Have you taken an interest in white dwarf or neutron stars, but aren’t sure of what they are?
In this article, you’ll find a detailed description of both neutron and white dwarf stars, how they are formed, along with a comparison between the two.
White Dwarf vs Neutron Star (Explained)
Summary
The main difference between a white dwarf and a neutron star is the way in which they’re formed.
Both are products of ‘dead’ stars that have stopped producing nuclear fuel.
White dwarfs are formed from low mass to medium mass stars, such as the sun, whereas neutron stars are formed from stars with much higher mass.
For this reason, the sun will never become a neutron star.
What Is a Neutron Star?
When a star with a large mass reaches the end of its life, it explodes as a supernova.
The core of the star will collapse, creating a small, superdense object with a mass of around double to our sun.
The dense cores from exploded stars are called neutron stars.
Neutron stars are amongst some of the most bizarre objects in the universe.
These are the smallest known stars, only stretching to the size of an earthly city with a radius of 10 miles.
Our sun has about 100 times the diameter of the earth, yet, a neutron star has more material.
Despite its small size, a neutron star can have between 1.4 to 2 times the amount of mass of the sun.
A mere teaspoon of a neutron star would weigh around 4 billion tons; to compare, that’s more than the entire weight of Mount Everest.
There are around 1 billion neutron stars, however, with an estimated 400 billion stars in the Milky Way, neutron stars are a rarity making up only 0.25% of the total star population.
What Is a White Dwarf Star?
White dwarf stars are also the final evolutionary state of ‘dead’ stars that have exhausted their nuclear fuel.
Stars with a low to medium mass (anything less than 8 times the mass of the sun), will expel into white dwarfs.
One day, in around 5 billion years’ time, our sun will too become a dwarf star.
When a star with low to medium mass nears the end of its nuclear burning stage, it expels most of its outer material creating what’s known as a planetary nebula.
Only the hot core of the star will remain, becoming a white dwarf.
The original temperature of a white dwarf will exceed 100,000 Kelvin, and cool down over the next few billion years.
Neutron stars are the only star that surpasses a white dwarf’s density.
Although a white dwarf is only slightly bigger than the earth, they have around half the mass of the sun, and 200,000 times the mass of the earth.
White Dwarf vs. Neutron Star – How Are They Similar?
- A white dwarf is the corpse of a low-mass star, whereas a star with a high mass ends their lives as a neutron star or a black hole.
- White dwarfs are countered by electron degeneracy which prevents any further gravitational collapse, but electron degeneracy is not sufficient to prevent a neutron star from gravitational collapse. They are however partially supported from gravitational collapse by neutron degeneracy.
- Dwarf stars are around 600 times bigger than neutron stars.
- At birth, a neutron star spins much faster with around 716 rotations per second. A white dwarf will only fully rotate every 25 seconds.
- Although neutron stars produce no heat, they are still hotter than white dwarf stars. At the core of a white dwarf, the temperature at birth is around 180,000 degrees Fahrenheit. At the core of a neutron star at birth, it is around 1.8 million degrees Fahrenheit.
- Neutron stars are the only stars with a higher density than white dwarfs.
What Are White Dwarf Stars Made Of?
Although only the outermost stellar layers of a white dwarf are accessible to astronomical observation, we do know that the typical central region is composed of a combination of oxygen and carbon.
Surrounding the central region is a thin envelope of helium, and in most cases, there is an even thinner layer of hydrogen.
On rare occasions, a white dwarf could also have an envelope of carbon.
White dwarf stars will continue to generate light.
This is caused by a steady release of the prodigious energy that has been stored through billions of years spent as a powerhouse.
It is the combined pressure from the electrons that hold up the white dwarf, preventing further gravitational collapse.
How Many White Dwarf Stars Are There?
Amongst the hundred star systems nearest the sun, there are currently thought to be 8 white dwarfs projecting their unusual faintness.
However, within the Milky Way there are around 10 billion white dwarf stars.
This is a result of many sun-like stars reaching the point of ‘dying’, signifying a coincidental reflection on the current age of the universe.
According to UCSC News, approximately 90% of all stars end their lives as white dwarfs.
How Does a White Dwarf Star Die?
Technically a white dwarf is already considered ‘dead’ because the atoms inside of it no longer fuse to give the star energy.
However, since the star continues to produce heat for billions of years afterward it still has detectable light, therefore it ‘shines’.
Although it will take hundreds of millions of years, white dwarfs will too eventually completely cool.
The white dwarf will exhaust all of its carbon, oxygen, and free-flowing electrons and slowly burn out.
When this happens they turn into a black dwarf, known as the true death of a star.
Black dwarfs are theorized objects made of electron degenerate.
They produce very little (if any) heat or light of their own.
At this stage, the star will no longer be visible.
Conclusion
Neutron and white dwarf stars share some compatibility due to the fact that they are both the final evolutionary state of ‘dead’ stars.
Despite this, there are several differences.
They vary in size, temperature, rotational cycles, and quantity.
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