For the past 15 years, scientists have been searching for evidence of a form of star that has only been hypothesised but never observed: one driven not by atom fusion like the sun and other ordinary stars, but by a mysterious substance known as dark matter. The first good candidates for “dark stars” have been detected thanks to the James Webb Space Telescope’s ability to see back to the beginning of the cosmos.

The three objects found by Webb, which was launched in 2021 and began collecting data last year, were initially identified last December as some of the universe’s earliest-known galaxies but may instead be huge black stars, according to astronomers.

Dark matter, an invisible substance whose presence is known primarily by its gravitational effects on a galactic scale, would be a minor but critical component of dark stars. These stars are said to be almost entirely comprised of hydrogen and helium, the two elements present in the early universe, with dark matter accounting for 0.1% of their mass. Their engine, however, would be self-annihilating dark matter.

Dark matter is invisible to us because it does not emit or directly interact with light, but it is considered to account for approximately 85% of the universe’s matter, with the remaining 15% made up of normal matter like as stars, planets, gas, dust, and Earthly things such as pizza and people.

Dark stars would have a mass at least a million times that of the sun, a brightness at least a billion times that of the sun, and a diameter around ten times that of the sun. “They’re big puffy beasts,” said Katherine Freese, senior author of the study published in the journal Proceedings of the National Academy of Sciences.

“They are made of atomic matter and powered by the little bit of dark matter that’s inside them,” Freese added. Unlike conventional stars, they would be able to grow mass by absorbing gas from space.

“They can continue to accrete the surrounding gas almost indefinitely, reaching supermassive status,” said Cosmin Ilie, an astronomer at Colgate University and the study’s principal author. They would not have been as hot as the first generation of regular stars in the universe. The nuclear fusion that took place in the centres of those stars created elements heavier than hydrogen and helium.

The three hypothetical black stars date from early in the universe’s history, with one from 330 million years after the Big Bang event 13.8 billion years ago, and the others from 370 million and 400 million years after the Big Bang.

According to Freese, these objects could be either early galaxies or dark stars based on the Webb data.

“One supermassive dark star is as bright as an entire galaxy, so it could be one or the other,” Freese continued.

While there is insufficient data to make a clear judgement on these three, Freese believes Webb may be able to collect more detailed information on other equally primitive objects that could yield “smoking gun” evidence of a dark star.

Early universe conditions may have been favourable for the production of dark stars, with large dark matter densities near the locations of star-forming clouds of hydrogen and helium. Such circumstances are extremely uncommon today.

In 2008, Freese and two colleagues postulated the existence of dark stars, naming them after the 1960s Grateful Dead song “Dark Star.”

“It would be really super exciting to find a new type of star with a new kind of heat source,” Freese added. “It could lead to the detection of the first dark matter particles.” Then, by observing a range of dark stars of varying masses, you can learn about the properties of dark matter particles.”

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