Newest LIGO signal raises a huge question: do merging black holes emit light?
Gravitational waves and electromagnetic ones don’t need to go together. But physics says it’s possible; what do the observations say?
“The black holes collide in complete darkness. None of the energy exploding from the collision comes out as light. No telescope will ever see the event.”
-Janna Levin
Billions of years ago, two black holes much more massive than the Sun — 31 and 19 solar masses each — merged together in a distant galaxy far across the Universe. On January 4th of this year, those gravitational waves, traveling through the Universe at the speed of light, finally reached Earth, where they compressed and stretched our planet by the width of no more than a few atoms. Yet that was enough for the twin LIGO detectors in Washington and Louisiana to pick up the signal and reconstruct exactly what happened. For the third time ever, we had directly detected gravitational waves. Meanwhile, telescopes and observatories all over the world, including in orbit around Earth, were looking for an entirely different signal: for some type of light, or electromagnetic radiation, that these merging black holes might have produced.
