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STS-70: Launching TDRS

NASA completed its initial constellation of Tracking and Data Relay Satellites with deployment of the TDRS-G by shuttle Discovery.


STS-67: UV astronomy

A package of ultraviolet telescopes flew aboard shuttle Endeavour in March 1995 to observe Jupiter, stars and galaxies. The crew explains its mission in this film.


Phoenix: At the Cape

NASA's Mars lander named Phoenix has arrive at Kennedy Space Center to begin preparations for launch in August.

 Full coverage

STS-63: A rendezvous with space station Mir

As a prelude to future dockings between American space shuttles and the Russian space station Mir, the two countries had a test rendezvous in Feb. 1995.


"Apollo 17: On The Shoulders of Giants"

Apollo's final lunar voyage is relived in this movie. The film depicts the highlights of Apollo 17's journey to Taurus-Littrow and looks to the future Skylab, Apollo-Soyuz and shuttle programs.


Atlantis returns to pad

Two months after rolling off the launch pad to seek repairs to the hail-damaged external fuel tank, space shuttle Atlantis returns to pad 39A for mission STS-117.

 Part 1 | Part 2

"Apollo 10: To Sort Out The Unknowns"

The May 1969 mission of Apollo 10 served as a final dress rehearsal before the first lunar landing later that summer. Stafford, Young and Cernan went to the moon to uncover lingering spacecraft problems that needed to be solved.


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Galaxy cluster takes it to the extreme, Chandra finds
Posted: May 29, 2007

Evidence for an awesome upheaval in a massive galaxy cluster was discovered in an image made by NASA's Chandra X-ray Observatory. The origin of a bright arc of ferociously hot gas extending over two million light years requires one of the most energetic events ever detected.

In this side-by-side comparison, an apparently ordinary star field in optical light (left) is shown to be dramatically different when observed in X-rays (right). Chandra's image of 3C438, the central galaxy within a massive cluster, reveals evidence for one of the most energetic events in the local Universe. Credit: X-ray: NASA/CXC/CfA/R.P.Kraft; Optical: Pal.Obs. DSS
The cluster of galaxies is filled with tenuous gas at 170 million degree Celsius that is bound by the mass equivalent of a quadrillion, or 1,000 trillion, suns. The temperature and mass make this cluster a giant among giants.

"The huge feature detected in the cluster, combined with the high temperature, points to an exceptionally dramatic event in the nearby Universe," said Ralph Kraft of the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass., and leader of a team of astronomers involved in this research. "While we're not sure what caused it, we've narrowed it down to a couple of exciting possibilities."

The favored explanation for the bright X-ray arc is that two massive galaxy clusters are undergoing a collision at about 4 million miles per hour. Shock waves generated by the violent encounter of the clusters' hot gas clouds could produce a sharp change in pressure along the boundary where the collision is occurring, giving rise to the observed arc-shaped structure which resembles a titanic weather front.

"Although this would be an extreme collision, one of the most powerful ever seen, we think this may be what is going on," said team member Martin Hardcastle, of the University of Hertfordshire, United Kingdom.

A problem with the collision theory is that only one peak in the X-ray emission is seen, whereas two are expected. Longer observations with Chandra and the XMM-Newton X-ray observatories should help determine how serious this problem is for the collision hypothesis.

Another possible explanation is that the disturbance was caused by an outburst generated by the infall of matter into a supermassive black hole located in a central galaxy. The black hole inhales much of the matter but expels some of it outward in a pair of high-speed jets, heating and pushing aside the surrounding gas.

Such events are known to occur in this cluster. The galaxy 3C438 in the central region of the cluster is known to be a powerful source of explosive activity, which is presumably due to a central supermassive black hole. But the energy in these outbursts is not nearly large enough to explain the Chandra data.

"If this event was an outburst from a supermassive black hole, then it's by far the most powerful one ever seen," said team member Bill Forman, also of CfA.

The phenomenal amount of energy involved implies a very large amount of mass would have been swallowed by the black hole, about 30 billion times the Sun's mass over a period of 200 million years. The authors consider this rate of black hole growth implausible.

"These values have never been seen before and, truthfully, are hard to believe," said Kraft.

These results were presented at the American Astronomical Society meeting in Honolulu, HI, and will appear in an upcoming issue of The Astrophysical Journal. NASA's Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for the agency's Science Mission Directorate. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass.