A white dwarf doesn't collapse against gravity because of the pressure of electrons repelling each other in its core. A red giant star with more than 7 times the mass of the Sun is fated for a more spectacular ending. These high-mass stars go through some of the same steps as the medium-mass stars. First, the outer layers swell out into a giant star, but even bigger, forming a red supergiant. Next, the core starts to shrink, becoming very hot and dense.
Then, fusion of helium into carbon begins in the core. When the supply of helium runs out, the core will contract again, but since the core has more mass, it will become hot and dense enough to fuse carbon into neon.
In fact, when the supply of carbon is used up, other fusion reactions occur, until the core is filled with iron atoms. Up to this point, the fusion reactions put out energy, allowing the star to fight gravity. However, fusing iron requires an input of energy, rather than producing excess energy.
With a core full of iron, the star will lose the fight against gravity. The core temperature rises to over billion degrees as the iron atoms are crushed together. The repulsive force between the positively-charged nuclei overcomes the force of gravity, and the core recoils out from the heart of the star in an explosive shock wave. In one of the most spectacular events in the Universe, the shock propels the material away from the star in a tremendous explosion called a supernova.
The material spews off into interstellar space. The fate of the left-over core depends on its mass. If the left-over core is about 1. If the core is larger, it will collapse into a black hole. To turn into a neutron star, a star must start with about 7 to 20 times the mass of the Sun before the supernova. Only stars with more than 20 times the mass of the Sun will become black holes.
Advanced Basic Stars A star is a sphere of gas held together by its own gravity. Tell me more about the Sun A star's life is a constant struggle against the force of gravity.
Diagram showing the lifecycles of Sun-like and massive stars. Stars Stars are the most widely recognized astronomical objects, and represent the most fundamental building blocks of galaxies.
Star Formation Stars are born within the clouds of dust and scattered throughout most galaxies. Black Holes. The Big Bang. Helpful Links Organization and Staff. Astrophysics Fleet Mission Chart. Spacecraft Paper Models. Related Content Mysteries of the Sun. Death of Stars video. Life Cycles of Stars. More About Stars. Stellar Evolution. Recommended Articles. August 19, July 29, July 06, Nancy Grace Roman's Legacy. May 20, Ask a Question. Average Stars Become White Dwarfs For average stars like the Sun, the process of ejecting its outer layers continues until the stellar core is exposed.
This dead, but still ferociously hot stellar cinder is called a White Dwarf. White dwarfs, which are roughly the size of our Earth despite containing the mass of a star, once puzzled astronomers - why didn't they collapse further? What force supported the mass of the core? Quantum mechanics provided the explanation. Pressure from fast moving electrons keeps these stars from collapsing.
The more massive the core, the denser the white dwarf that is formed. Thus, the smaller a white dwarf is in diameter, the larger it is in mass! These paradoxical stars are very common - our own Sun will be a white dwarf billions of years from now.
White dwarfs are intrinsically very faint because they are so small and, lacking a source of energy production, they fade into oblivion as they gradually cool down. This fate awaits only those stars with a mass up to about 1. Above that mass, electron pressure cannot support the core against further collapse.
Such stars suffer a different fate as described below. White Dwarfs May Become Novae If a white dwarf forms in a binary or multiple star system, it may experience a more eventful demise as a nova.
Nova is Latin for "new" - novae were once thought to be new stars. Today, we understand that they are in fact, very old stars - white dwarfs. If a white dwarf is close enough to a companion star, its gravity may drag matter - mostly hydrogen - from the outer layers of that star onto itself, building up its surface layer.
Meanwhile, the heavy elements coalesce together, eventually forming planetary systems around the stars in the nebula. By studying supernovae, researchers not only grow to understand the life cycles of these massive stars, but also the origins of the planets too.
There are two main categories depending on how much hydrogen is seen in the afterglow — Type I supernovae contain a small amount of hydrogen, Type II contain more.
Type II supernovae originate from the biggest stars, which have a very short lifespan so their outer layers of hydrogen gas are still intact when they explode.
But slightly smaller stars might lose this layer over time, either through their own solar wind or because a neighbouring star strips away the gas. In Type Ib supernovae, the outer layer of hydrogen has been lost, while Type Ic have shed their helium as well. Type Ia supernovae, meanwhile, are created by smaller stars that get locked in a tight binary pair with a smaller white dwarf.
Over time, the white dwarf steals material away from its neighbour, until it reaches the critical mass to cause an explosion. This means astronomers can work out how far away one happened, and so they can be used to trace out distances in the Universe. Her first book about the history of robotic planetary landers is out now from The History Press.
Home Science When stars collapse: what is a supernova? Over time, the white dwarf steals material from its neighbour and eventually explodes, causing a Type Ia supernova.
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