* Astronomy

Backwards Black Holes Might Make Bigger Jets

Black holes are immense distortions of space and time with gravity that is so great, even light itself cannot escape. Astronomers have known for more than a decade that all galaxies, including our own Milky Way, are anchored by tremendous, so-called supermassive black holes, containing billions of suns' worth of mass. The black holes are surrounded and nourished by disks of gas and dust, called accretion disks. Powerful jets stream out from below and above the disks like lasers, and fierce winds blow off from the disks themselves.
The black holes can spin either in the same direction as the disks, called prograde black holes, or against the flow -- the retrograde black holes. For decades, astronomers thought that the faster the spin of the black hole, the more powerful the jet. But there were problems with this "spin paradigm" model. For example, some prograde black holes had been found with no jets.
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Black holes and galaxy death

Black holes are thought to reside at the centre of almost every galaxy, with some growing to more than a billion times the mass of the Sun. Now a team of UK astronomers believe that these supermassive black holes are commonplace, release more than enough energy to strip their host galaxies apart and in the process shut down these galaxies' star formation for good. On Friday 16th April, team member Asa Bluck of the University of Nottingham, who led this research, will explain the dramatic impact of these monster black holes in his talk at the RAS National Astronomy Meeting (NAM 2010) in Glasgow.
For many years black holes have fascinated scientists and the public alike, with their peculiar ability to warp space and time and their almost sinister tendency to devour everything they encounter. Before it falls in, as matter swirls around the black hole it forms an "accretion disk", where it heats up and radiates energy. The supermassive black holes have such a strong gravitational field that the infalling matter releases a vast amount of energy, making each accretion disk far brighter than the combined output of the hundreds of billions of stars in the galaxy around it.

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Retrograde spin of supermassive black holes may create jets that control galaxy evolution

Scattered throughout every galaxy are black holes, regions that gobble up matter and energy. Although we can't see black holes, scientists can infer their size, location and other properties by using sensitive telescopes to detect the heat they generate. This heat, which we see as X-rays, is produced as material spirals around a black hole faster and faster until it reaches a point of no return - the "event horizon" - from which nothing, not even light, can escape.
In addition to a galaxy's collection of black holes, which includes black holes up to 10 times the sun's mass, there is a supermassive black hole embedded in the heart of each galaxy that is roughly one million to one billion times the mass of the sun. About 10 percent of these giant black holes feature jets of plasma, or highly ionised gas, that extend perpendicularly from each side of the event horizon. By spewing huge amounts of mostly kinetic energy, or energy created by motion, from the black holes into the universe, the jets affect how stars and other bodies form, and play a crucial role in the evolution of clusters of galaxies, the largest structures in the universe.
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A team of astronomers recently discovered 33 sets of double black holes in distant galaxies. Though these black hole pairs had been predicted theoretically, only a handful had been observed so far.

"[The findings] show that dual supermassive black hole systems are much more common than previously known from observations" - researcher Julia Comerford, an astrophysicist at the University of California, Berkeley.

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