Deep into a South-African desert lies a unique set of telescopes. Called the Hydrogen Epoch of Reionization Array, or HERA, this telescope project is in the early stages of looking for the effects of light from the first set of stars that formed in our universe. The first stars and galaxies began forming when the universe was a few hundred million years old in a period known as the “Cosmic Dawn.” This is one of the most important yet poorly understood stages in the cosmic evolution. Along with the birth of stars and galaxies, another radical transformation marked this period: the hydrogen gas that permeated the universe changed from electrically neutral to nearly fully ionized, and it remains in this ionized state until the present time.
Existing astronomical instruments — such as large optical telescopes, conventional radio telescopes and probes of the cosmic microwave background radiation — provide only weak constraints on the timing of the Cosmic Dawn and conditions that led to the formation of first stars and galaxies. Because of this, astronomers are developing an alternative approach to investigating Cosmic Dawn; one based on measuring feeble radiation from hydrogen gas that permeated the ancient universe. This radiation has a wavelength of 21 centimeters when emitted by a hydrogen atom, but is being redshifted due to the expansion of the universe and reaches the earth with a wavelength of several meters. Special types of telescopes are needed to detect this kind of radiation and they consist of a large number of relatively simple antennas connected by a powerful computer into a single telescope.
The Moore Foundation recently awarded a $5.8 million grant to MIT to support construction of HERA — ranked a top scientific priority for this decade by the Radio, Millimeter and Sub-millimeter panel of the 2010 Decadal Survey in Astronomy and Astrophysics. Through this funding, the HERA project team can increase the sensitivity of the array and potentially detect signals coming from a time before the “epoch of reionization” — a period in the history of the universe, the cosmic dawn, roughly 400 million years after the Big Bang. Using this next-generation in instrumentation for 21-centimeter cosmology — the wavelength of neutral hydrogen gas radio waves — HERA will probe the 3-D structure of the universe during the very first appearance of stars, galaxies and black holes. This first generation of hot massive stars and black-hole binaries filled the intergalactic medium with X-rays.
“These X-rays would have heated up the hydrogen surrounding galaxies and should produce detectable fluctuations in the 21cm line,” said Jacqueline N Hewitt, lead investigator on the Moore Foundation grant, and director of the MIT Kavli Institute for Astrophysics and Space Research. “Measurements of the ‘Epoch of X-rays’ power spectrum could, in principle, distinguish between different scenarios for the very first generation of stars.”
Read more in a recent news story from MIT here and an informative article in Space.com.