Hello, SFIA audio listeners. In this month's Nebula exclusive, big alien theory,

we're asking the reason alien civilizations might be rare is because most aliens are huge.

To hear it and every episode early and ad-free, plus hours of bonus content,

check out go.nebola.tv slash Isaac Arthur and use my code, Isaac Arthur.

Under the shadow of an eternal night, could a world opening a black hole be more than just a cosmic curiosity?

Could it also be a crater for life?

Black holes are among the most enigmatic and fascinating objects in the universe, remnants of stars so massive that even light cannot escape their grasp.

While they are often depicted as destroyers of worlds, recent scientific speculations suggest that, under the right conditions, a black hole could become a cosmic cradle for life instead.

Indeed, we've contemplated them as

the last refuge of post-biological life at the end of the universe in our civilizations at the end

of time series. But today, and in the present era of the cosmos, let us imagine a world orbiting

a black sun, a planet thriving in the gravitational and radiative embrace of a black hole, where

time flows differently, and energy comes from some binary of that black sun, or not from

the starlight at all, but from the extreme physics of the black hole itself.

Could such a place exist, and what would life be like under the eternal shadow of the

event horizon? We might ask ourselves if such worlds could be at all common, and the surprising answer is

yes, indeed there may be thousands, if not millions, of such planets in our galaxy alone.

We estimate there are somewhere between 100 and 400 billion stars in the Milky Way galaxy.

The exact number depends on how we define what constitutes a star and where we draw the boundaries

of the galaxy.

Most of these stars are much dimmer and less massive than our sun, and as a result, they

have significantly longer lifespans.

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