* Astronomy

An international team of astronomers has used the world's biggest radio telescope to look deep into the brightest galaxies that NASA's Fermi Gamma-ray Space Telescope can see. The study solidifies the link between an active galaxy's gamma-ray emissions and its powerful radio-emitting jets.

"Now we know for sure that the fastest, most compact, and brightest jets we see with radio telescopes are the ones that are able to kick light up to the highest energies" - Yuri Kovalev, a team member at the Max Planck Institute for Radio Astronomy in Bonn, Germany.

The brightest galaxies Fermi sees are active galaxies, which emit oppositely directed jets of particles travelling near the speed of light. Some, called blazars, are especially bright because one of the jets happens to be directed toward us. Astronomers believe that these jets somehow arise as a consequence of matter falling into a massive black hole at the galaxy's center, but the process is not well understood.

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A team of Yale University astronomers say that galaxies stop forming stars long before their central supermassive black holes reach their most powerful stage, meaning the black holes cant be responsible for shutting down star formation.  
 Astronomers believe that active galactic nuclei (AGN), the supermassive, extremely energetic black holes at the centers of many young galaxies, were responsible for shutting down star formation in their host galaxies once they grew large enough. It was thought that AGN feed on the surrounding galactic material, producing enormous amounts of energy (expelled in the form of light) and heat the surrounding material so that it can no longer cool and condense into stars.

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Astronomers have long assumed there were far more so-called "active" black holes than had been observed, but were unable to find any trace of them.
An international team of astronomers unexpectedly found hundreds of expanding "supermassive" black holes buried deep inside galaxies billions of light years from earth. The findings more than double the total number of black holes known to exist at that distance, and suggest there were hundreds of millions more growing in the early universe.
These super-massive entities are known as high-energy quasars, a form of black hole, found in a young galaxies, that is surrounded by a thick halo of gas and dust which shoot off X-rays as they are sucked into the void.
The X-rays, which can be detected as a general glow in space even when the quasars themselves cannot be seen, are what tipped off the scientists that they had stumbled across something extraordinary.
The astounding discovery is the first direct evidence that most - perhaps all - huge galaxies in the far reaches of the universe generated cavernous black holes during their youth, when about 3.5 billion years old.

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Title: Spitzer Uncovers Active Galactic Nuclei Missed by Optical Surveys in 7 Late-type Galaxies
Authors: S. Satyapal, D. Vega, R. P. Dudik, N. P. Abel, T. Heckman

We report the discovery using Spitzers high resolution spectrograph of 7 Active Galactic Nuclei (AGN) in a sample of 32 late-type galaxies that show no definitive signatures of AGN in their optical spectra. Our observations suggest that the AGN detection rate in late-type galaxies is possibly 4 times larger than what optical spectroscopic observations alone suggest. We demonstrate using photoionisation models with an input AGN and an extreme EUV-bright starburst ionising radiation field that the observed mid-infrared line ratios cannot be replicated unless an AGN contribution, in some cases as little as 10% of the total galaxy luminosity, is included. These models show that when the fraction of the total luminosity due to the AGN is low, optical diagnostics are insensitive to the presence of the AGN. In this regime of parameter space, the mid-infrared diagnostics offer a powerful tool for uncovering AGN missed by optical spectroscopy. The AGN bolometric luminosities in our sample range from ~3 X 10^41 - ~2 X 10^43 ergs s^-1, which, based on the Eddington limit, corresponds to a lower mass limit for the black hole that ranges from ~3 X 10^3Mdot to as high as ~1.5 X 10^5Mdot. These lower mass limits however do not put a strain on the well-known relationship between the black hole mass and the host galaxy's stellar velocity dispersion established in predominantly early-type galaxies. Our findings add to the growing evidence that black holes do form and grow in low-bulge environments and that they are significantly more common than optical studies indicate.

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