While NASA considered building a large space telescope to image black holes for a year, a
coordinated effort of the eight radio telescopes from across the globe has helped achieve the milestonedecades ahead of time…
Introduction
In April 2019, the entire world was awestruck looking at the stunning images of a supermassive black
hole at the center of Messier 87 (M87) – an elliptical galaxy some 53 million light-years from Earth. A
team of international astronomers had achieved the impossible by imaging a black hole 6.5 billion timesthe mass of the Sun; considering the fact that scientists were expecting completely black images asthey believed no light ever escapes it. The greatest challenge of the project was to capture hot glowinggas falling into the black hole from thousand or even millions of light-years away. Working for well overa decade, the scientists of EHT – an international network of radio telescopes called the ‘Event HorizonTelescope’ finally achieved this historic feat.
The Challenge: Building an Earth-sized telescope
We are all familiar with the fact that distant space objects are seen using a telescope. The ability of thetelescope to see further into the space is determined by its diameter or aperture. The greater its
diameter, more light it will gather and higher will be the resolution of its images.Now, in order to see the black hole situated approximately 53 million light-years from Earth, thescientists were faced with a unique challenge of gathering as much light coming from it onto Earth, invery high resolution. It had to create a telescope on land with a very large aperture, preferably with adiameter as big as the planet Earth.
Achievement
The scientists decided to resort to a popular technique called Very Long Baseline Interferometry (VLBI),which had been often used for imaging of far-away objects. The crux of this technique was setting upan array of smaller telescopes across locations that are synchronised to focus on the same object atthe same time, acting as one giant virtual telescope.The aperture of a large telescope is as large as the distance between the two farthest-apart telescopestations. In this case with stations at the South Pole and in Spain, the scientist had achieved to createan aperture of the size of Earth. So in a coordinated effort, the EHT operated from across its eight radiotelescopes using different wavelengths of light in such a manner that the images it managed to captureseem to look as though taken from one huge telescope of the size of planet earth.
Where to look for?
‘Sagittarius A’, a supermassive black hole was the closest to the Earth at the centre of our Milky Way
galaxy at a distance of 26,000 light-years. Definitely, it was not the only black hole in our galaxy, but
being closest it would appear largest of all. Being the closest to Earth and in the same Milky Way,
Sagittarius A may seem a natural choice, but it had several technical challenges.
Located in the same galaxy meant that while imaging the black hole, one had to be conscious of
‘pollution’ caused by stars and space dust, meaning that scientists would have more data and that theywould have to filter it while processing it.
Why Messier 87 (M87)?
Located at the center of the gigantic elliptical galaxy Messier 87 or M87, is one of the largest known
supermassive black hole, 53 million light-years away. It is more massive that ‘Sagittarius A’ containing6.5 billion solar masses (i.e. one solar mass is equivalent to mass of our Sun). Importantly, it was anactive black hole with matter falling into it and spewing out in the form of jets of particles. While itsdistance made its imaging a challenge as compared to ‘Sagittarius A’, processing the data of the imagewas comparatively easier.
Mission Accomplished
Thirteen partner institutions worked together to achieve this exceptional breakthrough, which a
generation ago was presumed to be ‘impossible’, undoubtedly a rare example of ‘global teamwork’.
Once again, in a joint pursuit to ‘know more about the unknown’, scientists from across the globe havemanaged to harness their unique technological expertise to write this innovative algorithm of ‘mankind’striumph over matter’.
–Manoj Mahanta
Team, ScienceNow Digital
