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An international team of astronomers has
gathered new data that helps to explain the origins of quasar
particle jets. These are enormous jets, hundreds of thousands of
light-years long, emanating from the supermassive black holes at the
heart of distant galaxies. They’re mysterious because the energy of
particles they emit goes down across the length of the jet. This new
theory proposes that the jets are emitting particles through
synchrotron radiation; where the environment close to the black hole
acts as a natural particle accelerator.
An international team of astronomers led by researchers at Yale has
obtained key infrared observations that reveal the nature of quasar
particle jets that originate just outside super-massive black holes
at the center of galaxies and radiate across the spectrum from radio
to X-ray wavelengths; a complementary study of jet X-ray emission
led by astronomers at the University of Southampton, reaches the
same conclusion.
Both studies involve the jet of the quasar 3C273, famous since its
identification in 1963 as the first quasar. It now appears that the
most energetic radiation from this jet arises through direct
radiation from extremely energetic particles, and not in the way
expected by most astronomers based on the previously available data.
The two reports, available now online in the Astrophysical Journal,
will appear in print in the September 10 issue.
“Quasar jets, although extremely luminous, are so distant as to be
relatively faint and difficult to observe. Thanks to the sensitivity
of NASA’s Great Observatories, we have been able to map the 3C273
jet in infrared, visible light and X-rays,” said C. Megan Urry,
Israel Munson Professor of Physics and Astronomy at Yale, and an
author on one study. “These combined data strongly suggest that
ultra-energetic particles in the 3C273 jet are producing their light
via synchrotron radiation.”
There have been two competing theories of how emissions arise from
the particles — the “Inverse-Compton” theory proposing that the
emissions occur when jet particles scatter cosmic microwave
background photons, and the “Synchrotron Radiation” theory
postulating a separate population of extremely energetic electrons
or protons that cause the high-energy emission.
“The Yale team used the Spitzer Space Telescope to observe 3C273
because it is located in space and is more sensitive to faint
infrared jet emission than any previous telescope,” said Yasunobu
Uchiyama, a team leader and former postdoctoral fellow at the Yale
Center for Astronomy. Spitzer observations enabled the team, with
collaborators at Stanford, University of Southampton, Goddard Space
Flight Center, and the Brera Observatory in Milan, to determine the
infrared spectrum for the first time and thus to realize its close
connection to the X-ray emission.
Sebastian Jester, now at the University of Southampton, led a
complementary study that used the Chandra X-ray Observatory. This
team, with collaborators at MIT Kavli Institute for Astrophysics and
Space Research and the Smithsonian Astrophysical Observatory (SAO)
in Cambridge, MA, and at the Max Planck Institute for Astronomy in
Heidelberg, obtained the first detailed study of energy distribution
of X-rays from the jet, which also supported the synchrotron theory.
According to the researchers, while the lifetime of the X-ray
producing particles is only about 100 years, the data indicate that
the visibly brightest part of the jet has a length of about 100,000
light years. Since there would be insufficient time for the
particles to shoot out from the black hole at close to the speed of
light and then release their energy as radiation as far out as they
are seen, the particles have to be accelerated locally, where they
produce their emission.
Both teams also used data from the third of NASA’s Great
Observatories, the Hubble Space Telescope, and the radio telescopes
of the Very Large Array (VLA). The three space telescopes and the
VLA “see” emission of different wavelengths from celestial objects,
and the combined data was essential to reveal the new comprehensive
perspective on the jets.
“The new observations show that the flow structure of this jet is
more complicated than had been assumed previously,” Jester explains.
“That the present evidence favors the synchrotron model deepens the
mystery of how jets produce the ultra-energetic particles that
radiate at X-ray wavelengths.”
“Our results call for a radical rethink of the physics of
relativistic jets that black holes drive,” said Uchiyama. “But, we
now have a crucial new clue to solving one of the major mysteries in
high-energy astrophysics.”
Other authors on the papers include Jeffrey Van Duyne and Paolo
Coppi at Yale; C.C. Cheung at Stanford University; Rita Sambruna at
NASA/GSFC, Greenbelt, MD; Tadayuki Takahashi at ISAS/JAXA, Japan;
Laura Maraschi and Fabrizio Tavecchio at the Osservatorio
Astronomico di Brera, Milan; Dan Harris from the SAO; Herman
Marshall at MIT; and Klaus Meisenheimer at Max Planck Institute for
Astronomy in Heidelberg. Grant and contract funding from NASA
supported the research.
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