New research suggests that galaxies avoid an early death thanks to supermassive black holes that act like "hearts" and "lungs," regulating their growth and preventing them from becoming too large.

Without this mechanism, the universe would age much faster, and today's galaxies would be overwhelmed with dead and dying stars.

A study published in the Monthly Notices of the Royal Astronomical Society addresses one of the great mysteries of the universe - why galaxies are not as large as expected.

Something seems to limit their potential to absorb gas that turns into stars, rather than growing indefinitely; something inside resists gravity.

Astronomers from the University of Kent believe they have discovered the secret. They propose that galaxies control their growth through the way they "breathe".

Researchers compare the supermassive black hole at the center of a galaxy to a heart, and the two bipolar supersonic jets of gas and radiation it emits to the respiratory pathways that feed the lungs.

The pulsations of the black hole - or "heart" - can lead to oscillations in the shock fronts of the jets, similar to how the diaphragm in the human body moves within the chest cavity to inflate and deflate the lungs.

This results in the transfer of jet energy widely into the surrounding medium, slowing the accretion of gas and the growth of the galaxy.

PhD student Carl Richards developed this theory using new simulations. He allowed the black hole to pulsate and the jets to be under high pressure, mimicking hypertension in the human body. This setup caused the emission of sound waves similar to ripples on a pond.

The phenomenon is akin to the sound and shock waves produced when opening a bottle of champagne, screeching car tires, rocket exhaust, and breaking pressure seals.

"We realized there must be a way for the jets to support the body - the surrounding gas of the galaxy - and we discovered this in our computer simulations," said Richards.

"Unexpected behavior was revealed when we analyzed high-pressure simulations and allowed the heart to pulsate. This sent a series of pulsations into the jets, causing a change in shape due to the action of the oscillating shock fronts."

These high-pressure jets effectively expanded "like lungs full of air," the researchers said. In doing so, they transmitted sound waves into the surrounding galaxy in the form of a series of pressure waves, which then showed to suppress the growth of the galaxy.

Evidence of waves in extragalactic media, such as those observed in the Perseus galaxy cluster, points to sound waves generated by jets from the supermassive black hole. These waves have already been considered responsible for maintaining the ambient environment around galaxies.

Conventional cosmological simulations are unable to explain gas flows in galaxies, leading to one of the great mysteries of the universe, so it relies on a highly active black hole at the galaxy's center to provide resistance.

"It's not easy to achieve, we have constraints on the type of pulsation, the size of the black hole, and the quality of the lungs," said co-author Professor Michael Smith.

"Breathing too fast or too slow won't provide the necessary tremors to maintain the galactic medium and supply the heart with fuel."

Researchers concluded that a galaxy's lifespan can be extended with the help of its "heart and lungs," where the supermassive black hole motor helps inhibit growth by limiting the amount of gas turning into stars in the early stages.

This mechanism helps create the galaxies we see today.

Without this process, galaxies would have exhausted their fuel and gone extinct by now, like some "red and dead" or "zombie" galaxies.

Source: Royal Astronomical Society