For the First Time in History, Astronomers Are Seeing a Black Hole Waking Up in Real-Time

The monster is awake, and it’s hungry. In December 2019, a quiet and uninteresting galaxy 300 million light-years from Earth began to glow brightly. Astronomers now believe they’re witnessing the awakening of a supermassive black hole.

The dramatic transformation of SDSS1335+0728. For years, a bland galaxy in the Virgo constellation had been known by this “handy” name. Although it had always been calm and dull, it turned into a glowing beast at the end of 2019.

Phenomena like a supernova or a tidal disruption event—where a star is spaghettified by the gravity of a black hole—can cause a one-off increase in a galaxy’s brightness. But these events last for days, not years. And SDSS1335+0728 is still shining brighter and brighter four years after its first flare.

The best-fitting explanation. In the search for alternative explanations, astronomers at the European Southern Observatory (ESO) combined archival data with new observations and found that the galaxy now emits much more light in the ultraviolet, visible, and infrared wavelengths, and also began emitting X-rays in February 2024.

The researchers say the most likely explanation for this behavior is that, for the first time, we’re observing the live activation of a supermassive black hole at the center of a galaxy.

The awakening of a black hole. According to this hypothesis, the supermassive black hole at the center of SDSS1335+0728 has begun to feed on the surrounding gas, becoming extremely bright.

Supermassive black holes have masses that are 100,000 times that of the Sun. They’re usually dormant, preventing direct observation, although they reside at the center of most galaxies, including the Milky Way. In the case of the Milky Way, our black hole is called Sagittarius A* and has also shown recent signs of activity.

Image | ESO

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