The Pulsar in Space: A Galaxy's Ultimate Powerhouse.
A pulsar is a highly magnetized, rotating neutron star that emits a beam of electromagnetic radiation. These beams are often observed as pulses, hence the name. With sizes and masses comparable to those of planets and moons, these stars pack some serious gravity. The intense gravity of this neutron star manages to compress the matter so densely that it can fit more than 1.4 suns inside its 10km diameter, which then leads to an incredible weight at the surface area of about 1 billion tons per square inch!
Pulsars emit their radiation at such a high frequency that they cannot be seen by the naked eye; however, some pulsars emit some visible light as well as X-rays and gamma rays, which can be observed on Earth with appropriate equipment.
The first pulsar was discovered in 1967 and only about 2000 have been found since then (in 2017). Although we know less about them than we do for other astronomical bodies, we’ve still learned a lot about.
What is a pulsar
A pulsar is a highly magnetized, rotating neutron star that emits a beam of electromagnetic radiation. These beams are often observed as pulses, hence the name. It's often compared to a lighthouse because the emission of the beam is only observable for a brief interval and at regular intervals.
Pulsars emit their radiation at such a high frequency that they cannot be seen by the naked eye; however, some pulsars emit some visible light as well as X-rays and gamma rays, which can be observed on Earth with appropriate equipment. As it rotates, the beam sweeps around like a lighthouse beacon and these pulses can be detected by an observer if they're pointed in that direction.
The first pulsar was discovered in 1967 and only about 2000 have been found since then (in 2017). Although we know less about them than we do for other astronomical bodies, we've still learned a lot about them since then.
Pulsars and gravity
The intense gravity of these stars has led scientists to believe that they could be the most dense and smallest stars in the universe. With a diameter of only 10km, they can pack more than 1.4 suns worth of material into their surfaces, which means that the weight at their surface is about 1 billion tons per square inch!
Pulsars emit radiation so quickly and powerfully that they cannot be seen by the naked eye. However, some pulsars do emit visible light as well as X-rays and gamma rays. These can be observed with appropriate equipment on Earth.
The first pulsar was discovered in 1967 and about 2000 have been found since then (in 2017). We know less about them than we do other astronomical bodies, but we’ve still learned a lot about them.
The discovery of pulsars
Neutron stars were first theorized in 1934 and the first pulsar was discovered in 1967 by University of Cambridge graduate student Jocelyn Bell. The discovery was a complete accident and she had to go through a lot of work to convince her supervisors that she wasn't just picking up interference from somewhere else.
The first pulsar was dubbed LGM-1, for “Little Green Men-1”, as Bell's supervisors thought it must be coming from an alien civilization. Once they realized it was just a neutron star, they named it CP 1919, which stood for Cambridge Pulsar 1.
How we know what they're made of?
Pulsars are dense enough that their matter is close to the “nuclear density” which means that protons and neutrons are smashed together. This smashing of nuclei leads to an increase in neutrinos, which are subatomic particles that have very little mass. The intense gravitational pressure also causes electrons to combine with protons, creating positrons (a particle with the same mass but opposite charge).
We know what they're made of largely because of these changes in subatomic particles. Pulsars emit beams of radiation which are generally observed as pulses. These pulsars can be observed by astronomers on Earth with appropriate equipment, such as X-rays and gamma rays. We can observe the radiation coming from these pulsars and this allows us to see how many positrons and electrons there are relative to each other. This tells us how rich the star is in certain elements like iron and cobalt.
How do we measure their spin rate?
Pulsars emit radiation in the form of a beam, which can be seen on Earth with appropriate equipment. The periodic flashes of light (or pulses) on the pulsar’s surface are measured and the spin rate is calculated by dividing this pulse rate by the time it takes for one complete rotation. We measure this time in seconds per revolution, or hertz (Hz). The higher the spin rate, the more often you will see pulses.
The fastest spinning pulsar rotates at 720 revolutions per second (or 720 Hz). The slowest one rotates at 0.761 Hz. Pulsars range greatly in their spin rates, but they all emit beams of radiation that can be observed by scientists here on Earth.
Comparison with other astronomical objects
The universe is filled with a variety of objects that can emit electromagnetic radiation. A pulsar, however, is unique in that it's the only one that emits a beam of radiation consistently.
A neutron star is a type of pulsar, but not all pulsars are neutron stars. All neutron stars are pulsars, but not all pulsars are neutron stars - for example, a magnetar.
To understand how a pulsar compares to other astronomical objects, we will explore three different types: black holes, white dwarfs and pulsars.
Radio pulses and pulses in visible light
The main way in which pulsars are categorized is by the frequency of their radio pulses. Typically, the more frequent the pulses, the greater the energy emission. Pulsars are usually found by searching for these pulses in radio waves, but pulsars that emit visible light can also be found using optical telescopes.
Another interesting thing to note about pulsars is that they can pulse at different rates even though they are all rotating at a constant rate. This occurs because of glitches in the star's magnetic field or when it's in what's called a "spin-up" phase.
Do you know what would happen if we could only see one pulsar? We might not have discovered them! That’s because we need to wait for this type of star to rotate and send out its pulse before we can find it and study it. Luckily there are thousands that we can observe and learn from, so many questions remain unanswered about these amazing celestial bodies.