Evidence for Ultra-Energetic Particles in Jet from Black Hole

An international team of astronomers, led by Dr Sebastian Jester from the University of Southampton, has obtained key X-ray observations that reveal the nature of quasar particle jets which originate just outside super-massive black holes at the centre of galaxies and radiate across the spectrum from radio to X-ray wavelengths. A complementary study of jet infrared emission, led by astronomers at Yale University, 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 attain nearly the speed of light and emit infrared-visible light and X-rays. But the jets have been too distant and faint to collect sufficient data to decide the nature of the emission until now," said Sebastian Jester, working at the University of Southampton with funding from an Otto Hahn fellowship from Germany's Max Planck Society, the leader of one study and a co-author on the other. "These data are a significant advance in what we know about jets, and the results clearly suggest ultra-energetic particles are emitting synchrotron radiation in 3C273."

There have been two competing theories of how X-ray emission arises 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.

Dr Jester led a team of collaborators at MIT and the Smithsonian Astrophysical Observatory (SAO) in Cambridge, MA, and at the Max Planck Institute for Astronomy in Heidelberg, to observe the 3C273 jet with the Chandra X-ray Observatory. Their more detailed Chandra data allowed the first in-depth study of the energy distribution of the X-rays from the jet, which supported the synchrotron theory.

In a complementary study, a team led by Dr Yasunobu Uchiyama, former postdoctoral fellow at the Yale Center for Astronomy, observed the 3C273 jet with the Spitzer Space Telescope, "because it is located in space and is more sensitive to faint infrared jet emission than any previous telescope," said Uchiyama. Spitzer observations enabled the team, with collaborators at Stanford, the 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 deduce the origin of the radio through X-ray 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 combination is essential to reveal a new comprehensive perspective on the jets.

"The new multiwavelength data clearly show the emission at radio, infrared, optical and X-ray wavelengths is linked," said C. Megan Urry, Israel Munson Professor of Physics and Astronomy at Yale, and an author on the Uchiyama study. "This strongly suggests that ultra-energetic particles in the 3C273 jet are producing all their light via synchrotron radiation."

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.

"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." Sebastian Jester adds: "The new observations show that the flow structure of this jet is more complicated than had been assumed previously. 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. Fermilab, CERN and DESY would be jealous!"

Other authors on the Uchiyama paper include Jeffrey Van Duyne and Paolo Coppi from Yale; C.C. Cheung, Stanford University; Rita Sambruna, NASA/GSFC, Greenbelt, MD; Tadayuki Takahashi, ISAS/JAXA, Japan; and Laura Maraschi and Fabrizio Tavecchio, Osservatorio Astronomico di Brera, Milan. Other authors on the Jester paper include Dan Harris from the Smithsonian Astrophysical Observatory (SAO), Herman Marshall from the MIT Kavli Institute for Astrophysics and Space Research; and Klaus Meisenheimer, Max Planck Institute for Astronomy in Heidelberg. Grant and contract funding from NASA supported the research.