When a black hole and a companion star orbit one another, the star’s motion will change over time owing to the gravitational influence of the black hole, while matter from the star can accrete onto the black hole, resulting in X-ray and radio emissions. Recently, a 70 solar mass black hole was found fitting this scenario, the highest stellar mass black hole ever discovered like this. But this was a relief for astronomers, not a surprise! (JINGCHUAN YU/BEIJING PLANETARIUM/2019)

Sorry Science Fans, Discovering A 70-Solar-Mass Black Hole Is Routine, Not Impossible

If this discovery came in a pre-LIGO era, maybe it would have been a surprise. But in 2019, there’s no mystery at all.

Did you hear that astronomers had recently discovered a stellar mass black hole that was so heavy, it shouldn’t exist? At 70 solar masses and closer to the galactic center than we are, it’s certainly an interesting system to discover, entirely worthy of its publication in Nature last week. (Full, free preprint available here.) It ranks, at the moment, as the heaviest stellar mass (as opposed to supermassive) black hole ever discovered through optical techniques.

But on the theory side, claiming that this object shouldn’t exist is not only foolish, it requires that you ignore a number of basic facts about astronomy and the Universe. We’ve already discovered a handful of comparably massed black holes through gravitational waves, and have a very good idea of how they form and why. Here’s the science of these heavy black holes that goes beyond the superficial.

While numerous black holes and even black hole pairs have been detected, we’d have to wait millions of years for any of the ones we’ve identified so far to actually merge. (NASA/GODDARD SPACE FLIGHT CENTER/S. IMMLER AND H. KRIMM)

When it comes to detecting black holes in general, there are three ways to do it.