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)]


Julio Villalobos says:

Who are the people that dislike these videos!?!?!?

[ FJX - 576 ] says:

The Universe lasted forever, before and since the beginning of time.

Zeratul Rus says:

So will the sun eventually turn into a cool, giant ball of carbon?

Ben Maghsoodi says:

I find it ignorant to suggest human species last billions of years.

Renae says:

"stars in the sky look prettyyy"
thanks phil

Govinda Dasu says:

I wonder why we have to live on a planet. We need to figure out a way of life that let's us live on man made structures floating through space.

Austin Prince says:

Very low mass/energy. Sad!

E Sotta says:

your videos are so entertaining and informative. i love them all

Admiral Trickster says:

Actually stars can live for 10 trillion years I read like 10 articles and i have seen like 10 more videos about dwarf stars and the all say the like a lot longer than you said

Dinofan 15 says:

phil's hair didn't last forever…………………

usernamesrlamo says:

Funny how he worries about sounding bleak, if a person is worried about the fate of the Earth six billion years from now, they were already quite bleak before watching this video.

Cherry_ _Wolf says:

so how exactly is the sun made?

TheSquigy says:

when our sun and stars of similar mass reach the end of their life and are just a giant ball of Carbon, would it be safe to assume that this carbon would cool into a diamond unit cell?

Ivan Benko says:

So low mass stars are basically Yoda-s of star world

nastropc says:

4:10 'The density in the Sun's core slowly increases. When you compress a gas it heats up"
But if the process in the core is 4p -> 1He shouldn't this decrease the pressure and, by Guy-Lussac's Law, decrease the temperature? (Assuming the extra energy released is radiated away)
Isn't the only way it can heat up for the core to be shrinking enough to offset the pressure decrease? Or am I missing something?

resoof says:


Sticky Situation says:

gas, grass or mass

Thomas West says:

Wait if our star is middle aged. What happens when is has a mid life crisis?

Elijah 314 says:

can a low mass star be a G spectral class or can it only be K and M?

Stop Lyin says:

hearing billion so many times takes the bang out of it, everything seems proximal, maybe everything should be expressed in thousands

U WOT M8 says:

so in red dwarfs, the hydrogen and helium go out an come in (only the hydrogen) in a cycle?

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