The Degenerate Era

The Degenerate Era is the age of dead stars. From about 10¹⁵ to 10³⁹ years after the Big Bang, fusion has stopped and most ordinary matter sits in stellar remnants: white dwarfs, brown dwarfs and neutron stars. Galaxies slowly dissolve, and if protons decay, the remnants themselves evaporate.

It is the third era in the scheme of Fred Adams and Gregory Laughlin, covering cosmological decades 15 to 39 in their 1999 book The Five Ages of the Universe. Their 1997 review “A dying universe” gave slightly different edges, η = 15 to 37, because it tied the end to a representative proton lifetime of 10³⁷ years. You can scroll it in the Deep Time explorer.

What fills the universe in the Degenerate Era?

Once the Stelliferous Era ends, what remains are the objects stars leave behind. They are called degenerate because a quantum effect, degeneracy pressure, holds them up instead of heat from fusion.

• White dwarfs: the Earth-sized cores of stars like the Sun. Adams and Laughlin found that roughly half of all remnants will be white dwarfs, and that they will hold most of the mass. Their maximum mass, about 1.4 solar masses, is the Chandrasekhar limit.
• Brown dwarfs: failed stars too small to fuse hydrogen, most of the remaining objects.
• Neutron stars: the crushed cores of massive stars, first proposed by Baade and Zwicky in 1934.
• Black holes, which outlast everything else and take over in the next era.

White dwarfs cool and dim toward invisibility, eventually becoming “black dwarfs”. Planets can survive around them: the Webb telescope recently showed how the giant planet WD 1856 b survived its star’s death, a preview of systems in this era.

Timeline of the Degenerate Era

All times follow Adams and Laughlin’s table of events (1997) and are rough by design.

Event	When (years)	η
Planets detach from their stars through encounters	1015	15
New stars form by brown dwarf collisions	1016	16
Stars evaporate from the galaxy	1019	19
Planetary orbits decay by gravitational radiation	1020	20
Dark matter particles in the halo annihilate (if they are WIMPs)	About 1022.5	22.5
Black holes swallow stars on galactic scales	1030	30
Protons decay (assumed lifetime)	1037	37
White dwarfs destroyed by proton decay	1039	39

Galaxies evaporate

In a galaxy of dead stars, close encounters slowly trade energy. Most stars gain enough to escape into intergalactic space, while a minority lose energy and sink toward the center. Adams and Laughlin estimate most stars leave around η = 19, with perhaps 1% to 10% ending in the central black hole. The galaxy as we know it simply comes apart.

A trickle of new stars

Star formation does not stop completely. When two brown dwarfs collide, the merged object can exceed the minimum mass for fusion and ignite as a small star. Adams and Laughlin found this would be the main source of new stars between about 10¹⁵ and 10²³ years, though at an extremely low rate.

Dark matter as fuel

If dark matter is made of weakly interacting massive particles (WIMPs), white dwarfs can capture them and the particles annihilate inside, keeping old white dwarfs warmer than they would otherwise be. This depends on what dark matter is, and direct searches have not detected WIMPs.

How the Degenerate Era ends: proton decay

The end depends on whether protons, the building blocks of every atom’s nucleus, last forever. Grand unified theories predict they decay. If so, a white dwarf powered by proton decay would glow with about 400 watts, Adams and Laughlin calculate, “enough power to run a few light bulbs”, and slowly evaporate until nothing is left by about η = 39. Planets and neutron stars dissolve on similar timescales.

Proton decay has never been observed. Super-Kamiokande, a 50,000-ton water detector in Japan, found no events in more than two decades of data and set a lower limit of 2.4 × 10³⁴ years on the proton’s lifetime for its main predicted decay mode (2020). Adams and Laughlin’s suggested range for the lifetime, 10³² to 10⁴¹ years, has so far been narrowed only at its lower end.

If protons are stable, the Degenerate Era lasts far longer. Remnants would then change only through much slower processes; Adams and Laughlin cite Freeman Dyson’s estimate that nuclear reactions by quantum tunneling act on timescales around 10¹⁵⁰⁰ years.

A contested shortcut

In 2025, Heino Falcke, Michael Wondrak and Walter van Suijlekom proposed that spacetime curvature alone makes any compact object evaporate in a Hawking-like way. In their picture neutron stars last at most about 10⁶⁸ years and the last white dwarfs vanish after roughly 10⁷⁸ years. Their earlier 2023 paper on the mechanism drew a published comment arguing it conflicts with exact results in simpler settings, which the authors dispute. It is a proposal, not established physics, and it would end remnants after this era’s nominal end anyway, in the Black Hole Era.

What comes next

When the degenerate remnants are gone, black holes are the only large objects left. The Black Hole Era begins. For the full sequence of eras, read our guide to the future of the universe.