12.04.2019 change 12.04.2019

Astronomers reveal the first ever photo of a black hole

Source: Event Horizon Telescope Collaboration Source: Event Horizon Telescope Collaboration

Astronomers from the Event Horizon Telescope Collaboration released the first ever photo of a black hole this week. It was taken by eight telescopes that formed a "virtual telescope" the size of Earth, team member Dr. Monika Mościbrodzka told PAP.

The image was presented during six press conferences, which took place simultaneously in Brussels, Santiago, Shanghai, Tokyo, Taipei and Washington. It shows the black hole with a mass of 6.5 billion solar masses in the centre of the Messier 87 galaxy, 55 million light years from Earth.

Black holes are predicted in Albert Einstein`s general relativity theory, although the possibility of the existence of these objects was considered earlier. A black hole is an object with a huge mass and small dimensions, which has such strong gravity that even light can not escape it. The research project took its name from the black hole boundary called event horizon.

The image was taken with an astronomical telescope called Event Horizon Telescope, co-funded by the European Research Council. It is a virtual telescope, which means that it consists of many telescopes that are scattered around the globe. In 2017, when observations were made, it had eight components located in Europe, South America, Central America, North America, Hawaii and the South Pole.

"The observation technique we have used is that all these telescopes are pointed at a specific object at the same time and collect data" - says Monika Mościbrodzka from Radboud University in Nijmegen (the Netherlands), member of the Event Horizon Telescope team. Together, these telescopes form a virtual telescope the size of Earth. "This allows to achieve unprecedented resolution. The Event Horizon Telescope event has the observational power that a person in Paris could use to read a newspaper in New York" - she adds.

Observations of two black holes were conducted as part of the Event Horizon Telescope project. The first of them is in the very centre of our galaxy - the Milky Way; the second in the centre of the Messier 87 galaxy 53 million light years away from us. Both were chosen for a simple reason: they were already quite well known. "As a result, we are certain that the resolution of our telescope is sufficient to capture their image" - says Dr. Mościbrodzka.

She explains that the black hole in the centre of the Milky Way has been an object of observation since the 1970s. Thanks to this, astronomers know quite a lot about it - for example, they know its mass and exact distance from Earth.

The situation is similar in the case of the black hole from the Messier 87 galaxy. Although this particular object is much further from the Earth, it is very interesting for researchers as it is a thousand times more massive than the black hole in the centre of the Milky Way.

"Supermassive black holes are scattered all over the Universe" - says Dr. Mościbrodzka. "At the moment, we have a lot of evidence that they are at the centre of every galaxy. The problem is that they are often too far away to be captured with our telescope. Meanwhile, the black holes we have selected are fairly bright, they are relatively near and have sufficient dimensions" - she adds.

The initiative to photograph a black hole is not a completely new idea. The first such experiments were carried out in the previous decade. However, the technology was not well developed at that time and the network of telescopes was too small. Now technological progress has been made that allows to capture an image of an object such as a black hole.

Dr. Mościbrodzka explains that astronomical observations are carried out at different lengths of electromagnetic waves. This means that astronomical telescopes can record not only the image visible to the human eye (visible light), but also radio, infrared or X-ray waves. "The Event Horizon Telescope observes on millimetre waves (waves with lengths between radio and infrared), which is innovative" - she says.

Researchers hope that the possibility of acquiring images of black holes and their immediate surroundings will provide new information on gravity - the least understood of the four fundamental forces in the Universe. "Black holes are objects that have the strongest possible gravitational fields. Each new method of observing them gives us a unique opportunity to study the nature of gravity" - explains Dr. Mościbrodzka.

She participated in the research as a member of the BlackHoleCam project, which launched in 2014, and in which the European Research Council (ERC) allocated EUR 14 million for image acquisition, measuring and testing the properties of black holes. The Event Horizon Telescope has also received support from the ERC as part of the RadioNet project seeking to integrate research infrastructure in the field of radio astronomy (the EU has invested 30.3 million euros in this project over the past 15 years).

In addition to Dr. Mościbrodzka, another Polish researcher was involved in the project: Dr. Maciek Wielgus from the Black Hole Initiative at Harvard University in the USA.

Dr. Wielgus explains that scientists have strong arguments that that they have observed the shadow of a black hole and not another effect or object.

"The image size is consistent with the predictions of general relativity for a black hole with a mass of 6.5 billion solar masses, suggested by independent results based on the analysis of star dynamics in the M87 galaxy" - explains the scientist.

"We have achieved something presumed to be impossible just a generation ago. Breakthroughs in technology, connections between the world`s best radio observatories, and innovative algorithms all came together to open an entirely new window on black holes" - said Sheperd S. Doeleman. from the Center for Astrophysics (Harvard & Smithsonian) and the EHT project leader.

The results of the observations were described in six scientific articles which appeared in this week`s special issue of The Astrophysical Journal Letters.

PAP - Science in Poland, Katarzyna Florencka

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