A new thought experiment from Universe Today examines the hypothetical scenario of the Sun ceasing fusion. For the first ten thousand years, nothing noticeable would happen on Earth. Then the Sun would begin a slow, strange death, shrinking and briefly brightening before eventually collapsing into a black hole.
During this process, the Sun would coast on gravitational heat for tens of millions of years. The most immediate signal of the shutdown would come from neutrinos—these ghostly particles would stop arriving at Earth in just eight minutes, providing the first clue that something had gone wrong.
The timeline reveals a long, drawn-out demise rather than an instant catastrophe. After the initial pause, the Sun would contract, its core heating up as gravitational energy replaces fusion. This phase could last tens of millions of years before the Sun becomes a black hole.
Such a black hole would have a radius of just under 3 kilometers, far smaller than today's Sun. Its gravitational pull at Earth's orbit would remain the same, so planets would continue orbiting, but the lack of light and heat would freeze the surface within weeks.
The scenario is purely hypothetical—the Sun has billions of years of fuel remaining. But it illustrates how dependent Earth is on the continuous, stable fusion happening in the Sun's core, and how quickly that stability could unravel.