With the help of a future generation of telescopes in space, faint rings of light surrounding enormous black holes could be spotted.
The doughnut-shaped glow spotted in the first image of a black hole, released in April 2019 by the Event Horizon Telescope (EHT) collaboration is more complex than the worldwide network of radio telescopes could discern.
The black hole’s gravity is so intense that some particles of light, called photons, can circle the black hole partway or once, twice or multiple times before escaping to be picked up by telescopes.
Those orbiting photons produce a “photon ring,” made up of a series of subrings circles of light that appear successively thinner and harder for telescopes to pick out.
The Event Horizon Telescope, or EHT, combines the powers of telescopes across the world, via a technique called very long baseline interferometry, so that they operate like one, larger telescope. But to tease out more details, such as black hole subrings, researchers would need to add telescopes separated by even larger distances.
Scientists previously have proposed such telescopes, but the plans haven’t yet gotten off the ground. Johnson says that the new study provides new motivation for adding a space-based telescope to the EHT’s network.
Although the EHT wouldn’t directly photograph the subrings, it could detect their existence. That detection would reaffirm Einstein’s theory of gravity, the general theory of relativity, which predicts the rings’ existence.
It also could allow for better measurements of the black hole’s mass and how fast it is spinning.
