Galaxies’ lives can be extended if their supermassive black holes, which provide their “hearts and lungs”, support their “breathing” and prevent them from expanding too much.
That’s the suggestion of new research, which suggests that the universe would be aging much faster today and full of “zombie” galaxies containing dead or dying stars if it weren’t for the supermassive black holes thought to sit at the hearts of all large galaxies. The astrophysicists behind the discoveries compare the jets of gas and radiation that supermassive black holes blow from their poles into the airways that feed our lungs.
The University of Kent crew think that pulses from each “heart” of the black hole cause shock fronts that oscillate back and forth across the two jets. This is similar to when a part of our body called the diaphragm moves up and down inside our chest cavities to inflate and deflate our lungs.
In galaxies, this breathing-like action transfers the energy of supermassive jets blown out by black holes into the surrounding medium, just as you might exhale warm air into cooler air on a cold winter morning. Stars form when clouds of interstellar gas cool and condense. This means that this “breathing out” can slow star formation and limit the growth of galaxies.
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The team came to this conclusion after analyzing simulations designed to replicate the impact of supersonic supermassive jets blown out by black holes, which could play a role in inhibiting galaxy growth. Simulations have shown that the supermassive heart of a black hole can pulsate and create high pressure in the jets – almost like a person suffering from high blood pressure, or “hypertension”.
When this happened, the team saw the jets begin to behave like bellows, setting off sound waves that ripple through the surrounding material of galactic gas and dust.
“We realized that there would have to be some means for the jets to support the body — the ambient gas surrounding the galaxy — and that’s what we discovered in our computer simulations,” team member Carl Richards, Ph.D. student at the University of Kent, said in a statement. “The unexpected behavior was revealed when we analyzed computer simulations of high pressure and kept the heart beating.”
This sent a stream of pulses into the high-pressure jets, causing them to change shape due to the bellows-like action of the oscillating jet faces. The researcher added that these jets expanded “like lungs filled with air”. In doing so, they sent pressure waves into the galactic material around them, stopping the growth of galaxies in the simulations.
In addition to the team’s simulations, there is other evidence of this phenomenon in real galaxies. For example, about 240 million light-years from Earth in the Perseus galaxy cluster, astronomers saw evidence of large gas bubbles in this collection of thousands of galaxies immersed in a vast cloud of gas at a temperature of many millions of degrees. They are thought to be the result of sound waves rippling through the galactic medium in this cluster.
Achieving a balance between black hole activity and the flow of gas into galaxies is extremely difficult – however, supermassive black holes require a steady supply of gas and dust to create jets.
“Breathing too fast or too slow doesn’t provide the life-sustaining vibrations needed to sustain the galaxy while keeping the heart fueled,” team member and University of Kent researcher Michael Smith said in a statement. “But it’s not easy, and we have limitations regarding the type of pulsation, the size of the black hole, and the quality of the lungs.”
The team concluded that the galaxy’s lifespan can be extended by its supermassive black hole “heart” and that the black hole’s jet “lungs” blowing out of its core because they stunt growth by limiting the amount of gas that collapses into stars from an early stage. .
Without this mechanism, many galaxies would have exhausted the fuel needed to form stars in our 13.8-billion-year-old universe. As a result, they would “extinguish”, with most galaxies at this point resembling so-called “red and dead” zombie galaxies, full of ancient burnt-out stars.
The team’s research is published July 12 in the journal Monthly Notices of the Royal Astronomical Society.