Word: formedical
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At the start of the dark ages, there were no galaxies, no stars, no planets. Even if there had been, we wouldn't be able to spot them. That's because hydrogen-gas clouds are nearly opaque to visible light; no ordinary telescope will ever be able to see what...
Because they were so hot, the first stars would have poured out not just visible light, but also copious amounts of high-energy ultraviolet radiation. One effect of that radiation would have been to knock apart hydrogen atoms, thus destroying their ability to block light. That process is known as...
It's this radiation--the ultraviolet light from hot, newly formed stars--that many theorists suspect finally reionized the remaining hydrogen, making it transparent again and bringing the Dark Ages to a close. Others suggest that the process may have been powered instead by black holes spewing out X-rays...
In any event, the accepted scenario is that this new generation of small galaxies, containing no more than a million second-generation stars, gradually collided, merging to form ever bigger objects that eventually reached the size of the Milky Way. One piece of evidence: the faintest and oldest galaxies found...
Guessing how the very first stars formed is relatively easy, since the universe was so simple at the start of the Dark Ages. By the end, however, things were starting to get complicated. The stars had begun to affect their environment, and the environment in turn affected the stars in...