The FAST telescope caught two "poisonous spiders"!

Author: Banana Leaf

The article comes from the Science Academy official account (ID: kexuedayuan)

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You said FAST is a radio wave astronomical telescope, so how come it is catching spiders for fun?

Astronomical telescopes are still used for astronomy~ But sometimes we have to consider that astronomers will give nicknames to celestial bodies...

In fact, the two "poisonous spiders" captured by FAST are both special types of pulsars.

These two poisonous spiders are of different species. One is the famous "black widow" spider and the other is called the redback spider.

Black Widow vs. Redback Spider

I guess everyone is familiar with the name "Black Widow". First, this spider is one of the most poisonous spiders in South America, and it is named because the female eats the male after mating; second, there is a classic female character in Marvel called Black Widow.

Black widow spider (Image source: https://www.nationalgeographic.com/)

The redback spider may sound unfamiliar to you. As a close relative of the black widow spider in Australia, the redback spider looks similar to the black widow spider, the only difference is that the redback spider has a red stripe on its back. Like the black widow spider, the redback spider is also a highly venomous spider, and the male spider is often eaten by the female spider after mating.

Redback spider in Australia (Photo source: https://australianmuseum.net.au/)

Spider Pulsar

In 1988, astronomers first discovered a millisecond pulsar binary system with eclipse phenomenon. In this binary system, the primary star is a millisecond pulsar, and the companion star is a star with a mass of only 0.02 times that of the sun. As the two stars revolve around each other, whenever they revolve to a certain position, the electromagnetic wave signal emitted by the pulsar will be blocked by the companion star and its surrounding matter. When the pulsar is blocked, we cannot observe the signal of the pulsar, which is the eclipse phenomenon. The solar eclipse caused by the sun being blocked by the moon is also an eclipse phenomenon.

Astronomers speculated through observational data that in such a binary star system, the companion star's matter would be heated and carried away by the primary star's stellar wind (similar to the solar wind). In other words, the pulsar, the primary star, is "killing" its companion! Isn't this the same as the infamous black widow spider? So astronomers call this type of pulsar a "black widow" pulsar.

Under the influence of the stellar wind of the primary star (a millisecond pulsar), the companion star is heated and matter is blown away (Source: https://svs.gsfc.nasa.gov/)

In subsequent observations, astronomers have discovered similar millisecond pulsar binary systems. These binary systems all have eclipses, and the mass of the companion star is less than 0.1 times the mass of the sun.

As the observations deepened, astronomers discovered similar binary star systems in globular clusters, but with one difference: their companion stars were more massive. Later, astronomers also discovered such systems outside of globular clusters.

Because the companion stars have different masses, astronomers feel it is necessary to classify the later discovered companion stars as larger ones. Since these two millisecond pulsar binary systems look so similar and both kill their companion stars, let's call the later discovered one the Redback Spider Pulsar!

Black widow and redback, these two types of pulsars are collectively called spider pulsars.

FAST’s Discovery

We just mentioned a few days ago that FAST discovered a pulsar binary in the Hercules globular cluster. This is the first time FAST has discovered a pulsar binary. In fact, there is another "first" in this study, which is FAST's first pulsar timing observation. Through this timing observation, astronomers measured that the mass of the companion star of an unclassified spider pulsar in this globular cluster is 0.02 times that of the sun, which is a black widow.

Recently, FAST has brought good news again. A pulsar binary was discovered in the globular cluster M92! This is the second pulsar binary discovered by FAST, and it is also the first pulsar detected in this globular cluster. This pulsar binary has several conditions to become a spider pulsar: 1. It is a millisecond pulsar; 2. It has eclipses. It is estimated that the mass of the companion star in this binary system is about 0.18 times the mass of the sun, which should be a red-back spider.

Conclusion

In such a short period of time, FAST has achieved great results one after another, demonstrating its potential as the world's largest single-aperture radio telescope. I believe that in the near future, FAST will continue to achieve great results and help us better understand the vast universe.