Scientists have caught a supermassive black hole in a distant galaxy
in the act of spurting energy into a jet of electrons and magnetic
fields four distinct times in the past three years, a celestial take
on a Yellowstone geyser.

This quasar-like "active" galaxy is essentially a scaled-up model of
the so-called microquasars within our Milky Way Galaxy, which are
smaller black holes with as much as ten times the mass of the sun.
This means that scientists can now use their close-up view of
microquasars to develop working models of the most massive and
powerful black holes in the universe.

These results — published in the June 6 issue of Nature — are the
fruit of a three-year monitoring campaign with the National Science
Foundation’s Very Long Baseline Array (VLBA), a continent-wide
radio-telescope system, and NASA’s Rossi X-ray Timing Explorer.

"This is the first direct, observational evidence of what we had
suspected: The jets in active galaxies are powered by disks of hot
gas orbiting around supermassive black holes," said Alan Marscher
of the Institute for Astrophysical Research at Boston University,
who led this international team of astronomers.

Active galaxies are distant celestial objects with exceedingly bright
cores, often radiating with the brilliance of thousands of ordinary
galaxies, fueled by the gravity of a central million- to
billion-solar-mass black hole pulling in copious amounts of
interstellar gas.

Marscher and his colleagues have established the first direct
observational link between a supermassive black hole and its jet.
The source is an active galaxy named 3C120 about 450 million
light-years from Earth. This link has been observed in microquasars,
several of which are scattered across the Milky Way Galaxy, but
never before in active galaxies, because the scale (distance and
time) is so much greater.

The jets in galaxy 3C120 are streams of particles shooting away
perpendicularly from the plane of a black hole’s accretion disk,
moving at 98 percent of the speed of light. In microquasars,
radio-emitting features become visible in a jet shortly after
X-rays from the accretion disk get dimmer — as if the accretion
disk suddenly flushes into the black hole and disappears, fueling
the jet. These radio "blobs" then appear to move at
faster-than-light speeds, an illusion caused by their ultra-high
speeds and their orientation with respect to Earth.

Now the team of scientists sees this same phenomenon in 3C120.
Roughly every ten months, the X-ray-emitting accretion disk around
its supermassive black hole becomes suddenly dim, and a month later
the telltale bright spot of radio emission appears in the jet. Over
a three-year period, the team observed a series of radio blobs
floating along the particle jet like smoke puffs, each time
following a dip in the brightness of X rays from the accretion

"What we are likely seeing is the inner part of the accretion disk
becoming unstable and suddenly plunging into the black hole," said
Marscher. "We detect a ‘dip’ in the X-ray flux as the hot gas in
the disk disappears after it passes the event horizon. The remainder
of the disk is channeled into the jets, which we see as a knot of
radio emission bubbling away from the black hole. Slowly the
accretion disk fills with more interstellar gas until about ten
months later, when something disturbs the accretion disk orbit, and
the whole thing flushes and blows again."

Joining Marscher on this observation and analysis are Svetlana
Jorstad of Boston University; Jose-Luis Gomez of the Astrophysical
Institute of Andalucia in Granada, Spain; Margo Aller of the
University of Michigan; Harri Terasranta of the Helsinki University
of Technology; Matthew Lister of NRAO; and Alastair Stirling of the
University of Central Lancashire, England.

The VLBA is a continent-wide radio-telescope system, with one
telescope on Hawaii, another on St. Croix in the Caribbean, and
eight others in the continental United States. Part of the National
Radio Astronomy Observatory, the VLBA offers the highest resolving
power, or ability to see fine detail, of any telescope available.
The National Radio Astronomy Observatory is a facility of the
National Science Foundation, operated under cooperative agreement
by Associated Universities, Inc.

The Rossi Explorer was launched by NASA in 1995 to study black
holes, neutron stars and pulsars. The Rossi Explorer is operated
by NASA Goddard Space Flight Center in Greenbelt, Md.

The research on 3C120 was supported by funding from the National
Aeronautics and Space Administration and the National Science

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Scene from an animation of 3C 120. CREDIT: Cosmovision