The Moon may be the key to unlocking how the first stars and galaxies shaped the early Universe. A team of astronomers led by Dr Benjamin McKinley observed the Moon with a radio telescope to help search for the faint signal from hydrogen atoms, in research published today in the journal Monthly Notices of the Royal Astronomical Society.
“Before there were stars and galaxies, the Universe was pretty much just hydrogen, floating around in space,” said Dr McKinley, an astronomer at Curtin University – node of the International Centre for Radio Astronomy Research (ICRAR) – and the ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D).
“Since there are no sources of the optical light visible to our eyes, this early stage of the Universe is known as the ‘cosmic dark ages’”.
The astronomers describe how they have used the Murchison Widefield Array (MWA) radio telescope to help search for radio signals given off by the hydrogen atoms. “The MWA takes the radio signals from space and we can then convert them into images of the sky,” explains Dr McKinley.
This radio signal from the early Universe is very weak compared to the extremely bright objects in the foreground, which include accreting black holes in other galaxies and electrons in our own Milky Way.
Radio waves from our galaxy, the Milky Way, reflecting off the surface of the Moon and observed by the Murchison Widefield Array radio telescope located in Western Australia. Credit: NASA / GSFC / Arizona State University. Click for a larger image
The key to solving this problem is being able to precisely measure the average brightness of the sky. However, built-in effects from the instruments and radio frequency interference make it difficult to get accurate observations of this very faint radio signal.
In this work, the astronomers used the Moon as a reference point of known brightness and shape. This allowed the team to measure the brightness of the Milky Way at the position of the occulting Moon.
The astronomers also took into account ‘earthshine’—radio waves from Earth that reflect off the Moon and back onto the telescope. Earthshine corrupts the signal from the Moon and the team had to remove this contamination from their analysis.
“If we can detect this radio signal it will tell us whether our theories about the evolution of the Universe are correct,” added Dr McKinley.
With more observations, the astronomers hope to uncover the hydrogen signal and put theoretical models of the Universe to the test.