Table of Contents
Where are Cepheids found?
The classical Cepheids have periods from about 1.5 days to more than 50 days and belong to the class of relatively young stars found largely in the spiral arms of galaxies and called Population I.
What are Cepheids used for?
Cepheids, also called Cepheid Variables, are stars which brigthen and dim periodically. This behavior allows them to be used as cosmic yardsticks out to distances of a few tens of millions of light-years.
What important role do Cepheids play in the study of astronomy?
The cepheid variables are used as standard candles to measure distances within our galaxy and nearby galaxies. That is the importance of cepheid variables.
What kind of stars are Cepheids?
Cepheid stars are stars that have evolved off the main sequence into the Cepheid instability strip. They are regular radial-pulsating stars, with a well-defined period-luminosity relationship, which makes them ideal stars to be used as primary distance indicating standard candles.
What causes the expansion and contraction of Cepheids?
In ordinary stars, hydrostatic equllibrium diminishes these pulsations. Basically, Starr’s in this stage can create conditions that trap their radiated energy in the outer layers. The pressure increases enough so that the outer layers expand.
How did Cepheids help Hubble?
Astronomer Edwin Hubble used these Cepheid variable stars to discover that the more distant a galaxy is from Earth the faster it moves away. There is a proportionality between the distance to a galaxy and its recessional velocity. This relationship is called the Hubble Law.
How are Cepheids used to estimate astronomical distances?
Through observations of Cepheid variables, astronomers have determined the distances to other galaxies. They compare the Cepheid variable’s apparent brightness with its intrinsic brightness. The difference between observed and actual brightness yields the distance.
What do Globular clusters tell us about our galaxy?
Globular clusters are densely packed collections of ancient stars. Roughly spherical in shape, they contain hundreds of thousands, and sometimes millions, of stars. Studying them helps astronomers estimate the age of the universe or figure out where the center of a galaxy lies.
What is the meaning of Cepheids?
Definition of Cepheid : any of a class of variable stars whose very regular light variations are related directly to their intrinsic luminosities and whose apparent luminosities are used to estimate distances in astronomy.
How do Cepheids pulsate?
A Cepheid pulsates in a regular and predictable cycle. It is thought that Helium is involved in its cycle. Doubly ionized Helium is more opaque than singly ionized helium, meaning it lets little light through. At the dimmest part of the cycle, doubly ionized Helium makes up the outer layers of the star.
Why do Cepheids vary?
(2) Cepheid stars and RR Lyrae stars are variable because they pulsate in and out. Cepheid variables are named after the star Delta Cephei (the fourth brightest star in the constellation Cepheus). The luminosity of Delta Cephei varies by a factor of two, with a period of 5 days.
Why are Cepheids used as standard candles?
Cepheid variable stars are stars that appear to pulsate over regular intervals. If astronomers can measure the period of a Cepheid variable, they can calculate the absolute magnitude of the star, making Cepheid variables standard candles.