Astronomers: Black holes help form galaxies

2011-06-20 14:05

Cape Town - Black hole study is important because they help form galaxies, astronomers theorise.

"Black holes are important because we think they actually help form galaxies. We think that nearly every galaxy has a black hole in the middle," Southern African Large Telescope astronomer Dr Nicola Loaring told News24.

Astronomers think that the growth of a black hole is linked to the growth of galaxies, including our Milky Way galaxy.

The idea that there might be stars from which light cannot escape was first suggested by a British geologist and clergyman John Michell in 1783. The first good black hole candidate that was discovered is Cygnus X-1.

Theoretical physicists, such as Michio Kaku, author of Physics of the Impossible, suggested the possibility that black holes may be the entrance to wormholes which may take a traveller anywhere in spacetime.

Practical application

Loaring said that wormholes have little practical application because they are unpredictable and it is virtually impossible to send objects through them.

"There are these theoretical ideas about these links to another part within the universe, but one of the problems is that these things are predicted to just last for fractions of a second and spontaneously collapse so you never know where they're going to be and for how long they will last," she said.

"You can't actually pass matter through the tunnels. If you passed matter or energy through the tunnels, they'll collapse."

She said that to keep a wormhole that would link to parts of spacetime open, you would need an exotic material that would prevent the tunnel's collapse, but there is no such material known to science at present.

"They [wormholes] haven't been observed, they're predicted to exist; they don't have any practical purpose for us."

While it is generally believed that supermassive black holes form at the centre of galaxies, stellar mass black holes form from the collapse of massive stars. There's even an idea that some primordial black holes may have formed at the dawn of the universe.


"Primordial black holes are just black holes on their own that are thought to have been formed at the beginning of the universe and they are predicted to just be out in space on their own, but no primordial black holes have been observed yet," Loaring said.

She said that all matter falling into a black hole gets compressed into an accretion disc due to the angular momentum of the material. As the material is accreted it is heated to millions of degrees.

Despite the black having such a massive gravity that not even light can escape, objects need to get close to a black hole to be absorbed. The event horizon for black holes is relatively small compared to the size of the body.

"The fact that there's a black hole somewhere is the universe doesn't necessarily affect us, for example if the sun were replaced by a black hole of the same mass, the event horizon would be about 3km," said Loaring.

"The bigger the mass, the bigger the event horizon."

- Loaring will be giving a presentation titled Black holes and where we find them at the South African Astronomical Observatory on June 25.

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