neutron star facts
Neutron Star Facts
Spinning neutron stars or pulsars are the afterlife stage of high mass stars. These stellar remnants being the most spectacular objects in the universe, superseded in bizarreness only by black holes, the facts compiled in this article will certainly boggle your mind.
A Mountain in a Spoonful
Due to extreme compactification, a spoonful of a neutron star may weigh billions of tons, which is equivalent by mass, to a few mountains on Earth.Interesting Facts About Neutron Stars
Formation
Neutron stars are created in violent explosions called supernovas, triggered by gravitational collapse of massive stars, which have run out of fuel. The core of the massive star is compressed by intense gravitational pressure which results into a highly dense stellar remnant.
Any star that has a mass greater than 10 ten times the mass of our Sun (i.e. greater than 1.9891 × 1031 Kg), will most likely end up as a neutron star.
In such a high mass star, the crunching force of gravity is halted by the heat generated through fusion of progressively heavier elements, until the core becomes iron-rich, which is an element that cannot be fused further. At this point, the core starts collapsing due to the ceasing of fusion and the density goes on increasing, with the temperature rising to about 5 billion Kelvin.
At this point, a process called photodisintegration is triggered, which splits iron nuclei into alpha particles (helium nuclei). As the temperature goes on rising further, protons and electrons start fusing to form neutrons, which releases a dense flux of neutrinos.
As the climbing density reaches the mark of 4 x 1017 kilograms per cubic meter, the degeneracy pressure exerted by neutrons halts the collapse. This pressure arises due to the Pauli Exclusion principle which doesn't allow fermions like neutrons to occupy the same quantum mechanical state. This leads to an implosion, which ejects the entire outer envelope of the star, triggering a Type II or Type 1b supernova, with the core remaining at the center, forming a neutron star.
Just as a ballerina rotates faster as she wraps her hands around her body, the neutron star rotates very fast as its radius is reduced by gravitational compression. This happens due to conservation of angular momentum.
Considering the large decrease in radius during the collapse, the neutron star spins very fast, at a rate greater than 43,000 per minute, with periods ranging from 1.4 ms to 30 seconds. In a binary system, they can rotate at a rate greater than 600 per second due to mass accretion around them.
Neutrons stars form, only when the mass of the stellar core is greater than 1.44 solar masses, which is known as the Chandrasekhar limit. On the other hand, if the core mass is greater than 3 solar masses (known as the Tolman-Oppenheimer-Volkoff limit), it will most probably end up as a black hole, as even neutron degeneracy pressure won't be able to halt the gravitational collapse to a point of singularity. A star with mass in the range of 15 to 20 solar masses, will most certainly end up as a black hole.
Neutron stars are some of the most compact objects in the universe and due to compression, their surface gravity is phenomenally high, that is about 1011 times that of Earth. An object falling towards the star surface will be accelerated at about 1012m/s2 which will shred and rip it out into constituent atoms.
To escape from such a star's surface gravity, one would have to travel at a velocity of 100,000 km/s, which is about a third of the speed of light.
Properties
The stars are so dense that a spoonful of neutron star will weigh more than a mountain. A teaspoon of the star could weigh as much as 5 x 1012 kg.
Typically, a neutron star extends about 20 km in diameter. As depicted in the graphic presented below, such a star will be comparable in size to the island of Manhattan, but will weigh several times more than the Sun.
These stars have very high magnetic fields. The measured fields are in the order of 1012 Gauss, which is about 1013 times our Earth's magnetic field. They are the strongest magnets in the world. The rapid spinning of the magnetic field causes the creation of an electric charge and emission of electromagnetic radiation along the magnetic axis. This axis may not be necessarily pointed towards the Earth, as it is mostly non-aligned with the rotation axis. When it is pointed towards the Earth, we observe it as a pulsar.
Structure
The structure of a neutron star is nothing like any other object in the universe. Here are some facts about its dense and exotic structure.
The surface of the star at a temperature of about 1 million Kelvin, is made up of atomic nuclei of mostly iron, which are solidified in the form of a dense lattice.
The atmosphere is 1 meter thick and completely dominated by the intense magnetic field of the order of 1012 Gauss.
As you go deeper, density of the star increases and the core is populated by nuclei of high neutron numbers. The central core is supposed to be a superconducting fluid of protons and electrons.
Discovery
Neutron stars were first hypothesized right after discovery of the neutron, in 1933, by Walter Baade and Fritz Zwicky, to explain the triggering of a supernova.
In 1965, Antony Hewish and Samuel Okoye first discovered an object emitting radiation in radio waves, in the Crab Nebula, located in the Orion constellation. After intense research, it was confirmed to be a neutron star and later a rotating neuron star, called a pulsar. It is known as the Crab Pulsar (PSR B0531+21), which is one of the youngest known pulsars, created through a supernova, whose occurrence was recorded by Chinese astronomers on July 4, 1054.
Among the known neutrons stars, almost 5% are part of binary stellar systems (Two stars revolving around each other).
The closest known pulsar (PSR J0108-1431) has been detected at a distance of 770 light years, in the Cetus constellation.
PSR B1919+21 was the first radio-pulsar to be detected and was nicknamed as LGM-1 (denoting 'Little Green Men'), as its periodic pulse was prima facie suspected to be an intelligent signal from alien life forms.
PSR B1257+12 is a pulsar, located about 1000 light years away, that was the first to be detected with a planetary system. It has two planets revolving around it.
Magnetars are a type of neutron stars, known to possess extremely strong magnetic fields, emitting X-ray and gamma radiation.
A millisecond pulsar is a neutron star radiating X-rays and gamma rays, while spinning at a very high rate. Among the 200 such objects discovered so far, the first was PSR B1937+21, which was known to spin about 641 times per second. PSR J1748-2446ad is the fastest of the lot, spinning at a phenomenal rate of 716 times per second.
Neutron stars in the form of pulsars are a subject of intense research today. The various phenomena associated with their magnetic fields and emission spectra are particularly interesting. Hope this rapid fire overview of this unique astrophysical object has inspired you to explore stellar phenomena at a deeper level.