Jul 2nd 2018

Oldest Stars in the Universe May Shed New Light on Dark Matter


Hollywood has nothing on science when it comes to surprise plot twists and unexpected discoveries. A team of astronomers learned this lesson while seeking out the oldest stars in the universe. Their experiment not only succeeded in detecting the ancient stars, but it also turned up new clues about the most mysterious stuff in the universe: so-called dark matter.

A Window Into the Early Universe

The story begins with a look back in time. By nature, astronomers are always doing this, as the light we see from distant stars takes time to reach Earth. It can take light several years to reach us from the nearest stars beyond the sun and up to billions of years for stars in remote galaxies. A team of American astronomers set out to detect the oldest stars in the universe, more than 13 billion light years away, according to Sky & Telescope.

Because the universe is expanding, light crossing this enormous distance is stretched out and reaches us as radio waves. Detecting the ancient stars’ faint signal is tricky, because electronic detectors also produce radio waves, Sky & Telescope added.

Where Did the Energy Go?

To minimize background noise, astronomers set up shop in the remote Australian Outback with their instrument, the Experiment to Detect the Global Epoch of reionization Signature (or EDGES), which resembles a metal table more than a telescope. The goal was not to take snapshots of individual stars, but rather to detect the stretched-out radio signal from groups of these ancient stars.

In fact, the detective work involved finding telltale indications of missing light, which result from a process called absorption, according to Sky & Telescope.

After years of effort, the astronomers succeeded in detecting the oldest stars in the universe. The results show that these early stars appeared when the universe was only around 180 million years old.

But something also surprised the astronomers. The absorption was stronger than predicted, meaning that the ancient interstellar gas that the starlight passed through was colder than expected. Something had robbed the gas of some of its energy. But what?

A Weighty Mystery

Enter dark matter. As Nola Taylor Redd observed at Space.com, astronomers have known for decades that most of the matter — about 80 percent by mass — in the universe is not like the ordinary matter found here on Earth, other planets or even distant stars.

We know that dark matter is out there, because we can weigh it by measuring the rotational speed of galaxies, which demonstrates that galaxies are much heavier than the combined mass of their stars and planets. Mass is actually the only thing about it that we can readily detect.

Is Dark Matter the Answer?

Discovery of the oldest stars has also given us some tantalizing hints about dark matter. As Sky & Telescope explained, if something unknown was draining energy from the gas surrounding those early stars, or cooling it down, as the EDGES findings suggest, dark matter is the likeliest candidate. This means that it can interact with ordinary matter and probably did so in the early days of the universe.

As always on the frontiers of science, these findings are still tentative. On the path to understanding the universe, the one thing we can be sure of is that more plot twists are sure to come.

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