|
+ Play
Audio
|
+ Download Audio | +
Email to a friend | +
Join mailing list
Editor's
preface : Astronomers have long thought that supernovas
explode two or three times a century here in the Milky Way.
They arrive at that figure by watching other galaxies similar
to our own, and counting the stars as they explode. But this
leads to a mystery: The last time anyone actually saw a supernova
explode in the Milky Way was the year 1680, almost 330 years
ago. So where are the Milky Way's missing supernovas?
At
long last, one of them has been found. Astronomers using NASA's
Chandra X-ray Observatory (an x-ray telescope in space) and
the NRAO's Very Large Array (a radio telescope in New Mexico)
recently located the remains of a young supernova hiding in
a dense field of gas and dust near the center of our galaxy.
Read today's story to learn how a decades-long "galactic
hunt" landed its prey.
May
14, 2008: The most recent supernova in our galaxy
has been discovered by tracking the rapid expansion of its
remains. This result, obtained by NASA's Chandra X-ray Observatory
and the National Radio Astronomy Observatory's Very Large
Array, will help improve our understanding of how often supernovas
explode in the Milky Way galaxy.
The explosion occurred about 140 years ago, making it the
most recent supernova in the Milky Way as measured in Earth's
time frame. Previously, the last known supernova in our galaxy
occurred around 1680, an estimate based on the expansion of
its remnant, Cassiopeia A.
Above:
Young supernova remnant G1.9+0.3 is hidden in the dust fields
of the galactic center. [more]
The
remains of this young supernova are known to astronomers as
"G1.9+0.3." The numbers denote the galactic coordinates
of the supernova's expanding debris cloud, located deep in
the heart of the Milky Way. The explosion itself was not seen
because it occurred in a dense field of gas and dust. This
made the object about a trillion times fainter, in optical
light, than an unobscured supernova. However, the remnant
it left behind can be seen by X-ray and radio telescopes.
"We
can see some supernova explosions with optical telescopes
across half of the universe, but when they're in this murk
we can miss them in our own cosmic backyard," says Stephen
Reynolds of North Carolina State University in Raleigh, who
led the Chandra study. "Fortunately, the expanding gas
cloud from the explosion shines brightly in radio waves and
X-rays for thousands of years. X-ray and radio telescopes
can see through all that obscuration and show us what we've
been missing."
Astronomers
regularly observe supernovas in other galaxies like ours. Based
on those observations, researchers estimate about three explode
every century in the Milky Way.
"If
the supernova rate estimates are correct, there should be
the remnants of about 10 supernova explosions that are younger
than Cassiopeia A," said David Green of the University
of Cambridge in the United Kingdom, who led the Very Large
Array study. "It's great to finally track one of them
down."
The
tracking of this object began in 1985, when astronomers, led
by Green, used the Very Large Array to identify the remnant
of a supernova explosion near the center of our galaxy. Based
on its small size, it was thought to have resulted from a
supernova that exploded about 400 to 1000 years ago.
Twenty-two
years later, Chandra observations revealed the remnant had
expanded by a surprisingly large amount, about 16 percent,
since 1985. This indicates the supernova remnant is much younger
than previously thought.
 Right:
The supernova's expanding shell images by Chandra in 2007.
The central circle traces the shell's approximate size in
1985. [more]
That
young age was confirmed in recent weeks when the Very Large
Array made new radio observations. This comparison of data
pinpoints the age of the remnant at 140 years - possibly less
if it has been slowing down - making it the youngest on record
in the Milky Way.
Besides
being the record holder for youngest supernova, the object
is of considerable interest for other reasons. The high expansion
velocities and extreme particle energies that have been generated
are unprecedented and should stimulate deeper studies of the
object with Chandra and the Very Large Array.
"No
other object in the galaxy has properties like this,"
Reynolds said. "This find is extremely important for
learning more about how some stars explode and what happens
in the aftermath."
These
results are scheduled to appear in The Astrophysical Journal
Letters.
SEND
THIS STORY TO A FRIEND
Editor: Dr.
Tony Phillips | Credit: Science@NASA
| more
information |
|
Chandra
X-ray Observatory -- home page
Credits:
NASA's Marshall Space Flight Center in Huntsville, Ala.,
manages the Chandra program for NASA's Science Mission
Directorate in Washington. The Smithsonian Astrophysical
Observatory controls Chandra's science and flight operations
from Cambridge, Mass.
NASA's
Future: The
Vision for Space Exploration |
|
