What happens when the black hole at the centre of our galaxy acts up. – By Jeff Wise

Nothing is as tranquil as the expanse of the Milky Way floating in the summer night sky – or so you’d think. In reality, the centre of our galaxy is a chaos of fast-whirling stars, super-novae debris and intensely magnetic neutron stars, all orbiting around a monster black hole 4 million times the mass of the Sun.

And things are going to get even more violent. Astronomers have detected a blob of gas, called G2, that’s being ripped apart as it plunges towards the black hole. Later this year the hole will start to consume that cloud of gas. As the gas accelerates to terrific speeds, it collides with other incoming matter, heats up, and radiates energy at a ferocious rate. A similar flare-up 100 years ago created a burst of light as bright as a million Suns; we know because the light echoes are still bouncing around the centre of the galaxy. According to radio astronomer Shep Doeleman, the upcoming annihilation event could last for a year or more and rank as “a once-in-a-lifetime event”.

Watch a 3D simulation showing the evolution of G2 from 2010 to 2010…

(Video credit and source: Dr P Chris Fragile et al)

How to see the centre of the galaxy
Huge as it is, the central black hole is still a thousand times too small to be seen with the Hubble Space Telescope. Plus, it’s obscured by interstellar dust that blocks all visible light. But radio waves of about 1 millimetre wavelength can get through. Doeleman is organising the Event Horizon Telescope, a project to create an international network of radio dishes that together will constitute a system with an effective diameter as large as Earth’s.

1 The radio dishes work like TV receivers: they gather the incoming microwave radiation, which is exactly like light but at a longer wavelength. It’s a one-way process: that is, the dishes passively receive the radio signals that are emitted by sources in the centre of the galaxy.

2 There’s no physical connection among the dishes: data are recorded simultaneously by dishes around the world.

3 A supercomputer at MIT aggregates the data, storing them on huge hard drives and processing them to create, eventually – Doeleman says by 2015 – an image of the shadow of the black hole itself.