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Spacewalk highlights

This highlights movie from the July 23 station spacewalk shows the jettisoning of a support platform and a refrigerator-size tank.


Expedition 16 crew

Members of the upcoming space station Expedition 16 crew, led by commander Peggy Whitson, hold a pre-flight news briefing.


ISS spacewalk preview

This is a preview the planned July 23 EVA by members of the space station crew to jettison two objects from the outpost and perform maintenance.

 Briefing | Animation

STS-118: The mission

Officials for Endeavour's trip to the space station present a detailed overview of the STS-118 flight and objectives.

 Briefing | Questions

STS-118: Spacewalks

Four spacewalks are planned during Endeavour's STS-118 assembly mission to the space station. Lead spacewalk officer Paul Boehm previews the EVAs.

 Full briefing
 EVA 1 summary
 EVA 2 summary
 EVA 3 summary
 EVA 4 summary

STS-118: Education

A discussion of NASA's educational initiatives and the flight of teacher Barbara Morgan, plus an interactive event with students were held in Houston.

 Briefing | Student event

The Endeavour crew

The Endeavour astronauts, including teacher-astronaut Barbara Morgan, meet the press in the traditional pre-flight news conference.


Mars lander preview

A preview of NASA's Phoenix Mars lander mission and the science objectives to dig into the arctic plains of the Red Planet are presented here.


Phoenix animation

Project officials narrate animation of Phoenix's launch from Earth, arrival at Mars, touchdown using landing rockets and the craft's robot arm and science gear in action.


Dawn launch delay

Jim Green, director of the Planetary Science Division at NASA Headquarters, explains why the agency decided to delay launch of the Dawn asteroid probe from July to September.


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Chandra observatory catches 'piranha' black holes
Posted: July 24, 2007

Supermassive black holes have been discovered to grow more rapidly in young galaxy clusters, according to new results from NASA's Chandra X-ray Observatory. These "fast-track" supermassive black holes can have a big influence on the galaxies and clusters that they live in.

These two galaxy clusters, known as CL 0542-4100 and CL 0848.6+4453, are part of a sample used to count the fraction of galaxies with rapidly growing black holes, also known as active galactic nuclei (AGN). In the Chandra images of these two galaxy clusters, red corresponds to low-energy X-rays, the green to intermediate-energy, and the blue to high-energy X-rays. Credit: NASA/CXC/Ohio State Univ./J.Eastman et al.
Using Chandra, scientists surveyed a sample of clusters and counted the fraction of galaxies with rapidly growing supermassive black holes, known as active galactic nuclei (or AGN). The data show, for the first time, that younger, more distant galaxy clusters contained far more AGN than older, nearby ones.

Galaxy clusters are some of the largest structures in the Universe, consisting of many individual galaxies, a few of which contain AGN. Earlier in the history of the universe, these galaxies contained a lot more gas for star formation and black hole growth than galaxies in clusters do today. This fuel allows the young cluster black holes to grow much more rapidly than their counterparts in nearby clusters.

"The black holes in these early clusters are like piranha in a very well-fed aquarium," said Jason Eastman of Ohio State University (OSU) and first author of this study. "It's not that they beat out each other for food, rather there was so much that all of the piranha were able to really thrive and grow quickly."

The team used Chandra to determine the fraction of AGN in four different galaxy clusters at large distances, when the Universe was about 58% of its current age. Then they compared this value to the fraction found in more nearby clusters, those about 82% of the Universe's current age.

The result was the more distant clusters contained about 20 times more AGN than the less distant sample. AGN outside clusters are also more common when the Universe is younger, but only by factors of two or three over the same age span.

"It's been predicted that there would be fast-track black holes in clusters, but we never had good evidence until now," said co-author Paul Martini, also of OSU. "This can help solve a couple of mysteries about galaxy clusters."

One mystery is why there are so many blue, star-forming galaxies in young, distant clusters and fewer in nearby, older clusters. AGN are believed to expel or destroy cool gas in their host galaxy through powerful eruptions from the black hole. This may stifle star formation and the blue, massive stars will then gradually die off, leaving behind only the old, redder stars. This process takes about a billion years or more to take place, so a dearth of star-forming galaxies is only noticeable for older clusters.

The process that sets the temperature of the hot gas in clusters when they form is also an open question. These new results suggest that even more AGN may have been present when most clusters were forming about ten billion years ago. Early heating of a cluster by large numbers of AGN can have a significant, long-lasting effect on the structure of a cluster by "puffing up" the gas.

"In a few nearby clusters we've seen evidence for huge eruptions generated by supermassive black holes. But this is sedate compared to what might be going on in younger clusters," said Eastman.

These results appeared in the July 20th issue of The Astrophysical Journal Letters. 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.