July 19 shuttle launch to give Chicago scientists X-ray vision

University of Chicago scientists soon will begin scanning the sky with an orbiting X-ray telescope named after one of their colleagues.

The Chandra X-ray Observatory is named after Nobel laureate Subrahmanyan Chandrasekhar, who helped create the field of astrophysics and advanced the understanding of black holes and other celestial objects during a career at the University that spanned nearly six decades.

The Chandra Observatory is scheduled for launch aboard the space shuttle Columbia at 11:36 p.m. CDT Monday, July 19 (12:36 a.m. EDT Tuesday, July 20), from pad 39-B at Kennedy Space Center in Florida. Astronaut Eileen Collins will serve as the first female shuttle commander during the mission. Following its deployment from the shuttle, the Chandra Observatory will join NASA’s other two Great Observatories, the Hubble Space Telescope and the Compton Gamma-ray Observatory, which also are named for University of Chicago scientists.

Attending the launch will be Mrs. Lalitha Chandrasekhar, University Provost Geoffrey Stone, and three of Chandra’s Chicago colleagues: Don Lamb, Professor in Astronomy & Astrophysics; Robert Wald, Professor in Physics; and Michael Turner, the Bruce and Diana Rauner Distinguished Service Professor and Chairman of Astronomy & Astrophysics.

“Chandrasekhar opened our minds to some of the most exotic and interesting objects in the universe––white dwarfs, neutron stars and black holes,” Turner said. “These objects are by and large invisible, even with the most powerful optical telescopes. It is indeed fitting that the X-ray observatory that will allow us to see the invisible side of the universe with the clarity and vision of the Hubble Space Telescope is named in his honor.”

The Chandra Observatory’s launch comes at an opportune time, said Lamb, because the study of X-ray bursts and other burstlike phenomena is experiencing a period of breakthroughs and intellectual ferment. “The Chandra Observatory has wonderful capabilities for advancing our understanding of these incredibly energetic and violent phenomena,” he said.

Lamb and a colleague at the Massachusetts Institute of Technology will use the telescope to study mysterious X-ray afterglows that follow intense gamma-ray bursts. Robert Rosner, the William Wrather Distinguished Service Professor in Astronomy & Astrophysics, will observe X-ray emissions from stars to better understand the sun’s X-rays.

Both men, who knew Chandra as a fellow Chicago faculty member, and their research associates also have helped design and test the observatory’s analysis software. The software will help the observatory to find X-ray emitting objects, such as stars, quasars (young, distant galaxies), supernova remnants (exploded stars), galaxies and galaxy clusters, and to detect fluctuations in their intensity.

John Carlstrom, Professor in Astronomy & Astrophysics, working in collaboration with a NASA colleague, will use data collected by the Chandra Observatory to help determine more precisely the expansion rate and mass density of the universe.

And Paul Ricker, Research Associate in Astronomy & Astrophysics, will work jointly with a University of Virginia scientist to study a galaxy cluster that may be merging with other galaxy clusters.

Lamb’s research group is especially eager for a gamma-ray burst to occur. When one of these sudden and spectacular bursts occurs, the Chandra Observatory will swing around to look for X-ray afterglow. This afterglow holds clues about the origin of the bursts, but it is too faint for existing X-ray satellites to detect.

The origins of gamma-ray bursts have remained unknown since their discovery in the 1960s. But at least two gamma-ray burst afterglows resembled supernovae in recent optical telescope observations.

“This gives us a big hint that whatever is causing them is simultaneously causing a supernova, which suggests that the origin of gamma-ray bursts is coming from some type of massive star,” said Dan Reichart, a Chicago graduate student in Astronomy & Astrophysics. A variety of theories has emerged to explain the observations, Reichart said: colliding neutron stars, a black hole colliding with a neutron star, or a massive star on the brink of collapse.

Coleman Miller, a Research Scientist on Lamb’s team, is especially interested in phenomena called soft gamma-ray repeaters. These are less intense than other gamma-ray bursts but still emit in one second the amount of energy the sun radiates in a year. Scientists suspect that soft gamma-ray repeaters are produced by magnetars, neutron stars with exceptionally strong magnetic fields.

By turning the Chandra Observatory toward stars similar to the sun, Rosner will able to infer how the sun’s activity would respond to a change in its rotation rate, mass, age or intensity.

“We’d like to be able to change the rotation rate of the sun and see what happens to the X-ray emission,” Rosner said. “You can’t do that with the sun. We can accomplish the same thing by looking at stars that have the same mass as the sun but rotate more quickly or more slowly and measure the X-ray properties.”

Scientists are unsure exactly why stars emit X-rays, though the phenomenon is almost certainly related to the existence of complex magnetic fields on the surface of stars, Rosner said.

“We have some ideas, and the problem is there are too many ideas. The question really is how to sort out which ones are right, which ones are wrong,” he said.

Chicago’s John Carlstrom and Marshall Joy of NASA’s Marshall Space Flight Center in Huntsville, Ala., will address some important cosmological questions by combining X-ray data from the Chandra Observatory with radio data they have collected with ground-based instruments.

Carlstrom and Joy have been using a special radio interferometry system to detect the cosmic microwave background radiation, the big bang’s afterglow, as it is distorted by intervening galaxy clusters on the way to Earth. Their observations have enabled them to measure the expansion rate and mass density of the universe. Such data allow them to roughly calculate the age of the universe and whether it will expand forever, ultimately collapse or remain precisely balanced between the two. But more definitive answers require X-ray measurements that the Chandra Observatory can provide.

Chicago’s Paul Ricker has teamed with the University of Virginia’s Craig Sarazin to investigate the evolution of large structures in the universe with the Chandra Observatory.

“;We think that galaxy clusters and other structures are formed in the universe by coalescence of smaller objects,” Ricker said. “Clusters in particular would be built up by mergers and accretion of smaller clusters.”

As much as 20 to 30 percent of the mass in a galaxy cluster consists of hot gas––ranging in temperature from 10 million to 100 million degrees––that emits large quantities of X-ray radiation. In detecting this radiation, the Chandra Observatory can help astronomers determine whether or not particular clusters are merging and how often such events occur.

“If you just look at the galaxies it’s difficult to tell a relaxed-looking cluster from one that’s really undergoing a lot of ferment. The gas tends to react more to what’s going on,” Ricker explained. He and Sarazin plan to examine galaxy cluster Abell 85, which might be merging with one and possibly two other clusters nearby.

S. Chandrasekhar Press Kit

1. S. Chandrasekhar facts
2. Chandra photo and video advisory
3. NASA’s Great Observatories named for Chicago trio
4. Comments from S. Chandrasekhar’s colleagues
5. Lalitha Chandrasekhar
6. Namers of orbiting telescope to receive Chandra mementos
7. Simulated X-ray observation of a simulated merger between galaxy clusters.