For the first time, scientists reveal black hole's 'photon ring'
In 2019, when we saw an image of a black hole for the first time courtesy of the Event Horizon Telescope (EHT), scientists believed that there is more to the image than we saw. Now, in another historical first, astrophysicists have remastered that image to reveal the photon ring of a black hole. The bright, glowing circle is a creation of intense gravity.
Why does this story matter?
The Event Horizon Telescope has taught more about black holes than we ever knew. The discovery of the 'photon ring' is another golden feather in its hat. Earlier this year, it showed an image of our very own Sgr A* black hole for the first time. EHT's discoveries become more significant because it shows how cutting-edge algorithms can be the difference makers.
Image captured by EHT only showed black hole's outer surface
The image of the supermassive black hole located at the heart of the Messier 87 (M87) galaxy captured by the EHT was not very detailed. It showed the light-trapping outer edge of the black hole called the Event Horizon. Scientists were, however, more interested in finding an artifact of the black hole's gravitational influence. The new discovery is a result of that search.
What is a 'photon ring'?
A 'photon ring' of a black hole is caused due to its gravitational pull. Black holes can deflect any light that passes close to them, causing the light to change direction. The closer the light is to the black hole, the more significant the deflection. We see a photon ring when the deflected light loops around the black hole and heads our way.
Space-time warping can trap nearby light in a black hole
A black hole's gravity is so intense that it can lead to space-time warping. There is light passing in different directions near the black hole. We, however, only see the one that's focused toward us. The warping of space-time causes some photon particles to be trapped in an infinite loop around the black hole. This is how we see the thin circle of light.
Why did we never see photon rings before?
We learned that we only see the light from a black hole that is heading toward us. However, the space between a black hole and us is not empty. On their way, some of the light gets scattered, making the image blurrier than we'd like. This is where the study comes in. The team used new imaging algorithms to reveal the photon ring.
Elements of the image were stripped to see 'photon ring'
The team of astrophysicists led by Avery Broderick stripped away various elements of the image using an imaging algorithm THEMIS built into the EHT to isolate and extract the golden ring. They also spotted the distinct 'footprint' of an astrophysical jet being blasted outward by the black hole. "We turned off the searchlight to see the fireflies," said Broderick about the discovery.
Scientists followed a new approach to find the 'photon ring'
The discovery of the 'photon ring' is an example of how theoretical understanding can be leveraged to manipulate the available data. Scientists used the EHT data to deconstruct the initial image into two - one of the photon ring itself and the other of the outer region. It is this individualized study that led them to find the hidden 'photon ring.'
