NASA Telescopes Join Forces To Observe Unprecedented Explosion
WASHINGTON -- NASA's Swift satellite, Hubble Space Telescope andChandra X-ray Observatory have teamed up to study one of the most
puzzling cosmic blasts ever observed. More than a week later,
high-energy radiation continues to brighten and fade from its location.
Astronomers say they have never seen such a bright, variable,
high-energy, long-lasting burst before. Usually, gamma-ray bursts
mark the destruction of a massive star, and flaring emission from
these events never lasts more than a few hours.
Although research is ongoing, astronomers feel the unusual blast
likely arose when a star wandered too close to its galaxy's central
black hole. Intense tidal forces probably tore the star apart, and
the infalling gas continues to stream toward the hole. According to
this model, the spinning black hole formed an outflowing jet along
its rotational axis. A powerful blast of X- and gamma rays is seen
when the jet is pointed in our direction.
On March 28, Swift's Burst Alert Telescope discovered the source in
the constellation Draco when it erupted with the first in a series of
powerful blasts.
"We know of objects in our own galaxy that can produce repeated
bursts, but they are thousands to millions of times less powerful
than the bursts we are seeing. This is truly extraordinary," said
Andrew Fruchter at the Space Telescope Science Institute in Baltimore.
Swift determined a position for the explosion, which now is cataloged
as gamma-ray burst (GRB) 110328A, and informed astronomers worldwide.
As dozens of telescopes turned to study the spot, astronomers quickly
noticed a small, distant galaxy very near the Swift position. A deep
image taken by Hubble on Monday, April 4, pinpointed the source of
the explosion at the center of this galaxy, which lies 3.8 billion
light-years away from Earth. That same day, astronomers used NASA's
Chandra X-ray Observatory to make a four-hour-long exposure of the
puzzling source. The image, which locates the X-ray object 10 times
more precisely than Swift, shows it lies at the center of the galaxy
Hubble imaged.
"We have been eagerly awaiting the Hubble observation," said Neil
Gehrels, the lead scientist for Swift at NASA's Goddard Space Flight
Center in Greenbelt, Md. "The fact that the explosion occurred in the
center of a galaxy tells us it is most likely associated with a
massive black hole. This solves a key question about the mysterious event."
Most galaxies, including our own, contain central black holes with
millions of times the sun's mass; those in the largest galaxies can
be a thousand times larger. The disrupted star probably succumbed to
a black hole less massive than the Milky Way's, which has a mass four
million times that of our sun.
Astronomers previously have detected stars disrupted by supermassive
black holes, but none have shown the X-ray brightness and variability
seen in GRB 110328A. The source has undergone numerous flares. Since
Sunday, April 3, for example, it has brightened by more than five times.
Scientists think the X-rays may be coming from matter moving near the
speed of light in a particle jet that forms along the rotation axis
of the spinning black hole as the star's gas falls into a disk around the black hole.
"The best explanation at the moment is we happen to be looking down
the barrel of this jet," said Andrew Levan at the University of
Warwick in the United Kingdom, who led the Chandra observations.
"When we look straight down these jets, a brightness boost lets us
view details we might otherwise miss."
This brightness increase, which is called relativistic beaming, occurs
when matter moving close to the speed of light is viewed nearly head
on. Astronomers plan additional Hubble observations to see if the
galaxy's core changes brightness.
Goddard manages Swift and Hubble. NASA's Marshall Space Flight Center
in Huntsville, Ala., manages Chandra. Hubble was built and is
operated in partnership with the European Space Agency. Science
operations for all three missions include contributions from many
national and international partners.
For more information and images associated with these observations, visit:
http://www.nasa.gov/topics/
Source: NASA
