Astronomers sifting through
the radiation signals emanating from a distant black hole have separated the
emission into its two component parts, a key step in understanding how such
massive objects work.
Two Italian researchers pored
through a series of black hole observations taken over about five years to
separate its X-ray emissions into those belched by powerful polar jets and those
originating from a disk of material swirling around the object's maw.
Pinpointing both X-ray sources from
a general signal is a first for researchers, whose efforts have been typically
hindered by the angles of view on black holes and interference from other
radiation sources in space, researchers said. But the new research could bolster
scientists' present understanding of the physics behind black holes and their
roles as galactic engines.
"X-rays are emitted from a disk by a
different mechanism than those emitted by the jet," said the study's lead
researcher Paola Grandi, with the Istituto di Astrofisica Spaziale e Fisica Cosmica in Bologna,
Italy, in an e-mail interview. "Separation of components has been the
winning strategy to untangling [their] radiative contributions."
Although astronomers have never seen
a black hole directly, they can infer their presence by gravitational effects on
nearby stars and the radiation oozing from a disk
of material that feeds the object. Supermassive
black holes, which theorists say could sit at the center of some galaxies and
hold more than a billion Suns of material, can also fire off powerful jets
from their rotational poles, beaming X-rays, radio waves and other radiation
into space.
Grandi and colleague Giorgio
Palumbo, of Italy's Universita degli Studi de Bologna, studied a series of black
hole observations taken over a wide X-ray spectrum by the Italian-Dutch X-ray
satellite BeppoSAX between 1996 and 2001. The research will appear in the Nov. 5
issue of the journal Science.
The black hole in question appears
to be the engine behind the active galactic nucleus (AGN) of a quasar called 3C
273, sitting some 3 billion light-years away in the constellation Virgo, Grandi
said. One light-year is the distance light travels in a year, about 6 trillion
miles (10 trillion kilometers).
Since 3C 273 was used as a
calibration target for BeppoSAX researchers, Grandi and Palumbo found a number
of observations that depict the object at different periods of activity. In some
observations, the jet emissions overwhelm the meager emanations of the accretion
disk, while in others the disk signals are stronger.
"This set of data provided, for the
first time, enough information to obtain 'snapshots' of the AGN in different
stages," Grandi said. "It is understandable that no one was able to observe this
behavior before because broad band data combined with multiple exposures were
not available."
In principle, Grandi and Palumbo's
method could be applied to other AGN and black holes, so long as the right set
of data is available. The BeppoSAX 3C 273 data, for example, has been available
for years, though no one analyzed it as a whole until this recent study, Grandi
said.
"There are so many things, in this
field, which remain to be done," Grandi said, adding the method could help
determine why only some of the black holes within AGN's spew off jets. "We may
be lucky and find some other AGN to apply the same method."
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