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Speaker 1: Welcome to brain Stuff, a production of I Heart Radio,

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Speaker 1: Hey brain Stuff Lauren Vogelbon. Here, imagine the number four.

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Speaker 1: Now imagine that it's at the head of a number

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Speaker 1: with eighty four zeros behind it. And that is the

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Speaker 1: number of photons emitted by all of the stars in

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Speaker 1: the observable universe, going back to when the now thirteen

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Speaker 1: point seven billion year old universe had been around for

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Speaker 1: just a billion years or so. And that's according to

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Speaker 1: a team of researchers headed by one Marco A. YAlO,

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Speaker 1: an astrophysicist in the College of Science at Clemson University.

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Speaker 1: It's based on an analysis of data from NASA's ten

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Speaker 1: year old Fermie Gamma Rays space telescope, which enabled the

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Speaker 1: researchers to compile a history of star formation over most

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Speaker 1: of the universe's lifetime. The scientists detailed their findings in

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Speaker 1: a paper published in eighteen in the journal Science. Measuring

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Speaker 1: starlight for most of the universe's history required considerable ingenuity

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Speaker 1: for the article. This episode is based on hows To

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Speaker 1: Forks obtained prepared remarks from a yellow via email. He

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Speaker 1: explained that the total amount of light emitted by stars

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Speaker 1: is comprised of two types. Quote. One is stellar light

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Speaker 1: that survives absorption by dust. This is what we measured.

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Speaker 1: The rest is stellar light absorbed by dust and re

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Speaker 1: emitted in the infrared. We are not sensitive to that.

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Speaker 1: It turns out half of the energy emitted by stars

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Speaker 1: across the history of the universe is reprocessed by stars.

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Speaker 1: At longer infrared wavelengths, the sky is filled with photons

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Speaker 1: emitted long ago by distant stars. This is called the

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Speaker 1: extra galactic background light, or e b L. And nevertheless,

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Speaker 1: except for the Moon and stars from our own galaxy,

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Speaker 1: the sky appears dark to our eyes according to a

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Speaker 1: yellow that's because most of the starlight that reaches Earth

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Speaker 1: from the rest of the vast universe is extremely faint,

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Speaker 1: the equivalent of a sixty watt lightbulb viewed in complete

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Speaker 1: darkness from about two point five million miles away. To

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Speaker 1: get around that problem, A. YAlO and his team perused

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Speaker 1: ten years of data from the FAMI telescope and looked

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Speaker 1: at the e b LS interaction with gamma rays emitted

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Speaker 1: by distant blazers. Blazers being black holes that can send

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Speaker 1: powerful streams of radiation out into the universe. The researchers

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Speaker 1: calculated the extent to which the gamma rays from those

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Speaker 1: blazers had been absorbed or altered by collisions with the

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Speaker 1: e b l's photons. A. Yelo describes tracking the e

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Speaker 1: b L as the astrophysicists equivalent of quote following the

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Speaker 1: rainbow and discovering a pot of gold. The e b

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Speaker 1: L is the rainbow, and its knowledge can finally disclose

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Speaker 1: a lot of useful information. The researchers technique enabled them

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Speaker 1: to see the history of star formation in the universe,

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Speaker 1: which they found had peaked about three billion years after

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Speaker 1: the Big Bang and has slowed dramatically since then. Slowed

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Speaker 1: but never completely stopped. The Milky Way, for example, creates

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Speaker 1: about seven new stars each year. A note that the

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Speaker 1: researchers count does not include the amount of starlight emitted

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Speaker 1: in the first billion years of the universe's existence. Yelo said,

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Speaker 1: this is an epoch we can't really probe yet. That's

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Speaker 1: one reason he and other scientists are looking forward to

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Speaker 1: the launch of the James Webb Space Telescope, which NASA

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Speaker 1: says will be sufficiently sensitive to detect the first stars.

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Speaker 1: It's currently set to launch on December. Today's episode is

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Speaker 1: based on the article how much starlight has been omitted

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Speaker 1: since the beginning of time on house to works dot com,

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Speaker 1: written by Patrick da Tiger Brainstuff is production of I

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Speaker 1: Heart Radio in partnership with house to works dot com,

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Speaker 1: and it's produced by Tyler Klang. For four more podcasts

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Speaker 1: from my heart Radio, visit the heart Radio app, Apple Podcasts,

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