What are Cepheid variables?

In astronomy, the variable Cepheid is a variable star whose brightness changes in a particular period in a characteristic, manner. Normally, the outer pressure from the nuclear fusion in the center of the star is balanced by pressure due to the gravity of the star and the star remains in constant size and brightness. Variable stars go through the expansion and contraction cycle that affects their brightness. In the Cepheid variables, the length of the cycle increases with the brightness of the star a predictable way, so when the period is measured, astronomers can tell the real brightness of cepheid and to calculate how far it is. These variable stars are an important tool for measuring distances to other galaxies. When helium is fully ionized, there is less transparent electromagnetic radiation, causing it to heat and expand. As it extends, cools and becomes less ionized, absorbs less heat and contracts. This results in a regular pattern of expansion and contraction with parallel brightness changes that have a period in the range of onewithin about 50 days.

There are two main types of cepheid variables. Type I or classic CEFEIDS are relatively young, highly light stars that contain a relatively large part of heavier elements, indicating that they have been created in areas where these elements were created by explosion of supernum older stars. Cefeids of type II are older, less light stars that have low heavy elements. There are also anomalous cepheids that have more complex cycles and dwarfs Cepheids. The classic Cefeids, because of their greater luminous intensity and simple normal cycles, are more useful for astronomers to determine the galactic distance.

Regular brightness changes and the firm relationship between the brightness and length of the cycle were discovered by astronomer Henrietta Leitt in 1908, when she studied these stars in a small Magellan cloud, a small galaxy near our own. The term Cepheid variable comes from one of the stars studied by Leavitt, called DeltaCephei. Since it was possible to determine the real brightness of Cepheid's variable from its period, it was also possible to determine its distance from the fact that the amount of light reaching the country is inversely proportional to the distance from the source. Such objects of known brightness are called "standard candles".

Comparison of the results of these calculations for Cepheid variables in our own galaxy with distances calculated parallax confirmed that the method worked. Cefeids type I are up to 100,000 times brighter as the sun. This means that they can be detected by binoculars based on Earth in another galaxy of up to about 13 million light -years. The Hubble Space Binoculars were able to detect these stars at a distance of 56 million light -years. Cepheid variables provided confirmation at the beginning of the 20th century that the universe spread far beyond our own galaxy, which was only one of many.

These stars also provided the first strong evidence that the universe was expanding. In 1929 Edwin Hubble compared VZ measurementsFurther with a number of galaxies acquired by Cepheid variables and red shift measurements, indicating how quickly they retreat from us. The results showed that the speeds at which the galaxies were receding were proportional to their distances and led to the formulation of Hubble's law.