Celestial Tour: A Star’s Fight for Life—Star Life Cycles

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When you look up at the night sky, the stars seem peaceful and eternal. But the stars are alive--they are born and they die, sometimes catastrophically.

Produced by the Space Telescope Science Institute’s Office of Public Outreach in collaboration with NASA’s Universe of Learning partners: Caltech/IPAC, Center for Astrophysics | Harvard & Smithsonian, NASA Jet Propulsion Laboratory, and Sonoma State University
All images, illustrations, and videos courtesy of NASA, ESA, and STScI except:
  • Taurus constellation drawing from Firmamentum Sobiescianum sive Uranographia by Johannes Hevelius, courtesy of the United States Naval Observatory
  • Winter Circle star field image created with Stellarium
  • Omega Centauri ground-based image courtesy of F. Lehman (South Florida Dark Sky Observers)
  • Photo of night sky at twilight courtesy of ESO/H. H. Heyer
  • Milky Way star field photo courtesy of ESO/C. Malin
  • Orion Nebula 3D animation courtesy of ESO/M. Kornmesser
  • Star formation animation courtesy of NCSA/NASA/A. Kritsuk and M. Norman (UC San Diego) and A. Boley (Univ. of Florida)
  • Photo of the Milky Way over the Austrian Alps copyright Babak A. Tafreshi (TWAN)
  • Written by Vanessa Thomas
  • Designed by John Godfrey

A blazing orange star. Text, A star's fight for life. 
The horizon glows faintly under a night sky full of stars and the long pale mottled stripe of of the milky way. Text, When you look up at the night sky the stars seem peaceful and eternal. But the stars are alive, they are born and they die, sometimes catastrophically. To stay alive, stars must fight a constant battle against gravity, a battle they ultimately will lose. 
A three dimensional nebula in space, a pale yellow cloud colored purple, red, and green at the edges, filled with glowing stars. Text, Stars are born in giant clouds of gas and dust called nebulae. Gravity builds a star by drawing gas together tighter and tighter. An animation of small particles floating in reddish gas. Text, When a clump of gas gets hot and dense enough, hydrogen atoms smash and fuse together forming helium and releasing energy. the particles collide and combine, and small waves and particles of energy are released. Text, A star is born. A glowing spherical object in the clouds. Yet gravity doesn't give up once a star is born. An animation of arrows pushing inward in a ring around the star. Gravity relentlessly works to crush the new star ever smaller. However, the star fights back. Arrows push outward from the rim of the star. Its fusion of hydrogen to helium releases energy which applies an outward pressure. 
This counteracts the inward crush of gravity. As long as the star keeps fusing atoms, it stays alive. 
A star's lifespan and its ultimate fate depend on how massive the star is. with more mass comes more gravity. 
The most massive stars go through nuclear fusion at greater rates than smaller stars, allowing them to resist the greater gravitational stress they're under. 
They run out of fuel much faster than less massive stars. When a massive star runs out of nuclear fuel, gravity takes over and the star's core collapses. 
The animated star shrinks and bursts into white light. Text, The collapse generates tremendous amounts of energy which blows the star apart in a supernova explosion. The white dissipates into space. Text, The most massive stars can exhaust their fuel and explode after just a few million years of life. 
The daintiest of stars however can live for many billions of years. 
In fact, in the 13.7 billion year history of the universe none of the least massive stars in the cosmos has died. A small orb glowing deep red. We do not know how these stars will end their lives. 
Our sun is between these extremes. It will live for about 12 billion years in total. When the sun runs out of hydrogen to fuse, gravity will start to take over and crush our star. 
The pressure will turn up the heat inside the Sun, starting new nuclear reactions in its center. 
These new nuclear reactions will fight back gravity, and the star's outer layers will expand, turning the Sun into a "red giant." 
Text, eventually, the star will lose its gravitational grip on these outer layers and they will gently float away. 
Meanwhile, the core of our sun will be squeezed by gravity to the size of planet earth. 
this stellar remnant, called a white dwarf, will slowly cool down. 
Our sun will send the rest of its days as a victim of gravity and a phantom of what it once was. A small white glowing sphere.