Scientists trace origins of 1st stars in universe
By Amanda Jermyn

So much about the early universe is still a mystery, but recently astronomers have caught a glimpse of what appear to be signals of the earliest stars. Furthermore, their discovery potentially provides the first indirect detection of dark matter.

The Big Bang, which occurred about 13.8 billion years ago, generated a soup of subatomic particles that cooled rapidly as the universe expanded. After about 370,000 years these particles began to combine to form atoms, mostly hydrogen. Over time, in places where the matter was slightly denser, these atoms clumped together under the force of gravity to form huge clouds of gas and dust. Gradually, these clouds condensed further under gravity, forming massive hot balls of nuclear fire, the first stars. The early universe was cold and dark, but now, with these first stars, there was light.

The signal that stirred the recent excitement was detected about two years ago by a radio telescope in the Australian desert and was reported earlier this year in the journal Nature. Judd Bowman of Arizona State University, first author on the study, concluded that the signal came from the very first stars that appeared in the universe. While the signal dates from about 180 million years after the Big Bang it does not tell us exactly when the earliest stars were formed, only that at 180 million years they already existed. However, 180 million years fits with current theories as to when the earliest stars appeared.

Because these stars are so far away their light would be too faint to view directly, so the evidence for their existence is based on changes in the wavelengths of radio signals from hydrogen present in the early universe. When the first stars formed they emitted ultraviolet light that changed the behavior of the hydrogen atoms in the spaces between them, allowing them to interact with radiation from the cosmic microwave background, the afterglow of the Big Bang. So if there were stars present, the hydrogen would emit one particular energy signature , and if there were no stars, they’d emit another. What the astronomers detected was a clear but faint signal indicating the existence of stars.

Detecting such faint signals is not easy. Our own galaxy is filled with radio wave noise, and because the frequency the astronomers were looking for is part of the FM radio spectrum, the astronomers chose to install their antennae in the Australian desert to try and minimize interference.

According to Bowman, little is known about the nature of these early stars, but they were probably hotter and simpler than those formed more recently. While the team spent two years checking their results, further independent studies will be needed to confirm their findings. Bowman hopes that knowing where and how to look will help others to do so.
According to Rennan Barkana, an astrophysicist at Tel Aviv University who has published a related paper in Nature, a particularly intriguing finding of this study was that the hydrogen between stars was colder than thought possible. The astronomers expected the temperatures to be 10 degrees Centigrade above absolute zero but they were in fact 5 degrees above absolute zero. Barkana theorizes that dark matter, which has never been observed interacting with anything, may be cooling the hydrogen. While dark matter makes up 27% of the universe, we know little about it except that it is not made of normal matter particles, and we only know of its existence through its gravitational effects. If this finding is correct it could be the first indirect detection of dark matter, and the first indication that dark matter can interact with normal matter.

Join the Springfield Stars Club on Tuesday, May 22nd at 7pm at the Springfield Science Museum for a talk by Jack Megas on “Why the Earth is Special.” Megas is an astronomy educator at the Springfield Science Museum’s Seymour Planetarium, and a retired laboratory hematologist at Baystate Medical Center. He is a past president of the Springfield Stars Club and the Naturalist Club. Refreshments will be served, and the public is welcome. The meeting is free of charge for members, with a suggested donation of $2 per non-member.