Webb Telescope’s image of galaxy system ZS7 reveals the farthest black hole collision ever seen, just 780 million years after the Big Bang.
In astronomy, when you look deep into the cosmos, you’re looking back in time, because objects in space are so far away it takes their light millions of years to reach us.
The James Webb Space Telescope has detected evidence of a merger of two galaxies and their central supermassive black holes, so far away we’re seeing it unfold shortly after the Big Bang.
The collision is occurring at a time when the Universe was just 740 million years old, which, given the current age of the Universe is estimated to be 13.8 billion years old, makes this quite a feat.
The system is known as ZS7, and one of the two black holes is of a mass 50 million times the mass of the Sun.
The importance of observing black hole collisions
Most galaxies have supermassive black holes at their centres, and these can reach masses of millions to even billions times that of our own Sun.
There’s even one at the centre of our own galaxy, the Milky Way.
These central supermassive black holes pull in cosmic material, which heats up as it falls inward and generates dazzling energy that can be seen as a bright core at the centre of galaxies.
Even though they have a reputation for being dark, black holes can be some of the brightest objects in the Universe.
And these supermassive black holes are part of a key cosmological quandary: do galaxies form and evolve around black holes, or do black holes form at the centre of existing galaxies?
And how do they grow to be so massive?
This discovery of huge black holes already existing in the first billion years after the Big Bang shows supermassive black hole must have grown very quickly, and very early on.
Making the observations
Black holes that are accreting matter have distinctive spectrographic features that astronomers can use to identify them.
“We found evidence for very dense gas with fast motions in the vicinity of the black hole, as well as hot and highly ionised gas illuminated by the energetic radiation typically produced by black holes in their accretion episodes,” says study lead author Hannah Übler of the University of Cambridge in the United Kingdom.
“Thanks to the unprecedented sharpness of its imaging capabilities, Webb also allowed our team to spatially separate the two black holes.”
“The mass of the other black hole is likely similar, although it is much harder to measure because this second black hole is buried in dense gas,” says team member Roberto Maiolino of the University of Cambridge and University College London in the United Kingdom.
“Our findings suggest that merging is an important route through which black holes can rapidly grow, even at cosmic dawn,” explains Übler.
“Together with other Webb findings of active, massive black holes in the distant Universe, our results also show that massive black holes have been shaping the evolution of galaxies from the very beginning.”
“The stellar mass of the system we studied is similar to that of our neighbor the Large Magellanic Cloud,” says team member Pablo G. Pérez-González of the Centro de Astrobiología (CAB), CSIC/INTA, in Spain.
“We can try to imagine how the evolution of merging galaxies could be affected if each galaxy had one super massive black hole as large or larger than the one we have in the Milky Way.”
Read the full paper at arxiv.org/abs/2312.03589