The lives of galaxies can be extended if their supermassive black holes provide them with “hearts and lungs” to keep them “breathing” and prevent them from getting too big.
That’s the assumption of new research, which shows that the universe would have aged much faster and today would be full of “zombie” galaxies containing dead or dying stars if it weren’t for the supermassive black holes thought to are found at the hearts of all major galaxies. The astrophysicists behind the findings compared jets of gas and radiation that supermassive black holes blow from their poles to the airways that feed our lungs.
The University of Kent team believes that pulses from each black hole’s “heart” cause shock fronts to oscillate back and forth through the two jets. This is similar to how a part of our body called the diaphragm moves up and down in our chest cavity to inflate and deflate our lungs.
In galaxies, this breathing-like action transfers the energy of the supermassive jets blown out by black holes to their surroundings, much like how on a cold winter morning you might breathe warm air into colder air. Stars form when interstellar gas clouds cool and condense. This means that this “exhalation” can slow star formation, limiting the growth of galaxies.
Connected: The James Webb Space Telescope sees an ancient black hole dance with colliding galaxies
The team came to this conclusion after analyzing simulations designed to reproduce the effects of supersonic supermassive jets blown out by black holes, which can play a role in inhibiting galaxy growth. The simulations showed that the heart of the supermassive black hole could pulsate, creating 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 act like bellows, firing sound waves that passed through the surrounding material of galactic gas and dust.
“We realized that there must be some means for the jets to support the body — the atmospheric gas surrounding the galaxy — and that’s what we found 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 allowed the heart to beat.”
This sent a stream of pulses into the high-pressure jets, causing them to change shape as a result of the bellows-like action of the jet’s oscillating shock fronts. The researcher added that these jets expand “like lungs filled with air.” In doing so, they send pressure waves into the galactic material around them, stopping the growth of galaxies in the simulations.
Besides the team’s simulations, there is some other evidence of this phenomenon in real galaxies. For example, about 240 million light-years from Earth in the Perseus galaxy cluster, astronomers have seen evidence of large gas bubbles in this collection of thousands of galaxies immersed in a vast cloud of multimillion-degree gas. They are thought to be the result of sound waves traveling through the galactic medium in this cluster.
The balance between the activity of black holes and the flow of gas into galaxies is extremely difficult to achieve – however, because supermassive black holes require a steady supply of gas and dust to create jets.
“Breathing too fast or too slow will not provide the life-giving tremors needed to sustain the galactic environment and at the same time keep the heart fueled,” team member and University of Kent researcher Michael Smith said in the statement. “However, doing this is not easy, and we have limitations on the type of pulsation, the size of the black hole, and the quality of the lungs.”
The team concluded that a galaxy’s lifespan could be extended with the help of its supermassive black hole “heart” and the black hole’s jet “lungs” that blow from its core, as they impede growth by limiting the amount gas collapsing into early-stage stars.
Without this mechanism, many galaxies would have exhausted their supplies of star-forming fuel by now in our 13.8-billion-year-old universe. As a result, they would “disappear”, with most galaxies resembling so-called “red and dead” zombie galaxies at this point, full of ancient burnt-out stars.
The team’s research was published July 12 in the journal Monthly Notices of the Royal Astronomical Society.
