Low Mass Stars: Crash Course Astronomy #29

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Today we are talking about the life — and death — of stars. Low mass stars live a long time, fusing all their hydrogen into helium over a trillion years. More massive stars like the Sun live shorter lives. They fuse hydrogen into helium, and eventually helium into carbon (and also some oxygen and neon). When this happens they expand, get brighter, and cool off, becoming red giants. They lose most of their mass, exposing their cores, and then cool off over many billions of years.

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Table of Contents
Low Mass Stars Live a Long Time 0:57
Larger Stars (Like Our Sun) Live Shorter Lives 3:10
Fueled By Fusion 3:58
How They Turn Into Red Giants 5:45

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Stars http://skycenter.arizona.edu/sites/skycenter.arizona.edu/files/n6522_32in.jpg [credit: Adam Block/Mount Lemmon SkyCenter/University of Arizona]
The Sizes of Stars http://www.eso.org/public/usa/images/eso1030c/ [credit: ESO/M. Kornmesser]
Fusion in the Sun https://commons.wikimedia.org/wiki/File:FusionintheSun.svg [credit: Borb, Wikimedia Commons]
Mega Flares http://scitechdaily.com/images/Swift-Mission-Observes-Mega-Flares-from-a-Mini-Star.jpg [credit: NASA’s Goddard Space Flight Center/S. Wiessinger]
Proxima Centauri https://www.spacetelescope.org/images/potw1343a/ [credit: ESA/Hubble & NASA]
Physics in the Core http://solarscience.msfc.nasa.gov/images/cutaway.jpg [credit: NASA / Marshall Space Flight Center]
Three Years of SDO Images http://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=11255 [credit: NASA’s Goddard Space Flight Center/SDO]
Sun & Red Giants http://kepler.nasa.gov/files/mws/kasc3.jpg [credit: NASA]
Sun as Red Giant https://commons.wikimedia.org/wiki/File:Sun_red_giant.svg [credit:Oona Räisänen, Wikimedia Commons]
Gone with the Wind https://www.eso.org/public/usa/images/wr124/ [credit: ESO]
Expanding & cooling https://www.cfa.harvard.edu/sites/www.cfa.harvard.edu/files/images/pr/2009-23/1/base.jpg [credit: ESO/L. Calçada]
Looking down a barrel of gas at a doomed star http://hubblesite.org/newscenter/archive/releases/1999/01/image/a/ [credit: The Hubble Heritage Team (AURA/STScI/NASA)]
Expanding star orbit http://www.nasa.gov/centers/goddard/images/content/415775main_earthlike-exoplanet-full.jpg [credit: SO/L. Calçada]
Red Giant Earth https://commons.wikimedia.org/wiki/File:Red_Giant_Earth.jpg [credit: Fsgregs, Wikimedia Commons]
Crab Nebula https://en.wikipedia.org/wiki/Crab_Nebula#/media/File:Crab_Nebula.jpg [credit: NASA, ESA, J. Hester and A. Loll (Arizona State University)]


Eric Loesch says:

Emo Phil was amazing.

Nicklas Hansson says:

Is this guy by any change related to Adam Savage?

The similarities in both apperance and the way they talk is striking.

Adriano Kury says:

Excellent video!

GokaiTitan says:

This series are really helping me with my Astronomy class 🙂 Thank you so much everyone at CrashCourse!

Blue says:

Thank you for that Interstellar quote Phil :D

Andrea Ramirez says:


Colin Warn says:

6:50 "At some point the core will contract…"


accordeonist says:

oh gawd. So depressing.

joesette spinner says:

watching YOUTUBE in science class crash course is great

Penny Lane says:

Wait, if the Sun got 40% hotter just by the core getting denser, that means about a third of its luminosity doesn't come from fusion but just from the Sun passively collapsing in on itself? That's mind-boggling. I mean, that's the same heat source Brown Dwarfs use and you don't see them boiling Earth's oceans in a billion years. They just slowly cool and die.

Naruedyoh says:

I love Crash Course, but i hate the American Billions and Trillions. Makes it harder for the european

Mallu hima tejeshwar reddy says:

the most emotional episode of the astronomy crash course

titop 222 says:

Sooo we have 7 billion years to figure out how to establish life on another planet… I like those odds.

Hyunjin Park says:

Even in this universe, love lasts forever.

Ron Arguelles says:

I'm curious, when fusion finally ceases, would there be anything left of our sun's core? say a planet sized Diamond?

Ryan McAleer says:

So, right after the first hydrogen phase it enters red graint phase?

judas30 says:

03:23 So the core for bigger mass stars is just like Las Vegas.

ChillsandThrills says:

Do you guys believe we were meant to just die like this?

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