Out of the Dark Age

In the sky this week…

  • Saturn is well up in the eastern sky by dark. Look for a moderately bright, yellowish “star”.
  • Jupiter, Mars, Venus and Mercury form a procession coming out of the sunrise glow.
  • The Moon will reach First Quarter on June 8.

Ken Tapping, June 8, 2011

In the 1930’s, Monseigneur Georges Lemaître proposed that the universe was once very small and extremely dense. Billions of years ago it started to expand, eventually forming the universe we see around us today. Since the 1930’s, many additional observations and research have been conducted, and it appears that Lemaître’s idea is still correct. A lot of progress has been made in filling in the details between the beginning of the expansion, commonly known as the “Big Bang”, and the modern universe.

The expansion started roughly 14 billion years ago. The universe expanded and cooled so that, a few days after the beginning, the temperature was low enough for particles like electrons, protons and neutrons to form. If we were able to go back to that time and survive, we would find it impossible to see anything. We would be surrounded by a featureless, very hot, glowing fog.

SKA dishes by night. Image: SPDO/TDP/DRAO/Swinburne Astronomy Productions

SKA dishes by night. Image: SPDO/TDP/DRAO/Swinburne Astronomy Productions

Even though the processes involved were somewhat different, the effect was very similar to what we see in a thick fog. The rays of light coming from objects we would like to see are deflected multiple times by water droplets, until all detail blurs out. This foggy period lasted until about 400,000 years after the beginning, at which point the universe had cooled significantly. The particles that had been freely moving around and contributing to the fog condensed into atoms, and the fog cleared.

Acceleration in the expansion of the Universe. Image: SPDO/TDP/DRAO/Swinburne Astronomy Productions

Acceleration in the expansion of the Universe. Image: SPDO/TDP/DRAO/Swinburne Astronomy Productions

The temperature soon reached a point where there was nothing in the young universe hot enough to give off light or other high-energy radiation. All that was left was the fading glow from the end of the foggy era, which is still detectable today, and is known as the cosmic microwave background radiation. If we visited this point in our universe’s history, we would find it dark. This period is known, not surprisingly, as the “Dark Age”. In the darkness, temperatures continued to fall and the universe became filled with cooling clouds, mainly of hydrogen gas. This situation remained until about 400 million years after the beginning, at which point the temperatures had fallen enough for the clouds to start collapsing to form the first stars. This was the “Let There Be Light” (LTBL) moment, marking the formation of the first stars and galaxies, and the universe started to look like the one we see today.

At the moment we can study the end of the bright but foggy era by observations of the cosmic microwave background. Our other telescopes, by looking further and further out into space, and therefore further back in time, are seeing galaxies closer to the time the Dark Age ended. We would like to know more about that LTBL moment, usually referred to as the era of reionization, and we are working on a telescope project that should help. It is called the Square Kilometre Array, and will be the biggest radio telescope in history. It will be at least 100 times more sensitive than anything we have at the moment and will have high-quality imaging capability. This project is being undertaken by an international consortium that includes Canada, with major technical development work being done here, at our observatory in the Okanagan.

Artist's impression of the SKA dishes. Image: SPDO/TDP/DRAO/Swinburne Astronomy Productions

Artist's impression of the SKA dishes. Image: SPDO/TDP/DRAO/Swinburne Astronomy Productions

Ken Tapping is an astronomer with the National Research Council's Dominion Radio Astrophysical Observatory, Penticton, BC, V2A 6J9.

Telephone: 250-497-2300
Fax: 250-497-2355
E-mail: ken.tapping@nrc-cnrc.gc.ca

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