Black holes are the most mysterious objects in the entire universe. Their gravitational influence has the power to wrench apart stars, send ripples through space-time, and act as an inescapable trap for anything that dares come too close. And until very recently, we had never seen one before.
Imaging the Black Hole
Of course, this changed with the work performed by the Event Horizon Telescope. It’s important to note that the EHT is not one single instrument – it is a series of 8 separate radio telescopes, spread around the world. They worked in unison to capture an image of the black hole at the heart of M87, a huge galaxy, unimaginably far from our own. By using multiple stations spread across Earth’s surface, a virtual telescope the size of Earth itself was formed, allowing the now world famous image to be captured, and released to the public on April 10th, 2019. The black hole itself is huge.
At thirty eight billion kilometres across, its scale is effectively inconceivable – it’s larger than our entire solar system. But it is this insane size that made the imaging of the object possible, despite its immense distance from Earth – it’s positioned fifty three million light years from Earth.
Katie Bouman has been credited with making the image possible. The computer scientist developed the algorithm which made generating the image possible. It was produced with the different sets of data from the eight EHT telescopes, terabytes of data which had to be filtered through and combined. But, Dr Bouman has been quick to make sure she doesn’t get all the credit, saying “No one of us could’ve done it alone. It came together because of lots of different people from many different backgrounds.”
The image itself shows a blurry ‘blob’ – at the centre is a dark circle, the place where the black hole itself has absorbed all light. Around it is an orange ‘glow’ – this is light, curved around the black hole’s singularity, light which likely comes from what’s known as an accretion disk. An accretion disk is a red-hot disk of matter, orbiting the black hole at unimaginable speeds, heated up to glowing temperatures by gravity and friction. This is what we can see in the image.
Looking into the future
The M87 has been observed before, but not so closely. NASA’s hubble telescope has observed a luminous jet of gas, projected by the black hole’s magnetic field. But the EHT image is the first time a black hole has ever had a genuine visual put to it. The teams who run the EHT plan to continue making observations. With the addition of four more telescope sites in the coming years, and the advantage of experience, higher resolution pictures are expected over time. As well as further observations of the M87 black hole, there’s been talk of imaging the Milky Way’s own central supermassive black hole, Sagittarius A*. This image is just the first step in a new era of black hole research.