What Causes Cepheid Variable Stars to Pulsate?

TL;DR

Cepheid variable stars pulsate due to the interplay between doubly and singly ionized helium. In their dim phase, the presence of doubly ionized helium makes them opaque, causing them to heat and expand. As they cool down and transition to singly ionized helium, they become more transparent, allowing more light to escape and leading to their bright phase before the cycle repeats.

Transcript

• [Voiceover] In the last video we learned that there are a class of stars called Cepheid variables. And these are the super giant stars, as much as 30000 times as bright as the sun. A mass, as much as 20 times the mass of the sun. And what's neat about them is, one, because they're so large and so bright, you can see them really really far away. A... Read More

Key Insights

• 🤩 Cepheid variable stars are supergiant stars that are much brighter and larger than the sun.
• 🤩 The pulsations of Cepheid variable stars are related to their actual luminosity, making them valuable for measuring distances in space.
• 🤩 The presence of doubly and singly ionized helium affects the transparency and heating of the outer layers of Cepheid variable stars.
• 🤩 Doubly ionized helium makes the star more opaque and causes it to heat up and expand during the dim phase of the pulsation.
• 🙂 Singly ionized helium forms during the bright phase, allowing more light to pass through and causing the star to cool down and collapse back in.
• 🤩 The cycle of ionization and deionization of helium causes the pulsations of Cepheid variable stars.
• 🤩 Cepheid variable stars can be used as cosmic distance indicators due to their known luminosity and pulsation periods.

Questions & Answers

Q: Why are Cepheid variable stars important for measuring distances in space?

Cepheid variable stars are important for measuring distances in space because their pulsations are related to their actual luminosity, which allows us to determine their distance based on their apparent luminosity.

Q: What causes Cepheid variable stars to pulsate?

The pulsations of Cepheid variable stars are caused by the presence of doubly and singly ionized helium, which affects the transparency and heating of the star's outer layers.

Q: How does doubly ionized helium affect the brightness of Cepheid variable stars?

When a Cepheid variable star is in its dim state, the presence of doubly ionized helium makes the star more opaque and absorbs light, causing it to heat up and expand. This results in a dim phase of the pulsation.

Q: Why do the outer layers of a Cepheid variable star cool down and become transparent during the bright phase of the pulsation?

When a Cepheid variable star expands during its dim phase, the outer layers cool down, allowing singly ionized helium to form. Singly ionized helium is more transparent, allowing more light to pass through and creating the bright phase of the pulsation.

Summary & Key Takeaways

• Cepheid variable stars are supergiant stars that are up to 30,000 times brighter than the sun and have a mass up to 20 times that of the sun.

• These stars are valuable for measuring distances in space because their pulsations are related to their actual luminosity, allowing us to determine their distance based on their apparent luminosity.

• The pulsations of Cepheid variable stars are caused by the presence of doubly and singly ionized helium, which affects the transparency and heating of the star's outer layers.