Neutron Stars

It is commonly known that the sun is the densest object in our universe. It is quite interesting to know that there are bodies in the solar system that are denser than the sun. One such body is the neutron star. The neutron star is the densest object in the universe except for black holes. Its mass would be around 1.4 times that of the sun. Neutron stars have different properties that help us better understand their structure and existence.

Neutron star

A neutron star is the collapsed core of a massive star. The neutron star mainly consists of neutrons and small quantities of mixtures of protons and electrons. This dense object can be observed by the astronomers directly. The neutron stars also have a limiting mass. To become a neutron star, the collapsing core of the massive star must be between 2 and 3 solar masses. If the collapsing core of the massive star exceeds this limit, it cannot be stopped at the densities of the neutron star because of the pressure gradient and it collapses further to form a black hole.

Stars with a total original mass of 10 and 25 solar masses form cores of 1.4 solar masses. They then become supernovae and leave a neutron star. Thus, the radius of the neutron stars is about 6 miles(10 kms) and the mass is about 1.4 solar masses. Normally the solar mass is represented by M0.

Neutron star gravity and neutron star density

The Neutron star’s gravity is about 2×10¹¹(or 2 billion) times stronger than on earth.The neutron star’s gravity functions as a gravitational lens as it is strong enough to bend radiation from the neutron star. The neutron star’s density is about 3.7×10¹⁷ to 5.9×10¹⁷kg/m³, while the earth’s density is about 5×10³kg/m³. In simple terms, a teaspoon of neutron star would have material of about 5.5×10¹²kg/m³, which is several billion tonnes.

Discovery of neutron stars

Walter Baade and Fritz Zwicky proposed the existence of neutron stars in December 1933 and published a paper in January 1934.

In the supernova explanation, neutron stars occurred by the conversion of ordinary stars into massive enormous stars consisting of closely packed neutrons. Later a radio astronomer named Antony Hewish and his assistant Jocelyn Bell founded pulsars, quickly spinning and highly magnetising radio pulses from the stars. 

Neutron star pressure and temperature 

The isolated neutron star’s temperature is around 106K (kelvin), as much of the energy is carried away by many neutrinos. However, a newly formed neutron star’s temperature will be around 10¹¹ to 10¹² kelvins. Moving from the inner crust to the centre, the pressure of the neutron star is increased from 3.2×10³¹ to 1.6×10³⁴Pa (Pascal). 

Radiations of a neutron star

• The neutron stars normally pulse radio waves that are quickly spinning and highly magnetised, called the pulsars.The spinning and acceleration takes place around the magnetic poles.The pulsars of neutron stars around the magnetic poles are termed as magnetospheric radiation.

• Some young and isolated neutron stars, called the non pulsating neutron stars, possess the characteristics of x-rays.

• Electromagnetic radiations such as the x-rays, gamma rays, ultraviolet and near infrared rays etc are also found.

Examples of neutron stars

Some of the notable neutron stars are 

• PSR J0108-1431

• PSR B1509-58

• PSR B1257+12

• LGM-1

• Black Widow Pulsar 

• Swift J1818.0-1607

Conclusion

We now understand what a neutron star is and the manifestations of neutron stars in our galaxy. We have learnt interesting facts about the neutron star, including its tremendous density and gravity.