In an article recently published in popular journal ‘Nature,’ a team of scientists outlined their observations on a black hole named ‘I Zwicky1,’ elaborating on how their observations portrayed an extreme case of gravitational lensing, built upon a prediction made by Einstein’s theory of general relativity, which they did by observing light from behind the black hole.
Einstein’s theory of general relativity describes gravity through its interaction with space and time. It iterates that an object’s gravity bends the spacetime around it, similar to the effect that a tennis ball would have on a bedsheet that you’ve pulled tight. The gravitational field of an object alters the manner in which objects around it behave, resulting in them bending or curving based on the magnitude of the object’s gravity.
Using the same example of a tightly-pulled bedsheet, if you roll a marble on top of it, in the absence of the ball, the marble travels straight, but when the ball is present, the marble’s trajectory curves. Furthermore, if you replace the tennis ball with a bowling ball, the bed sheet would (other than getting harder to hold) show more of a depression and the same marble would now bend a lot further in its path and could potentially even fall into the depression the bowling ball causes.
Now, replace the marble with a wave of light and the bowling ball with an object as massive as the black hole. The deflection of the light’s path, caused by a massive object’s gravity, is defined as gravitational lensing (much like how a glass lens bends rays of light), confirming Einstein’s prediction in his theory of general relativity.
When ‘I Zwicky 1’ was observed, scientists focused on its corona, the part of a black hole that produces maximum X-rays. While the scientists were observing Zwicky, an X-ray flare occurred. An X-ray flare occurs when multiple bright X-rays are observed for short periods of time (10,000 seconds, in this case). These flares also cause X-rays to echo off of the spinning disc of matter around the black hole. However, the scientists found some echoes that they didn’t expect. When they investigated and analysed the different frequencies of these X-Rays, they occurred from the side of the black hole that was actually obscured from view.
This means that I Zwicky 1’s mass and gravitational force “bent” the light around the black hole, showing the scientists what lies directly behind it. This is one of the most extreme cases of general relativity ever observed, or simply, it’s general relativity after a heavy dose of steroids.
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