise known as the Ursa Major constellation. It was
discovered by the Palomar Transient Factory (PTF) survey, which is designed to
observe and uncover astronomical events as they happen.
“We caught this supernova very soon after explosion. PTF 11kly is getting
brighter by the minute. It’s already 20 times brighter than it was yesterday,”
says Peter Nugent, the senior scientist at Berkeley Lab who first spotted the
supernova. Nugent is also an adjunct professor of astronomy at UC Berkeley. “Observing PTF 11kly unfold should be a wild ride. It is an instant cosmic
classic.”
He credits supercomputers at the National Energy Research Scientific
Computing Center (NERSC), a Department of Energy supercomputing center at
Berkeley Lab, as well as high-speed networks with uncovering this rare event in
the nick of time.
The PTF survey uses a robotic telescope mounted on the 48-in Samuel Oschin
Telescope at Palomar Observatory in Southern California
to scan the sky nightly. As soon as the observations are taken, the data
travels more than 400 miles to NERSC via the National Science Foundation’s High
Performance Wireless Research and Education Network and DOE’s Energy Sciences
Network (ESnet). At NERSC, computers running machine learning algorithms in the
Real-time Transient Detection Pipeline scan through the data and identify
events to follow up on. Within hours of identifying PTF 11kly, this automated
system sent the coordinates to telescopes around the world for follow-up
observations.
Three hours after the automated PTF pipeline identified this supernova candidate,
telescopes in the Canary Islands (Spain) had captured unique “light
signatures,” or spectra, of the event. Twelve hours later, his team had
observed the event with a suite of telescopes including the Lick Observatory
(California), and Keck Observatory (Hawaii) had determined the supernova
belongs to a special category, called Type Ia. Nugent notes that this is the
earliest spectrum ever taken of a Type Ia supernova.
“Type Ia
supernova are the kind we use to measure the expansion of the universe. Seeing
one explode so close by allows us to study these events in unprecedented
detail,” says Mark Sullivan, the Oxford
University team leader
who was among the first to follow up on this detection.
“We still do not know for sure what causes such explosions,” says Weidong
Li, senior scientist at UC Berkeley and collaborator of Nugent. “We are using
images from the Hubble Space Telescope, taken fortuitously years before an
explosion to search for clues to the event’s origin.”
The team will be watching carefully over the next few weeks, and an urgent
request to NASA means the Hubble Space Telescope will begin studying the
supernova’s chemistry and physics this weekend.
Catching supernovae so early allows a rare glimpse at the outer layers of
the supernova, which contain hints about what kind of star exploded. “When you
catch them this early, mixed in with the explosion you can actually see
unburned bits from star that exploded! It is remarkable,” says Andrew Howell of
UC Santa Barbara/Las Cumbres Global Telescope Network. “We are finding new clues
to solving the mystery of the origin of these supernovae that has perplexed us
for 70 years. Despite looking at thousands of supernovae, I’ve never seen
anything like this before.”
“The ability to process all of this data in near real-time and share our
results with collaborators around the globe through the Science Gateway at
NERSC is an invaluable tool for following up on supernova events,” says Nugent. “We wouldn’t have been able to detect and observe this candidate as soon as we
did without the resources at NERSC.”
At a mere 21 million light-years from Earth, a relatively small distance by
astronomical standards, the supernova is still getting brighter, and might even
be visible with good binoculars in ten days’ time, appearing brighter than any
other supernova of its type in the last 30 years.
“The best time to see this exploding star will be just after evening
twilight in the Northern hemisphere in a week or so,” says Oxford’s Sullivan. “You’ll need dark skies and a good pair of binoculars, although a small
telescope would be even better.”
The scientists in the PTF have discovered more than 1,000 supernovae since
it started operating in 2008, but they believe this could be their most
significant discovery yet. The last time a supernova of this sort occurred so
close was in 1986, but Nugent notes that this one was peculiar and heavily
obscured by dust.
“Before that, you’d have to go back to 1972, 1937, and 1572 to find more
nearby Type Ia supernovae,” says Nugent.