[...] after about 380,000 years, hydrogen – the first atoms – started to form. Some of these atoms were pulled together into stars, where they fused into carbon, oxygen, nitrogen, iron and all of the other elements from which planets and life are built. With the formation of those first hydrogen atoms – each made of one negatively charged electron and one positively charged proton – the universe entered a period cosmologists call the Dark Ages. To solve this problem, my colleagues and I designed a new kind of telescope: an array of radio dishes that, instead of searching for distant galaxies, maps the intergalactic hydrogen itself throughout the process of being heated and reionized. HERA is sensitive to a specific kind of radio wave produced when the magnetic fields of the proton and electron inside of hydrogen switch their north-south polarity with respect to each other. Just as two oppositely aligned bar magnets attract each other and release energy in the process, the switching polarity of the electron and proton causes hydrogen to release a small amount of energy. A 21-cm radio wave emitted by hydrogen at this time in the history of our universe would be stretched by a factor of eight on its way to us; we would see it with a wavelength of 168 cm. [...] the same radio wave emitted when the universe was 940 million years old would be be stretched only by a factor of seven, appearing to us with a wavelength of 147 cm. Observations with the new facilities in the next several years are poised to transform our understanding of the first stars, galaxies and black holes, and their role in driving reionization at the end of cosmic dawn.
Comment on After our universe's cosmic dawn, what happened to all its original hydrogen?
Aaron Parsons, University of California, Berkeley, San Antonio Express-News: World
Mon, 10/10/2016 - 6:39pm
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