Black hole is starving its host galaxy of star-forming fuel

Astronomers have made a fascinating discovery which supports the theory that supermassive black holes can be the death knell for their host galaxies by depriving them of the fuel required for star formation.

An international team of scientists, co-led by the University of Cambridge, utilized the capabilities of the NASA/ESA James Webb Space Telescope to study a galaxy similar in size to the Milky Way.

Dead galaxy with minimal star formation

The galaxy, affectionately named Pablo’s Galaxy (officially GS-10578), hails from the early universe about two billion years after the Big Bang. However, the galaxy is far from thriving – it appears “dead” with minimal star formation.

“Based on earlier observations, we knew this galaxy was in a quenched state: it’s not forming many stars given its size, and we expect there is a link between the black hole and the end of star formation,” explained co-lead author Dr. Francesco D’Eugenio from Cambridge’s Kavli Institute for Cosmology.

The connection between the galaxy’s inactive state and the supermassive black hole was not confirmed until the Webb Telescope’s advanced observation power came into play, allowing researchers to examine whether this star-formation drought is temporary or permanent.

Cutting off the galaxy’s food source

Pablo’s Galaxy, with a mass about 200 billion times that of our Sun, formed most of its stars between 12.5 and 11.5 billion years ago.

“In the early universe, most galaxies are forming lots of stars, so it’s interesting to see such a massive dead galaxy at this period in time. If it had enough time to get to this massive size, whatever process that stopped star formation likely happened relatively quickly,” said Professor Roberto Maiolino.

Using Webb, the researchers confirmed that this galaxy is expelling gas at incredibly high speeds – around 1,000 kilometers per second – fast enough to escape the galaxy’s gravitational pull. These gas clouds, pushed out by the black hole, are critical for star formation.

“We found the culprit. The black hole is killing this galaxy and keeping it dormant, by cutting off the source of ‘food’ the galaxy needs to form new stars,” said Dr. D’Eugenio.

Insights from new observations

Webb’s unparalleled sensitivity even detected cold, dense gas clouds previously unseen with earlier telescopes. These clouds block light from behind the galaxy, helping researchers track the mass of gas being ejected.

The mass loss exceeds what the galaxy needs to sustain star formation, confirming the hypothesis that the black hole is starving the galaxy to death.

The next step in understanding this cosmic phenomenon will focus on observations by the Atacama Large Millimeter-Submillimeter Array (ALMA), which will target the coldest gas components of the galaxy.

Researchers plan to investigate whether any hidden fuel for star formation still exists and to further study the impact of the supermassive black hole.

Black holes and star formation

“We knew that black holes have a massive impact on galaxies, and perhaps it’s common that they stop star formation, but until Webb, we weren’t able to directly confirm this,” said Maiolino.

“It’s yet another way that Webb is such a giant leap forward in terms of our ability to study the early universe and how it evolved.”

The role of black holes in shaping galaxies has long intrigued astronomers, but the discovery of black hole winds driving star formation quenching adds a crucial piece to the puzzle.

Black hole starving its galaxy

The researchers observed powerful winds of gas, driven by the immense gravitational forces of the supermassive black hole, sweeping through the galaxy.

The winds expel gas at such high velocities that it escapes the galaxy’s gravitational pull, preventing new stars from forming.

This process, known as quenching, essentially halts the galaxy’s growth. The amount of gas removed is significant, and the fact that it happens so early in the galaxy’s development highlights the transformative role black holes play in galactic evolution.

The discovery confirms theories that black hole-driven winds can stifle a galaxy’s potential long before it reaches its full star-forming capability.

The study opens up new avenues for understanding how black holes can regulate galaxy life cycles, especially during the early stages of the universe.

The research was supported by the Royal Society, the European Union, the European Research Council, and the Science and Technology Facilities Council (STFC), part of UK Research and Innovation (UKRI).

The study is published in the journal Nature Astronomy.

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