“WASHINGTON -- NASA's Hubble Space Telescope has looked deep into the
distant universe and detected the feeble glow of a star that exploded
more than 9 billion years ago. The sighting is the first finding of
an ambitious survey that will help astronomers place better
constraints on the nature of dark energy, the mysterious repulsive
force that is causing the universe to fly apart ever faster.
"For decades, astronomers have harnessed the power of Hubble to
unravel the mysteries of the universe," said John Grunsfeld,
associate administrator for NASA’s Science Mission Directorate in
Washington. "This new observation builds upon the revolutionary
research using Hubble that won astronomers the 2011 Nobel Prize in
Physics, while bringing us a step closer to understanding the nature
of dark energy which drives the cosmic acceleration." As an
astronaut, Grunsfeld visited Hubble three times, performing a total
of eight spacewalks to service and upgrade the observatory.
The stellar explosion, nicknamed SN Primo, belongs to a special class
called Type Ia supernovae, which are bright beacons used as distance
markers for studying the expansion rate of the universe. Type Ia
supernovae likely arise when white dwarf stars, the burned-out cores
of normal stars, siphon too much material from their companion stars
and explode.
SN Primo is the farthest Type Ia supernova with its distance confirmed
through spectroscopic observations. In these types of observations, a
spectrum splits the light from a supernova into its constituent
colors. By analyzing those colors, astronomers can confirm its
distance by measuring how much the supernova's light has been
stretched, or red-shifted, into near-infrared wavelengths because of
the expansion of the universe.
The supernova was discovered as part of a three-year Hubble program to
survey faraway Type Ia supernovae, opening a new distance realm for
searching for this special class of stellar explosion. The remote
supernovae will help astronomers determine whether the exploding
stars remain dependable cosmic yardsticks across vast distances of
space in an epoch when the cosmos was only one-third its current age
of 13.7 billion years.
Called the CANDELS+CLASH Supernova Project, the census uses the
sharpness and versatility of Hubble's Wide Field Camera 3 (WFC3) to
assist astronomers in the search for supernovae in near-infrared
light and verify their distance with spectroscopy. CANDELS is the
Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey and
CLASH is the Cluster Lensing and Supernova Survey.
"In our search for supernovae, we had gone as far as we could go in
optical light," said Adam Riess, the project's lead investigator, at
the Space Telescope Science Institute and The Johns Hopkins
University in Baltimore, Md. "But it's only the beginning of what we
can do in infrared light. This discovery demonstrates that we can use
the Wide Field Camera 3 to search for supernovae in the distant
universe."
The new results were presented on Jan. 11 at the American Astronomical
Society meeting in Austin, Texas.
The supernova team's search technique involved taking multiple
near-infrared images over several months, looking for a supernova's
faint glow. After the team spotted the stellar blast in October 2010,
they used WFC3's spectrometer to verify SN Primo's distance and to
decode its light, finding the unique signature of a Type Ia
supernova. The team then re-imaged SN Primo periodically for eight
months, measuring the slow dimming of its light.
By taking the census, the astronomers hope to determine the frequency
of Type Ia supernovae during the early universe and glean insights
into the mechanisms that detonated them.
"If we look into the early universe and measure a drop in the number
of supernovae, then it could be that it takes a long time to make a
Type Ia supernova," said team member Steve Rodney of The Johns
Hopkins University. "Like corn kernels in a pan waiting for the oil
to heat up, the stars haven't had enough time at that epoch to evolve
to the point of explosion. However, if supernovae form very quickly,
like microwave popcorn, then they will be immediately visible, and
we'll find many of them, even when the universe was very young. Each
supernova is unique, so it's possible that there are multiple ways to
make a supernova."
If astronomers discover that Type Ia supernovae begin to depart from
how they expect them to look, they might be able to gauge those
changes and make the measurements of dark energy more precise. Riess
and two other astronomers shared the 2011 Nobel Prize in Physics for
discovering dark energy 13 years ago, using Type Ia supernova to plot
the universe's expansion rate.
The Hubble Space Telescope is a project of international cooperation
between NASA and the European Space Agency. NASA's Goddard Space
Flight Center manages the telescope. The Space Telescope Science
Institute (STScI) conducts Hubble science operations. STScI is
operated for NASA by the Association of Universities for Research in
Astronomy, Inc., in Washington, D.C.”
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