Black holes “gigantic amplifiers” of star formation in the early universe

By Morgan Owen

Our Universe has a long, 13.8-billion-year history. Imagine translating this to a 12-month calendar and zooming in onto only the first few days of January. This is exactly what lead author Joseph Silk and an international team of astronomers, using the James Webb Space Telescope (JWST), did in work recently published in the Astrophysical Journal Letters.

Their work aimed to tangle with a fundamental, cosmic chicken and the egg question, the answer to which has been thus far hidden in the infant Universe. With our Universe full of galaxies, and supermassive black holes at the centre of many of these, then which came first: black holes or galaxies?

The research focuses on a cosmic chicken and egg question: which came first, black holes or galaxies?

Supermassive black holes (SMBHs) are celestial objects with extremely high density and a strong gravitational field from which even light cannot escape. They exist at the centre of many galaxies in our Universe, including our own galaxy the Milky Way. In 2022, the Event Horizon Telescope Collaboration confirmed the existence of the SMBH (Sgr A*) at the centre of the Milky Way by producing the first ever image of a black hole.

The JWST, however, is looking beyond our galaxy toward those that formed much earlier in time. Despite it only being in its first year of operation, the JWST has already been shedding light on the secrets of the early Universe. It is allowing astronomers to peer into the most distant galaxies, and to their surprise these appear much brighter, meaning that they contain more young stars and SMBHs than previously predicted. The lead author Joseph Silk poses the question that since these galaxies are typically smaller in the early Universe, “why on earth should they be making stars so rapidly?”

Insights from these observations have led astronomers to suggest that black holes and galaxies co-existed, and influenced each other’s evolution, during the first 100 million years of cosmic existence. According to Silk, “We know these monster black holes exist at the centre of galaxies near our Milky Way, but the big surprise now is that they were present at the beginning of the universe as well and were almost like building blocks or seeds for early galaxies.”

100 million years is but a tiny fraction of the history of our Universe, but these black holes “…really boosted everything, like gigantic amplifiers of star formation”, says Silk, and that this could “…completely shake up our understanding of how galaxies form.”

This research is now challenging astronomer’s classical understanding of the formation of the first black holes and galaxies. For decades, it has been believed that the first black holes only formed after the first, lonely stars lit up a dark Universe. These earliest massive stars would ultimately shed their outer layers, exploding in a hugely energetic supernova event, and their cores would collapse, forming a black hole.

In addition, astronomers have argued that galaxies form after the collapse of giant clouds of gas, which triggers waves of star formation. This picture is not entirely false, but it does not explain the existence of these SMBHs in the early Universe, nor does it explain why these galaxies appear much brighter than expected.

The big surprise is that supermassive black holes were like building blocks for early galaxies

This begs the question: how should this picture be modified? According to Silk, “The big surprise is that there was a seed in the middle of that cloud [of gas] – a big black hole – and that helped rapidly turn the inner part of that cloud into stars at a rate much greater than we ever expected. And so, the first galaxies are incredibly bright.”

So, why exactly do these SMBHs help accelerate star formation? These objects have strong magnetic fields that create violent storms, strong enough to act like particle accelerators on a huge scale, shooting out jets of material. These high-speed outflows in the form of jets and winds “crush nearby gas clouds, turning them into stars.”

As these outflows then slow down, and as the amount of gas available for star formation reduces, the rate of star formation also decreases. The formation of the first galaxies in our Universe have therefore been tremendously influenced by their black hole cosmic companions, far exceeding what we see today, billions of years later, in the local Universe.

To confirm their predictions, more observations from the JWST in the form of precise counts of stars and SMBHs in the early Universe are to be completed. Silk is optimistic that “Within a year we’ll have so much better data, and a lot of our questions will begin to get answers.”

Now that we know the link between black holes and galaxies in the infant Universe, astronomers want to answer questions about the SMBHs we see in galaxies today. With a cosmic evolutionary timeline spanning 13.8-billion years to explain, there are yet more pieces that must be added to this puzzle of the cosmos.

Image: NASA/CXC/M. Weiss