Astronomers have long been fascinated by the concept of black holes having no distinct features beyond their mass and spin. However, recent data from colliding black holes may have shed new light on this phenomenon.
According to Einstein’s general theory of relativity, the behavior of a black hole depends solely on its mass and spin. But when it comes to detecting subtle deviations from this prediction, things get complicated. Researchers have detected hundreds of signals from colliding black holes over the past decade, sending ripples called gravitational waves cascading outward through space-time.
The question remains: can we spot any “hair” – a hint of a deviation from Einstein’s theory? A team of scientists led by Vitor Cardoso has analyzed data from multiple black hole collisions and found that any deviations must occur closer than 40 kilometers to the event horizon. This means that if there is indeed a new effect, it would be extremely challenging to spot with current detectors.
To address this challenge, researchers are exploring alternative theories, such as quantum hair or firewalls, which propose new effects outside the event horizon. However, these ideas have yet to be directly tested by observational data.
The next generation of gravitational wave detectors will play a crucial role in resolving this mystery. The planned Einstein Telescope and Cosmic Explorer will enable precise measurements of black hole properties, potentially revealing subtle deviations from Einstein’s theory.
While it is uncertain what future observations will reveal, the ongoing efforts of researchers like Vitor Cardoso and Gregorio Carullo demonstrate the commitment to unraveling the enigma of black holes. As astrophysicist Simon Maenaut noted, “It’s possible that we will confirm Einstein’s theory to five decimal places… but it’s also possible that we come across something that we didn’t expect.”
Source: https://www.quantamagazine.org/astrophysicists-find-no-hair-on-black-holes-20250827