Flashes in the Night

Celestial transients shine furiously and briefly. Astronomers are just beginning to understand them

- ANN FINKBEINER

Ann Finkbeiner is a science writer based in Baltimore. She specializes in writing about astronomy and cosmology, grief, women in science, and the intersection of science and national security. She is co-proprietor of the science blog The Last Word on Nothing.

LONG, LONG AGO A CLOUD OF STARS CIRCLED A GALAXY-SIZE BLACK HOLE, safely at a distance. Then about 200 million years ago one member of the cloud bumped another, a sun-size star, and sent it toward the black hole. The black hole was a million times more massive than the sun-size star, and its gravitational pull proportionately stronger, so the star was drawn closer and closer—until it got too close. Some of the star's gas was pulled into an orbiting stream around the black hole that widened into a flat pancake called an accretion disk. The rest of the star came apart in a sudden and great flash of light.

On September 19, 2019, just before noon, the flash reached the 1.2-meter mirror of the Zwicky Transient Facility in southern California. Astronomers named the flash AT2019qiz and noted that they hadn't seen it three days before. On September 25, 2019, the 10-meter Keck I telescope in Hawaii identified AT2019qiz as a so-called tidal disruption event—a flareup that occurs when a black hole's gravitational tides rip a small object apart. The star the size of the sun exploded with 10 billion times the sun's luminosity.