Dark Age (Cosmology)

In cosmology, the dark age is an early period in the formation of our universe ; it can be classified in the time after the formation of the cosmic background radiation and before the formation of the first stars . During this time, matter was neither absorbed nor emitted light, so it was transparent. At that time the universe was much smaller than it is today. Due to the expansion of the universe , the radiation of the cosmic microwave background (originally in visible and infrared light ) was shifted into the range of microwaves .

Origin and End

After the universe had cooled down so much that light - or rather electromagnetic radiation in general - had separated from matter, around 380,000 years after the Big Bang , all matter was neutral and transparent (today visible as cosmic background radiation). There were no light sources that could illuminate the cooling plumes of electrically neutral gas, no larger objects, and not even tiny specks of dust , because carbon and all the other heavier elements didn't exist then either. The dark age was replaced by the age of the formation of the first stars and galaxies after further cooling of the gas masses and their compression through the effect of gravity , which began about 100 million years after the Big Bang. These first stars were about a hundred times heavier than the Sun and were only short-lived. Their UV light led to the reionization epoch , they ionized the surrounding gas clouds and thus formed bubbles in interstellar space.

It is hoped that the observation of the 21 cm line of neutral hydrogen in radio astronomy will provide evidence of the end of the dark age and the beginning of the reionization epoch and the subsequent development . Due to the redshift due to the expansion of the universe, the radiation from that epoch is now in a completely different frequency range (from 1420 MHz to the range around 50 to 100 MHz). Due to the reionization, there should be a drop in the absorption in the area of ​​the 21 cm line. Such observation at 78 MHz (corresponding to time about 180 million years after the Big Bang) was in 2018 by the compact EDGES telescope (Experiment to Detect the Global Epoch of Reionization Signature) of the MIT made. It was also reported that evidence of dark matter might have been found, since the temperature of the neutral hydrogen found from the absorption spectrum was lower than can be explained by the expansion of the universe (coupling to the cosmic background radiation). One possible explanation is an additional cooling through coupling to dark matter. Much better data is expected from the planned Square Kilometer Array (SKA).

Individual evidence

1. ↑ Rüdiger Vaas, The End of the Dark Age, Image of Science ( Memento of the original from March 9, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. 4/2009 
2. ↑ Johann Grolle, The First Suns, Der Spiegel No. 13, 2018, pp. 114ff
3. ^ Judd Bowman, Alan Rogers, Raul Monsalve, Thomas Mozdzen, Nivedita Mahesh: An absorption profile centered at 78 megahertz in the sky-averaged spectrum, Nature, Volume 555, 2018, pp. 67-70, abstract
4. ↑ EDGES, MIT Haystack Observatory
5. ↑ Joshua Kerrigan, First Detection of the 21cm Cosmic Dawn Signal , Astrobites, March 14, 2018