What is a Neutron Star? Let us put it this way, “It is the living corpse of a dead star”! Sounds weird, right? Don’t worry! We will walk you through the explanation. But before we start with our explanation through 20 interesting Neutron Star facts, we strongly recommend that you read our two earlier posts:
The reason you should read them is that you will get a quick background about the types of stars that lead to the formation of Neutron Stars. So, let us begin.
Interesting Neutron Star Facts: 1-10
1. Neutron stars are formed from stars that has initial mass of at least 8 Solar Masses (M☉) as main sequence stars.
2. Over billions of years, these massive stars burn out their fuel, leaving behind a white dwarf star that features a core rich in iron. At this stage, the electron degeneracy pressure at the core tries to balance out the inward gravitational pull of the dense mass.
3. However, some helium and hydrogen still continue to fuse at the outer layers of the white dwarf and further iron is produced which travels towards the core. This happens over several billions of years.
4. As the iron deposit continues to grow, the electron degeneracy pressure at the core fails to nullify the inward gravitational pull of the accreting mass because of shell burning. As gravitation takes over, the white dwarf starts collapsing on itself.
5. This collapse increases the temperature of the core to about 5×109 Kelvin. At this temperature, high energy gamma rays are produced, which breaks down the iron nuclei into what is known as alpha particles.
6. This is when temperature increases even more and starts fusing protons and electrons of iron atoms into neutrons and in the process, releases neutrinos. This is when the density of the core continues to increase and reaches the figure of 4 x 1017 kg/m3. This actually is the density of the nucleus present in the atom and is known as nuclear density.
7. When the nuclear density is achieved, the gravitational collapse is halted because now, instead of electron degeneracy pressure, the gravitation tug is balanced out by outward pressure of neutron degeneracy.
8. At this stage, the matter that was falling in from the shell of the white dwarf no longer falls in. Rather, in a stellar explosion, the matter is thrown out in space. This is known as supernova explosion.
9. After the supernova explosion which is either Type II or Type Ib, only the very dense core is left behind. This is the Neutron Star.
10. The dense Neutron Star left behind has a number of unusual properties. The most notable of all is its extreme density and miniscule size. When we say miniscule (in context of celestial bodies), we actually mean size smaller than the size New Delhi.
Interesting Neutron Star Facts: 11-20
11. In such a small size, the Neutron Star packs the mass of around 1.1 M☉ to all the way up to 3.0 M☉. Can you imagine it? Well, let us try it this way. If you can squeeze the star which is 1.1 times to 3 times bigger than our Sun and put that mass inside New Delhi, what kind of density do you think will be achieved?
12. In fact, scientist say that kind of mass is packed within a diameter of 24 to 26 kilometers. If someone somehow manages to scoop out a matchbox full of matter from Neutron Star, the weight of the matchbox will be nearly 5 trillion tons! Put in Earth’s perspective, about 1000 cubic kilometers of rock on Earth weighs 5 trillion tons.
13. Neutron Stars also spin at an extremely high speed. They complete one rotation within a timeframe of 1.4 milliseconds to 30 seconds.
14. Because of the extreme mass of Neutron Stars they have surface gravity higher than that of Earth by 1011 times. That is, 100,000,000,000 times higher gravity than Earth! With such high gravity, the escape velocity of a Neutron Star ranges between 100,000 to 150,000 km/s. This is anywhere between 1/3rd and ½ the speed of light which 300,000 km/s.
15. As far as the structure of a Neutron Star is concerned, current mathematical models estimate that a typical Neutron Star has four layers: Outer Crust, Inner Crust, Outer Core and Inner Core.
- Outer Crust: Has a thickness between 0.3 and 0.5 kilometers. It is made up of electrons and ions.
- Inner Crust: Has a thickness between 1 and 2 kilometers. It is made up of nuclei, neutrons and electrons.
- Outer Core: Has a thickness of approximately 9 kilometers. It is made up of neutron-proton Fermi liquid and a few percentage of electron Fermi gas.
- Inner Core: Has a thickness between 0 and 3 kilometers. It is thought that the inner core is made up of quark gluon plasma.
16. There are different variants of Neutron Stars available. The most popular ones are Pulsars and Magnetars. Again, there are hypothetical variations like Quark Star, Electroweak Star and Preon Star. We will cover these in separate articles.
17. Since the Neutron Stars rotate at extremely high speed and they have extreme gravity, the spin produces strong magnetic fields. Because of this, Neutron Stars emit radiation from their spin axes.
18. Neutron Stars are known to spin several times in a single second. Gradually they do slow down but the spin down or the slowdown of these stars are very slow. Just how slow this spin down can be? For the purpose of simplicity, let us assume that a Neutron Star spins only once in one second. It will spin down at a rate of 10-10 to 10-21 seconds for one rotation. This means that the star will slow down and complete 1 rotation in 1.000003 seconds after 100 years and it will take 1.03 seconds for one rotation in 1,000,000 years!
19. As of now, scientists estimate that there are 2000 Neutron Stars in our Milky Way galaxy and most of them are Radio Pulsars. The most massive of all know Neutron Star so far is PSR J0348+0432 which is estimated to have a density of 2.01+0.04 M☉ or 2.01-0.04 M☉.
20. The closest Neutron Star (the one that the closest to our Earth) is PSR J0108-1431 and sits at a distance of 130 parsecs (which is equal to 424 light years).
Image credit: ESO/L. Calçada