A supernova explosion occurs every second somewhere in the Universe. New images captured by NASA's Chandra X-Ray Observatory
suggests a rare explosion may have created our galaxy's youngest black
hole. The 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. Journal reference: Astrophysical Journal
Image Credit: Chandra X-ray Image of W49B showing just the iron
(purple) and silicon (blue). Credit:
X-ray: NASA/CXC/MIT/L.Lopez et al;
Infrared: Palomar; Radio: NSF/NRAO/VLA
Source: The Daily Galaxy via Chandra X-ray Observatory
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