Hubble Space Telescope discovers an invisible black hole: What does this mean? 

The first ever direct image of a black hole was captured in 2019. This was an achievement which took quite a long time to reach, and the hole was only made perceivable to the lens due to the material that was glowing in its presence. Detecting black holes in space is a notoriously challenging task. However, NASA’s famous Hubble Space Telescope recently managed to capture the unprecedented- a black hole which is completely invisible! Read on to find how this was possible and what this means. 

What exactly are black holes? 
A black hole is essentially a region in space with an incredibly strong presence of gravity. The gravitational intensity is so high that absolutely nothing, not even the tiniest particles or even electromagnetic radiation including light, has the ability to escape from it. These holes are formed after massive stars die and their cores collapse. Astronomers are particularly interesting in studying them as they reveal the truth of what exactly went down while the stars were dying and how exactly their cores collapsed. 

Why are black holes so tricky to detect? 
It is a common assumption that black holes are inherently invisible, owing to their unique ability to trap light. However, although tricky, it is not impossible to detect them. Up until now, astronomers have successfully detected hundreds of small black holes. This is because their interactions with other space objects are noticeable due to their intense gravity. However, it is also presumed that there are a large number of black holes floating in space which have not yet been detected, as they have not interacted with any other space object yet. 

How did NASA’s Hubble Space Telescope manage to detect this black hole? 
NASA’s Hubble Telescope recently managed to detect a black hole, and what makes it unique is that it is an invisible one for the first time in history! It was a free-floating black hole, close to 5,000 light years from our planet, which actually is relatively close. It was no easy task, discovering this one as scientists had to combine primarily two different types of observations spanning over several years. They spotted sudden magnification in light from a distant star, however, they did not find any foreground object which was causing this change in the star. This was their first hint of the black hole. But, there also stood the possibility that it was merely a faint star. After 6 long years of capturing its images through the Hubble telescope, they finally had enough data to measure how far the star appeared to be displaced while its light was getting deflected. After calculating its mass and distance from the data available, they were stunned to find that it was 7x more than the mass of the sun! This led them to conclude that it was an isolated black hole, as a star of that magnitude should ideally be visible to us.