The Black Hole Era

The Black Hole Era is the fourth age of the universe, from about 10⁴⁰ to 10¹⁰⁰ years after the Big Bang. Stars and stellar remnants are gone; black holes are the only large objects left. They slowly evaporate through Hawking radiation, the smallest first, until the largest vanish around 10¹⁰⁰ years.

In the scheme of Fred Adams and Gregory Laughlin it covers cosmological decades 40 to 100 in their 1999 book (38 to 100 in their 1997 review, “A dying universe”). It is the longest of the finite eras on the logarithmic clock: 60 powers of ten. Explore it in the Deep Time explorer.

Why black holes are the last objects

At the end of the Degenerate Era, if protons decay, white dwarfs, neutron stars and planets have dissolved into radiation and light particles. Black holes are unaffected by proton decay. What remains are black holes of every size: stellar ones from the deaths of massive stars, and supermassive ones that grew in the centers of galaxies and swallowed some of the stars that did not escape when galaxies evaporated.

Adams and Laughlin found that black holes dominate the production of energy and entropy in the universe from about η = 36 to 100.

How black holes evaporate: Hawking radiation

In 1974 Stephen Hawking showed that black holes are not completely black. Quantum effects near the horizon make them emit particles as if they were hot bodies, with a temperature inversely proportional to their mass. They lose mass and, eventually, disappear. Hawking gave the full derivation in 1975.

Two features set the pace of this era:

1. Bigger is colder and slower. A black hole of one solar mass has a temperature of about 6 × 10^-8 kelvin. Ten times more mass means one tenth the temperature.
2. Lifetime grows as the cube of the mass. Don Page’s 1976 calculation gave the emission rates in detail; double the mass and the lifetime grows eightfold.

How long do black holes last?

Black hole	Mass (Suns)	Approximate lifetime (years)	η
Stellar black hole	1	1065 to 1067	65 to 67
Sagittarius A*	About 4.3 million	About 1085 to 1087	85 to 87
M87*	6.5 billion	About 1094 to 1096	94 to 96
Galaxy-mass black hole	100 billion	About 1098 to 10100	98 to 100

The range in each row reflects two normalizations. Adams and Laughlin’s rounded formula gives 10⁸³ years for a million solar masses, scaling as the cube of the mass, so 10⁶⁵ years for one solar mass and 10⁹⁸ for a galaxy-mass hole. Page’s 1976 result, a total power of about 2 × 10^-4 ħc⁶/(G²M²), implies about 2 × 10⁶⁶ years for one solar mass if, as he assumed, neutrinos are massless. Neutrinos do have mass, so a cold black hole mostly emits photons and gravitons, which lengthens that toward 10⁶⁷ years. Either way, the last black holes are gone near 10¹⁰⁰ years, a googol.

Waiting for the universe to cool

Black holes cannot even start shrinking yet. Today the cosmic microwave background is 2.725 kelvin, far warmer than any stellar or supermassive black hole, so they absorb more energy than they radiate. They begin to lose mass only once expansion cools the background below their temperature.

Here is a rough estimate for a solar-mass black hole. The background must cool by a factor of 2.725 ÷ (6 × 10^-8) ≈ 4.5 × 10⁷, which takes ln(4.5 × 10⁷) ≈ 17.6 factors of e of expansion. With dark energy dominating, each factor of e takes about 17.5 billion years (Planck 2018 values), so the wait is roughly 300 billion years. For a black hole of 10 billion solar masses it is roughly 700 billion years. Tiny compared with the evaporation times above.

The end of a black hole

As a black hole shrinks, it gets hotter and radiates faster. The final moments are violent: Hawking estimated that a black hole releases about 10³⁰ erg in its last tenth of a second. Across the Black Hole Era, these flashes are the last bright events in the universe, spaced ever more widely in an ever larger and darker space.

Classically, black holes never shrink: the 2025 gravitational-wave event GW250114 confirmed Hawking’s 1971 area theorem, which says the total horizon area cannot decrease when black holes merge. Hawking radiation is the quantum exception, and it has never been observed directly. What happens to the information that fell into a black hole once it evaporates, the black hole information paradox, is still debated.

Other things that happen in this era

Adams and Laughlin’s table of events lists a few more processes, all speculative:

• Axions, if they exist, decay into photons around η = 42.
• Positronium may form from leftover electrons and positrons around η = 85 in a flat, decelerating universe, as atoms wider than today’s observable universe. Accelerating expansion dilutes these particles further, so most may never pair up.
• Higher-order proton decay could still be eating away at matter, on timescales of 10¹⁰⁰ to 10²⁰⁰ years, if first-order decay does not occur.

A 2025 proposal by Falcke, Wondrak and van Suijlekom suggests that neutron stars and white dwarfs also evaporate by a Hawking-like process, by about 10⁶⁸ and 10⁷⁸ years. If correct, any remnants that survived proton decay would also be gone during this era. The idea is contested.

What comes next

When the last black hole has evaporated, there are no large objects left anywhere. The Dark Era begins. For the full sequence, read our guide to the future of the universe or the heat death of the universe.