Information



Tags



Share

Which types of stars become pulsars by collapsing into themselves?

Advertisement:


read_later

Read Later

Keywords



Keywords



read_later

Read Later

Information

Tags

Share





Advertisement

Advertisement



A pulsar is the last living sparkle of a dying star that its mass is high enough to preserve its core rotating, and the last way to resist collapsing into a black hole by being forced the gravitational force. Stars that its fusion force in their centre is not enough to support their core against the gravitational collapse start to lose volume by increasing the density of its core. Hence, the dying stars are getting smaller at the end of their life circles(a star's life circle) as balloons having leaks.

Figure - 6.1


Figure - 6.2

A pulsar had been a massive star during the beginning of its life in the universe. When massive stars collapse, their cores reach to the Chandrasekhar limit (approximately 1.4 M☉ or 2.765×1030kg) as a result of that a massive star cannot withstand against the gravitational force of its core through electron degeneracy pressure as a white dwarf can. Exceeding the Chandrasekhar limit causes a type II supernova and allow electrons and protons to combine for forming neutrons by increasing the heat of the core. According to NASA, “The second type of supernova occurs at the end of a single star’s lifetime. As the star runs out of nuclear fuel, some of its mass flows into its core. Eventually, the core is so heavy that it cannot withstand its own gravitational force. The core collapses, which results in the giant explosion of a supernova(1).” Once electrons and protons combined to form neutrons due to the heat of the core, neutron degeneracy pressure is the only thing resisting to the gravitational force in the core of the star. As to stellar evolution, the remnants of a type II supernova are called a neutron star. Because of the ballerina effect, every spinning object wants to retain their spins without changing the angular momentum hence neutron stars rotate rapidly (such as PSR J1748-2446ad spins 716 times per seconds(716 Hz)). The rapid-spinning of extremely massive and dense objects like neutron stars causes to beam electromagnetic radiation via very high rotation speed, which is the explanation of why pulsars are “blinking”.

Figure - 6.3


Figure - 6.4

According to Antony Hewish, the age of pulsars; “The ages of pulsars are estimated from accurate timing measurements, which show that, in general, their pulse rates are steadily slowing down. According to the aforementioned “lighthouse” theory, the decrease is due to the neutron star’s spinning more slowly and losing energy(2).”, the distance of pulsars; “The radio signals from pulsars also tell us something about their distances from the earth. We already know that the Crab pulsar is 6,000 light-years from us, by the study of its light. But distances of invisible pulsars can only be estimated roughly from the different wavelengths of the pulses, which arrive on earth at slightly different times(3).”, the energy of pulsars; “Knowing the distances to the pulsars enables us to calculate how much energy they are radiating(4).”

Figure - 6.5


Figure - 6.6


Figure - 6.7

What happens to the Sun at the ending of its life circle according to Bob Berman; “Billion upon billions of years now pass, the Sun shining mainly by its stored heat alone. Its white-hot surface gets further temperature replenishments not from fuel, for it has none, but from tiny contractions in size. The gravitational energy conversion is so powerful that when this white dwarf Sun collapses one inch smaller, that supplies ten thousand years’ worth of white sunshine. But now its electrons have been squeezed as close together as possible, thanks to Wolfgang Pauli’s exclusion principle, and there’s not much wiggle room left for further contraction. This final power source comes to an end. Now it cools ever so slowly to become yellow, then orange, then red, eventually fading to brown and ultimately black(5).”

Figure - 6.8

References

(1) May, Sandra. “What is a Supernova?” NASA. 4 September 2013. Web. 14 June 2018. https://www.nasa.gov/audience/forstudents/5-8/features/nasa-knows/what-is-a-supernova.html

(2) Hewish, Antony. "Pulsars." The New Book Of Popular Science Vol-1. Grolier Incorporated, 1988. 233. Print

(3) Hewish, Antony. "Pulsars." The New Book Of Popular Science Vol-1. Grolier Incorporated, 1988. 234. Print

(4) Hewish, Antony. "Pulsars." The New Book Of Popular Science Vol-1. Grolier Incorporated, 1988. 234-235. Print

(5) Berman, Bob. "Tomorrow’s Sun." The Sun's Heartbeat: And Other Stories from the Life of the Star That Powers Our Planet. New York: Little, Brown and Company, 2011. 253. Print.




1 ) Exoplanets: Diamond Worlds, Super Earths, Pulsar Planets, and the New Search for Life beyond Our Solar System