Galaxies manage to avoid early extinction by effectively controlling their growth through „heart and lungs”-like mechanisms, a new study suggests.
Without these mechanisms, the universe would be filled with massive „zombie” galaxies containing dead and dying stars.
Study, published Monthly Notices of the Royal Astronomical SocietyTackles the mystery of why galaxies aren’t bigger than expected.
Inhibits star growth
„Galaxies form under the influence of the flow of gas between their interstellar medium and the surrounding gas halo, known as the circum-galactic medium (CGM),” the researchers wrote.
„Although the CGM is significantly less dense than the corresponding interstellar medium, this vast reservoir contains 3-5 times more baryons and heavier elements.”
„However, the estimated star-formation rate in many galaxies is lower than expected, suggesting ambient cold-gas inflows.”
„Although jets from active galactic nuclei (AGN) are not well understood, it is possible that energy transfer from AGN’s gas jets heats the environment around the host galaxy and moderates this inflow.”
Heart at the center of galaxies
Supermassive black holes at the centers of galaxies act like hearts, while the bipolar supersonic jets they emit act like lungs, regulating the galaxy’s „breathing” and energy distribution.
This regulation limits the amount of gas that galaxies absorb to become stars, preventing uncontrolled growth.
Focus of the study
„Jets from the active core may provide heat, which moderates cooling and accretion from the circum-stellar medium,” the study authors wrote.
„While static high-pressure jets can drive blood flow, the lateral energy transfer rarely exceeds 3 percent of the jet power after the initial bow shock has advanced.”
„Here we investigate whether pulses in high-pressure jets are capable of transferring sufficient lateral energy to the ambient environment. We answer this by performing a systematic survey of numerical simulations in an axisymmetric hydrodynamic mode.
Unexpected behavior of galaxies
PhD student Carl Richards developed the theory through innovative simulations, showing that pulses from the black hole cause jet shock nozzles to oscillate like a diaphragm in a chest cavity. This process transports energy throughout the galaxy, reducing gas accretion and growth.
„We realized that there must be some way for the jets to support the body — the ambient gas around the galaxy — and that’s what we found in our computer simulations,” Richards said.
„Unexpected behavior emerged when we analyzed computer simulations of high pressure and allowed the heart to beat.”
Shock waves from high pressure jets
The high-pressure jets act like bellows, sending out sound waves that suppress the galaxy’s expansion. This is similar to the phenomenon seen in sound and shock waves produced by terrestrial activities, such as opening a bottle of champagne or rocket exhausts.
„This sent a stream of pulses into the high-pressure jets, changing their shape as a result of the bellows-like action of the oscillating jet shock nozzles,” Richards explained.
Resistance to unchecked growth
Evidence supporting this theory comes from observations of ripples in extra-galactic media, such as those in the Perseus galaxy cluster, which are believed to be examples of sound waves.
These waves maintain the ambient environment around a galaxy, preventing excessive growth. Conventional cosmological simulations have struggled to account for the flow of gas into galaxies, leading to the mystery of their finite size.
A highly active black hole at the heart of a galaxy provides the necessary resistance to unchecked growth.
Strikes the perfect balance of star formation
„It’s not easy to do, however, because we have constraints on the type of pulsation, the size of the black hole and the quality of the lung,” astronomer Michael Smith said. University of Ghent.
„Breathing too fast or too slowly doesn’t provide the life-giving jolt needed to maintain the galactic medium and, at the same time, fuel the heart.”
In addition, galaxies’ lifespans are extended by their internal „heart and lungs,” where the supermassive black hole engine at its core helps prevent growth by limiting the amount of gas that collapses into the stars from the initial stage.
This mechanism allows galaxies to remain in their current form and prevents them from burning up and becoming „zombie” galaxies.
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