The release of the first ever photograph of a supermassive black hole means that the theory of general relativity proposed by Albert Einstein has been put to the most exacting test. Researchers say that the test makes it harder to beat by 500 times.
We still do not fully understand gravity, but general relativity has been helping us thus far. Still, researchers know that our understanding could always be improved. When it comes to quantum mechanics, it doesn’t work, so there must be a better theory.
According to a report in the Physical Review Letters, a team compared the size of the black hole shadow imaged by the Event Horizon Telescope (EHT) to predictions calculated from general relativity. They found a huge amount of agreement there.
Lead author professor Dimitrios Psaltis of the University of Arizona said: “We expect a complete theory of gravity to be different from general relativity, but there are many ways one can modify it. We found that whatever the correct theory is, it can’t be significantly different from general relativity when it comes to black holes. We really squeezed down the space of possible modifications.”
Over the past century, general relativity has undergone many tests, and it has passed them spectacularly. In this study, researchers chose to focus on other theories that have also passed solar system tests. The latest one used the shadow of a black hole.
Co-author professor Feryal Özel, a senior member of the EHT collaboration at the University of Arizona shared: “Using the gauge we developed, we showed that the measured size of the black hole shadow in M87 tightens the wiggle room for modifications to Einstein’s theory of general relativity by almost a factor of 500, compared to previous tests in the solar system. Many ways to modify general relativity fail at this new and tighter black hole shadow test.”
However, there’s still a long way to go. Gravitational waves can be and are being used to create more similar tests. Additionally, the Event Horizon Telescope is going through upgrades that will further increase our abilities to understand gravity. Only time will tell what we will discover.