What can a collapsed star form?

CurioCity
23 January 2012

This article was reviewed and updated by the CurioCity Editing Team in August 2017.

Nothing, aside from a few light elements, would exist without stars. Stars are giant element-producing factories, and without those elements, you and I could not exist. You may not be a star, but you are certainly made up of star parts!

After a star is born, it goes through a sequence of events called stellar evolution. The elements that a star produces during its lifetime, and the ultimate fate of the star, depend mostly on its initial mass. Before we discuss what happens when a star collapses, let's take a quick look at the very beginning of the universe.

The Big Bang

Shortly after the Big Bang, the universe was extremely hot and dense. No atoms existed, and protons and neutrons existed freely. Over time, the universe expanded and cooled. Electrons and protons then combined to form hydrogen and helium, along with small amounts of the next three lightest elements: lithium, beryllium, and boron. During these early stages of the universe, elements heavier than boron did not exist. They didn't form until stars came along.

Stellar Evolution

Stars are born in nebulae, giant clouds of mostly hydrogen gas and dust. As the hot gas in the nebulae cools, it condenses and pockets of condensed gas form. Over time, gravity causes these pockets to become increasingly dense and massive, and they heat up and become protostars. As a protostar heats up, it eventually becomes hot enough for the "furnace" in the core of the star to turn on. In the core, nuclear fusion converts helium to hydrogen. Fusion produces a lot of energy, so much so that it creates an outward pressure. This pressure counteracts the force of gravity that wants to pull the star together and make it collapse.

When stars use up their hydrogen fuel, they continue to evolve. How they do so depends on their initial mass. Very massive stars are able to continue burning by fusing helium, which is turned into heavier elements like carbon, oxygen, and iron. However, when the fuel in the core of the star eventually runs out, gravity ultimately wins the epic battle with pressure - and the star collapses.

Stellar Collapse

Depending on the mass of a star, when it eventually collapses, it will form either a white dwarf, a neutron star, or a black hole. Smaller stars eventually become white dwarfs - very dense stars that no longer burn fuel. When mid-sized stars (like the Sun) collapse, they eject a glowing shell of gas, called a planetary nebulae, leaving a remnant core behind. The remnant core then becomes a white dwarf.

More massive stars go through a violent explosion called a supernova when they collapse. Through a process called supernova nucleosynthesis, elements heavier than iron are produced during supernovae. After the outer part of the star explodes, the remnant core becomes a black hole or a neutron star. The most massive stars form black holes. If a star is not quite massive enough to become a black hole, it will turn into a neutron star, which is made up almost entirely of neutrons.

So now you can see how important this question is. The remnant core of a collapsed star becomes one of three different things. But from the elements that stars have produced during their lifetime, including their collapse, they’ve ended up forming everything else, too!

Did you know? Our sun is, in fact, a star. Like all other stars, our sun is undergoing stellar evolution and will eventually collapse. Scientists are still debating over when this will occur and what it will mean for our planet, Earth.

Learn More!

Stellar Evolution (2009)
NASA Education

Life Cycle of a Star (2017)
National Schools’ Observatory

The Big Bang Theory (2016)
ESA Kids

Videos:

Stars (2015)
Neutron Stars (2015)
White Dwarfs and Planetary Nebulae
Crash Course Astronomy

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