What causes a star to turn into a Cepheid variable?

Answer 1

A star's entire lifeline is pretty well dictated by its mass. For example, when our Sun uses up all its Hydrogen in the core, it will become a red giant (in 5 billion years of so) and then become a white dwarf.

Stars more massive than our sun will have different evolutions. At some mass, the star runs out of hydrogen, puffs up into a red giant, then evolves along what is called (on the H-R graphic) the "horizontal branch".

At some specific period of this evolution, the star's luminosity pulsates in a cyclical manner. There are various reasons why massive stars pulsate (and each manner results in a kind of variable star with a specific name).

A Cepheid variable brightens and fades because the star's outer envelope cyclically expands and contracts. This happens because the rate at which the energy from core fusion (by this time, the star is fusing helium, not hydrogen) is transmitted to the surface varies with the transparency of the stellar material.

When the star is compressed, the material is not transparent enough and the heat gets trapped, expanding the star. As the star expands and becomes more transparent, the envelope becomes hotter and brighter. However, the more transparent envelope lets out heat a little too fast and the star cools down: the envelope contracts, becomes less transparent and dims (the cycle stars again).

The period of this cycle is measured in days (1 to 100 in most cases) and is very regular for a given star. If a specific Cepheid star has a cycle of 6.2 days, then the period is quite steady at 6.2 days.

The period is related to the star's mass. The amount of light that the star gives off is directly related to its mass. The difference between the star's real brightness and what we observe is a direct result of the distance. Thus, if we identify a star as a Cepheid and find it exact period, we can tell its distance from us.

The name Cepheid comes from the fact that the most studied star was the 4th brightest (delta) in the constellation Cepheus (the King).

Answer 2

I don't think a star "turns into one" it's simply a star that has certain properties that allow scientists to calculate it's distance. Below is some info from Wikipedia.org

A Cepheid is usually a population I giant yellow star, pulsing regularly by expanding and contracting, resulting in a regular oscillation of its luminosity. The luminosity of cepheid stars range from 103 to 104 times that of the Sun. Because Cepheids are from population I, they are sometimes called Type I Cepheids, while the similar (but belonging to population II) W Virginis variables are known as Type II Cepheids.

The exact mass of Cepheids with given brightness or oscillations is not known to any great precision, but astronomers hope to gather data for this from the newly-discovered third star of the Polaris system [1].

The variation in luminosity is caused by a cycle of ionization of helium in the star's atmosphere, followed by expansion and deionization. While ionized, the atmosphere is more opaque to light. This cycle has a period roughly equal to the star's dynamic time scale, therefore giving information on the mean density of the body as well as its luminosity.

Answer 3

a super nova

Answer 4

Is this in English?
I'll try the catagory that has fashion questions.

Answer 5

probably to much fame