I really like what Pulsar said: You don’t even want to call me a lighthouse.

Well-known

Black holes are not holes, they are collapsed stars

Very coincidental

Pulsars are stars too

Pay attention

Let's get into the serious topic

In the vast universe, there exists a mysterious and fascinating celestial body - pulsars. With their unique rotation mode and regular electromagnetic pulses, they have become an important tool for astronomers to study the universe.

Artistic conception of a pulsar. Image source: NASA

Recently, pulsars appeared in the 2024 Beijing High School Entrance Examination Physics Paper, which aroused the strong interest of teachers and students in this cosmic wonder. Let us walk into the world of pulsars and explore their mysteries.

The discovery of pulsars dates back to 1967, when astronomers Jocelyn Bell and Anthony Hewish first discovered an abnormal radio pulse source during a radio astronomy observation project at the University of Cambridge. After further research, they found that this pulse signal came from a very fast rotating celestial body, which was later called a pulsar.

Born from a cosmic-level "fireworks"

Pulsars are rotating neutron stars.

Image source: Xinhuanet

So, how are neutron stars formed? And why are pulsars called pulsars?

When a star with a mass of more than 8 times that of the sun runs out of fuel in its core, its matter will collapse toward the core and then explode violently. During the explosion, the outer layers of the star are thrown into space, while the core may collapse into an extremely dense celestial body - a neutron star.

When a neutron star rotates at a very high speed, its strong magnetic field generates a strong electric field at the magnetic poles, which in turn stimulates radio waves, X-rays, gamma rays, etc. These radiations are radiated from the magnetic poles in the form of pulses, forming the pulse signals we observe , hence the name pulsar.

Radio pulses from a pulsar sweep past Earth. Photo by Michael Kramer

How light is a cloud? About 500,000 kilograms

A spoonful of pulsars? It can lift up Mount Everest.

Pulsar superpowers

Regular pulse signal

The reason why pulsars can emit regular pulse signals is closely related to their rotation and the structure of their magnetosphere.

Most pulsars have extremely strong magnetic fields, which can be millions to billions of times stronger than the Earth's magnetic field. When a pulsar rotates, its magnetic field is asymmetric with its rotation axis, causing radio beams to continuously radiate from the magnetic poles, forming a regular pulse signal from the Earth's observation perspective.

The rotation period of a pulsar is usually very precise and stable, some can even reach a few milliseconds, and this rotation period will hardly change significantly. Some pulsars will only slow down by 1 second every trillion years, while the most accurate clock currently available to humans is 1 second slow every 15 billion years. Therefore, astronomers can use the signals of pulsars to perform very accurate time measurements and celestial navigation. Pulsars are also called "cosmic lighthouses" and "astronomical clocks."

Extreme physical conditions

Pulsars are one of the densest celestial bodies known in the universe . This extremely high density is due to the fact that the matter inside them is almost entirely composed of neutrons, and their cores are composed of neutrons and a certain amount of protons and electrons. They are squeezed together under extremely high pressure and temperature to form an extreme state of matter.

In this high-density state, the physical size of a pulsar is usually very small, with a diameter generally between 10 km and 20 km , even smaller than some asteroids.

The size of the pulsar is comparable to the "four rings" in downtown Beijing

One cubic centimeter of pulsar matter can weigh hundreds of millions of tons. The mass of a pulsar is usually between 1.4 and 2 times the mass of the sun. Although this mass is not large relative to a star, the high density gives them an extreme gravitational field that matches their mass, which is almost billions of times the gravity on the surface of the earth.

Pulsars have relatively high temperatures, typically between hundreds of thousands and millions of degrees Celsius. These temperatures are mainly derived from the heat of the pulsar's formation and the residual heat from its internal nuclear reactions and energy release. Despite their potentially high surface temperatures, pulsars cool very slowly because their surface heat is mainly dissipated through radiation and there is still a lot of heat inside.

Look up at the stars on a clear night

Guess

Which of the stars we see are pulsars?

Congratulations, you got the answer right. None.

How to observe pulsars?

Pulsars are usually observed in the radio band because the pulse signals they emit are mainly concentrated in the radio frequency range.

Currently, most pulsar detections are conducted using radio telescopes, which observe the pulse radiation of pulsars by receiving radio signals from the ground or space. Since these radiations are often very weak, radio telescopes must have high sensitivity and wide frequency coverage.

FAST is the world's largest single-aperture radio telescope, with an aperture of 500 meters and a receiving area equivalent to the size of 30 standard football fields. It is currently the most sensitive radio telescope in the world. Since its completion and commissioning in 2016, FAST has discovered more than 900 new pulsars, including more than 120 binary pulsars, more than 170 millisecond pulsars, and 80 faint sporadic pulsars.

Einstein predicted in his theory of general relativity that the movement of supermassive celestial bodies would disturb space-time and generate gravitational waves. Gravitational waves would change the time it takes for pulsar signals to reach Earth. The Chinese research team analyzed the data of 57 pulsars observed by FAST and successfully detected gravitational waves, verifying the prediction of Einstein's theory of general relativity.

In the future, I believe that with the further upgrading and improvement of FAST, it will play a more important role in pulsar observations and other astronomical research.

If the universe is a giant dance floor

Pulsar must be a DJ wearing a cool LED light hat

Sending invitations to the universe

If you received

Why not go and have a look?