Of all the forces of objects in the universe that are invisible, including dark matter and dark energy, none has captured human imagination or frustrated our curiosity as much as black holes, those massive collapsed-on-themselves stars that shred and swallow anything in their path. Astronomers began speculating about these omnivorous dark stars in the 18th century but no one has actually seen how a black hole looks like. Until now.
It took the combined power of eight telescopes stationed around the world, collectively called the Event Horizon Telescope (EHT) to capture the first ever image of a black hole that sits in a galaxy termed M87. The image was released to the public just two days ago. It is a seminal moment for science.
The ghostly image shows a circular dark center surrounded by a bright halo. The dark center is a “sink”, a region where the fabric of space and time has collapsed in on itself, forming a single point or singularity of infinite density. That point has such strong gravity that no object falling into it can escape – not even light. The light we do see in this image are the accretion of gas and other particles swirling around the black hole at close to the speed of light before vanishing down the sink. The intense radiation emitted by these particles, heated to billions of degrees within the disc, is what the EHT picks up (watch video below).
The EHT image is pretty much what artists and Hollywood film-makers have always imagined a black hole to be. More importantly, it agrees with the scientific expectations of what a black hole should look like based on Einstein’s general theory of relativity, which predicts how space-time is warped by the extreme mass of a black hole.
The black hole captured by the EHT is gargantuan. Situated 500 million trillion km away, it measures 40 billion km across or three times the size of the Earth and has a mass of 6.5 times that of the Sun. Professor Heino Falcke, of Radboud University in the Netherlands, who proposed the experiment, describes it as “an absolute monster, the heavyweight champion of black holes in the Universe.”
Prof Falcke had the idea for the project when he was a PhD student in 1993 but at the time, no-one thought it was possible. But he was the first to argue that a certain type of radio emission would be generated close to and all around the black hole, which would be powerful enough to be detected by telescopes on Earth. He also remember reading a scientific paper suggesting that due to their enormous gravity, black holes appear 2.5 times larger than they actually are. These two factors suddenly made the seemingly impossible, possible. After arguing his case for 20 years, the EHT project came to fruition, bankrolled by the European Research Council, the US National Science Foundation and various research bodies in East Asia. It is an investment that has been vindicated. “It has been a long journey, but this is what I wanted to see with my own eyes”, says Falcke [1].
Meet the Woman behind the Black Hole Image
Katie Bouman a 29-year old PhD student at MIT also played a crucial role in photo imaging the black hole identified by the EHT. As the information gathered by the EHT was too big to be sent across the internet, the data was stored on hundreds of hard drives and flown to central processing centers in the US and Germany where they were pieced together. Bouman developed the critical algorithm that helped to piecing together the data to produce the image. Her work has been hailed as “an extraordinary scientific feat” by Professor Sheperd Doeleman of the Harvard-Smithsonian Centre for Astrophysics.