IF A NEUTRON STAR ENTERED OUR SOLAR SYSTEM

Our universe consists of around 2 x 10^24 stars and around 100 billion galaxies. But the numbers are not fixed. Every moment, a star dies  a new one is formed. These massive celestial objects are the source of almost infinite energy. They could be the reason for life somewhere else  just like our sun. The sun is a major reason for the existence of life on Earth. These stars may look immortal from our perspectives but as we know, everything comes to an end. And when a star dies, it gets converted into a Neutron star. But first, we need to properly understand what a neutron star is.

  

WHAT IS A NEUTRON STAR

A star is a gigantic luminous ball of ionized gases or plasma, held by their own gravity. They consist of a dense core which comprises of gases like Hydrogen and Helium ( the star nearest to our Earth is our Sun). The temperature and pressure in these cores are so high due to the nuclear fusion reactions taking place, converting Hydrogen atom to Helium atom. The stars are so massive that they tend to collapse on their own due to their gravity. But this gravitational pull is countered by the pressure exerted by the nuclear fusion reactions going on inside the core. After a long period of time, the stars runs out of fuel due to which they do not have any resources to undergo nuclear fusion. And as a result they gets collapsed on their own due to their gravitational pull causing a small supernova. The upper crust gets spreaded into the space with a burst and its dense core keeps collapsing on its own.  Now we know the nuclear forces are attractive for a fixed distance and after that distance they become repulsive. That distance is usually 1.0 x 10^-15 metres. But what if they are pushed even further overcoming this force of repulsion and scrouching the protons and electrons together. They'll get combined and will turn into neutrons. Now in the case of a collapsing star, if this process keeps going on, then the star will be converted into a Neutron star "the big bad villain of the space".  So in short we can say that when a star runs out of fuel, its core collapses on its own creating a monster called "Neutron star".

Now why we need to replace sun here, can't our sun become a neutron star under a millions of years of time. Well the answer is quite simple.  The basic requirement for a star to get converted into a Neutron star is that its mass should be 1.4 solar masses(1.4 times the mass of our sun). This limit is called the Chandrashekhar Limit. Above this limit, the protons and electrons combines to form neutrons. Thus when our sun runs out of fuel (around 5 billion years), it will basically turn into a White dwarf instead of a Neutron star.

SOME FACTS ABOUT THE NEUTRON STAR

Now after understanding what a Neutron star is. Let's see what a Neutron star can do and what will be its effect if one entered our solar system. At first, Neutron star has a mass of 1.4 solar masses (or 1.4 x 1.98 x 1034  kg) packed in a sphere of radius of about only 10 kilometers. That's why they have a gravity around 2 billion times stronger than our Earth. This number is so much huge that they literally bend the light or radiations coming from distant stars or galaxies. This process is called Gravitational Lensing. And if they encounter a second star less massive than a sun, then just pulls of the mass from the companion star into its Roche lobe(a region around the star in which the material is bounded gravitationally with it). Furthermore for making them even more dangerous, a Neutron star, after the supernova, has a spin of about 700 times in one second conserving the angular momentum, and thus releasing huge amount of electromagnetic waves into the space, of course decreasing over a period of time. They do not rotate only, but they also have the linear motion of about 1/4 th of the speed of light which makes them even more dangerous as they can join the party as an uninvited guest.

WHAT IF IT ENTERS OUR SOLAR SYSTEM

Now let us discuss what will happen if one of these monsters entered our solar system. The results will totally depend upon the path of its trajection. Let us  say first it is headed towards the Earth. In this case the results will be most lethal. As soon as it enters the solar system, due to its strong magnetic fields, it will have an impact on the things made up of iron, nickel, steel etc. For example, our credit card's data will be lost, compass will stop working and the electric appliances which contains metals such as iron, cobalt or nickel will be malfunctioned. Furthermore, the nearby planets will be displaced from their orbit as they will try to revolve around the new cosmic entity due to its huge gravitational pull. And as it reaches a distance of 1000 km from the planets, it will start feeding on them. Yeah, the big mouth devourer in the space. The same will happen to the earth depending on the path the neutron star takes. So the Earth will leave its orbit and will be thrown out of its Circumstellar Habitable Zone( a habitable zone for a planet revolving around the star where temperature and pressure are sufficient so that the liquid water exists). As soon as the it crosses its habitual zone, all the water on the planet will start freezing due to the absence of the heat reached from the sun or respective star. This will cause a new era of ice age but much more intense this time. Everything, literally everything will freeze due to the immense fall in the temperature. This will lead to the end of humanity. 

In addition to this, it will affect our asteroid belt and will alter the movement of the asteroids, tossing around 1.9 million of asteroids into the space. Some of them may head towards our Earth causing a Meteor shower.

Now say, the Earth is headed towards our star. what will happen now. As we know the Neutron stars have huge amount of energy packed in them, so the heat coming out of it will be very high than that of our sun. So due to the intense heat, the temperature will start rising at a very high rate. So all the ice will melt, causing large scale global warming. Not only this, the heat will be so much that everything dry such as trees, bushes, clothes etc. will tend to catch fire burning all the surroundings. And as it approaches near, humans will be pulverized due to that intense heat. If it came more closer, our Earth will be stretched and ripped apart by its gravitational force. Scientists call it 'Spagettification'.

So extreme cold, immense heat or huge chunks of rocks, which way you like the most to die?

                                                         Image showing Binary stars

Now these all will be the impact on our planets, moon and asteroid belt. But what will happen to our Sun. Our sun itself is a big star so it will not be eaten by a small Neutron star. But as the star approaches the sun, it will suck all the gases from the surface of the sun and both of them will start revolving around each other forming a Binary star system. This is a system of 2 stars orbiting each other around a common centre, both bounded gravitationally.

Now it is difficult to say what will be the consequences on Earth because of this. but this will definitely affect the climate. In fact we could ever see 2 suns in the sky, leading to much much more brighter days and less darker nights.

Well, enough terrified from a Neutron star after reading through all of this. Don't worry, nothing like this is going to happen as the nearest neutron star plotted by the scientists is around 400 light years away which is more that enough of a safe distance. So a Neutron star is not going to kill you now. But hey, don't be so happy as there are other big monsters lurking in the space that can be even more dangerous. But that is a story for another "If it happens".

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Thank you for reading ;)