Context
∙ The Event Horizon Telescope (EHT) Collaboration has released new images of M87*, the supermassive black hole at the center of the galaxy Messier 87.
What is a Black Hole?
∙ A black hole is an extremely dense object whose gravity is so strong that nothing, not even light, can escape it.
∙ A black hole does not have a surface, like a planet or star. Instead, it is a region of space where matter has collapsed in on itself.
∙ This catastrophic collapse results in a huge amount of mass being concentrated in an incredibly small area.
∙ Formation: A black hole is formed when a really massive star runs out of fuel to fuse, blows up, leaving its core to implode under its weight to form a black hole.
∙ The center of a black hole is a gravitational singularity, a point where the general theory of relativity breaks down, i.e. where its predictions don’t apply.
∙ A black hole’s great gravitational pull emerges as if from the singularity.
Event Horizon Telescope (EHT)
∙ The EHT is not a single telescope but a worldwide network of radio telescopes that work together to study a common object in space.
∙ Very-long baseline interferometry: It is the technique, where the data each telescope collects about the object is correlated with data from the others using extremely precise clocks.
∙ In this setup, the maximum distance between the telescopes defines the network’s resolution.
∙ The Greenland Telescope has been commissioned to the array, which has improved the resolution of the EHT in the north-south direction.
Gravitational lensing
∙ The diameter of the asymmetric ring had not changed much between observations in 2017 and 2018 – meaning the black hole’s gravity bent light consistently over time to form the observed ring.
∙ This is in line with a prediction from the General theory of relativity, that light around a black hole is strongly lensed.
∙ Objects with a lot of mass bend spacetime more around them. When light travels in this region, its path is bent in the same way a magnifying glass does. Images carried by the light thus appear to be larger than they really are, and this phenomenon is called lensing.∙ The black hole is rotating, dragging the spacetime around it along the direction of its rotation and rendering more light in some areas. Hence the ring’s southwest corner appears brighter than other parts.
