Galaxies regulate their very own progress in order that they don’t run out of gasoline for star formation

Look at most spiral or barred spiral galaxies and you will see several regions where stars are forming. These star-forming regions are composed mostly of hydrogen gas and some other elements. The first galaxies in the universe had huge stores of this star-forming gas. Without control, they could have quickly used up the gas and generated enormous amounts of star formation. Life, however, is fast and dies young, for such an energetic burst of star formation would soon dry up, leaving behind dead and dying stars. In a way, galaxies seem to regulate their star formation thanks to supermassive black holes at their centers.

The first galaxies formed about 400 to 700 million years after the Big Bang, during the period known as reionization. These early galaxies were small and faint, composed mostly of hydrogen and helium, and contained dense clusters of massive, short-lived Population III stars (the first generation of stars). The intense radiation from these stars ionized the surrounding gas and cleared the fog that permeated space, making the universe transparent for the first time. These primordial galaxies began to merge and interact with each other, laying the foundation for the types of galaxies we see today.

A new study published in the Monthly Notices of the Royal Astronomical Society examines why galaxies are not as large as astronomers would expect. The research suggests that galaxies, even those that formed first, avoid early deaths because they have mechanisms similar to “hearts and lungs” that regulate their “breathing.” Without these regulatory processes, our bodies and galaxies would have aged much faster, resulting in massive galaxies full of dead and dying stars and no new star formation.

Observations show that galaxies are not that big, and are full of dying stars that have outgrown themselves. It seems that something is limiting their ability to form stars from gas. Astrophysicists at the University of Kent believe they have the answer: galaxies may control their growth rate through a process not unlike “breathing.” They compare the supermassive black hole at the center of a galaxy to a heart, and the supersonic jets emanating from the poles to the radiation and gas they release into airways that supply a pair of lungs.

The supermassive black holes appear to pulsate like a heart. These pulses cause a shock front to oscillate along the jets like a diaphragm inflating and deflating the lungs. This process transfers energy along the jet, slowly counteracting gravity and slowing gas accumulation and star formation. The idea was developed by graduate student Carl Richards and his simulations showed a black hole pulsating like a heart.

A spiral wind, aided by magnetic fields, helps the supermassive black hole in the galaxy ESO320-G030 grow. In this image, the core of the galaxy is dominated by a rotating wind of dense gas leading outward from the (hidden) supermassive black hole at the center of the galaxy. The motions of the gas, tracked by light from hydrogen cyanide molecules, were measured with the Atacama Large Millimeter/submillimeter Array. Image credit: MD Gorski/Aaron M. Geller, Northwestern University, CIERA, the Center for Interdisciplinary Exploration and Research in Astrophysics.

Richards explains: “We realized there must be some way for the jets to support the body – the gas surrounding the galaxy – and that's exactly what we found in our computer simulations,” he continues. “The unexpected behavior became clear when we analyzed the computer simulations at high pressure and made the heart pulsate.”

Evidence of waves similar to those in Richard's simulations in extragalactic media has been found in galaxy clusters such as the Perseus Cluster. These waves are thought to maintain a galaxy's environment, although their formation mechanism was unclear. Conventional simulations cannot explain gas flows in galaxies, but the work of the University of Kent team may well have answered this question.

Source: How the “heart and lungs” of a galaxy extend its life.

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