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There is a strange form in space, which is modeled using images taken by space telescopes, and we can find that in some clouds of gas and dust, a flash beats as rhythmically as a heart. These are pulsars, and pulsars are very important to astronomers-through them, astronomers have discovered the first exoplanets, and they hold time more accurately than atomic clocks. However, recent astronomers' discoveries about pulsars may subvert our inherent perception.

(by Mei Lin / tr. by Robert Taylor)

Before we learn about this new discovery, let's take a look at pulsars.

What is a pulsar? How was it discovered? A pulsar (Pulsar) is a highly magnetized compact star. It is usually a neutron star and is constantly spinning. The magnetic poles of pulsars emit electromagnetic radiation. If the electromagnetic radiation emitted by a pulsar points to the earth, scientists on earth can observe the radiation from the pulsar. And, more interestingly, the radiation travels in the form of pulses. In other words, the electromagnetic radiation emitted by pulsars has a periodic rhythm. So, as mentioned earlier, in the model, we can see a flash similar to the heartbeat.

There is a short story about the discovery of pulsars. In October 1967, a graduate student at the Cavendish Laboratory at the University of Cambridge detected signals detected by radio telescopes and found some strange signals-rhythmic pulses. Previously, most of the space signals detected by astronomers were disorganized, but this time the signals found by this graduate student were rhythmical. Is this a signal from an alien civilization?

At first, the graduate student thought the same way. Later, in less than half a year, astronomers discovered a series of rhythmic pulse signals one after another. Astronomers determined that this was a kind of electromagnetic radiation emitted by stars and named it pulsars. Antony Hewish, the tutor of the graduate student who first discovered the pulses, also won the 1974 Nobel Prize in physics for it, though many attribute it more to the graduate student.

Why do pulsars form "pulses"? Previously, astronomers generally believed that a pulsar was a rapidly rotating neutron star. The neutron star has a strong magnetic field, which produces strong electromagnetic radiation under the interaction between the magnetic field and the charged particles in the neutron star. This kind of electromagnetic radiation also moves with the rotation of the neutron star, the magnetic axis of the magnetic field is usually not parallel to the rotation axis, and some even reach an angle of 90 degrees, so the electromagnetic radiation will periodically point to the earth. The electromagnetic radiation from pulsars detected by astronomers on Earth is a rhythmic pulse signal.

But that changed in 2016, when astronomers discovered a pulsar that was not a neutron star, but a white dwarf.

The newly discovered pulsar breaks with conventional wisdom that the white dwarf star, AR Scorpii, lies in the sky in the direction of Scorpio. Astronomers detected its regular electromagnetic radiation, which has the same characteristics as the pulsar and identified it as a "white dwarf pulsar".

Just recently, scientists at the University of Warwick in the UK discovered such a pulsar, J1912-4410, which is not a neutron star but a white dwarf star. This pulsar lies in the sky in the direction of Cygnus, 773 light-years from Earth, and is the only pulsar found in the Milky way that is not a neutron star.

Like AR Scorpii, J1912-4410 has a red dwarf companion. Astronomers can find the periodic electromagnetic radiation of J1912-4410 not because its radiation will point to the earth, but because its super electromagnetic radiation will regularly bombard the red dwarf star, causing the red dwarf star to show periodic brightening in multiple bands.

Can a white dwarf be a pulsar? It was previously thought that neutron stars with extremely small radius and extremely high density could rotate rapidly to form powerful electromagnetic radiation because of the conservation of angular momentum. But the mass and density of white dwarfs are much smaller. Take the sun, for example, if the sun is compressed into a neutron star, its diameter is less than 10 kilometers, while if the sun is compressed into a white dwarf, its diameter is at least about the same as that of the earth. According to the law of conservation of angular momentum, the rotation speed of a white dwarf star is much smaller than that of a neutron star. According to our existing electromagnetic theory, the magnetic field of white dwarfs is also much weaker, and the electromagnetic radiation formed is much smaller, which is not enough to show the characteristics of pulsars.

So why did J1912-4410 become a pulsar? Some scientists speculate that it may be due to the influence of red dwarf companion stars. They speculate that the red dwarf may be close enough to J1912-4410 that under the gravitational pull of J1912-4410, it can gain mass from the red dwarf to ensure the rapid rotation of J1912-4410.

This is only a guess of scientists, and further research and observations are needed to confirm it. Maybe it's not that complicated, but in the deep space of the universe, there are laws of physics that we don't know, which are completely different from the theories of physics that we know now. We can think boldly that if, through the study of white dwarf pulsars, we really find that the laws of physics that we already have are not reasonable everywhere in the universe, then our existing physics will eventually be rewritten. our existing cognition may also be completely subverted.

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