Two discoveries from a distant quasar – an enormous X-ray jet and an
X-ray shadow cast by an intervening galaxy – are giving astronomers using
NASA’s Chandra X-ray Observatory cause to be doubly excited. These two
independent results reveal information about a supermassive black hole at
the center of the quasar as well as the amount of oxygen in a distant galaxy
billions of years ago.
In one set of Chandra observations of quasar PKS 1127-145,
researchers found an X-ray jet that extends over a length of at least a
million light years. The jet reveals explosive activity that occurred 10
billion years ago around the quasar’s central supermassive black hole.
“The X-rays from the jet are likely due to the collision of
microwave photons left over from the Big Bang with a high-energy beam of
particles,” said Aneta Siemiginowska of the Harvard-Smithsonian Center for
Astrophysics in Cambridge, MA, lead author on a paper which will appear in
the May 10, 2002 issue of the Astrophysical Journal. “The intensity of these
microwaves today is much less than it was 10 billion years ago, due to the
expansion of the universe.”
Chandra observations of quasar PKS 1127-145 demonstrate that
scientists can image these jets even though they are billions of light years
away. Studies of these extraordinarily large structures will allow
astronomers to test models for quasars and the supermassive black holes that
power them.
The length of the jet and the prominent knots of X-ray emission
observed suggest that the activity in the vicinity of the central
supermassive black hole is long-lived but maybe intermittent, perhaps due to
the mergers of other galaxies with the host galaxy.
In a separate result obtained by studying the same quasar,
scientists found an X-ray shadow cast by an intervening galaxy. On their
way to Earth, the X-rays from PKS 1127-145 pass through a galaxy located
about 4 billion light years from Earth, which gives astronomers information
about the amount of oxygen in the galaxy at that time.
Atoms of various elements in this galaxy absorb some of the X-rays,
yielding a dimming of the quasar’s X-rays. In a similar way, when our body
is X-rayed, our bones produce an X-ray shadow. In this case, the quasar
acts as the X-ray machine. By measuring the amount of absorption,
astronomers were able to estimate that the intervening galaxy contained only
about 20 percent as much oxygen as our Milky Way Galaxy has now. These
observations will give astronomers insight into how the oxygen supply of
galaxies is built up over the eons.
“We are looking at a galaxy at about the time in the history of the
universe when our sun formed,” said Jill Bechtold of the University of
Arizona, the lead author on another paper in the November 20, 2001 issue of
The Astrophysical Journal that describes these results. “It’s intriguing
that this galaxy had only about 1/5 of the oxygen that we now measure for
typical stars in our Galaxy.”
Scientists believe that elements such as oxygen, silicon and sulfur
are dispersed into the galaxy primarily by the explosion of massive stars.
As galaxies age, they become more enriched in oxygen and other elements
necessary for life. Using the fact that the light travel time from distant
galaxies can range from hundreds of millions to billions of years,
astronomers can study the rate of this enrichment.
“X-ray observations are especially important for this study,”
emphasized Bechtold. “They provide a direct measurement of the abundance of
oxygen atoms without the complications of dust and other factors that make
the interpretation of optical and ultraviolet observations difficult.”
Other members of the research teams were Thomas Aldcroft, Martin
Elvis, Dan Harris and Adam Dobrzycki (Harvard-Smithsonian Center for
Astrophysics). The Advanced CCD Imaging Spectrometer (ACIS) X-ray camera,
which was used in both observations, was developed for NASA by Pennsylvania
State University, University Park, Pa., and the Massachusetts Institute of
Technology, Cambridge, Mass. NASA’s Marshall Space Flight Center in
Huntsville, Ala., manages the Chandra program. TRW, Inc., Redondo Beach,
Calif., is the prime contractor for the spacecraft. The Smithsonian’s
Chandra X-ray Center controls science and flight operations from Cambridge.
More information on Chandra and images associated with this release
are available at:
and
– 30 –
Contact
Steve Roy
Media Relations Department
(256) 544-0034
steve.roy@msfc.nasa.gov
Megan Watzke
Chandra X-ray Observatory Center
(617) 496-7998
The Web
News release
http://www1.msfc.nasa.gov/NEWSROOM/news/releases/2002/02-022.html
Photos
http://www1.msfc.nasa.gov/NEWSROOM/news/photos/2002/photos02-022.htm
Fact Sheet
http://www1.msfc.nasa.gov/NEWSROOM/background/facts/axaf.htm
