431 Nepheli: Where did we put it this time, Adrian?
Adrian: They are some very peculiar stars that I want to see up close and learn more about them. Basically, they are dead stars. They’re called ‘pulsars’. They are rapidly rotating neutron stars. Usually, they emit two diametrically opposed beams of light. See better in the diagram below:
Radiation beam = beam of radiation
98 Ianthe: Slowly, Adrian. You’re speaking too fast and we can’t understand anything.
431 Nepheli: Initially: Are there living and dead stars?
Adrian: I would say that living stars are those that produce heat, like the Sun.
98 Ianthe: Do stars like the Sun die? I didn’t know that!
431 Nepheli: Think logically for a moment, 98 Ianthe. Since stars shine by burning their hydrogen. Don’t you think their hydrogen will eventually run out?
98 Ianthe: Okay, okay, I understand. And once the hydrogen runs out, what happens? They don’t shine again?
Adrian: They shine differently. The next photo shows the life of stars with different masses. It’s in English. Sorry, but you speak English well, don’t you?
431 Nepheli: From what I see in the above image, large stars with a mass greater than 8 times the mass of the Sun (for example, the large blue star in the top row) become red supergiants.
98 Ianthe: Then it becomes a Type II supernova explosion.
Adrian: Now is when the star shines again, very, very brightly. In a distant galaxy, a Type II supernova explosion occurred. The star shone so brightly that it became brighter than the entire galaxy containing it.
431 Nepheli: After the explosion, the remnant of the explosion can be a black hole or a neutron star.
Adrian: Girls, you’re amazing. How do you know all these things? 98 Ianthe: And even more!
431 Nepheli: Neutron stars become pulsars. I’m looking again at the diagram with the neutron star and the two beams of light. Now I feel like I can imagine pulsars quite easily.
98 Ianthi: Indeed, if these two opposed beams of light rotate, an observer at some distance from the neutron star perceives them as successive pulses.
Adrianos: The following video shows exactly what you’re saying, girls:
431 Nepheli: I believe I have seen a similar light at a lighthouse in Gerogombos in Kefalonia one summer.
Adrianos: Pulsars are like the lighthouses we have here on Earth to prevent ships from crashing into the rocks. They usually place them on steep and rocky shores. The next video shows such a lighthouse:
98 Ianthe: Look at this, too, Adrian! You’ll see what the student Jocelyn Bell-Burnell discovered back then! This is radiation from a pulsar, not from a lighthouse on Earth, right?
431 Nepheli: Pulsars were discovered in 1967 by a woman like us.
98 Ianthe: Jocelyn Bell-Burnell.
Adrianos: She was a student back then, and her professor, Antony Hewish, received the Nobel Prize for the discovery, not her. Yes, she is well-known, girls, don’t worry. She made the first observations shown in the next image.
Adrianos: No one could explain back then where those pulses observed were coming from. Joselyn Bell-Burnell couldn’t understand. She then speculated that they were coming from the Little Green Men, as she humorously named them (LGM).
98 Ianthe: But these pulses aren’t from the LGM, right?
431 Nepheli: We just learned that it’s radiation from pulsars.
Adrianos: We also learned that pulsars are rotating neutron stars.
98 Ianthi: I have a question that has been bothering me for a long time now, and I haven’t dared to ask.
Adrianos: We’re listening! Always ask about what you don’t know. Always search for the answers on your own.
431 Nepheli: We’re all ears.
98 Ianthe: Does the neutron star have only neutrons? How is that? Since matter is composed of atoms.
431 Nepheli: The atom has a nucleus with neutrons and protons. The electrons are located far away from the nucleus.
98 Ianthe: Since there is a neutron star, is there also an electron star?
431 Nepheli: Proton star?
Adrianos: Your questions are very logical, girls, and I’m glad you asked. As far as I know, only neutron stars have been observed. The theory that is generally accepted at the moment does not predict the existence of exotic electron-proton stars.
Under specific conditions, the protons of an atom interact with the electrons of the same atom, producing a neutron and a neutrino.
431 Nepheli: So, that’s how a star can have only neutrons.
98 Ianthe: And the distance between the nucleus and the electrons in atoms becomes very small.
Adrianos: You speak very accurately. That’s why neutron stars are so small. They may have a diameter of only 10 kilometers.
431 Nepheli: And from what I understand, the material that makes up the neutron star must be very dense.
98 Ianthe: Indeed, a teaspoon of this material weighs as much as a steam engine!
98 Ianthe: What curious objects these neutron stars are!!!
431 Nepheli: And imagine, Ianthe, they become pulsars and emit pulses that appear to come from the LGM.
Adrianos: The image below shows five different pulses. It shows how the intensity of the light of a pulse evolves over time from left to right.
98 Ianthe: Oh, and the five pulses are different!
431 Nepheli: The first one is square! Are all five from pulsars?
Adrianos: No, as far as I know, they are not from pulsars. But, girls, try to understand now. If you draw each of the five pulses on five playing cards and continue to draw pulses on each card. Then, you put all the playing cards together and make the deck.
That’s how the famous design on the t-shirt of the band Joy Division is created.
Each horizontal line is a pulse from the pulsar 1919+21, which was discovered in 1967 by the student Jocelyn Bell-Burnell.
I am very happy. I have this T-shirt now too!
431 Nepheli: Not only do you have it, but you also know what it represents!
98 Ianthe: I believe now is the right time to watch the next video, which has Greek subtitles.
431 Nepheli: It will be good to be careful on the return journey not to encounter any neutron stars.
98 Ianthe: That’s easy because they are usually pulsars. Like lighthouses at sea, they show the way for ships to avoid hitting the rocks.
431 Nepheli: So the pulsars will show us what to avoid.
Adrianos: Let’s go to our homes and dream about what else we want to learn.