A sleeping black hole has awoken: never before has a black hole been observed going from sleeping to active
A faint dot in the sky (as the galaxy SDSS1335+0728 appears) is growing brighter and brighter. The black hole that was sleeping inside it has been awakened and is very hungry.
Black holes are among the most interesting, fascinating but also little-known objects in the Universe. It seems that by all the most frequently asked question to astronomers is precisely related to the nature of black holes: what are black holes?
The black holes
We know that these are very massive stars that have ended their evolutionary cycle with a violent supernova explosion. This has left as a residue an ultra-compact object, whose force of gravity is such that it also retains light.
There are two types of black hole: active black holes and dormant black holes.
The active black holes are extremely bright but, not because the light can escape. They are bright as they have in their vicinity other objects that attracted by their immense force of gravity are coming from these swallowed. In their spiraling path that will end inside the black hole, the matter in strong acceleration emits an intense electromagnetic radiation that makes the black holes extremely bright.
In the case of quiescent black holes, no matter is falling into you so they remain invisible. Rather, if these are gravitationally related to other massive objects, such as a star, then the star will show an elliptical movement around the common center of mass. It will be precisely this movement of the companion that will reveal the existence of the black hole.
The awakening: from quiescent to active
The SDSS1335+0728 Galaxy recently had the honors of the news as it seems to be the first galaxy in which the awakening of a quiescent black hole has been observed.
Let's say that this galaxy, being extremely distant, about 300 million light years from Earth in the direction of the constellation of Virgo, even with the most powerful telescopes in this research (such as ESO's VLT telescope used in this research) appears as a dot.
In 2019 the brightness of this little dot (the galaxy) began to increase.
There are so many phenomena in the cosmos that can lead to a temporary increase in the brightness of a galaxy. The most common phenomenon is the supernova explosion. However, the duration of this increase in brightness in this case is short, no more than a few hundred days. For this reason, these phenomena are called 'transients'.
In the case of the galaxy SDSS1335+0728 the brightness started to increase but never stopped. It's now been more than 4 years and the brightness continues to increase.
Except that this increase is not due to a still unknown phenomenon, the most accredited hypothesis is that it is a galaxy in the center of which there is a black hole. This black hole, as a sleeper (therefore invisible) woke up and became active.
So, as mentioned before, it means that something approached it at such a distance that it was captured gravitationally and now, precipitating into it, it has begun to emit more and more light, from infrared to ultraviolet.
X-ray emission also began in 2014.
The distance of the galaxy does not allow to solve its components spatially and therefore to explore in detail where this emission originates from.
Certainly this is a unique event never before observed that has attracted the interest of the astronomical community. This is being activated to continue the observations with other telescopes and instruments as well.
Study references:
“SDSS1335+0728: The awakening of a ∼ 106M⊙ black hole” published in Astronomy & Astrophysics (https://aanda.org/10.1051/0004-6361/202347957).