We have had a “Eureka ” moment of this decade on April 10, 2019, when a team of 200 astronomers succeeded in capturing the image of a black hole. If you happen to be a person who happens to be interested in astronomy or have any social media account, you must’ve been aware of the recent brilliant achievement of the astronomers by capturing an image of the black hole in Messier 87 galaxy. The astronomers achieved a Herculean task by opening up intergalactic research and study of black holes in rendered images.
A black hole, in general, is a region in space-time with incredibly high gravitational effects that no particle can escape from it. Even light which has a speed of 3 * 108 m/s gets trapped by black holes massive gravitational effect. Black holes are formed when supermassive stars die at the end of their life cycle. Stars like our sun don’t have the mass to become a black hole. By the theory, a star that is of 20 times the mass of our sun has the probability to become a black hole.
On April 10th 2019 astronomers claimed that they captured the image of a black hole. Shep Doeleman, an astronomer Harvard-Smithsonian Center for Astrophysics said that “We have seen what we thought was unseeable”. They captured an image which is of a black hole that lies about 55 million light-years away from Earth in the giant galaxy known as Messier 87 (M87) in the Virgo constellation. The image looks like a lopsided ring of light surrounding a dark circle deep in the heart of the galaxy M87. This image was captured by focusing on the intergalactic space into the M87 galaxy in the Virgo constellation, where a black hole having several billion times more mass than our Sun unleashed a violent jet of energy some 5000 light years into space. The image also served as a proof for Einstein’s theory as the shadow of the image captured shows that it’s a circular shape. Astrophysicist Priyamvada Natarajan from Yale said that Albert Einstein must be extremely delighted. His theory has just been put through stress-test under conditions of extreme gravity, and it proved to have held up.”
The image emerged from 2 years of computer analysis of observations from a network array of radio antennas called the Event Horizon Telescope. In its entirety, eight radio observatories on six mountains and four continents observed the galaxy in Virgo on and off for 10 days in April 2017. The telescope array also monitored a dim source of radio noise called Sagittarius A* (pronounced Sagittarius A-star), at the heart of our Milky Way galaxy. There, 26,000 light-years from Earth, and cloaked in interstellar dust and gas, lurks another black hole, which has a mass of 4.1 million suns. The network is named after the edge of a black hole, the point of no return; beyond the event horizon, not even light can escape the black hole’s gravitational pull.
Any residual doubts about the reality and existence of black holes were wiped out 3 years ago when the Laser Interferometer Gravitational-Wave Observatory (LIGO), detected a pair of distant black holes colliding with each other, which resulted in sending a shiver through the fabric of space-time. Now the reality has a face. Peter Galison, a physicist, filmmaker and historian at Harvard, and a member of the Event Horizon team, noted that there is it is a wonderful open-ended sense to see something instead of just relying on statistical data. To prove that the monsters in Virgo and in the Milky Way’s centre were really black holes, it requires measuring the sizes of their shadows. That was no easy job. Both look extremely small from this distance, and resolving their tiny details would be a herculean task even the biggest individual telescope. Moreover, their view will be blurred by the presence of charged particles such as electrons and protons that fill the infinite interstellar space. Dr Doeleman the director of the Event Horizon Telescope (EHT) said that it is like looking through frosted glass. To peer into the shadows, the astronomers were in need of being able to tune their radio telescope to shorter wavelengths. And they needed a bigger telescope. There comes in the Event Horizon Telescope, the dream child of Dr Doeleman. By culminating the information from the different radio telescopes that lie as far apart as the South Pole, Hawaii, Chile and France, using a technique that is called as VLBI (very long baseline interferometry), Dr. Doeleman along with his team created a telescope that is just as big as the Earth itself, with an amazing power to resolve details as minute as an orange on the lunar surface. In April 2017, the network of eight telescopes, including the South Pole Telescope, synchronized by atomic clocks, stared at the two targets on and off for 10 days. For two years, the Event Horizon team reduced, analyzed and collated the results. The data were way too voluminous to transmit over the internet, so they were transferred to multiple hard disks and flown back to M.I.T.’s Haystack Observatory, in Westford, Massachusetts, and the MaxPlanck Institute of Radio Astronomy in Bonn, Germany.
The data from the South Pole could not be procured before December of 2017, Dr Doeleman said in an interview that it was because of the harsh Antarctic winter. In the last year, the team had divided into four different groups to assemble images procured from the data dump. To stay on objective and guard the results against bias, the teams were separated and had no contact with each other of the team. They readied themselves for an inconclusive or ambiguous result — a blur, perhaps. But the scientists were surprised at how clear the image actually was.
Dr Doeleman’s optimism increase last year at a dinner that was attended by some of his team’s younger members, who showed him the first data for M87. He said that there were clear signatures of ring-shaped structures. After dinner, he moved to his office to go through the data and made some crude calculations. He said that it was one of those great moments. “It was astonishment as to how clear the image was.” As matter spirals into a black hole, it accretes into a disk just outside the abyss’s edge. The ring of light that is present in the latest image is congruous with the innermost photon orbit, which are the quantum particles that makeup light. By laying a ruler across that ring, astronomers could measure the size of the black hole and see that it met Einstein’s prescription.
The measurement also gave a firm estimate of the mass of the Virgo black hole: 6.5 billion solar masses. The result shows that it is heavier than most of the previous determinations and calculations, and it also suggests that other big black holes masses may need to be revised upward. The observations also revealed that the accretion disk is on its side with regard to Earth, the hole facing us and spinning clockwise. The image is more luminescent where gas flows around the hole, which is toward us. Dr.Doeleman expressed his views on the black hole that lies in the centre of the Milky Way as “a captivating, beguiling object.” But it is much smaller than the Virgo constellation’s black hole, so its portrait is quite harder to capture.
The telescope network continues to grow. In April 2018, the collaboration was expanded when a new telescope from Greenland was added to it. Another set of observation run was made on the Milky Way and M87 and retrieved twice the amount of data when compared to the data of 2017. That information was not released along with the results today, but they will be used to aid and confirm the hypothesis and observations and further monitor the behaviour of the black holes. There are 2 more antennas on hold to join the EHT. Dr.Doleman said that “The strategy is to perform the experimental calculations and observe the difference in the observed and calculated results”, commenting on his new career as the tamer of beasts of the universe lies within and beyond our galactic borders. “It is astonishing to think that we, humans can turn the Earth into an effective telescope and focus it to see a black hole,” and he also appreciated his team saying that “They were undeniably the best.”
Well to this day, black holes were thought of as invisible huge stellar masses that devour anything their path. And with the recent advent in the field of astronomy and astrophysics, we have the ability to render images of these stellar bodies and calculate their masses and distance and also study their behaviour. We can also hope to study about supermassive black holes and the origins of the universe in the future by further advances in the field of astronomy.
- Vaishnavi Raghavan
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