Skylights Bite Size 13 - Black Holes: Gravity Gone Mad

By ANDY FLEMING

Gravitational distortions caused by a black hole in front of the Large Magellanic cloud.

Once people realise that you are an amateur astronomer they normally have two questions: have you ever seen a UFO and what are black holes.

Black holes usually result from the collapse of giant stars thousands of times the mass of our Sun and that end their relatively brief lives as supernovae.  Scientists are now certain that they exist, and were predicted by Albert Einstein in his Theory of General Relativity published in 1915.

This fascinating podcast takes a look at these bizarre objects and ponders the fact that most scientists believe there is a supermassive black hole in the centre of our own Milky Way, and indeed every large galaxy in the universe.

MP3 DOWNLOAD FOR YOUR FAVOURITE MEDIA PLAYER

Skylights Bite Size 13 - Black Holes: Gravity Gone Mad
Download this episode (right click and save)

Podcast also available on

Skylights is featured on Solid Gold Sunday each Sunday afternoon at 1425h UTC on 102.4FM in Hartlepool/East Durham, UK and live around the world online at www.radiohartlepool.co.uk
________________________________________________________________
Show Notes and Transcript

Once people realise that you are an amateur astronomer they normally have two questions: have you ever seen a UFO and what are black holes.

Black holes usually result from the collapse of giant stars thousands of times the mass of our Sun and that end their relatively brief lives as supernovae.  Scientists are now certain that they exist, and were predicted by Albert Einstein in his Theory of General Relativity published in 1915.

When a gargantuan star ends its life, the nuclear fusion reactions in its core end, and the star detonates, the resulting explosion seeding the nearby universe with heavy elements that make rocks, planets and people.  The matter that’s left is no longer held up by radiation pressure and collapses to a point of infinite density and gravity: what astro-physicists call ‘a singularlity’.  These are stellar mass black holes.

They are so dense and their gravity so strong that nothing can escape from them, not even light itself.  Hence the object appears mainly black and why it’s called a black hole!  Perversely they’re not completely black however as they do emit Hawking Radiation and energy from matter spinning and accreting around them at gargantuan velocities.  The Event Horizon is simply the point at which an object’s escape velocity from a black hole exceeds the speed of light.  In other words, it’s effectively lost to our visible universe.

In 1974 radio astronomers detected a massive object in the centre of our Milky Way galaxy in the direction of the constellation of Sagittarius.  By 1998 astronomers working at the 10 metre Keck Telescope on Mauna Kea, Hawaii confirmed it as a supermassive black hole four million times the mass of our Sun, inferred by the enormous velocities of its orbiting stars.  Further observations led to the profound discovery that all large galaxies including our next door neighbour the Andromeda Galaxy have supermassive black holes at their centres.  How they formed in the early universe is still a complete mystery.

There’s no need to worry about ours though! The monster of the Milky Way, otherwise known as Sagittarius A* is a massive 26,000 light years away from the Earth, and it’s not feeding on nearby stars (at the moment)!