You may have been one of the millions of people who tuned in to the BBC’s Stargazing Live, hosted by Professor Brian Cox and comedian Dara O’Briain from Jodrell Bank Observatory. This odd but very watchable duo have guided Britain through various astronomical principles over the past three evenings, including the moon, extra-terrestrial life, the hunt for exoplanets and – the most mysterious topic – black holes.

Dark spots in the cosmos

An artist's illustration of a supermassive black hole at the centre of a galaxy. Image: Wikimedia commons.

Black holes are notoriously misunderstood objects that both excite and baffle astronomers in equal measures. When an object – most often thought to be a dying star – gathers enough mass to reach a certain density, it collapses in on itself to a point the size of a pinprick. A theoretically infinite mass is contained in this tiny space, resulting in an incredibly strong gravitational field that warps and distorts the environment around it.

With black holes, it can never be a case of ‘seeing is believing’ – at a certain proximity to the hole itself (known as the event horizon), the gravitational pull is so strong that not even light can escape it. This results in dark spots in the inky-black cosmos that are detected usually by the strange and otherwise unexplainable behaviour of the surrounding matter – light included. Gravitational lensing is caused when light passes a black hole on its way to the observer and is bent due to the effect the black hole’s gravity has on the space around it.

It is thought that there is a supermassive black hole at the centre of most, if not all, galaxies. Our Milky Way is included in this, with a hole at its centre and around 25 smaller ones scattered throughout the galaxy.

A computer simulation of superheated plasma swirling around the black hole at the centre of our galaxy. (Image by Scott Noble/RIT).

Caught on camera?

A conference yesterday in Arizona discussed the possibility of imaging a black hole – a concept previously thought to be too difficult. Our telescopes are now sufficiently advanced to peer deep into the Milky Way and image the supermassive black hole at its centre; however, this still won’t be a direct image, but more an outline or shadow of the hole. This outline is caused by material that orbits the hole colliding, speeding up and subsequently heating up, resulting in the emission of detectable radiation.

Along with the apparently faster-than-light neutrinos, poor old Einstein has had a tough time of it recently; this imaging will be quite a thorough test of the theory of relativity, which predicts that this outline must be a perfect circle.

If this has piqued your interest for black holes, BBC Stargazing Live dedicated their 17th January episode to explaining the complicated dynamics of these “mysterious and destructive objects”.