Chandra telescope catches a galactic football
NASA NEWS RELEASE
Posted: November 8, 2000
Using NASA's Chandra X-ray Observatory, astronomers have found a giant football-shaped cavity within X-ray emitting hot gas surrounding the galaxy Cygnus A. The cavity in the hot gas has been created by two powerful jets emitted from the central black hole region in the nucleus of Cygnus A.
"This is a spectacular cavity, which is inflated by jets and completely surrounds the Cygnus A galaxy," said Dr. Wilson, who is professor of astronomy at the University of Maryland. "We are witnessing a battle between the gravity of the Cygnus A galaxy, which is trying to pull the hot gas inwards, and the pressure of material created by the jets, which is trying to push the hot gas outwards."
Cygnus A has long been famous as the brightest radio source in the sky. It is the nearest powerful radio galaxy. The Chandra X-ray image, which was taken with the Advanced CCD Imaging Spectrometer (ACIS), shows the cavity surrounded by a vast sea of extremely hot gas. The elongated oval shape comes from the force of the outwardly moving jets as they push through the hot gas. Bright bands around the "equator of the football" are also visible, and this may be evidence of material swirling toward the central black hole.
Without the jets, an X-ray image of Cygnus A, which is about 700 million light years from Earth, would appear as a more or less spherical region -- about 2 million light years across -- of hot gas slowly falling into the Cygnus A galaxy. However, the two jets powered by the nuclear black hole in this galaxy push this gas outward, like a balloon being inflated by a tank of gas.
Cygnus A is not alone in its galactic neighborhood, but is a member of a large cluster containing many galaxies. Extremely hot -- tens of millions of degrees Celsius -- gas is spread between the galaxies. Although it has a very low density, this gas provides enough resistance to slow down the outward advancement of the particle jets from Cygnus A. At the ends of the jets, astronomers find bright areas of radio and X-ray emission known as "hot spots." Scientists believe that fast atomic particles and magnetic fields from the jets spill out into the region, providing pressure that continuously inflates the cavity.
In a paper accepted by the Astrophysical Journal Letters, Wilson, Young and Shopbell discuss how the Chandra observations resolve a long-standing puzzle about the hot spots at the ends of the jets. By analyzing the X-ray emission of the hot spots, the astronomers have measured the strength of the magnetic field associated with them.
"The radio data themselves cannot determine the strength of the magnetic field, a limitation that has inhibited progress in our understanding of cosmic radio sources for 50 years," said Wilson. "Combination of the Chandra X-ray and the radio data allows a quite precise measurement of the field strength."
The Chandra observation of Cygnus A was made with the ACIS on May 21 for over nine hours.
The ACIS X-ray camera was developed for NASA by Pennsylvania State University and Massachusetts Institute of Technology of 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. This research was supported by the Chandra project at the NASA Marshall Space Flight Center.