Astronomers are going gaga over newborn supernova measurements taken
by NASA’s Kepler and Swift spacecraft, poring over them in hopes of
better understanding what sparks these world-shattering stellar
explosions. Scientists are particularly fascinated with Type la
supernovae, as they can serve as a lighthouse for measuring the vast
distances across space.“Kepler’s unprecedented pre-event supernova observations and Swift’s
agility in responding to supernova events have both produced important
discoveries at the same time but at very different wavelengths,” says
Paul Hertz, Director of Astrophysics. “Not only do we get insight into
what triggers a Type Ia supernova, but these data allow us to better
calibrate Type Ia supernovae as standard candles, and that has
implications for our ability to eventually understand the mysteries of
dark energy.”
Type Ia supernovae explode with similar brightness because the
exploding object is always a white dwarf, the Earth-sized remnant of a
star like the sun. A white dwarf can go supernova by merging with
another white dwarf or by pulling too much matter from a nearby
companion star, causing a thermonuclear reaction and blowing itself to
smithereens.
In studies appearing in Nature on Thursday, Kepler and Swift have found supporting evidence for both star-pulverizing scenarios.
Researchers studying the Kepler data have caught three new and
distant supernovae, and the dataset includes measurements taken before
the violent explosions even happened. Known for its planet-hunting
prowess and its unceasing gaze, the Kepler space telescope's exquisitely
precise and frequent observations every 30 minutes have allowed
astronomers to turn back the clock and dissect the initial moments of a
supernova. The finding provides the first direct measurements capable of
informing scientists of the cause of the blast.
"Our Kepler supernova discoveries strongly favor the white dwarf
merger scenario, while the Swift study, led by Cao, proves that Type Ia
supernovae can also arise from single white dwarfs," said Robert Olling,
research associate at the University of Maryland and lead author of the
study. "Just as many roads lead to Rome, nature may have several ways
to explode white dwarf stars."
To capture the earliest moments of Type Ia explosions, the research
team monitored 400 galaxies for two years using Kepler. The team
discovered three events, designated KSN 2011b, KSN 2011c and KSN 2012a,
with measurements taken before, during and after the explosions.
These early data provide a view into the physical processes that
ignite these stellar bombs hundreds of millions of light years away.
When a star goes supernova, the explosive burst of energy ejects the
star's material at hypersonic velocity, emitting a shock wave in all
directions. If a companion star is in the neighborhood, the disruption
in the shock wave will be recorded in the data.
Scientists found no evidence of a companion star and concluded the
cause to be the collision and merger of two closely orbiting stars, most
likely two white dwarfs.
Knowing the distance to a galaxy in the Kepler survey was key to
characterizing the Type of supernova uncovered by Olling and his
colleagues. To determine the distance, the team turned to the powerful
telescopes at the Gemini and the W. M. Keck Observatories atop Mauna Kea
in Hawaii. These measurements were key for the researchers to conclude
that the supernovae they had discovered were that of the Type Ia
lighthouse variety.
“The Kepler spacecraft has delivered yet another surprise, playing an
unexpected role in supernova science by providing the first
well-sampled early time light curves of Type Ia supernovae," said Steve
Howell, Kepler project scientist at NASA's Ames Research Center in
Moffett Field, California. "Now in its new mission as K2, the spacecraft
will search for more supernovae among many thousands of galaxies."
A separate group of astronomers have also found intriguing data on a
different supernova. Led by California Institute of Technology (Caltech)
graduate student Yi Cao, a team using Swift has detected an
unprecedented flash of ultraviolet (UV) light in the first few days of a
Type Ia supernova. Based on computer simulations of supernovae
exploding in binary star systems, the researchers think the UV pulse was
emitted when the supernova’s blast wave slammed into and engulfed a
nearby companion star.
"If Swift had looked just a day or two later, we would have missed
the prompt UV flash entirely," said Brad Cenko, a Swift team member at
NASA's Goddard Space Flight Center in Greenbelt, Maryland. "Thanks to
Swift's wavelength coverage and rapid scheduling capability, it is
currently the only spacecraft that can regularly make these
observations."
According to the analysis, the supernova debris slammed into and
swept around its companion star, creating a region of UV emission. The
peak temperature exceeded 19,000 degrees Fahrenheit (11,000 degrees
Celsius) or about twice the surface temperature of the sun.
The explosion, designated iPTF14atg, was first seen on May 3, 2014,
in the galaxy IC 831, located about 300 million light-years away in the
constellation Coma Berenices. It was discovered through a wide-field
robotic observing system known as the intermediate Palomar Transient
Factory (iPTF), a multi-institute collaboration led by the Caltech
Optical Observatories in California.
"We saw no evidence of this explosion in images taken the previous
night, so we found iPTF14atg when it was only about one day old," Cao
said. "Better yet, we confirmed it was a young Type Ia supernova,
something we've worked hard designing our system to find."
The team immediately requested follow-up observations from other
facilities, including ultraviolet and X-ray observations from NASA's
Swift satellite. Although no X-rays were found, a fading spike of UV
light was caught by Swift's Ultraviolet/Optical Telescope within a few
days of the explosion, with no corresponding spike at visible
wavelengths. After the flash faded, both UV and visible wavelengths rose
together as the supernova brightened.
The UV pulse from iPTF14atg provides strong evidence for the presence
of a companion star, but as white dwarfs crashing into each other can
also produce supernovae, as demonstrated by the Kepler results,
astronomers are working to determine the percentage of supernovae
produced by each one.
The scientists add that a better understanding of the differences
among Type Ia explosions will help astronomers improve their knowledge
of dark energy, a mysterious force that appears to be accelerating
cosmic expansion.
Ames manages the Kepler and K2 missions for NASA’s Science Mission
Directorate. NASA's Jet Propulsion Laboratory in Pasadena, California,
managed Kepler mission development. Ball Aerospace & Technologies
Corp. operates the flight system with support from the Laboratory for
Atmospheric and Space Physics at the University of Colorado in Boulder.
Swift blasted into orbit Nov. 20, 2004. Managed by Goddard, the
mission is operated in collaboration with Penn State University in
University Park, Pennsylvania, the Los Alamos National Laboratory in New
Mexico and Orbital Sciences Corp. in Dulles, Virginia. Other partners
include the University of Leicester and Mullard Space Science Laboratory
in the United Kingdom, Brera Observatory and the Italian Space Agency
in Italy, with additional collaborators in Germany and Japan.
Michele Johnson (Editor)
NASA’s Ames Research Center, Moffett Field, Calif.
650-604-6982
michele.johnson@nasa.gov
Lynn Chandler
NASA’s Goddard Space Flight Center, Greenbelt, Md.
301-286-2806
lynn.chandler-1@nasa.gov
Source: NASA's Ames Research Center
