'Search for first stars uncovers dark matter'

Astronomers claim to have found the first direct proof of the existence of the mysterious dark matter - one of the building blocks of the cosmos - while attempting to detect the earliest stars in the universe.
The study led by Professor Judd Bowman from Arizona State University in the US suggests that the signal is proof of interactions between normal matter and dark matter in the early universe.
The discovery, published in the journal Nature, offers the first direct proof that dark matter exists and that it is composed of low-mass particles.
The signal, recorded by a novel radio telescope called EDGES, dates to 180 million years after the Big Bang.

"Dark matter is the key to unlocking the mystery of what the universe is made of," said Professor Rennan Barkana from Tel Aviv University in Israel.
"We know quite a bit about the chemical elements that make up the Earth, the Sun and other stars, but most of the matter in the universe is invisible and known as dark matter," Barkana said.

"The existence of dark matter is inferred from its strong gravity, but we have no idea what kind of substance it is. Hence, dark matter remains one of the greatest mysteries in physics," said Barkana.
"To solve it, we must travel back in time. Astronomers can see back in time, since it takes light time to reach us. We see the Sun as it was eight minutes ago, while the immensely distant first stars in the universe appear to us on Earth as they were billions of years in the past," Barkana said.

Bowman and colleagues reported the detection of a radio wave signal at a frequency of 78 megahertz.
The width of the observed profile is largely consistent with expectations, however they also found it had a larger amplitude (corresponding to deeper absorption) than predicted, indicating that the primordial gas was colder than expected.
Barkana suggests that the gas cooled through the interaction of hydrogen with cold, dark matter.
"I realised that this surprising signal indicates the presence of two actors: the first stars, and dark matter," said Barkana.
"The first stars in the universe turned on the radio signal, while the dark matter collided with the ordinary matter and cooled it down. Extra-cold material naturally explains the strong radio signal," said Barkana.