Black Holes: Not Destroyers, But Protectors

Artist’s impression of bipolar jets of gas emanating from a supermassive black hole at the centre of a galaxy. Image credit: ESA/Hubble, L. Calcada (ESO)

A study has revealed that galaxies have a heart-and-lung-like regulatory mechanism that controls their growth by limiting gas absorption.

This mechanism, which involves a massive mass, Black hole Their jet emissions prevent galaxies from expanding too quickly, ensuring their longevity and preventing them from aging prematurely and turning into “zombie” galaxies.

Galaxies avoid early death because they have a “heart and lungs” that effectively regulate their “breathing” and prevent them from growing out of control, a new study suggests.

If this had not happened, the universe would have aged much faster, and all we would see today would be huge “zombie” galaxies teeming with dead and dying stars.

This is according to a new study published in Monthly Notices of the Royal Astronomical Society, Which investigates one of the greatest mysteries of the universe – why galaxies are not as big as astronomers expect.

Something seems to be stifling its enormous potential by limiting the amount of gas it absorbs to turn into stars, meaning that instead of growing indefinitely, something inside is resisting what was thought to be the inevitable force of gravity.

This clip shows a hypersonic jet generating a “bellows-like motion” by receiving pulses from the “heart” of the black hole, causing it to expand and contract “like an air-filled lung”, and “eject warm air” (pressure ripples) into its surroundings. The axes of the graph are dimensionless distance scales. Copyright: C Richards/MD Smith/University of Kent

Heart and lungs analogy in galaxies

Now astrophysicists at the University of Kent think they may have discovered the secret. They suggest that galaxies may control their growth rate by the way they “breathe”.

In their analogy, the researchers compared the supermassive black hole at the center of a galaxy to its core and the two supersonic, bipolar jets of gas and radiation it emits into the airways that feed the lungs.

The pulses from the black hole—or “heart”—can create jet shock fronts that oscillate back and forth along the jets’ axes, much as the human body’s diaphragm moves up and down within the chest cavity to inflate and deflate both lungs.

This could cause the jet’s energy to be transferred widely into the surrounding medium, just as we breathe warm air, slowing the accretion and growth of the galaxy’s gas.

Two different examples of a simulation of one side of a symmetric bipolar jet, where pressure ripples propagate through the extragalactic medium. Here the pressure differences are shown using a red temperature color scale (dark = low pressure, light = high pressure). Each jet enters from the left with a pressure that drops rapidly as it pushes against the surrounding medium. The axes are non-dimensional distance scales. Copyright: C Richards/MD Smith/University of Kent

Simulation Insights and Galactic Dynamics

PhD student Carl Richards came up with the theory after creating a new, never-before-tried simulation to investigate the role that supersonic jets might play in inhibiting galaxy growth.

This involved allowing the black hole’s “heart” to beat and putting the jets under high pressure – much like a form of high blood pressure, if we compare it to the human body.

He said this caused the planes to become “like bellows,” sending out sound waves “like ripples on the surface of a pond.”

This phenomenon is similar to the Earth’s equivalent of sound and shock waves produced when a bottle of champagne is opened, a car squeaks, rocket exhausts, or pressurized containers are punctured.

Sound waves (ripples) are visible in the hot gas filling the Perseus cluster in this artist’s impression. They are thought to be created by cavities ejected by jets from the supermassive black hole (bright white spot) at the galaxy’s center. Credit: NASA/NASA/XC Center/M. Weiss

“We realized that there must be some means by which the jets could support the body – the gas surrounding the galaxy – and that’s what we discovered in our computer simulations,” Richards said.

“The unexpected behavior was revealed when we analyzed computer simulations of high blood pressure and allowing 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 oscillating jet shock fronts.”

These overpressure jets actually expanded “like lungs filled with air,” the researchers said.

In doing so, they transmitted sound waves to the surrounding galaxy in the form of a series of pressure ripples, which were then shown to suppress the galaxy’s growth.

Conclusion and future prospects

There is some evidence for ripples in extragalactic media, such as those observed in the nearby Perseus cluster of galaxies associated with massive hot gas bubbles, which are thought to be examples of sound waves.

These ripples were already thought to be responsible for maintaining the galactic environment, although no mechanism for generating them was found.

Consequently, conventional cosmological simulations are unable to explain the gas flows into galaxies, leading to one of the greatest mysteries of the universe, so they rely on the extremely active black hole at the heart of the galaxy to provide some resistance.

“It’s not easy to do this, and we have limitations on the type of pulse, the size of the black hole, and the quality of the lungs,” said study co-author Professor Michael Smith.

“Breathing too fast or too slow will not provide the vital vibrations needed to maintain the galactic center and, at the same time, keep the heart fueled.”

The researchers concluded that the galaxy’s lifespan could be extended by its “heart and lungs,” with the supermassive black hole engine at its core helping to inhibit growth by limiting the amount of gas collapsing into early stars.

They say this helped create the galaxies we see today.

Without such a mechanism, the galaxies would have run out of fuel by this time and disappeared, as some do as “red dead” or “zombie” galaxies.

Reference: “Simulating Pulsed Overpressure Jets: Blower Formation and Ripples in Galactic Environments” by Carl Richards and Michael D. Smith, July 12, 2024, Monthly Notices of the Royal Astronomical Society.
DOI: 10.1093/mnras/stae1498