What's inside a black hole?

What's inside a black hole?

At the centre of the Milky Way lies a giant black hole, but can we shed light on what lurks in the darkness?



Thanks to German astronomers, we now have the most accurate measurements yet of the giant black hole that sits at the centre of our galaxy.

And what a beast it is: as wide as Earth's orbit around the sun and 4.3 million times more massive than our home star. Lucky, then, that it is 27,000 light years away.

Researchers from the Max Planck Institute for Extraterrestrial Physics used two telescopes operated by the European Southern Observatory in Chile to watch stars as they circled the centre of the Milky Way. The 16-year study, now published in the Astrophysical Journal, has proved beyond doubt that lurking at the very centre of the galaxy is a black hole.

Black holes are clearly intriguing, and not just to scientists. Earlier today, a colleague known more for his in-depth investigations into the wrongdoings of governments and multinationals than his knowledge of quantum gravity, asked what seems like a simple question: "What's inside a black hole?" Sensing my attempt at an answer wasn't good enough, I called Stefan Gillessen, one of the authors of the latest study, for an explanation.

To begin with, he pointed out that scientists should only ask questions that can be answered, and since it is impossible to get information out of a black hole (in the form of light, for example) we can never really know. But let's not give up just yet.

Black holes are created when large stars explode and collapse in on themselves. Many will have masses similar to our own sun, but others grow to much larger masses.

Theoretical physicists have thought long and hard about what goes on inside black holes and their conclusions are mind-bending to say the least. Despite the fact that they suck in material from anything and everything that strays too close, they are empty. The mass of a black hole is confined to an infinitely small point at its centre, called a singularity.

How much blackness surrounds a singularity – in effect, the size of the black hole – is defined by the strength of its gravitational pull. Far away from a black hole, light can zip around as usual, lighting up the heavens as it goes. But closer to a black hole, gravity becomes stronger and stronger until eventually, not even light can move fast enough to escape its pull. This is why a singularity is surrounded by a vast sphere of darkness. The point at which the hole's gravity becomes strong enough to prevent light escaping is known as the event horizon.

"To know what's inside a black hole, we need something to come out from behind the event horizon, and reach us via a telescope. The easiest thing for astronomers would be light, but a black hole is so massive not even light can escape so no information can get out," he said. "You could go and look, but once you're in you never come back out again."

Gillessen admits to feeling uncomfortable about the concept of singularities, but the late John Wheeler, who coined the term "black hole" in 1967, put it nicely in his 1999 autobiography, "Geons, Black Holes and Quantum Foam: A Life in Physics". He said black holes teach us that "space can be crumpled like a piece of paper into an infinitesimal dot, that time can be extinguished like a blown out flame, and that the laws of physics that we regard as sacred, as immutable, are anything but."

http://www.guardian.co.uk/science/bl...lcomments=true