We all know how weird black holes are, but did you know there is another type of star that is just as strange? Welcome to the universe of neutron stars.
First some background on star formation. Stars form when a massive cloud of hydrogen begins to collapse. The volume decreases, and the pressure and temperature increase. If the internal temperature reaches 15 million degrees Kelvin, hydrogen fusion begins to form helium and a star begins.
The type of star and its long-term fate depend upon the initial mass. A star with an initial mass of at least 8 times the mass of our Sun has the potential to become a neutron star. Over the lifetime of the star, it will go through various phases, gradually emitting energy; hence losing mass. Without going into great detail, such stars become red supergiants and then explode in a supernova. If the remnant core of the star is between 1 and 3 solar masses, then it is a neutron star. Remnants greater than this become black holes.
Neutron stars are the second most dense objects in the universe, exceeded only by black holes. A sugar cube of a neutron star has a mass roughly the same as all of Mount Everest. Neutron stars are only 12-15 miles in diameter, yet are more massive than our Sun.
All stars rotate, including neutron stars. Due to conservation of angular momentum, as neutron stars shrink in size, their rotational velocity increases. They can rotate as fast as several hundred times per second.
Neutron stars have very strong magnetic fields. Depending upon the orientation of its magnetic poles relative to Earth, astronomers observe pulses from neutron stars, much like the pulse of light from a rotating lighthouse. These are called pulsars. Most neutron stars are likely pulsars. However, we can only detect the pulses, if they are emitted in Earth’s direction.
The first pulsar was discovered in 1967 by Jocelyn Bell using the Interplanetary Scintillation Array radio telescope in Cambridge, England. While Bell and her supervisor Antony Hewish were unsure of the process that creates these pulses, they doubted they were due to intelligent life. Nevertheless, they nicknamed the object LGM-1 (Little Green Men), because all astronomers have a sense of humor. Now we understand the mechanism for the regular pulses and have identified several thousand pulsars.
In 1974, Antony Hewish and Martin Ryle became the first astronomers to be awarded the Nobel Prize in Physics for their research with radio telescopes… Hewish, specifically for his work on pulsars. Jocelyn Bell was not part of the award but still graciously congratulated both men.
Binary star systems are quite common in the universe. If BOTH stars are neutron stars, then they form a double neutron star system. Their mutual gravitational attraction results in their eventual coalescence. The interaction of the 2 immense gravitational fields generates gravitational waves that have been detected by the LIGO array on Earth, resulting in another confirmation of Einstein’s Theory of General Relativity.
Music written and produced by Kenny Mihelich. Western Slope Skies is produced by the Colorado Mesa University Astronomy Club, the Western Slope Dark Sky Coalition, and KVNF Community Radio. This feature was written and voiced by Bryan Cashion.