First it was a spark in the ultraviolet, then the X-rays arrived: this is how a supermassive black hole wakes up

A team of scientists led by Riccardo Middei, from the INAF Astronomical Observatory in Rome, has monitored the step by step of a black hole “resurrecting” after “taking a break.” After monitoring the galaxy that houses it for six years, they have been able to see how, after a clear decrease in its brightness, its activity increased significantly. This has allowed them to confirm that some physics standards were very well calculated. However, it has also been detected that some may not have been entirely correct.

In reality it is more than six years. All part of the observations of the Seyfert galaxy ESO 511-G030 that were carried out in 2007 and 2019 during the XMM Newton mission. It was found that the brightness of the center of the galaxy was 10 times weaker in 2019, whether measured in ultraviolet or when X-rays were detected. A previous detection indicated an increase in 2012, but since there were no measurements between 2012 and 2019, it was not possible to know exactly what happened in that period.

The authors of the study that has just been published wanted to have continuous monitoring, so they took regular data with the Neil Gehrels Swift Observatory from 2019 to 2025. Thus, they saw that, indeed, in 2019 the black hole at the center of the galaxy had practically fallen asleep. However, in 2021 a recovery began to be detected, first in the brightness measured in ultraviolet and then in X-rays. The black hole was waking up.

An active galactic nucleus. The Seyfert galaxy is a galactically active nucleus. That is, it emits a brightness higher than that which would correspond to the sum of all its stars. This is because at its center there is an active supermassive black hole. This attracts all matter that gets too close to it. In fact, from a boundary known as the event horizon, not even light can escape. Throughout this process of falling into the black hole, a lot of radiation is emitted.

Knowing this, we can see two parts to the black hole. On the one hand, the accretion disk, a rotating ring of hot gas and matter falling into the black hole. During its rotation, it emits optical light and ultraviolet radiation. On the other hand, on this disk is the corona, composed of hot plasma, whose emissions are mainly X-rays. This is the reason why, to measure the activity of a black hole, data are taken in both ultraviolet and

Step by step. The reactivation of the black hole occurred in two parts. First of all, the brightness in the ultraviolet clearly increased, between 2021 and 2023. Then, between 2022 and 2023 it was the turn of the X-rays. Therefore, it can be said that first the activity increased in the accretion disk and then in the corona of the black hole.

Size doesn't matter. By eliminating the contribution corresponding to the stars of the galaxy, the brightness corresponding to the black hole increased by 20 to 30 times. It was a radical increase in activity, which came at just the right time. And scientists calculate that the transition occurred at just under 1% of its Eddington rate. This is a theoretical figure that describes the universal threshold at which a black hole can accrete or attract matter before radiation pressure expels the incoming gas.

For it to truly be a universal figure, as predicted, it should be equivalent for both very large black holes and stellar ones. In the stars it has already been measured. Now, in this one, which has a mass equal to 17 million times that of the Sun, the figure is practically the same, so it can be considered universal.

What doesn't add up. The limit from which the black hole “falls asleep and wakes up” seems to coincide with the theory, but there is something that does not fit so much: the speed at which it does so. Both the fade and the recovery occurred too quickly than estimated in the standard models. Therefore, it is clear that the models still have a lot to perfect.

To be able to do this, it will be necessary to study more galaxies like this one. The Vera Rubin Observatory comes into play, in which so many astronomers are placing their hopes. Thus, based on observations, the missing piece may be found.

Image | NASA

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