Types of Standard Candles

Type of variable star.

Standard candles are astronomical objects that have a known luminosity. Their brightness, as observed from Earth, can be used to determine their distance from us. This is a fundamental concept in the field of astronomy, particularly when studying objects that are far away from our own galaxy. There are several types of standard candles, each with its own unique characteristics and uses. In this article, we will explore three main types: Cepheid Variables, Type Ia Supernovae, and RR Lyrae Variables.

Cepheid Variables

Cepheid Variables are a type of star that pulsates radially, varying in both diameter and temperature and producing changes in brightness with a well-defined stable period and amplitude. Named after the star Delta Cephei in the constellation Cepheus, these stars are very luminous and can be seen from great distances.

The period of a Cepheid Variable star—the time it takes to complete one cycle of brightness—is directly related to its luminosity. This means that by measuring the period of a Cepheid Variable, we can determine its true brightness, compare it to its apparent brightness, and calculate its distance from Earth.

Type Ia Supernovae

Type Ia Supernovae are stellar explosions that occur in binary star systems where at least one star is a white dwarf. The white dwarf accretes matter from its companion star until it reaches a critical mass, leading to a catastrophic explosion.

What makes Type Ia Supernovae excellent standard candles is their remarkable consistency. The peak brightness of a Type Ia Supernova is always the same, about 5 billion times the brightness of our Sun. This consistency allows astronomers to use them to measure distances to faraway galaxies.

RR Lyrae Variables

RR Lyrae Variables are pulsating horizontal branch stars of spectral class A or F, with a mass half that of the Sun. They are used as standard candles to measure (extra)galactic distances, as their absolute magnitude is fairly constant (-0.75 in the visual band).

RR Lyrae stars are often found in globular clusters, and they're particularly useful for determining the distances to these clusters. They're not as bright as Cepheid Variables or Type Ia Supernovae, so they can't be used to measure distances as great. However, they're still a crucial tool in the cosmic distance ladder.

In conclusion, standard candles are a fundamental tool in the field of astronomy. They allow us to measure vast cosmic distances and contribute significantly to our understanding of the Universe. Each type of standard candle has its unique characteristics and uses, making them collectively invaluable to astronomers.