Radio Telescope Reveals Secrets of Massive Black Hole (Forwarded)

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EMBARGOED For Release: 1:00 p.m. EDT, Wednesday, April 23, 2008

Radio Telescope Reveals Secrets of Massive Black Hole

At the cores of many galaxies, supermassive black holes expel powerful
jets of particles at nearly the speed of light. Just how they perform this
feat has long been one of the mysteries of astrophysics. The leading
theory says the particles are accelerated by tightly-twisted magnetic
fields close to the black hole, but confirming that idea required an
elusive close-up view of the jet's inner throat. Now, using the unrivaled
resolution of the National Radio Astronomy Observatory's Very Long
Baseline Array (VLBA), astronomers have watched material winding a
corkscrew outward path and behaving exactly as predicted by the theory.

"We have gotten the clearest look yet at the innermost portion of the jet,
where the particles actually are accelerated, and everything we see
supports the idea that twisted, coiled magnetic fields are propelling the
material outward," said Alan Marscher, of Boston University, leader of an
international research team. "This is a major advance in our understanding
of a remarkable process that occurs throughout the Universe," he added.

Marscher's team studied a galaxy called BL Lacertae (BL Lac), some 950
million light-years from Earth. BL Lac is a blazar, the most energetic
type of black-hole-powered galactic core. A black hole is a concentration
of mass so dense that not even light can escape its gravitational pull.
Supermassive black holes in galaxies' cores power jets of particles and
intense radiation in similar objects including quasars and Seyfert
galaxies.

Material pulled inward toward the black hole forms a flattened, rotating
disk, called an accretion disk. As the material moves from the outer edge
of the disk inward, magnetic field lines perpendicular to the disk are
twisted, forming a tightly-coiled bundle that, astronomers believe,
propels and confines the ejected particles. Closer to the black hole,
space itself, including the magnetic fields, is twisted by the strong
gravitational pull and rotation of the black hole.

Theorists predicted that material moving outward in this close-in
acceleration region would follow a corkscrew-shaped path inside the bundle
of twisted magnetic fields. They also predicted that light and other
radiation emitted by the moving material would brighten when its rotating
path was aimed most directly toward Earth.

Marscher and his colleagues predicted there would also be a flare later
when the material hits a stationary shock wave called the "core" some time
after it has emerged from the acceleration region.

"That behavior is exactly what we saw," Marscher said, when his team
followed an outburst from BL Lac. In late 2005 and early 2006, the
astronomers watched BL Lac with an international collection of telescopes
as a knot of material was ejected outward through the jet. As the material
sped out from the neighborhood of the black hole, the VLBA could pinpoint
its location, while other telescopes measured the properties of the
radiation emitted from the knot.

Bright bursts of light, X-rays, and gamma rays came when the knot was
precisely at locations where the theories said such bursts would be seen.
In addition, the alignment of the radio and light waves -- a property
called polarization -- rotated as the knot wound its corkscrew path inside
the tight throat of twisted magnetic fields.

"We got an unprecedented view of the inner portion of one of these jets
and gained information that's very important to understanding how these
tremendous particle accelerators work," Marscher said.

In addition to the continent-wide VLBA, an array of 10 radio telescopes
spread from Hawaii to the Virgin Islands, the team used telescopes at the
Steward Observatory, the Crimean Astrophysical Observatory, Lowell
Observatory, Perugia University Astronomical Observatory, Abastumani
Astrophysical Observatory, NASA's Rossi X-Ray Timing Explorer, the
University of Michigan Radio Astronomy Observatory, and the Metsahovi
Radio Observatory. The astronomers reported their findings in the April 24
issue of the journal Nature.

The National Radio Astronomy Observatory is a facility of the National
Science Foundation, operated under cooperative agreement by Associated
Universities, Inc.

IMAGE CAPTION:
[http://www.nrao.edu/pr/2008/bllac/bllac2.big.jpg (233KB)]
Artist's conception of region near supermassive black hole where twisted
magnetic fields propel and shape jet of particles (Credit: Marscher et
al., Wolfgang Steffen, Cosmovision, NRAO/AUI/NSF).

MOVIE:
Video of Black-Hole-Powered Jet (Credit: Cosmovision, Wolfgang Steffen)
http://www.nrao.edu/videos/scienceInnerJetAGN_high.mpg [4.52MB]

* NTSC Format (90MB)
http://www.bu.edu/blazars/bllac_file..._cam3_ntsc.mov
* PAL Format (90MB)
http://www.bu.edu/blazars/bllac_file...e_cam3_pal.mov