NASA's Chandra Suggests Rare Explosion Created Our Galaxy's Youngest Black Hole

Feb. 13, 2013

J.D. Harrington
Headquarters, Washington
202-358-5241
j.d.harrington@nasa.gov

Megan Watzke
Chandra X-ray Center, Cambridge, Mass.
617-496-7998
mwatzke@cfa.harvard.edu

RELEASE: 13-045

NASA'S CHANDRA SUGGESTS RARE EXPLOSION CREATED OUR GALAXY'S YOUNGEST BLACK HOLE

WASHINGTON -- New data from NASA's Chandra X-ray Observatory suggest a
highly distorted supernova remnant may contain the most recent black
hole formed in the Milky Way galaxy. The remnant appears to be the
product of a rare explosion in which matter is ejected at high speeds
along the poles of a rotating star.

The remnant, called W49B, is about a thousand years old as seen from
Earth and located about 26,000 light-years away.
"W49B is the first of its kind to be discovered in the galaxy," said
Laura Lopez, who led the study at the Massachusetts Institute of
Technology. "It appears its parent star ended its life in a way that
most others don't."

Usually when a massive star runs out of fuel, the central region of
the star collapses, triggering a chain of events that quickly
culminate in a supernova explosion. Most of these explosions are
generally symmetrical, with the stellar material blasting away more
or less evenly in all directions.

However, in the W49B supernova, material near the poles of the doomed
rotating star was ejected at a much higher speed than material
emanating from its equator. Jets shooting away from the star's poles
mainly shaped the supernova explosion and its aftermath.

The remnant now glows brightly in X-rays and other wavelengths,
offering the evidence for a peculiar explosion. By tracing the
distribution and amounts of different elements in the stellar debris
field, researchers were able to compare the Chandra data to
theoretical models of how a star explodes. For example, they found
iron in only half of the remnant while other elements such as sulfur
and silicon were spread throughout. This matches predictions for an
asymmetric explosion.

"In addition to its unusual signature of elements, W49B also is much
more elongated and elliptical than most other remnants," said
co-author Enrico Ramirez-Ruiz of the University of California at
Santa Cruz. "This is seen in X-rays and several other wavelengths and
points to an unusual demise for this star."

Because supernova explosions are not well understood, astronomers want
to study extreme cases like the one that produced W49B. The relative
proximity of W49B also makes it extremely useful for detailed study.

The authors examined what sort of compact object the supernova
explosion left behind. Most of the time, massive stars that collapse
into supernovas leave a dense, spinning core called a neutron star.
Astronomers often can detect neutron stars through their X-ray or
radio pulses, although sometimes an X-ray source is seen without
pulsations. A careful search of the Chandra data revealed no evidence
for a neutron star. The lack of such evidence implies a black hole
may have formed.

"It's a bit circumstantial, but we have intriguing evidence the W49B
supernova also created a black hole," said co-author Daniel Castro,
also of MIT. "If that is the case, we have a rare opportunity to
study a supernova responsible for creating a young black hole."

Supernova explosions driven by jets like the one in W49B have been
linked to gamma-ray bursts (GRBs) in other objects. GRBs, which have
been seen only in distant galaxies, also are thought to mark the
birth of a black hole. There is no evidence the W49B supernova
produced a GRB, but it may have properties -- including being
jet-driven and possibly forming a black hole -- that overlap with
those of a GRB.

The new results on W49B, which were based on about two-and-a-half days
of Chandra observing time, appear in a paper in Sunday's issue of the
Astrophysical Journal. The other co-author was Sarah Pearson from the
University of Copenhagen in Denmark.

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.

For Chandra images, multimedia and related materials, visit:

http://www.nasa.gov/chandra

For an additional interactive image, podcast, and video on the
finding, visit:

http://chandra.si.edu


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