In late 2019, the galaxy SDSS1335+0728 suddenly began to shine brighter than ever before. After studying it, astronomers concluded that they were watching the sudden awakening of the massive black hole at its core live.
“Imagine you’ve been observing a distant galaxy for years and it has always seemed quiet and inactive. Suddenly, its core starts to show dramatic changes in brightness, unlike any typical event we have seen in the past,” describes 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.
The astronomers used data from several space- and ground-based telescopes to track changes in the brightness of the galaxy, which is 300 million light-years away in the constellation Virgo.
As noted, some events, such as supernova explosions, can cause galaxies to suddenly brighten, but these changes in brightness usually last only 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. It is also worth noting that the changes detected in this galaxy are unlike any other changes observed in the past.
By comparing data taken before and after December 2019, the researchers found that this galaxy is now emitting much more light in ultraviolet and infrared wavelengths, and in February 2024 it started to emit X-rays as well.
Black holes, “these giant monsters are usually dormant and not directly visible. In the case of SDSS1335+0728, we saw the giant black hole wake up. It suddenly started to feed on the gas available in its environment, and as a result it became very bright,” explains Claudio Ricci of the University of Diego Portales, 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 that the process itself, the awakening of the black hole, has been observed in real time.
However, they point out that further observations are needed to rule out alternative explanations. Another possibility is that we are seeing a tidal disruption event, where a star passes so close to a black hole that it is pulled away by the tidal force of the black hole.
They also don’t rule out the possibility of a new phenomenon.
