Galactic 'Heart and Lungs' Mechanism Regulates Growth and Extends Lifespan
Without this mechanism, the Universe would have aged faster, leaving us with enormous "zombie" galaxies filled with dead and dying stars.
Published in the Monthly Notices of the Royal Astronomical Society, the study addresses a major cosmic mystery: why galaxies are not as large as expected.
Researchers propose that galaxies manage their growth by controlling the amount of gas they absorb to form stars. This internal resistance counteracts gravity's pull.
Astrophysicists from the University of Kent suggest that the "breathing" process of galaxies involves the supermassive black hole at the center acting like a heart, with bi-polar supersonic jets of gas and radiation functioning as airways to lungs.
Black hole pulses create jet shock fronts that oscillate like a diaphragm in a chest cavity, transmitting energy widely and slowing gas accretion and growth.
PhD student Carl Richards developed this theory using novel simulations to explore the role of supersonic jets in limiting galaxy growth. These simulations showed the black hole "heart" pulsing, causing jets to behave like bellows, emitting sound waves akin to ripples on a pond.
Richards noted the analogy to everyday phenomena like the sound of a champagne bottle opening or rocket exhausts, stating, "We realised that there would have to be some means for the jets to support the body - the galaxy's surrounding ambient gas - and that is what we discovered in our computer simulations."
"The unexpected behaviour was revealed when we analysed the computer simulations of high pressure and allowed the heart to pulse. 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 jets expanded like "air-filled lungs," transmitting sound waves into the galaxy as pressure ripples, which suppressed growth.
Evidence of such ripples exists in extra-galactic media, such as those observed in the Perseus galaxy cluster. These ripples were thought to sustain the surrounding environment, but their generation mechanism was unknown.
Standard cosmological simulations cannot fully explain gas flows into galaxies, highlighting the importance of a highly-active black hole to provide resistance.
"To do this is not easy, however, and 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 will not provide the life-giving tremors needed to maintain the galaxy medium and, at the same time, keep the heart supplied with fuel."
The study concludes that a galaxy's lifespan can be extended with the help of its "heart and lungs," where the supermassive black hole engine at its core limits gas collapse into stars from an early stage, shaping the galaxies we observe today.
The paper 'Simulations of Pulsed Overpressure Jets: Formation of Bellows and Ripples in Galactic Environments' by Carl Richards and Michael Smith is published in the Monthly Notices of the Royal Astronomical Society.