The Degenerate Era: When the universe stops making stars

When gazing up at a dark night sky, astronomers and the layperson alike are often awestruck by the sheer number of bright stars visible to the naked eye. From a good vantage point on a clear night with minimal light pollution, the average person can see about 2,500 individual stars.

It’s easy to imagine our ancestors looking up at the same night skies, with the twinkling beacons evoking the same (or stronger) emotions they arouse today. But though it may appear the universe is unchanging — with stars that will always shine for any creature curious enough to look up — in truth, that’s hardly the case.

We are living in what astrophysicists Fred Adams and Gregory Laughlin dubbed the Stelliferous Era, which stretches from when the universe was 1 million years old to when the universe will be 100 trillion years old. This time period is most notable for its many bustling galaxies composed of countless bright stars burning hydrogen. But massive stars quickly burn through their fuel, so the biggest stars die faster than the smallest (millions of years compared to hundreds of billions). Eventually, the last generation of stars will exhaust any remaining hydrogen fuel available for consumption.

During the Stelliferous Era, some supermassive stars will dramatically perish as supernovae. But most will simply fizzle out after passing through several phases of stellar evolution. Once this happens, the universe will be populated only by a variety of so-called degenerate stellar remnants: black holes, white dwarfs, brown dwarfs, and neutron stars. Adams and Laughlin termed this period the Degenerate Era, hypothesizing it will take place between 1015 (1 quintillion) and 1039 (1 duodecillion, or 1 followed by 39 zeros) years after the Big Bang.

While black holes, white dwarfs, brown dwarfs, and neutron stars all exist today, during the Degenerate Era they will dominate the universe. Degenerate stellar remnants are, by and large, much cooler and darker than most stars of our current era. The night sky we see today will no longer exist, instead replaced by one with fewer — and markedly dimmer — stars. Brown dwarfs, which were too small to ever undergo regular fusion reactions, will horde much of the hydrogen left in the universe. Black holes will become larger during the Degenerate Era, fed by any matter they can accumulate, including other degenerate stellar remnants.