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Moon helps reveal secrets of the Universe

The Moon may be the key to unlocking how the first stars and galaxies shaped the early Universe.

Find the peer-reviewed paper here.

Dr Benjamin McKinley during a trip to the Murchison Widefield Array telescope in outback Western Australia. The 16 metal ‘spiders’ form a single antenna ‘tile’, of which there are 256, spread out across an area of around 6 km in diameter. Dr McKinley and the team are using this radio telescope to observe the Moon in their search for radio signals from the early Universe.
Dr Benjamin McKinley with an MWA tile.

A team of astronomers led by Dr Benjamin McKinley at the 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) observed the Moon with a radio telescope to help search for the faint signal from hydrogen atoms in the infant Universe.

 

“Before there were stars and galaxies, the Universe was pretty much just hydrogen, floating around in space,” Dr McKinley said.

 

“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 period when the first stars and galaxies started forming out of the hydrogen is known as the ‘epoch of reionisation’, and has yet to be detected.

 

Artist’s impression of a portion in the timeline of the Universe, around the ‘epoch of reionisation’ – the process that ionised most of the material in the cosmos. This is the first moment in the history of the cosmos when matter was in an electrically neutral state (represented in yellow). After that, a few hundred million years passed before these atoms could assemble and eventually give rise to the Universe’s first generation of stars (left of centre, in the illustration). As these first stars came to life, they filled their surroundings with light, which subsequently split neutral atoms apart, turning them back into their constituent particles: electrons and protons. This process, called cosmic reionisation, is shown at the centre of the illustration. The yellow neutral hydrogen gives off a signal that we detect as faint radio waves on Earth. Image credit: ESA – C. Carreau
Artist’s impression of a portion in the timeline of the Universe, around the ‘epoch of reionisation’ – the process that ionised most of the material in the cosmos.

In research published in the Oxford University Press Monthly Notices of the Royal Astronomical Society today, 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.

 

“If we can detect this radio signal it will tell us whether our theories about the evolution of the Universe are correct.”

 

Dr McKinley said that in your car radio, you can tune into various channels and the radio waves are converted into sounds.

 

“The radio telescope, the MWA which is located in the Western Australian desert far away from earth-based FM radio stations, takes the radio signals from space which we can then convert into images of the sky,” he said.

 

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.

 

 

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.

 

With more observations, the astronomers hope to uncover the hydrogen signal and put theoretical models of the Universe to the test.


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