In late 2019 the galaxy SDSS1335+0728 suddenly began to shine brighter than ever. After a study, astronomers conclude that they watched live the sudden awakening of the huge black hole at its core.

“Imagine you’ve been observing a distant galaxy for years and it always seems calm and inactive. “Suddenly its core begins to show dramatic changes in brightness unlike any typical events we’ve seen before,” explains Paula Sanchez Saez, an astronomer at the European Southern Observatory (ESO) in Germany and lead author of the study, published in the journal “Astronomy & Astrophysics”.

Astronomers used data from various space and ground-based telescopes to track how the brightness of the galaxy, located 300 million light-years away in the constellation Virgo, changed. As noted, some phenomena, such as supernova explosions, can cause galaxies to brighten suddenly, but these brightness changes usually last for a few (tens or hundreds) of days. This particular galaxy is still getting brighter today, more than four years after this brightness was first observed. In addition, it is pointed out that the changes detected in the galaxy are unlike any other changes that have been observed in the past.

By comparing data taken before and after December 2019, the researchers found that this particular galaxy now emits much more light in the ultraviolet and infrared wavelengths, while in February 2024 it also began to emit X-rays.

Black holes, “these giant monsters are usually dormant and not directly visible. In the case of SDSS1335+0728 we managed to observe the wake of the massive black hole. “It suddenly started feeding on the gas that was available in its environment, making it very bright,” explains Claudio Ricci from Diego Portales University, one of the authors of the study.

Previous studies have reported that inactive galaxies become active after several years, but the scientists point out that this is the first time the process itself, the black hole’s wake, has been observed in real time.

However, they specify that follow-up observations are needed to rule out alternative explanations. Another possibility is that we are seeing a tidal disruption event, in which a star passes so close to a black hole that it is pulled away by the black hole’s tidal force. Also, they do not rule out that a new phenomenon could be happening.