In mid-April, a team of international astronomers released the first image of a black hole. Svetlana Jorstad, a senior research associate with the Laboratory of Observational Astrophysics at St Petersburg University, participated in the project. She was directly involved in the imaging, and told us about how the scientists were able to obtain these results.
The Event Horizon Telescope (or the EHT) project is the result of international collaboration involving some 200 astronomers from 20 countries. To directly image a black hole, the scientists employed a special technique known as Very Long Baseline Interferometry, or VLBI. In essence, VLBI ties an array of eight telescopes placed in six different locations across the globe to observe the same astronomical object at the same time and at the same frequency.
Messier 87 is an active galaxy with one of the largest known supermassive black holes which contains 6.5 billion solar masses.
To capture an image of the black hole at the heart of the galaxy Messier 87 (М 87), the observations were made at a wavelength of 1.3 millimetres. This enabled the EHT to achieve a resolution of 20 micro-arcseconds. According to Svetlana Jorstad, this resolution is enough to be able to see an orange on the surface of the moon, for instance.
‘Several research teams involved in the EHT Collaboration worked concurrently to obtain images of the black hole using different observation methods. We were advised that we should not consult each other to ensure the purity of the experiment,’ Svetlana Jorstad revealed.
Once the research teams had completed the task, the project participants gathered for the EHT Working Group at the end of July last year. They met at the Black Hole Initiative (BHI) at Harvard University, Cambridge, USA. It was then that the astronomers first found out that, regardless of the method used, they all had captured the same images, closely matching theoretical predictions about black holes. By definition, nothing can escape a black hole; however, light bends in the intense gravity around it, creating a circular shadow. Thus, a black hole image must show a bright ring with a dark circle in the centre. It is precisely this type of images that were obtained within the four days of the EHT observations in April 2017.
This experiment confirmed that it is a black hole at the centre of galaxy M 87, and not some other massive object. Secondly, the preliminary calculations based on Einstein’s theory of general relativity proved to be accurate, which means that the laws of relativity continue to hold true.
Svetlana Jorstad, Senior Research Associate with the Laboratory of Observational Astrophysics at St Petersburg University
The scientific results of the Event Horizon Telescope project were announced in a series of six papers published in a special issue of The Astrophysical Journal Letters.
St Petersburg astronomers led by Valery Larionov, the Head of the Laboratory of Observational Astrophysics at St Petersburg University, also contributed to the EHT project. They participated in the research study ‘Structure and Evolution of Active Galactic Nuclei’ supported by a grant from the Russian Science Foundation (No17-12-01029). The research team performed optical observations of calibration sources. This additional data resulted in a more complete picture of active galactic nuclei being obtained, and the relationship between black holes and plasma jets being studied. These are the jets of a black hole that emanate from active galactic nuclei.
The researcher told us about some other international projects in which Russian astronomers participate. They include RadioAstron, which is initiated by the Astro Space Centre of P. N. Lebedev Physical Institute at the Russian Academy of Sciences in Moscow. This project started in 2011 and came very close to achieving the resolution of the Event Horizon Telescope. Apart from that, Russia is planning to launch another space observatory project: Millimetron. It will enable far superior resolution to that of the EHT.