The Golden Age of Star Formation was presented in all its drama and glory by Dr. Mordecai-Mark Mac Low, Curator of the Department of Astrophysics at the American Museum of Natural History, on April 8 as part of the museum’s Frontiers Lecture series.
In the early days of the universe, according to Dr. Mac Low, there were no stars. The cosmos then was composed of nothing but dark matter, hydrogen and helium. As the gases experienced “slight perturbations”, Dr. Mac Low explained, they collapsed and fused under the force of gravity until stars began to form at their centers.
These were the very first stars.
“They were massive and hot, emitting ionizing radiation and they ionized the surrounding universe,” said Dr. Mac Low, a theoretical astrophysicist whose focus is the formation of planets, stars and galaxies.
“They eventually exploded as the first supernovae.”
A supernova is the explosion of a star that ejects most of the star’s mass, scattering heavy elements — gold, platinum, uranium — throughout the universe. It is the largest explosion in space.
This set into motion the cycle of star formation as heavy elements were incorporated into new stars.
These massive new stars didn’t last long – about 5 to 10 million years — a mere blip in the universe’s 13.8-billion-year history.
Stars were “living fast, dying young,” said Mac Low.
Along with new stars, this cycle nurtured the formation of the planets and galaxies, giving life to everything in the universe – in fact, 93% of the human body is composed of these same heavy elements.
Star formation actually reached its peak about 10 billion years ago, when stars were forming at ten times the rate of today.
To illustrate, Dr. Mac Low projected a series of graphs that tracked early star formation, based on data gathered from the Hubble Space Telescope and the James Webb Space Telescope. Even with this data and technology, said Dr. Mac Low, our telescopes aren’t sensitive enough to see and detect the earliest stars. “We may be seeing the remnants of some of those first stars,” he explained, “or at any rate, a very close second generation of those stars.”
The most dramatic moment of the lecture came when Mac Low projected Illustris, a computer simulation developed by an international team of researchers that created the first realistic version of the Universe.
The simulation picks up the story of the Universe right after the Big Bang starting with dark matter and hydrogen. A bewildering variety of galaxies lit up the planetarium’s dome as Dr. Mac Low described the action. “So there we had the very first stars starting to light up to push heavy elements out…forming more and more stars lighting up the universe, taking all this cold blue gas, dropping it onto galaxies where it becomes denser and denser until new stars form.”
After its golden age 10 billion years ago, star formation slowed down tremendously. This slowing down, known as “quenching”, has been attributed to large magnetic fields at the center of the galaxy. The magnetic fields exert pressure on large star-forming gas clouds and prevent them from collapsing and forming stars. The larger the field, the slower the star formation rate.
Though star formation has slowed down from its golden age, its legacy lives on. Surveys recently taken by NASA’s Hubble Space telescope and other observatories have led astronomers to conclude that there are at least two trillion galaxies in the observable universe. Some astronomers estimate that there are about 100 billion stars in an average sized galaxy.