|
|
|
|
|
Monster black holes grow after galactic mergers ARIZONA STATE UNIVERSITY NEWS RELEASE Posted: January 10, 2006 An analysis of the Hubble Space Telescope's deepest view of the universe offers compelling evidence that monster black holes in the centers of galaxies were not born big but grew over time through repeated galactic mergers.
The two teams will present their results in a press conference on Jan. 10 at the 207th meeting of the American Astronomical Society in Washington, D.C. The HUDF studies also confirm the predictions of recent computer simulations by Lars Hernquist, Philip Hopkins, Tiziana di Matteo, and Volker Springel of the Harvard Smithsonian Center for Astrophysics in Cambridge, Mass., that newly merging galaxies are enshrouded in so much dust that astronomers cannot see the black-hole feeding frenzy. The computer simulations, as supported by Hubble, suggest that it takes hundreds of millions to a billion years before enough dust clears so that astronomers can see the black holes feasting on stars and gas from the merger. The telltale sign that black holes are dining is seeing light from galaxies that varies with time. The two HUDF teams believe they are seeing two distinct phases in galaxy evolution: the first phase - the tadpole stage - representing the early-merging systems where central black holes are still enshrouded in dust, and the much later "variable-object phase," in which the merged system has cleared out enough gas for the inner accretion disk around the black hole to become visible. "The fact that these phases were almost entirely separate was a surprise, because it is commonly believed that galaxy mergers and central black-hole activity are closely related. Our nearby universe has mature galaxies, but in order to understand how they formed and evolved, we must study them over time," Windhorst explained. "The HUDF provides an actual look back in time to see snapshots of early galaxies so that we can study them when they were young." A link between the growth of galaxies through mergers and the feeding of the central black holes has long been suspected. The evidence, however, has been inconclusive for many years. "The HUDF has provided very high-quality information. It is the first data we could use to test this theory, since it allowed us to study about 5,000 distant galaxies over a period of four months," said Seth Cohen of Arizona State University and leader of one of the teams. The HUDF observations have now shed light on how the growth of monster black holes kept pace with that of galaxies. A team of astronomers, led by Amber Straughn of Arizona State University, searched the HUDF for "tadpole galaxies," so-called because they have bright knots and tails caused by mergers. These features are produced when the galaxies lose their gravitational grip on their stars, spewing some of those stars into space. The team found about 165 tadpole galaxies, representing about 6 percent of the 2,700 galaxies in the tadpole galaxy study. "To our surprise, however, these tadpole objects did not show any fluctuation in brightness," Straughn said. "The flickering light - when it is present - comes from the material swirling around an accretion disk surrounding a black hole. The material is heated and begins to glow. As it spirals down toward the black hole, it can rapidly change in brightness. This study of tadpole galaxies suggests that black holes in newly merging galaxies are enshrouded in dust, and therefore, we cannot see them accreting material." Cohen's team studied the brightness of about 4,600 HUDF objects over several weeks to many months. The Hubble team found that about 45 (non-tadpole) objects, representing 1 percent of the faint galaxies in the study, fluctuated significantly in brightness over time. This result indicates that the galaxies probably contain supermassive black holes that are feeding on stars or gas. "A black hole's typical mealtime lasts at least a few dozen million years," Windhorst said. "This is equivalent to black holes spending no more than 15 minutes per day eating all their food - a veritable fast food diet." The HUDF analysis also reinforces previous Hubble telescope studies of monster black holes in the centers of nearby, massive galaxies. Those studies showed a close relationship between the mass of a galaxy's "central bulge" of stars and that of the central black hole. Galaxies today have central black holes with masses ranging from a few million to a few billion solar masses. |
|
|
|
 |
|||||||||||||||||||||
This film looks at the highlights in NASA's history from its creation in the 1950s, through the glory days of the Mercury, Gemini and Apollo programs, birth of the space shuttle and the loss of Challenger, launch of Hubble and much more.
If at first you don't succeed, keep on trying. That is what the astronauts of space shuttle Endeavour's maiden voyage did in their difficult job of rescuing a wayward communications satellite. Spacewalkers were unable to retrieve the Intelsat 603 spacecraft, which had been stranded in a useless orbit, during multiple attempts using a special capture bar. So the crew changed course and staged the first-ever three-man spacewalk to grab the satellite by hand. The STS-49 astronauts describe the mission and narrate highlights in this post-flight presentation.
The mission for the crew of space shuttle Challenger's April 1984 flight was two-fold -- deploy the experiment-laden Long Duration Exposure Facility (LDEF) and then track down the crippled Solar Max spacecraft, capture it and perform repairs during spacewalks. Initial attempts by the astronauts to grab the craft while wearing the Manned Maneuvering Unit spacewalk backpacks failed, but the crew ultimately retrieved Solar Max and installed fresh equipment while it was anchored in the payload bay. The crew narrates this post-flight presentation of home movies and highlights from mission STS-41C.
The space shuttle program was grounded for 32 months in the painful wake of the 1986 Challenger accident. Americans finally returned to space in September 1988 when shuttle Discovery safely launched for its mission to deploy a NASA communications satellite. Enjoy this post-flight presentation narrated by the astronauts as they show movies and tell the story of the STS-26 mission.
Imagine a space shuttle mission in which the astronaut crew launched two commercial and one military communications spacecraft, then conducted a pair of incredible spacewalks to recover, fix and redeploy a satellite that malfunctioned just four months earlier. The rescue mission was a success, starting with an astronaut making a catch of the spinning satellite with just his gloved-hand. Enjoy this post-flight presentation narrated by the astronauts as they tell the story of shuttle Discovery's August 1985 mission known as STS-51I.
In our continuing look back at the classic days of the space shuttle program, today we show the STS-41D post-flight presentation by the mission's astronauts. The crew narrates this film of home movies and mission highlights from space shuttle Discovery's maiden voyage in August 1984. STS-41D deployed a remarkable three communications satellites -- a new record high -- from Discovery's payload bay, extended and tested a 100-foot solar array wing and even knocked free an icicle from the shuttle's side using the robot arm.
As the title aptly describes, this movie straps you aboard the flight deck for the thunderous liftoff, the re-entry and safe landing of a space shuttle mission. The movie features the rarely heard intercom communications between the crewmembers, including pilot Jim Halsell assisting commander Bob Cabana during the landing.
On Christmas Eve in 1968, a live television broadcast from Apollo 8 offered this message of hope to the people of Earth. The famous transmission occurred as the astronauts orbited the Moon.