News Release Number: STScI-2014-38
Hubble Finds Companion Star Hidden for 21 Years in a
Supernova's Glare
The full news release story:
Astronomers using NASA's Hubble Space Telescope have
discovered a companion star to a rare type of supernova. This observation
confirms the theory that the explosion originated in a double-star system where
one star fueled the mass-loss from the aging primary star.
This detection is the first time astronomers have been
able to put constraints on the properties of the companion star in an unusual
class of supernova called Type IIb. They were able to estimate the surviving
star's luminosity and mass, which provide insight into the conditions that
preceded the explosion.
"A binary system is likely required to lose the
majority of the primary star's hydrogen envelope prior to the explosion. The
problem is that, to date, direct observations of the predicted binary companion
star have been difficult to obtain since it is so faint relative to the
supernova itself," said lead researcher Ori Fox of the University of
California (UC) at Berkeley.
Astronomers estimate that a supernova goes off once
every second somewhere in the universe. Yet they don't fully understand how
stars explode. Finding a "smoking gun" companion star provides
important new clues to the variety of supernovae in the universe. "This is
like a crime scene, and we finally identified the robber," quipped team
member Alex Filippenko, professor of astronomy at UC Berkeley. "The
companion star stole a bunch of hydrogen before the primary star
exploded."
The explosion happened in the galaxy M81, which is
about 11 million light-years away from Earth in the direction of the
constellation Ursa Major (the Great Bear). Light from the supernova was first
detected in 1993, and the object was designated SN 1993J. It was the nearest
known example of this type of supernova, called a Type IIb, due to the specific
characteristics of the explosion. For the past two decades astronomers have
been searching for the suspected companion, thought to be lost in the glare of
the residual glow from the explosion.
Observations made in 2004 at the W.M. Keck Observatory
on Mauna Kea, Hawaii, showed circumstantial evidence for spectral absorption
features that would come from a suspected companion. But the field of view is
so crowded that astronomers could not be certain if the spectral absorption
lines were from a companion object or from other stars along the line of sight
to SN 1993J. "Until now, nobody was ever able to directly detect the glow
of the star, called continuum emission," Fox said.
The companion star is so hot that the so-called
continuum glow is largely in ultraviolet (UV) light, which can only be detected
above Earth's absorbing atmosphere. "We were able to get that UV spectrum
with Hubble. This conclusively shows that we have an excess of continuum
emission in the UV, even after the light from other stars has been
subtracted," said team member Azalee Bostroem of the Space Telescope
Science Institute (STScI), in Baltimore, Maryland.
When a massive star reaches the end of its lifetime,
it burns though all of its material and its iron core collapses. The rebounding
outer material is seen as a supernova. But there are many different types of
supernovae in the universe. Some supernovae are thought to have exploded from a
single-star system. Other supernovae are thought to arise in a binary system
consisting of a normal star with a white dwarf companion, or even two white
dwarfs. The peculiar class of supernova called Type IIb combines the features
of a supernova explosion in a binary system with what is seen when single
massive stars explode.
SN 1993J, and all Type IIb supernovae, are unusual
because they do not have a large amount of hydrogen present in the explosion.
The key question has been: how did SN 1993J lose its hydrogen? In the model for
a Type IIb supernova, the primary star loses most of its outer hydrogen
envelope to the companion star prior to exploding, and the companion continues
to burn as a super-hot helium star.
"When I first identified SN 1993J as a Type IIb
supernova, I hoped that we would someday be able to detect its suspected
companion star," said Filippenko. "The new Hubble data suggest that
we have finally done so, confirming the leading model for Type IIb
supernovae."
The team combined ground-based data for the optical
light and images from two Hubble instruments to collect ultraviolet light. They
then constructed a multi-wavelength spectrum that matched what was predicted
for the glow of a companion star.
Fox, Filippenko, and Bostroem say that further
research will include refining the constraints on this star and definitively
showing that the star is present.
The results were published in the July 20
Astrophysical Journal.
For images and more information about Hubble, visit:
The Hubble Space Telescope is a project of
international cooperation between NASA and the European Space Agency. NASA's
Goddard Space Flight Center in Greenbelt, Md., manages the telescope. STScI
conducts Hubble science operations. STScI is operated for NASA by the
Association of Universities for Research in Astronomy, Inc., in Washington,
D.C.
CONTACT
Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4514
Space Telescope Science Institute, Baltimore, Maryland
410-338-4514
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