How does a black hole warp space around it? Why do we see gas flowing away from their poles in strong jets, while everything else around them churns and disappears into the hole for eternity? With what technology can we unravel the physics behind black holes?
A black hole is literally a hole in spacetime. With its enormous mass density, it warps the space around it into a hole into which everything from its surroundings disappears for eternity. That same mass also makes time seem to stand still to a distant observer. Clocks start ticking at different speeds in different places around the hole. A black hole is also truly pitch-black because it warps space around it so much that not even light can escape from it.
Astronomers investigate many of these issues with X-ray telescopes, because the matter around a black hole gets so hot that it mainly emits X-rays. How do we give these telescopes the resolution and sensitivity needed to investigate black holes?
Getting a picture of motion
To investigate dynamics such as rotations and velocities close to a black hole, astronomers look at elements common to it, such as iron. Iron reveals itself with a recognisable sharp peak in the X-ray spectrum. If the peak is distorted and appears at a different spot in the spectrum, it betrays the speed and direction of the iron within the gas disk around the black hole. How do we measure these iron peaks at high resolution so that astronomers can see how the black hole curves the space around it?
SRON is collaborating on a space mission with sensors that will determine the energy of each individual X-ray particle down to 1.6 electronVolts. That’s like seeing a rainbow in over two thousand colours. That provides enough spectral resolution to measure a spectrum with sharp lines in it, which together give the barcodes of the substances around a black hole.
Getting more pixels in the picture
Apart from more X-ray colours, how can researchers get more pixels in their observations of black holes? For that, X-ray interferometry must be ‘invented’. Combining telescope dishes that act as one giant dish already works with radio telescopes. Since X-rays do not pass through the Earth’s atmosphere, for X-rays you would have to do that trick in space. SRON is working on a test rig as a demonstration that the theory can be put into practice..
