Brightest ultrafast jets in active galaxies found to be powerful gamma-ray beacons
New observations reveal further details on the functioning of the most violent and energetic objects known: the jets produced by supermassive black holes in active galaxies. An international team of astronomers, including scientists at the Max Planck Institute for Radio Astronomy in Bonn, has combined data from some of the world's most advanced astronomical instruments, including the U.S. Very Long Baseline Array (VLBA) and the Fermi Gamma-ray Space Telescope, to study how supermassive black holes manage to produce copious quantities of the most energetic form of light: gamma-rays.
The international team has combined observations of the bright gamma-ray sky by NASA's orbiting Fermi Gamma-ray Space Telescope with those from the ground-based Very Long Baseline Array radio telescope to observe the material expelled with enormous speeds away from the black holes in the heart of very remote galaxies. These ejections take the form of narrow jets in radio telescope images, and appear to be producing the gamma-rays detected by Fermi. Their findings are being reported in two publications in the 2009 May 1 issue of the Astrophysical Journal Letters. Yuri Kovalev, Humboldt Fellow and scientist at the Max Planck Institute for Radio Astronomy, is enthusiastic: "These objects are amazing: finally we know for sure that the fastest, most compact, and brightest jets that we see with radio telescopes are the ones which are able to kick the light up to the highest energies".
Figure 1: The Gamma-ray Sky as seen by Fermi (background). The inserts show radio images of the jets of selected active galactic nuclei observed by the VLBA in the framework of the MOJAVE project, showing how the VLBA works as magnifier to see the finest details in the radio jets. The VLBA images have an angular resolution of about one thousandth of a second or arc - about a million times better resolution than the gamma-ray observations and more than a factor of fifty better than any optical telescope such as the Hubble Space Telescope. Collage: Matthias Kadler and NASA/DOE/Fermi LAT Team and NRAO/AUI/MOJAVE team. Higher Resolution
Distant galaxies host deep in their nucleus spinning supermassive black holes, which are billions of times heavier than our Sun but are confined to a region no larger than our solar system. These rapidly rotating black holes attract stars, gas and dust, creating huge magnetic fields. The magnetic forces can trap some of the infalling gas and focus it into narrow jets that flow away from the core of the galaxy at velocities approaching the speed of light. The jets, when they happen to be pointed directly at Earth, display one of the most spectacular phenomena in the Universe, since a quirk of Einstein's theory of special relativity can make their speeds appear faster than the speed of light. Theoreticians and observers alike have been asking themselves for decades about the nature and composition of these energetic radio-emitting jets, and if they also radiate in other parts of the electromagnetic spectrum. And this is indeed the case! Some hints were provided by the EGRET instrument on the Compton Gamma Ray Observatory telescope in the late 1990s and more recent discoveries of X-ray emission made by the Chandra Observatory. But now, the prediction of the link between radio and gamma-ray mission has been confirmed by the several of world's most advanced astronomical instruments, such as the VLBA and Fermi. "The marriage of a prime instrument such as the VLBA with a new gamma-ray telescope is generating exciting insights into the acceleration and emission mechanisms of these mysterious black hole phenomena", says Anton Zensus, director at the Max Planck Institute for Radio Astronomy and Fermi Affiliated Scientist. "The gamma-ray bright sources are now proven to be brighter, more compact and faster at light year scales than the gamma-ray quiet sources."
The gamma-ray observations have been performed with NASA's Fermi Gamma-ray Space Telescope, which has been operational since the summer of 2008. The Fermi Large Area Telescope records an image of the whole sky every few hours to explore the most extreme environments in the universe, including pulsars and gamma-ray bursts, as well as black holes in galactic nuclei. Gamma-ray observations alone are not enough to discern the exact location of the radiation, however. The VLBA serves as a magnifying glass under which the details of the most energetic processes in the distant universe appear as if they were happening in our own Galactic backyard. Interestingly, many objects found by Fermi to be extreme in gamma-rays are emitting strong bursts of radio emission at the same time.
The Very Long Baseline Array of the U.S. National Science Foundation is a continent-wide system of ten radio telescope antennas, ranging from Hawaii in the west to the U.S. Virgin Islands in the east. Dedicated in 1993, the VLBA is operated by the NRAO and is designed to monitor the brightest objects in the Universe at the highest available resolution in astronomy. Matthew Lister, Physics Professor in Purdue University and guest investigator on the Fermi project, says: "For more than a decade, we have collected images of the brightest galaxies in the radio sky to study the changing structures of their jets. We have waited a long time to compare our measurements with the findings in the gamma-ray sky, and now we finally have it!"
The work for astronomers does not stop here: the team has concluded that the region of the jet closest to the black hole is undoubtedly the place where the gamma-ray and the radio bursts of light originate in about the same time. However, some parts of the puzzle have yet to be resolved: some bright gamma-ray sources in the sky appear to have no radio or optical counterpart - their nature is still completely unknown. With this new joint eye on the universe provided by Fermi and the VLBA, astronomers look forward to investigating these intriguing mysteries, and anticipate many new exciting discoveries to come.
The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.
NASA's Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership mission, developed in collaboration with the U.S. Department of Energy and important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden, and the U.S.
Additional graphical material:
Labeled Version (source names) and Labeled Version (source names, image title, and logos) of Figure 1 (Collage: Matthias Kadler and NASA/DOE/Fermi LAT Team and NRAO/AUI/MOJAVE team.)3C 84. High-resolution VLBA image of the radio galaxy 3C 84, central galaxy of the Perseus cluster in a distance of approx. 230 million light years. (Image: Yuri Kovalev and NRAO/AUI/MOJAVE team.)
3C 454.3. High-resolution VLBA image of the quasar 3C 454.3 at a distance of approx. 7 billion light years. This quasar was found by Fermi to be the brightest on the gamma-ray sky in August-October 2008 (Figure 1). (Image: Yuri Kovalev and NRAO/AUI/MOJAVE team.)
Original Publications:
The Relation Between AGN Gamma-Ray Emission and Parsec-Scale Radio Jets , Y. Y. Kovalev, H. D. Aller, M. F. Aller, D. C. Homan, M. Kadler, K. I. Kellermann, Yu. A. Kovalev, M. L. Lister, M. J. McCormick, A. B. Pushkarev, E. Ros and J. A. Zensus, The Astrophysical Journal Letters, 696, L17-L21 (2009).A Connection Between Apparent VLBA Jet Speeds and Initial AGN Detections Made by the Fermi Gamma-ray Observatory , M. L. Lister, D. C. Homan, M. Kadler, K. I. Kellermann, Y. Y. Kovalev, E. Ros, T. Savolainen and J. A. Zensus, The Astrophysical Journal Letters, 696, L22-L26 (2009).
Further Information:
Max Planck Institute for Radio Astronomy (MPIfR) and its Very Long Baseline Interferometry (VLBI) research group.Alexander von Humboldt Foundation (AvH).
Monitoring Of Jets in Active galactic nuclei with VLBA Experiments (MOJAVE).
Very Long Baseline Array (VLBA).
Fermi Gamma-ray Space Telescope (formerly GLAST).
Parallel and earlier press releases:
Continent-sized radio telescope takes close-ups of Fermi active galaxies, NASA Web Feature at the Fermi Mission Area, April 22, 2009.Fermi's Best-Ever Look at the Gamma-Ray Sky, NASA Press Release, March 11, 2009.
VLBA Movies Reveal New Details of Cosmic Jets, NRAO Press Release, January 08, 2008.
Fifty Times sharper than Hubble, MPIfR Press Release, October 05, 2007.
NRAO Teams With NASA Gamma-Ray Satellite, NRAO Press Release, June 05, 2007.
Contact:
Dr. Yuri KovalevMax-Planck-Institut für Radioastronomie, Bonn.
Fon: +49-228-525-395
Fon: +7 915 1546281
E-mail: ykovalev@mpifr.de
Prof. Dr. Eduardo Ros
Max-Planck-Institut für Radioastronomie, Bonn.
Fon: +49-228-525-292
E-mail: ros@mpifr.de
Dr. Norbert Junkes,
Public Outreach,
Max-Planck-Institut für Radioastronomie, Bonn.
Fon: +49-228-525-399
E-mail: njunkes@mpifr.de
