The earliest observable moments of the Universe are shown in this rather abstract-looking image – it is actually a map of the whole sky, showing a very faint signal that appears across the sky
, an afterglow known as the Cosmic Microwave Background radiation (‘CMB’). This radiation was emitted over 13 billion years ago, less than 400,000 years fter the Big Bang. The image you see here is the result of the detailed mapping of the CMB carried out by NASA's WMAP mission between 2001 and 2010. ESA's Planck mission has subsequently mapped it in even more detail.
Although the CMB is almost uniform all over the sky, there are very small variations in temperature which you can see represented by different colours - by analysing these variations, astronomers have been able to discover much about the structure and evolution of the early universe. However, perhaps not surprisingly given the amount of time involved, there are still many unknowns about this distant epoch.
In my last post I mentioned the current Chang-E mission to the far side of the moon – just maybe, this historic first soft landing of an unmanned explorer in this mysterious region of our nearest neighbour in space could be a first stop in exploring the mysterious period of cosmic time between the emission of the CMB and the birth of the first stars.
How come? An intriguing part of the mission involves researching the Moon’s far side as a potential location for radio astronomy. This location is very special because the Moon’s mass itself blocks any direct signals from Earth from reaching its far side.
This is a major disadvantage for communication during exploration, but the Chang-e mission has resolved this by putting a relay satellite named 'Queqiao' into orbit around a point beyond the Moon, as shown in this diagram, to receive signals from Earth and pass them on to the lander on the far side of the Moon.
On the other hand, the fact that direct signals from the Earth are blocked here is also seen as a potentially great advantage for radio astronomy at very low frequencies. Radio observation at these frequencies is very difficult from Earth because of interference other Earth-based radio activities and blocking by the atmosphere, so the far side of the Moon has been proposed as an ideal site, shielded from earthly interference and with no atmospheric issues.
But why are astronomers interested in low frequency radio astronomy? Observing this type of signal is seen as a key method of investigating the very early Universe, the period known as the ‘Dark Ages’, after the emission of the CMB but before the first stars were born.
This means looking far beyond the galaxies that we can see, to the ancient clouds of hydrogen gas from which they were formed. And astronomers believe they can observe them best against the background of the CMB at a specific low frequency radio wavelength, 21.2 centimeters.
Change-e and its relay satellite will be carrying out investigations into the possibilities for radio astronomy on the far side of the moon. Maybe this is indeed a first step to revealing some more of the mysteries of how our Universe came to be.
https://www.universetoday.com/135288/what-is-the-cosmic-microwave-background/
http://www.planetary.org/blogs/guest-blogs/2018/0519-change-4-relay-satellite.html
Put telescopes on the far side of the Moon https://www.nature.com/articles/d41586-017-08941-8
https://map.gsfc.nasa.gov/mission/ (WMAP)
https://www.esa.int/Our_Activities/Space_Science/Planck_overview
Image Credits:
1. NASA
2. The Bruce Murray Space Image Library Revised from Lunar Exploration and Space Engineering Center http://www.planetary.org/multimedia/space-images/charts/queqiao-relay.html
3. NASA / WMAP Science Team https://map.gsfc.nasa.gov/media/060915/index.html