Black holes are extremely difficult to find simply because they are massive gravity wells; from which nothing -- not even light, can escape. Using the strictest definition, we have only positively identified about 20 of these objects. Even Sagittarius A*, the impressive object at the center of our galaxy, is an unconfirmed supermassive black hole. Scientists are experimenting with a new method, science magic, if you will, that could make these invisible objects visible.
For those of you familiar with Submarines, you’ll know there are certain classes of subs which are so quiet, the only way to find them is to look for a silent spot in the ocean where the sub is covering up the natural background noise. Scientists hope to use a similar idea to find black holes – look for a shadow darker than the space around it. ESO officials, when describing this process, said, "The shadow — a dark region seen against a brighter background — is caused by the bending of light by the black hole, and would be the first direct observational evidence for the existence of a black hole’s event horizon, the boundary from within which not even light can escape."
How are scientists able to achieve this? Through a process called Very Long Baseline Interferometry (VLBI). I’m sure you’ve all heard the phrase ‘the bigger, the better’, in astronomy, the same also applies to telescopes. The larger the telescope, the more detail you can capture. Using VLBI, scientists are able to link multiple telescopes together, these telescopes then act as a single telescope as large as the distance between them.
As an example, using this method, scientists were recently able to take the sharpest image ever captured of the quasar 3C 279 located in a galaxy 5-billion light-years from Earth. They used the SMA Hawaii, SMT Arizona, and APEX Chile radio telescopes to image a resolution of about 8 billionths of a degree (the full moon, for reference, covers about a half of a degree of night sky – in other words, the full moon appears 63 million times larger than 3C 279).
This is the precursor to a new telescope called the Event Horizon Telescope. This would link about 50 radio telescopes together, spread across the surface of the Earth, to form one large telescope the size of our planet. If this project is successful, scientists will be able to directly image black holes for the first time.