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Chandra reveals new features of cosmic explosions

E0102-72 is a supernova remnant
(click image for larger version)

Star gazing
Clickable Chandra

September 21, 1999
Web posted at: 2:04 p.m. EDT (1804 GMT)

In this story:

Shell now looks like a ring

Bright nebula surrounded by diffuse cloud

Pulsar surrounded by shell

Researchers work around spectrometer glitch


By Robin Lloyd
CNN Interactive Senior Writer

(CNN) -- NASA's newest space telescope has snapped detailed pictures of the remnants of three stellar explosions, presenting mysteries about their odd shapes and the power-generating neutron stars thought to be at the center of two of them.

Two of the remnants imaged this month by the Chandra X-ray Observatory seem to have rapidly rotating neutron stars at their center that spit out high-energy particles. All three are surrounded by oddly shaped shells or clouds of highly charged gas.

"It's a thrill to see them," said Fred Seward of the Harvard-Smithsonian Center for Astrophysics in Massachusetts.

Seward and his colleagues discovered X-rays emitted from two of the three supernova remnants with the Chandra's predecessor, NASA's Einstein Observatory, over a decade ago.

"We're seeing more detail and features we haven't seen before," he said.

One of remnants, called E0102-72 and found in the Small Magellanic Cloud -- a satellite galaxy of our Milky Way, resembles a flaming cosmic wheel and stretches across 40 light years of space. A light year is the distance it takes light to travel in a year -- about 6 trillion miles.

The Small Magellanic Cloud is 190,000 light years from Earth. Like the other two remnants, E0102-72 resulted from the explosion of a massive star several thousand years ago.

Astronauts aboard the space shuttle released the $1.2 billion Chandra space telescope into orbit in July.

Shell now looks like a ring

PSR 0540-69 is a pulsar, or rotating neutron star
(click image for larger version)

When Seward and his colleagues looked at E0102-72 in 1980, they could see it was surrounded by hot gas that had formed what looked like a bright spherical shell.

With Chandra, the shell now looks like a ring, proving the dramatic improvement in resolution that Chandra provides.

Seward and his colleagues have two explanations for the ring shape -- either the explosion itself was asymmetrical or it encountered material nearby that was oddly shaped and contorted the material blown from the star.

Previously, astrophysicists thought the remnant harbored a central neutron star, but the Chandra data clearly shows the opposite -- no neutron star at the center, making it easier to identify the type of the supernova explosion that produced the remnant.

Supernova explosions start either as explosions of white dwarfs (dim, planet-sized stars) that eject all their material into space or from the gravitational collapse of massive stars that leave behind neutron stars or black holes.

Now it is clear that the E0102-72 remnant is a result of the first type of explosion, Seward said.

Bright nebula surrounded by diffuse cloud

A second supernova remnant imaged by Chandra shows a bright nebula, thought to be a rotating, magnetized neutron star, surrounded by a diffuse cloud.

Called G21.5-0.9, the second remnant is about 16,000 light years from Earth.

The neutron star at its center acts like a powerful generator, Seward said, creating intense electric voltages that accelerate electrons to nearly the speed of light and generating power equal to the output of more than 1,000 suns.

Detailed explanations for this remnant and the other two new images are yet to come, said Chandra project scientist Martin Weisskopf of NASA's Marshall Space Flight Center in Alabama.

"You can no longer simply wave your arms and say a star is there. It spins. There is plenty of energy avail. Somehow it all hangs together," he said.

"Now you've got to go and get into the meat of how does that really work. How do I explain the first remnant, E0102-72? You've got to go through the whole scenario and produce that ring. You've got to explain the so-called spokes."

G21.5-0.9 is also a supernova remnant
(click image for larger version)

Pulsar surrounded by shell

A previously known pulsar called PSR 0540-69 also was observed with much more clarity by Chandra.

This pulsar -- located in the Large Magellanic Cloud, a 180,000 light-year-distant satellite galaxy to our Milky Way -- emits pulses of radio, optical and X-ray energy at a rate of 50 per second.

These pulses, which come from an inner neutron star, make up only a tiny fraction of the total energy output of the neutron star powerhouse.

"With Einstein, just about all we could see is it looked like a point source," Seward said of the pulsar. "With Chandra we can see there is the bright neutron star but there is material around it forming a gaseous shell."

This remnant must have originated through gravitational collapse, he said.

Overall, the Chandra data will give astrophysicists clues about how supernova explosions occur and the types of stars that explode, Seward said.

Researchers work around spectrometer glitch

The new images show that the Chandra telescope is working fine, despite a resolution problem, reported last week, involving the front side of chips on its spectrometer instrument. The chips convert electromagnetic radiation like X-rays into digital data.

The source of the problem is yet to be fully diagnosed, Weisskopf said, but for now it reduces the daily rate of data that Chandra can collect.

"It is not going to affect the science of the mission," he said. "We may have to be less efficient than we were before. But our back-illuminated devices are working perfectly fine, showing absolutely no change in performance."

Chandra's testing period has concluded. Researchers who competed for time on the telescope got their first shot at making observations over the weekend.

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August 26, 1999
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August 24, 1999

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