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Creeping up on a big black hole

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International collaboration pinpoints region of high-energy emissions at galactic core

By Roger Snodgrass

There are probably few scenes of violence in the universe that can compare to what goes on in the energetic activity of an accretion disk spiraling down around a monster black hole at the center of a large galaxy.

This appears to be especially true of the largest galaxies, like the giant elliptical galaxy named M87, a luminous and highly evolved system in the Constellation Virgo.

“M87 is a key object, one of the Rosetta Stones of intergalactic astronomy.” Bill Junor said, a staff member at Los Alamos National Laboratory in Space and Remote Sensing Sciences. “It has a very big black hole.”

It’s also in the neighborhood, relatively speaking. Only 50 million light years away, as Junor said: “It’s just down the street.”

One of the nebular objects first cataloged by Charles Messier in the late 1700s, M87 has been a convenient and steady source of new knowledge about the mysteries beyond our local galaxy.

Among M87’s remarkable features is a an enormous jet, or energetic plume, which is several thousand light years long and was first identified in 1918.

Junor is one of several hundred people who shared authorship on a new scientific paper in Science magazine this month that locates the source of the flare and its relationship to the mechanism of galactic black holes.

In the mid-’90s, astronomers at the Hubble Space Telescope “found seemingly conclusive evidence for a massive black hole in the center of the giant elliptical galaxy M87,” one of the first objects to provide that evidence.

Scientists from LaPlace to Einstein and Schwarzschild had developed a theoretical understanding of what black holes might be.

The American physicist John Wheeler, who was a key figure on the Manhattan Project, coined the term, “Black Hole” in the ’60s. The centers of galaxies are hidden by curtains of dust and dense gases and atoms torn into particles.

The black hole is invisible, by virtue of its mass and can only be inferred by its effects, movements and emissions that can be seen to emerge from the central region.

In the ’90s, astronomers found very powerful gamma rays coming out of M87, with a trillion times the energy of visible light, but the gamma ray telescopes could not pinpoint the source within the thick gaseous fog of the inner galaxy.

Using a worldwide combination of diverse telescopes, astronomers have discovered a relationship between gamma ray bursts at the core of the galaxy and the accretion disk that surrounds it.

In parallel with all these other observations, Junor  and his colleagues at the Very Large Baseline Array were focusing on mapping the jets themselves in fine detail.

“These are long pieces of matter that are being squirted out from these very energetic systems,” Junor said. Because of the weak signal to noise in this investigation, lots of angles of confirmation were needed.

More images came in from the High Energy Stereoscopic System (H.E.S.S.) in Namibia, Africa; the MAGIC system (a budding array of two gamma ray telescopes) on La Palma, in the Canary Islands; and VERITAS (Very Energetic Radiation Imaging Telescope Array System) in Arizona. These readings were taken during 50 nights between January and May 2008.

With its Array Operations Center in Socorro, N.M., the VLBA consists of 10 large telescopes from the Virgin Islands to Hawaii. One is located at LANL.

Together comprising one large virtual telescope, it is capable of images that have 50 times the resolution of the Hubble Space Telescope.

“Combining the gamma ray observations with the super-sharp radio ‘vision’ of the VLBA, allowed us to see that the gamma rays are coming from very near the black hole itself,” said Craig Walker of the National Radio Astronomy Observatory (NRAO) in a press release.

Putting the gamma ray and radio ray stories together connected both to the monstrous black hole.

“The story is that where this energetic stuff is happening establishes the connection between the radio and the gamma ray emissions,” Junor said, noting that the large collaboration is in the nature of modern astronomical science.

“It’s very hard to study things so close to a black hole,” he said, adding that these new findings offer new insights into the engine that black holes are driving and the environment that surrounds them.