First ever Image of a Black Hole captured by Astronomers: Finally Karl Schwarzschild's super idea has a visible form.

   

First Image of a Black Hole captured by Event Horizon Telescope

A dark core surrounded by a flame-orange halo of hot gas and plasma: thats what the first ever image of a black hole (BH) looked like when it was captured by the astronomers for the first time today on 10th April, 2019.  There was a great build up to the event during the last few days when a lot of speculations were floating in the air. Different types of opinions were given on this by different people. Some believed, some did not. It was finally announced during a simultaneous press conference in Brussels, Shanghai, Tokyo, Washington, Santiago and Taipei. The image is of a super-massive BH 50 million lightyears away in a galaxy named M87.

Black holes are star devouring monsters scattered throughout the universe. It is a highly compact object having immense gravitational pull such that even light cannot escape its gravity. According to American physicist John Archibald Wheeler "A black hole is a point in space where matter is so compressed so as to create a gravity field from where even light (with so much energy) cannot escape". These are formed as a final state of gravitational collapse of massive stars. This is the reason why it is very difficult to capture the image of a BH.

In fact the image that was recorded actually captured the surrounding mass (white hot gas and plasma) that it collected in an accretion procedure forming a luminous disc called the accretion disc. It did not record the interior of the black hole. In that sense it could only record the black hole shadow and not the black hole itself.

The image was recorded by the Event Horizon telescope installed specifically for this purpose.  Now it is the turn of Sagittarius A*, the black hole at the centre of our own galaxy, Milky way. Compared to M87, Sagittarius A* is just 26000 lightyears from Earth and is the next target of the Event Horizon telescope. Given its relatively shorter distance from Earth it is assumed that we will receive images of greater precision and clarity. In fact according to the reports the images already received from Sagittarius A* were blurred and lacked clarity due to its high activity. 

During the last two weeks eight telescopes positioned at Hawaii, Arizona, Spain, Mexico, Chile and the south pole zeroed in on M87 and Sagittarius A*. It was like a system of telescopes knit together to form a giant virtual observatory around 12000 kilometers across the globe. This image has been analyzed in six different studies by around 200 experts from 60 different institutions all over the world and was published in Astrophysical Journal Letters on 10th April, 2019.

There are obviously various technical procedures that had to be undertaken in this project. Actually what the telescopes recorded were astrophysical data which were simulated into the image of the black hole. In fact four different groups independently undertook this work of getting the image from the data and all the four finally produced the same image. The event marked the dream come true for many famous astrophysicists who never thought that they will be able to see the image of a black hole in their lifetime. 

Finally its another test passed by Einstein's General Relativity. This along with the discovery of Gravitational waves are the major advances in astronomy that we have made in the present decade and more importantly both upholds the flag of General Relativity.
Today is a time for celebration for astrophysicists and black hole lovers all over the world. Finally Karl Schwarzschild's super idea has a visible form.


Image Courtesy:  NASA

By Prabir Rudra