Laura Faye Tenenbaum

Feb 13th 2023

The Mystery of Dark Stars


Dark stars are thought to be some of the earliest stars in the universe, forming in the genesis of it all. That would be nearly 13 billion years ago, or about 80 to 100 million years after the Big Bang, when clouds of hydrogen and helium gas began to cool. Astrophysicists suspect that dark matter might have fueled these early stars. And now, with the new James Webb Space Telescope, scientists are looking back through time to find out more about dark stars and the unseen dark matter that makes up about 95% of all matter in the universe.

What Is a Dark Star?

Scientists believe that dark stars might be the oldest stars in the history of the universe and may represent the first phase of stellar evolution. These stars are giant, much larger than our sun or any of the other stars around today. A single dark star could be as much as 400 to 200,000 times wider than our sun and 500 to 1,000 times more massive. (If we had one of these stars instead of our sun, it would reach past the orbit of Saturn.)

Dark stars are puffy and cool. And surprisingly, they aren’t actually dark; they just don’t emit any visible light. That’s because instead of nuclear fusion, which is the process that converts hydrogen into helium in the core of an ordinary star, dark stars are powered differently. Astronomers believe that dark matter heating is what powers them.

Imagine the universe about 200 million years after the Big Bang. That extremely early universe was different from today’s. It was a lot smaller and denser, with all the material of the cosmos crammed into a tinier volume. The earliest universe was also a lot darker because stars and galaxies had not formed yet. But there was dark matter (whatever that is) as well as hydrogen and helium gases plus trace amounts of lithium that had been created by the Big Bang.

The stars in the early universe are believed to be very large compared to the sun and in their short lives started to produce the heavier elements. It is possible that some of these early stars are the so-called dark stars. With a little luck, Webb might collect some data indicating that they do exist.

Still, no dark star has ever been observed. And even though they’d be massive — and potentially spewing gamma rays, neutrinos and antimatter — so far, they’ve been too faint to be detected because they don’t emit visible light.

Researchers’ Theories About Dark Stars

Scientists believe that dark stars probably reside at the centers of galaxies where the density of dark matter is highest. They’ve calculated that about 26% of what makes up our universe is dark matter, 69% is dark energy and only about 5% of the universe is visible. Scientists also believe that dark energy causes the expanding universe to accelerate.

But remember, since dark matter doesn’t emit light, researchers have been trying to measure it indirectly via its gravitational fingerprints, such as the way it bends light around massive galaxies. Scientists predict that there may be white dwarf and neutron stars fueled by dark matter at the centers of galaxies. And while these stars should be observable, they’ve remained mysterious because they have yet to be found.

Astronomers have used gravitational wave detectors such as LIGO to find signatures of colliding black holes and neutron stars, so there’s potential to also use these types of instruments to detect the gravitational signatures of two dark stars colliding. Someday, infrared detectors on ground-based telescopes might even be able to find white dwarfs and neutron stars fueled by dark matter near the center of the Milky Way.

Seeing Through the Dark

It is possible that the Hubble Space Telescope may have already seen a dark star. Some researchers have speculated that they might have found one located in the most distant galaxy ever observed. But it’s been too hard to uniquely identify dark stars with Hubble, which means that astronomers can’t be sure.

Now, scientists are hoping that the recently launched James Webb Space Telescope might be sensitive enough to finally find some dark stars. Since dark stars are relatively cool, they’d likely radiate at longer wavelengths in the infrared spectrum. And Webb, which is the largest, most complex and most powerful space telescope ever built, has instruments specifically created to capture that sort of infrared light. Webb’s NIRCam and MIRI cameras could be sensitive enough to detect the infrared light that a supermassive dark star would emit. What this means is that if dark stars exist, then Webb should be able to see them.

In fact, Webb has already detected young stars in stellar nurseries that have never been seen before, as well as previously invisible areas of star birth inside nebulas.

What If Dark Matter Is Some Sort of New Particle?

For astrophysicists, dark matter is an enduring, frustrating and confusing mystery. Most theories of the universe don’t make sense without it, and the evidence for dark matter is everywhere. We understand it via its gravitational influence: the bending of light around massive structures, the rotation curves of galaxies, the entire structure of the universe plus the cosmic microwave background. But dark matter doesn’t interact with light or with ordinary matter. So, does it do anything? Does it simply sit there gravitating?

For now, it’s beyond the edge of our scientific knowledge.

But Webb, launched on Dec. 25, 2021, gives us hope. Webb’s infrared cameras are sensitive enough to view objects that have been too distant or too faint for other telescopes, even the first galaxies. The telescope has been specifically designed to study the early universe and the formation of the first stars, which could alter our understanding of the entire universe.

Remember that scientists still don’t know what the universe’s first stars looked like and when exactly they formed. These are some of the questions Webb was designed to help answer. The next few years will surely be an exciting time for astronomers as Webb begins to uncover secrets of the distant universe and help scientists observe how the universe evolved.

And maybe, when the next generation asks, “What is a dark star?” — we’ll have the full answer, with images to boot. But more likely, we’ll just have more questions.

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