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Saturn's spongy moon
Stunning images of Saturn's moon Hyperion taken by the Cassini spacecraft show a surface dotted with craters and modified by some process, not yet understood, to create a strange, "spongy" appearance, unlike the surface of any other moon around the ringed planet.

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Astronaut parade
The astronauts from space shuttle Discovery's return to flight mission recently paid a visit to Japan, the homeland of mission specialist Souichi Noguchi, and were treated to a grand parade.

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ISS command change
The International Space Station's outgoing Expedition 11 crew and the new Expedition 12 crew gather inside the Destiny laboratory module for a change of a command ceremony, complete with ringing of the outpost's bell, as the human presence in space continues.

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Expedition 11 in review
The Expedition 11 mission of commander Sergei Krikalev and flight engineer John Phillips aboard the International Space Station is winding down, and this narrated retrospective looks back at the key events of the half-year voyage in orbit.

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Pluto spacecraft
The Pluto New Horizons spacecraft, destined to become the first robotic probe to visit Pluto and its moon Charon, arrives at NASA's Kennedy Space Center in advance of its January blastoff.

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Life on the station
NASA astronauts Bill McArthur and John Phillips chat with Associated Press space reporter Marcia Dunn about life aboard the International Space Station in this live space-to-Earth interview from the Destiny laboratory module on October 5.

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West Coast Delta 4
In preparation for the West Coast launch of Boeing's next-generation Delta 4 rocket, the two-stage vehicle is rolled out of its horizontal hangar and driven to the Space Launch Complex-6 pad for erection. The nose cone for the NRO payload is then brought to the pad.

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West Coast shuttle
Boeing's Delta 4 rocket pad at Vandenberg Air Force Base was renovated in recent years, transforming Space Launch Complex-6 from the West Coast space shuttle launch site into a facility for the next-generation unmanned booster. This collection of footage shows the 1985 launch pad test using NASA's orbiter Enterprise.

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New star generation found
Posted: October 14, 2005

NASA's Chandra X-ray Observatory revealed a new generation of stars spawned by a super-massive black hole at the center of the Milky Way galaxy. This novel mode of star formation may solve several mysteries about these super-massive black holes that reside at the centers of nearly all galaxies.

Chandra's image of the Galactic Center (left) has provided evidence for a new and unexpected way for stars to form. A combination of infrared and X-ray observations indicates that a surplus of massive stars has formed from a large disk of gas around Sagittarius A*, the Milky Way's central black hole (illustration on right). Credit: X-ray: NASA/CXC/MIT/F.K.Baganoff et al.; Illustration: NASA/CXC/M.Weiss
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"Massive black holes are usually known for violence and destruction," said Sergei Nayakshin of the University of Leicester, United Kingdom. "So it's remarkable this black hole helped create new stars, not just destroy them."

Black holes have earned their fearsome reputation because any material, including stars, that falls within their "event horizon" is never seen again. These new results indicate immense disks of gas, orbiting many black holes at a safe distance from the event horizon, can help nurture the formation of new stars. This conclusion comes from new clues that could only be revealed in X-rays. Until the latest Chandra results, researchers have disagreed about the origin of a mysterious group of massive stars discovered by infrared astronomers.

The stars, orbiting less than a light year from the Milky Way's central black hole, are known as Sagittarius A* ( Sgr A*). At such close distances to Sgr A*, the standard model for star forming gas clouds predicts they should have been ripped apart by tidal forces from the black hole. Two models, based on previous research, to explain this puzzle have been proposed. In the disk model, the gravity of a dense disk of gas around Sgr A* offsets the tidal forces and allows stars to form.

In the migration model, the stars formed in a cluster far away from the black hole and then migrated in to form the ring of massive stars. The migration scenario predicts about a million low mass, sun-like stars in and around the ring. In the disk model, the number of low mass stars could be much less.

Researchers used Chandra observations to compare the X-ray glow from the region around Sgr A* to the X-ray emission from thousands of young stars in the Orion Nebula star cluster. They found the Sgr A* star cluster contains only about 10,000 low mass stars, thereby ruling out the migration model. Because the galactic center is shrouded in dust and gas, it has not been possible to look for the low-mass stars in optical observations. X-ray data have allowed astronomers to penetrate the veil of gas and dust and look for these low mass stars.

This research, coauthored by Nayakshin and Rashid Sunyaev of the Max Plank Institute for Physics in Garching, Germany, will appear in an upcoming issue of the Monthly Notices of the Royal Astronomical Society.

"In one of the most inhospitable places in our galaxy, stars have prevailed," Nayakshin said. "It appears star formation is much more tenacious than we previously believed." "We can say the stars around Sgr A* were not deposited there by some passing star cluster, rather they were born there," Sunyaev said. "There have been theories that this was possible, but this is the first real evidence. Many scientists are going to be very surprised by these results."

The research suggests the rules of star formation change when stars form in the disk surrounding a giant black hole. Because this environment is very different from typical star formation regions, there is a change in the proportion of stars that form. For example, there is a much higher percentage of massive stars in the disks around black holes.

NASA's Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for the Science Mission Directorate. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass.