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A Bonsai Black Hole in Our Own Backyard

Radio image of Fornax A

Radio image of Fornax A, an iconic radio galaxy with extended lobes (orange). The grey region between the lobes is stellar light from the much smaller host galaxy. Fomalont et al. 1989, Astrophysical Journal Letters, 346, 17.

By Robert Soria

The discovery of powerful jets from a nearby black hole reveals new clues about the behaviour of massive quasars in the early universe.

Roberto Soria is a research fellow at University College London’s Mullard Space Science Laboratory, and will join the Curtin Institute of Radio Astronomy in Perth this year.

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Black holes are popularly portrayed as a place of darkness and gloom, but to astronomers they are the cleanest and most efficient source of energy in the universe. The recent discovery of a very large glowing bubble of ionised gas inflated and heated by a black hole in the nearby galaxy NGC 7793 helps us to understand their role as cosmic powerhouses.

While stars use nuclear fusion to extract energy from their gas, black holes extract gravitational energy from the infalling matter before it disappears into the hole – a process known as accretion. Indeed hydrogen bombs and hydro power plants are based on the same physical principles as stars and black holes, respectively.

Hydro power may seem less efficient than nuclear fusion. While it takes a lot of falling water to produce the same energy as we would get from nuclear fusion, this is only because the gravitational field of the Earth is so weak. But gravity near a black hole is much stronger, and accretion power can be up to 50 times more efficient than nuclear fusion.

This is why black holes – or, more exactly, the gas in the region immediately outside the black hole horizon – can be the most luminous and powerful objects in the universe when enough matter is falling towards them. The end result is that black holes get bigger over time as long as there is matter to fuel them.

The general...

The full text of this article can be purchased from Informit.