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Celestial Sunday Presents: Michelle Thaller explains cosmic dawn.

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Hi i'm Michelle Thaller from NASA's Goddard space\h
flight center and I'm an astronomer and one of\h\h

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the terms that you'll be hearing a lot when we\h
talk about the James Webb Space Telescope and also\h\h

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the upcoming Nancy Grace Roman Space Telescope,\h
is the term cosmic dawn and that sounds really\h\h

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dramatic and lovely. So the cosmic dawn is in\h
fact the end of the cosmic dark ages it's a time\h\h

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when the universe changed. It used to be very\h
long ago that the universe expanded and cooled\h\h

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and when it did it formed what we think of as\h
normal atoms, atoms that have nucleus and electrons\h\h

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going around them and the thing about an atom is\h
that it can actually absorb light really well, when\h\h

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you shine light on an atom, electrons can absorb\h
the light and jump around to different orbits\h\h

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in the atom and basically the light goes away the\h
light was absorbed. And so there was a time I would\h\h

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say you know maybe about 200 million\h
years, 300 million years after the big bang when\h\h

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the gas between the stars and galaxies was very\h
good absorbing light, it had atoms with electrons\h\h

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and everything just got absorbed. Then something\h
really mysterious happened that actually broke\h\h

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all of the atoms apart in the gas between the\h
stars and galaxies and we think it may have had\h\h

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to do with the formation of the first giant black\h
holes. Black holes often have huge high-energy jets\h\h

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that come out of them these jets can extend for\h
hundreds of thousands of light years and basically\h\h

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rip apart any atom in their path so what happened\h
then is that all the atoms got ripped apart\h\h

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light could actually go through the universe and\h
for the first time we were really able to see\h\h

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distant stars and galaxies but, if we look\h
so far back in time and so far away there\h\h

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becomes a point where the universe is very good\h
absorbing light it's very hard to see any further.\h\h

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so Webb and Roman will be right up against that\h
limit seeing if we can peer a little bit into that\h\h

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barrier and see what was going on when the\h
universe was still cool enough to absorb light\h\h

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the era of the very first stars and galaxies,\h
So I hope you understand a little bit more\h\h