And there was light

Scientists have for some time now theorised scenarios in which black hole mergers are accompanied by light. We now have evidence, maybe

- ADITYA MISRA

WHEN THE darkest objects in the universe interact, you do not expect to see fireworks. Except that in this instance we have, believes a group of scientists. In a galaxy billions of light years from Earth, two black holes, each with a mass dozens of times of our Sun, collided and merged, giving off a bright flare. Until now, black hole collisions were registered from the gravitational waves—jiggling of space and time—that the event generated. An accompanying flash means that not only can the collision of these unimaginably dense bodies be heard but also seen, which gives researchers a new tool to study them and the galaxies they are in.

Researchers have for long theorised that black hole mergers can be accompanied by light. They might have some evidence now, but they still do not rule out that other factors could have caused the flare.

It began on May 21, 2019, when two observatories on either side of the Atlantic ocean—the Laser Interferometer Gravitational-wave Observatory (LIGO) operated by the California Institute of Technology (Caltech) and the Massachusetts Institute of Technology, US; and the Virgo detector at the European Gravitational Observatory in Italy—announced a “candidate” gravitational wave event, which they named S190521g. “If confirmed #S190521g is most likely about 2 billion light years distant,” said a tweet by LIGO on May 21, 2019. “Preliminary analysis indicates that, if confirmed, #S190521g is most likely a pair of merging #BlackHoles,” said another tweet the same day. LIGO is yet to confirm the event.