Scientists Create Most Detailed Radio Map of Early Universe Using MWA

Astronomers are narrowing down on the evidence of the universe in its dark ages by searching for the faint 21-centimeter radio signal emitted by early-day hydrogen. It is a very faint emission, which happens due to a spin-flip transition in the hydrogen atoms, and it functions as a cosmic thermometer showing when the earliest stars and black holes started heating the gas between galaxies. Based on close to ten years of observations of the Murchison Widefield Array (MWA) in Australia, scientists have produced the most detailed radio map of the early universe so far and placed the most stringent constraints on this ancient signal.

Methods and Challenges

According to the research, the team led by Nunhokee relied on more than nine years of the MWA observations in the Western Australian region to seek a weak signal of hydrogen 21-cm. They simply attacked the line that is normally obscured by bright foreground noise of the Milky Way and the telescope.

Their sophisticated statistical filtering methods were able to isolate the signal and produced a cosmic radio sky map that was cleaner than ever before and a narrower upper limit on its strength.

Implications and Future Prospects

The team found no evidence for a cold early universe's absorption feature, ruling out an extremely cold cosmic dawn. Instead, the limits suggest the intergalactic medium was warmed by this epoch, consistent with models where X-rays from early black holes and stellar remnants heated the gas.

This work provides the first observational hint of a heated intergalactic medium at redshifts ~6.5-7.0. The next-generation Square Kilometer Array (SKA) radio telescope is expected to detect the 21-cm signal, with only a few hours of data needed to reveal this cosmic signal.