Does the alien world sound a bit scary? China's Sky Eye detects new phenomenon of "Black Widow" pulsar

Recently, the "China Sky Eye" observed and studied the eclipse phenomenon of the black widow pulsar B1957+20, and for the first time detected the extreme turbulence of plasma in a compact binary system, providing new clues to the eclipse mechanism of black widow pulsars. Does it sound a bit "obscure"? Let's start with the basic concept: What is a black widow pulsar?

The world's largest single-aperture radio telescope (commonly known as the Sky Eye) is located in Guizhou. Photo credit: China News Service

Let's talk about pulsars first. They belong to the category of neutron stars. They are one of the densest celestial bodies in the universe and have a strong magnetic field. During the rotation process, when its magnetic pole points to the earth, we can detect pulsed radiation with radio telescopes, which is why pulsars are named. 40 years ago, astronomers discovered a pulsar that rotates at a high speed. Its rotation period is only 1.5577 milliseconds, that is, it can rotate 642 times per second. This type of pulsar with a rotation period of 1 to 10 milliseconds was later called a millisecond pulsar. However, the astronomical theory at the time could not explain the existence of millisecond pulsars at all. After all, it is impossible for the energy of the pulsar itself to support such a fast rotation.

After years of observation and research, astronomers believe that millisecond pulsars are generally binary star systems, consisting of a pulsar and another star. Pulsars maintain their high-speed rotation by constantly accreting matter from their companion stars. Coincidentally, there is a spider in North America that has a strong neurotoxin, commonly known as the black widow spider. After mating, the strong female spider often eats the weak male spider as an energy reserve for feeding the offspring. The way millisecond pulsars accrete matter from their companion stars is similar to that of black widow spiders, so they are also called black widow pulsars.

With the successful launch of the Fermi Gamma-ray Telescope in 2008, more black widow pulsars were discovered, confirming astronomers' predictions about the binary millisecond pulsar system. In 2012, a black widow pulsar named PSR J1311-3430 was discovered. The primary star is a neutron star with a mass of about 2.7 times that of the sun, which is also one of the most massive neutron stars known. The mass of the companion star is "only" about 12 times that of Jupiter, and the volume is "only" 60% of Jupiter, which is much smaller than the primary star. The orbital period of this binary star system is 93 minutes, which is shorter than the length of many commercial movies.

However, the primary star rotates 390 times per second, and the strong radiation heats the surface of the companion star to 12,000 degrees Celsius, which is twice the surface temperature of the sun, causing the matter evaporated by the high temperature on the surface of the companion star to be quickly accreted onto the pulsar.

So far, humans have discovered 24 groups of black widow pulsars, mostly thanks to X-ray or gamma-ray space telescopes. In May 2022, astronomers at the Massachusetts Institute of Technology discovered a black widow pulsar system 3,000 light-years away from us, with the primary star and the companion star orbiting in just 62 minutes. Surprisingly, there seems to be a third object in this binary system, because the companion star actually emits visible light, which is unique in the history of millisecond pulsar detection.

Astronomers believe that the companion star is about 600 times farther away from the sun than the earth, and has an orbital period of 10,000 years. Through simulations, it is likely that the celestial body was "captured" by the gravity of the pulsar during a close encounter.

Of course, to unlock the secrets of this star system, more observations and research are needed, as well as the support of more advanced telescopes.