How Galaxies are Formed

In 1924, American astronomer Edwin Hubble discovered a Cepheid star—a pulsating or variable luminosity star— in the Andromeda nebula. Until then the Andromeda nebula was believed to be a cluster of stars and dust within the Milky Way. Indeed, the Milky Way was then thought to encompass the entire universe, but that misconception was about to be revised along with notions of what galaxies were and how they came about.

Based on research established by  Harvard astronomer Henrietta Leavitt, Hubble determined that the Cepheid star he had discovered in the Andromeda nebula put the star and the nebula far beyond the boundary of the Milky Way  correctly concluding Andromeda was in fact a separate galaxy millions of light years beyond the Milky Way. It was a profound realization.  

Around the same time, George Lamaître was developing his primeval atom theory of the origin of the universe later coined the “Big Bang”  by Fred Hoyle, and based on Einstein’s theories of special and general relativity. Most astronomers and physicists discounted Lamaître’s theory, but when Hubble discovered through red shift, that all the many galaxies by then cataloged appeared to be moving away from earth suggesting an expanding universe, Lamaître’s theory gained credence.  

While Hubble was star gazing Werner Heisenberg was defining a new way to look at the relationships between energy and matter, called quantum mechanics. Meanwhile, two Soviet physicists discovered a new particle in the nucleus of atoms called neutrons. Three years later, Leo Szilard proposed that atoms of matter could be dismantled and converted in to energy through a process of neutron fission. Szilard’s theory along with special relativity were confirmed on July 16, 1945 in the New Mexico desert with the explosion of the first atomic bomb.

A couple of other pieces of the greater cosmic puzzle provided vital clues as to how galaxies formed. In the late 1940’s, physicists figured out they could use the heat of an atomic bomb to create fusion reactions like that taking place in the Sun. By learning about fusion astrophysicists developed an understanding of how stars and the universe evolved. Then, in 1964, two scientists working of Bell Laboratories discovered the Cosmic Back ground radiation representing  the smoking gun of the Big Bang. From this point forward, quantum physics would play a significant roll in figuring out galaxies, as we know them today, evolved out of the big bang.  

“The passage from the Chaos of the Big Bang to the Cosmos that we are beginning to know is the most awesome transformation of matter and energy that we have ever been privileged to glimpse.” Dr. Carl Sagan -Cosmos

From its primeval atom stage the universe evolved and cooled for between 150 million to a billion years. What began as quark gluon plasma in the first minutes of universal existence congealed through a process called nucleogenesis into common hydrogen atoms consisting of a single proton with a single electron.  The rate or velocity of expansion of the universe also slowed and gravity became stron enough to draw atoms together. Matter was still quite dense and uniformly distributed in the universe at this point but gravity would quickly begin to redistribute it. As hydrogen amassed in one area it was compressed by gravity and heated up forming a proto-star. These proto-stars grew much bigger and faster than stars in the universe today do, the mass of just one star equal to all the stars in the Milky Way galaxy. They were also very short lived.

Before photons of light generated by fusion taking place in the core of these first behemoth proto-stars could reach the surface of the star, the star would implode and then explode blowing off its outer layers and  leaving behind a shrinking core made almost entirely of neutrons. When stars implode they spin very fast like an ice skater drawing in his or her arms. Black holes spin with even higher velocities. The material ejected from the outerlayers of an exploding/imploding proto-star would eventually be drawn back in by the immense gravity of the black hole at its center. This material would form new smaller stars and begin to orbit the black hole. A galaxy is born.        

Today we can not see the visible light of any of the galaxy creating behemoth proto-stars because none escaped from them. Since then many of the original galaxies have merged together. Indeed, in about 3 billion years, the Andromeda galaxy which is headed in this direction will tear our galaxy apart adding more mass to its own. If we are ever to witness the formation of a galaxy from a super massive proto-star, the best we can hope to detect, just beyond the current event horizon of the visible universe, will be a puff of gamma rays. While little or no visible light would have escaped from the galaxy forming proto-stars, an incredible release of gamma radiation as the star collapsed into its own black hole should still be detectable. Today, astronomers are developing deep space telescopes that will be able to detect these faint puffs of gamma radiation just beyond the current event horizon.  

Since no one yet has actually observed evidence of a galaxy forming, no one can descried with certainty how it happened. All we can say for sure right now it that it did because otherwise we wouldn’t be here to contemplate the quandary. What we can say, based on our understanding of quantum mechanics, is how the universe likely evolved to become the reality we know it to be. All the galaxies we can see are part of that reality and most astrophysicists are in agreement that they all have black holes at their centers.