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What Is a Neutron Star? Differences, Facts & FAQ

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Eso1733q Artist’s impression of merging neutron stars

Space is full of wondrous objects that seem so otherworldly that we can barely wrap our heads around them. One such object is the neutron star.

If you compressed all the mass on Earth to the same density of a neutron star, it would be about a third of a mile in diameter. That’s an extremely dense object, and there are millions of neutron stars in the Milky Way alone.

A neutron star is one of the most mind-boggling objects out there, so we dedicated this article to these mystifying objects.

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What Is a Neutron Star?

Imagine something that weighs as much and has as much mass as the Sun squished down to the size of Chicago. That’s the general basis of a neutron star, although sizes can range between 1.18 and 1.97 solar masses¹.

The average mass of a neutron star is about 1.35 times that of the Sun, but they’re typically only about 12.5 miles across¹.

These objects might be small, but they have extremely large masses and are incredibly dense, so they have extremely strong gravitational pulls.

In fact, a piece of a neutron star the size of a sugar cube¹ has about the same mass as an entire mountain on Earth!

How Do Neutron Stars Form?

Colliding neutron stars ESA385307
Colliding neutron stars ESA385307 (Photo Credit: ESA, via Wikimedia Commons CC BY-SA 3.0 IGO)

Neutron stars form when extremely large stars run out of fuel and collapse on themselves. According to NASA and Hubble¹, any star with at least eight solar masses can turn into a neutron star¹.

However, it comes down to the core region of the star. The core of the collapsing star needs to have between one and three solar masses, as this is the amount of weight necessary to hold everything together.

If the core of the collapsing star is larger than that, it will continue to collapse, and a black hole will form instead of a neutron star¹.

How Common Are Neutron Stars?

Compared to other types of stars, neutron stars are relatively rare. In fact, for every 1,000 stars out there, there’s only one pulsar¹.

Still, since there are an estimated 200 billion trillion stars in the universe¹, there are likely about 1 quintillion neutron stars out there. (That’s a one with 18 zeros after it!) That’s a great deal of neutron stars! It also means that the Milky Way alone likely has between 1 and 4 million neutron stars.


Pulsar image
Photo Credit: Pixabay, StockVault

Most neutron stars out there are pulsars. Pulsars are essentially rapidly rotating neutron stars that emit pulses of radiation at regular intervals¹.

The exact science behind pulsars is complicated, but the result is that we see pulses of light turn on and off from these stars. It works much like a lighthouse, and you can only see the light from a pulsar when it’s pointing directly at Earth. When it’s shining in other directions, we simply can’t see it!


While pulsars make up the majority of neutron stars, another type of neutron star out there is the magnetar. Pulsars have strong magnetic fields, several trillion times stronger than the magnetic field on Earth¹.

But magnetars take it to a whole new level. They have magnetic fields that are about 1,000 times stronger than those of pulsars¹!

All these extra magnetic forces lead to a large amount of electromagnetic radiation anytime the crust of the star shifts. For reference, one observed shift of a magnetar’s crust¹ released more energy than the Sun has over the last 100,000 years. Even more impressive, the magnetar released this amount of energy in just 1/10 of a second.

What’s the Difference Between a Neutron Star and a Black Hole?

The difference between a neutron star and a black hole all comes down to the size of the core of the star before it runs out of energy. While both black holes and neutron stars form from the collapsing of giant stars, black holes form from even more massive stars than neutron stars.

Once they form, the biggest difference is that a black hole is so massive, nothing can escape it, not even light. While neutron stars bend light quite a bit¹, they also emit light. Black holes can’t do this, and it’s the primary difference between the two (that we know of).

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Neutron stars might seem like something straight out of science fiction, but the truth is that there are millions of neutron stars in the Milky Way and trillions upon trillions of them out in the universe.

The more that we learn about them, the more amazed we become, so if you’re interested in learning about the mystery of neutron stars and the rest of the universe, they’re a great place to start doing research!

Featured Image Credit: Eso1733q Artist’s impression of merging neutron stars (ESO/L. Calçada/M. Kornmesser, via Wikimedia Commons CC BY 4.0)

About the Author Robert Sparks

Robert’s obsession with all things optical started early in life, when his optician father would bring home prototypes for Robert to play with. Nowadays, Robert is dedicated to helping others find the right optics for their needs. His hobbies include astronomy, astrophysics, and model building. Originally from Newark, NJ, he resides in Santa Fe, New Mexico, where the nighttime skies are filled with glittering stars.