Space Telescope Science Institute astronomers and their co-investigators have gained their first glimpse of the mysterious region near a black hole at the heart of a distant galaxy, where a powerful stream of subatomic particles spewing outward at nearly the speed of light is formed into a beam, or jet, that then goes nearly straight for thousands of light-years. The astronomers used radio telescopes in Europe and the U.S., including the National Science Foundation's Very Long Baseline Array to make the most detailed images ever of the center of the galaxy M87, some 50 million light-years away.
This is the first time anyone has seen the region in which a cosmic jet is formed into a narrow beam, said Bill Junor of the University of New Mexico, in Albuquerque. "We had always speculated that the jet had to be made by some mechanism relatively near the black hole, but as we looked closer and closer to the center, we kept seeing an already-formed beam. That was becoming embarrassing, because we were running out of places to put the formation mechanism that we knew had to be there."
Junor, along with John Biretta and Mario Livio of the Space Telescope Science Institute, in Baltimore, MD, now have shown that M87's jet is formed within a few tenths of a light-year of the galaxy's core, presumed to be a black hole three billion times more massive than the sun. In the formation region, the jet is seen opening widely, at an angle of about 60 degrees, nearest the black hole, but is squeezed down to only 6 degrees a few light-years away.
The 60-degree angle of the inner part of M87's jet is the widest such angle yet seen in any jet in the universe, said Junor. "We found this by being able to see the jet to within a few hundredths of a light-year of the galaxy's core â€" an unprecedented level of detail." The scientists reported their findings in the October 28 issue of the journal Nature.
At the center of M87, material being drawn inward by the strong gravitation of the black hole is formed into a rapidly-spinning flat disk, called an accretion disk. The subatomic particles are thought to be pushed outward from the poles of this disk. The scientists believe that magnetic fields in the disk are twisted tightly as the disk spins and then channel the electrically-charged particles into a pair of narrow jets.
Our new image of M87 supports this idea of magnetic fields doing the work of forming the stream of particles into a narrow jet, said Biretta.
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