The allure of black holes

Black holes are one of the greatest inventions astronomy enthusiasts have ever known. Hypothesized in 1783, not confirmed until 1990, they relentlessly teased astronomers for many decades. The idea of a region with gravity so strong that nothing, not even light, can escape, seems straightforward enough. But finding black holes is hard — really hard. They are, after all, black. And so is space.

There should be many millions in our Milky Way Galaxy alone; we know of only about two dozen. Practically every large galaxy more massive than dwarfs has one in its center. Yet we didn’t detect any of those until the repaired Hubble Space Telescope got going in the early 1990s. For all intents and purposes, it seems that black holes have made more appearances in movies (most of them frightfully bad) than in reality. But we know they are out there.

This month, astronomer Yvette Cendes of the University of Oregon describes the ongoing search for the nearest black holes using the Gaia satellite. This European Space Agency orbiting observatory is designed for astrometry — precise positional measurements of astronomical bodies. The ongoing mission is assembling the most voluminous three-dimensional catalog of astronomical objects ever made, totaling some 1 billion targets. That is quite a dataset.

Gaia’s enormous dataset has allowed enterprising astronomers to search for anomalies in the positions of stars, recorded over spans of time. Stars that show a wobble over time but have no visible companion are promising candidates for hosting a black hole. Astronomers can even calculate the mass of the unseen companions, courtesy of our old friend Johannes Kepler. The result is an emerging list of probable black holes in our galaxy that resulted from the deaths of massive stars of about 18 times or more mass than our Sun.

The revolutionary approach demonstrates a clever technique astronomers are using to unveil new discoveries about the cosmos that surrounds us. For astronomy enthusiasts, it’s a good time to be alive.

EHT COLLABORATION This image, produced by the Event Horizon Telescope, shows the shadow of the supermassive black hole in the giant elliptical galaxy M87 in Virgo. It has the mass of a staggering 6.5 billion Suns.