A Brand New Way to Search for the First Stars in the Cosmos

Observing the earliest stars is among the holy Grails of astronomy. Now, a University of Hong Kongteam led by astrophysicist Jane Lixin Dai is proposing a new technique for detecting them. If it succeeds, the approach has the potential to open a window on the origin of the universe itself.

The earliest stars in the Cosmos formed immediately after the Big Bang. Astrophysicists call them “Population III” (or Pop III) stars. They’re dissimilar from the Sun and other stars in the modern universe for a variety of reasons. They formed chiefly from the hydrogen and helium in the newborn universe. From there, they grew to shocking sizes and masses very fast. That growth had a cost. Those stars had quite short lives as they blew through their core fuels very hastily. Nonetheless, fusion at their cores and the conditions of their deaths created the first elements heavier thanhelium and hydrogen. Those new elements sowed the next generations of stars.

Population III stars were the Universe’s first stars. They were extremely massive, luminous stars, and many of them exploded as supernovae. How did they shape the early galaxies? Image Credit: DALL-E

Pop III stars were the Cosmos’s first stars. They were tremendously massive, luminous stars, and several of them exploded as supernovae. So, why are we unable to detect these early stellar behemoths? For one reason, they were too far away, too early in history, and their light is too faint. That doesn’t mean they are undetectable. Astronomers just require advanced techniques and technology to spot them.

How to “See” the First Stars

Professor Dai’s team just recently published a study that proposes a connection between these first stars and proximate black holes. In short, they looked at what ensues when a Pop III star interacts with a black hole. Essentially, it gets shredded and gobbled up. For instance, the supermassive one within our Milky Way Galaxy—termed Sagittarius A*— does this. It has a consistent habit of ripping apart stars that meander too close. When such a tidal disruption event (TDE) occurs, it discharges huge amounts of radiation. If the same thing ensues in another galaxy—no matter how distant—the light from the event is detectable. As it turns out these TDE flares have unique and interesting properties used to infer the existence of the ancient Pop III stars.

“As the energetic photons travel from a very faraway distance, the timescale of the flare will be stretched due to the expansion of the Universe. These TDE flares will rise and decay over a very long period of time, which sets them apart from the TDEs of solar-type stars in the nearby Universe,” stated Dai. Additionally, the expansion of the Cosmos stretches the wavelengths of light from the flares, according to RudraniKar Chowdhury (Dai’s colleague). “The optical and ultraviolet light emitted by the TDE will be transferred to infrared emissions when reaching the Earth,” Chowdhury stated. Those emissions are just the kind of light new generations of telescopes are built to observe.