A team of European astrophysicists has been given almost €14m to map the black hole at the centre of our galaxy, the Milky Way.
The project will combine observations from several telescopes around the world with advanced computer simulations of the way light and matter behave around black holes.
A key part of the study will involve measuring the “shadow” cast by the black hole’s event horizon: the boundary beyond which nothing caught by the grip of unimaginable gravitational force can escape, not even light.
Black holes are places where matter is compressed by gravity to a point where the normal laws of physics break down, bending and distorting space and time.
By definition, they cannot be seen in the conventional sense, making them hard to study. Their presence is inferred from radiation emitted as gas and debris swirl around them.
“While most astrophysicists believe black holes exists, nobody has actually ever seen one,” said Professor Heino Falcke, one of the scientists from Radboud University in Nijmegen, the Netherlands.
“The technology is now advanced enough that we can actually image black holes and check if they truly exist as predicted. If there is no event horizon, there are no black holes.”
At the centre of the Milky Way is a mysterious radio source called Sagittarius A which is believed to mark the position of a black hole four million times more massive than the Sun.
Gas drawn towards the black hole’s event horizon generates a strong radio signal before disappearing. In theory, the event horizon should cast a dark shadow on this bright emission that can be detected.
Given the huge distance to the centre of the Milky Way, around 27,000 light years, the shadow would be equivalent in size to an apple on the Moon as seen from Earth.
The scientists hope to spot the shadow by combining the power of high-frequency radio telescopes around the world, using a technique called very long baseline interferometry, or VLBI.
In addition, the group plans to use the same radio telescopes to find and measure pulsars around the black hole. Pulsars are rapidly spinning neutron stars, tiny but incredibly dense stars, which emit signals at regular intervals, much like a lighthouse. They act as highly accurate natural clocks in space.
“A pulsar around a black hole would be extremely valuable,” said Dr Michael Kramer, managing director of the Max Planck Institute for Radio Astronomy in Bonn, Germany.
“They allow us to determine the deformation of space and time caused by black holes and measure their properties with unprecedented precision.”
Professor Luciano Rezzolla, another member of the team from Goethe University in Frankfurt, said: “We have made enormous progress in computational astrophysics in recent years.
“We can now calculate very precisely how space and time are warped by the immense gravitational fields of a black hole, and determine how light and matter propagate around black holes.
“Einstein’s general theory of relativity is the best theory of gravity we know, but it is not the only one. We will use these observations to find out if black holes – one of the most cherished astrophysical objects – exist or not.
“Finally, we have the opportunity to test gravity in a regime that, until recently, belonged to the realm of science fiction. It will be a turning point in modern science.”
The €14m funding is in the form of a synergy grant, the largest type of award made by the European Research Council.