What Is a Dark Star?

Dark stars wouldn't run on nuclear fusion, but rather dark matter. nienora/Shutterstock

Black stars may be the most influential celestial bodies in the universe that no one knows for sure ever existed.

In fact, they may be the elder stars of the cosmos, twinkling long before stars — at least as we know them now — showed up.

So why is there no evidence of them today?

They may have literally faded to black. As in, black hole.

At least that's the theory posited by University of Michigan physicist Katherine Freese in a recent interview with Astronomy.

Freese suggests dark stars are actually the seeds of the supermassive black holes that lurk in the heart of every galaxy. After all, even time-bending, light-hoovering regions of space have to grow from something. And that something may be a dark star.

But how does a bright and shiny celestial body take such a dramatically dark turn? Well, for one thing, a dark star — unlike the stars we know and occasionally wish upon — would already have darkness, literally, running through its veins.

The stars we see today all abide by the same general rule of nuclear fusion. The sheer mass of a star means it's always in a state of collapsing on itself. But that kind of constant pressure on its core also produces energy that radiates outward. The result is a perfect balance of inward pull and outward radiation.

Our sun, for example, has reached that perfect equilibrium, parlaying gravitational pressure into the giant battery that essentially powers the solar system.

Dark stars, on the other hand, do things a little differently.

Sure, they've got hydrogen and helium running in their veins — but also, a touch of dark matter.

Yes, that's another material that no one has seen or even detected — making dark star theory even more ... theoretical.

But here's how Freese suggests it could work:

About 13 billion years ago, when dark stars were forming, the universe was a very different, and much denser, place. They likely incorporated dark matter in their DNA, in the form of Weakly Interacting Massive Particles, or WIMPs.

Even as a microscopic ingredient in a star's makeup, dark matter could keep a body huffing and puffing for a billion years thanks to a unique process called dark matter annihilation.

Essentially, dark matter gives a dark star its superpowers — it could expand and radiate energy without having to rely on that delicate dance known as nuclear fusion. That would also unburden a dark star from its core, allowing it to sprawl outward and, despite its name, shine much brighter and bigger.

"They can keep growing as long as there is dark matter fuel," Freese tells Astronomy. "We've assumed they can get up to 10 million times the mass of the Sun and 10 billion times as bright as the Sun, but we don't really know. There is no cutoff in principle."

And, she suggests, at some point, a star with that much mass would have to collapse, becoming a black hole.

But how does a theory that hinges on theory ever end up becoming a reality? We just have to spot one on the endless haystack that is the cosmos.

And that may be a job for the James Webb Space Telescope.

A full-scale model of the James Webb Space Telescope — the most powerful optical and infrared space observatory ever created — is displayed in Austin, Texas. Chris Gunn/NASA

Scheduled for a March 2021 launch, the space-borne eye will be "the biggest, most powerful telescope ever to be put in space."

While astronomers are rightly excited about the prospect of countless new planet discoveries, the telescope may also finally catch a glimpse of that most elusive and ancient celestial body known as a dark star.

"If a dark star of a million solar masses were found [by James Webb] from very early on, it's pretty clear that such an object would end up as a big black hole," Freese says. "Then these could merge together to make supermassive black holes. A very reasonable scenario!"