Darkness Brought to Light

Who would have thought a dark, blurry image could hold so much signifcance? Rarely does a picture give rise to as much excitement as the one of a glowing orange ring surrounding a dark centre released early last year. The centre of the ring of light contains an object nobody had ever laid eyes on before: a black hole.

Black holes are massive, dense regions of space that form when a star more than thirty times the mass of the sun collapses. When these stars collapse, they have such high gravity that their cores are compressed into a single point called a singularity. The gravity of singularities is so strong that black holes pull all light and matter towards them, enshrouding themselves in clouds of dust and gas and making them so far invisible. Many astronomers believed imaging black holes to be impossible, relying on the gravitational waves emitted by two black holes colliding to reveal them instead.

Last year, however, work from the past 12 years fnally bore fruit when scientists from around the world announced they had produced the frst-ever image of a black hole, called M87*. M87* is located in the Messier 87 galaxy, which (despite being over 50 million light years away) is considered relatively close to Earth. More importantly, it is around 6.5 billion times larger than the Sun, making it what is known as a supermassive black hole. When early attempts to image a nearby black hole stumbled upon M87*, its size made it an attractive candidate for imaging, and the Event Horizon Telescope (EHT) consortium was born. The consortium consists of around 200 scientists around the world who used eight telescopes located from Arizona to the Antarctic to collect data.

Technological developments of the last decades were key to the imaging of M87*. A technique called verylong-baseline interferometry (VLBI) allowed data from widely spaced telescopes to be combined to simulate one single large telescope. This enables faraway objects to be imaged in much fner detail. Additionally, developments in antennas and other telescope components allowed scientists to capture the radiation released by the swirling clouds of gas surrounding the black hole. In April 2017, the eight observatories involved collected readings over the course of a week, with exceptionally good weather contributing to the quality of the data. The EHT scientists then spent the next two years evaluating and analysing, with four teams working independently of each other and with separate methods to avoid infuencing each other’s results. When the teams came together to compare, they had generated four similar images, which were then collated into one. At this point, technological advances failed them—the data, which was stored on almost half a ton of hard disks, was too much for any web information system to handle. It had to be physically fown to a lab at Harvard for the fnal evaluation to take place.

The image revealed may look unspectacular to some. For astrophysicists, however, it represents not only visual evidence for the black hole at the centre of the Messier 87 galaxy, but also an afrmation of Einstein’s general theory of relativity. According to general relativity, the shadow of a black hole should be perfectly round. The image of M87* hits relatively close to the mark, being just 10% of a perfectly round shadow. The EHT consortium plans to reduce that margin by sharpening the images collected in their next round of observations, set to begin in 2020. Ultimately, they dream of collecting data from space which would bring more black holes into range and enable them to generate moving images of black holes sucking in the matter around them. Rather than being the culmination of the project, this is just the beginning of a quest to bring more of our Universe’s darkness into the light. Nicole Hasler is a Medicine undergraduate at Lincoln College.

“Many astronomers believed imaging black holes to be impossible”

Above Dominika Syska