What is a Neutron Star? - Mass, Density & Weight

Instructor: Jeff Fennell

Jeff has a master's in engineering and has taught Earth science both domestically and internationally.

Neutron stars are dense objects found throughout the universe. Composed of neutrons, they have more mass than the sun, but are only a few kilometers wide. This lesson will cover the properties of neutron stars.


A neutron star is composed almost entirely of neutrons, so let's first take a look at what a neutron is. Neutrons are found in the nuclei of every particle except hydrogen. A neutron is a fundamental particle of an atom, having approximately the same mass as a proton. It is located in the nucleus along with protons. A neutron has a mass equal to 1,838 electrons and a mass equal to 1.0014 protons.

Properties of a neutron

In order for a neutron star to form, high temperatures and pressures are needed. Such pressures and temperatures only occur in the aftermath of a supernova during the collapse of massive stars. The resulting neutron star is composed almost entirely of neutrons. Neutron stars are some of the densest known objects in the universe, with a diameter roughly equal to an average city, but a mass equal to nearly 500,000 Earths or 2 suns.

Structure of a neutron star
neutron star


In astronomy, large masses are usually measured in solar masses; one solar mass is equal to the mass of our sun (1.9891 x 10^30 kilograms). A typical neutron star has a mass between 1.3 and 2 solar masses. This means a neutron star can have twice the mass as our sun. For example, a neutron star named 1002.3825, discovered by Cornell University in the 4U region of the universe, was found to have a mass of 1.58 +/- 0.06 solar masses or 3.13 x 10^30 kilograms.


While the mass of neutron stars is almost beyond comprehension, the diameter is more within our normal range of measurement. The average range in diameter for a neutron star is only 10 - 20 kilometers. Going back to our example above, the neutron star 1002.3825 has a diameter of D = 18.22 +/- 0.80 km.

To unlock this lesson you must be a Member.
Create your account

Unlock Your Education

See for yourself why 10 million people use

Become a member and start learning now.
Become a Member

Already a member? Log In

Earning College Credit

Did you know… We have over 49 college courses that prepare you to earn credit by exam that is accepted by over 2,000 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Transferring credit to the school of your choice

Not sure what college you want to attend yet? has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

Click "next lesson" whenever you finish a lesson and quiz. Got It
You now have full access to our lessons and courses. Watch the lesson now or keep exploring. Got It
You're 25% of the way through this course! Keep going at this rate,and you'll be done before you know it.