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The Hertz-Sprang-Russell diagram: How does this diagram help us understand the age of stars?
Estimating the age of stars is an important topic in astronomy, helping us better understand the evolution of the universe and the life cycles of stars. Various methods and tools are applied in this process, including models of stellar evolution, cluster membership, adaptation of standard spectroscopic and photometric classification systems, and the presence of protoplanetary disks.
Almost all methods of age determination require knowledge of the star's mass, which can be obtained in a variety of ways.
The key to determining the age of a star lies in the tendency of its luminosity to increase with age. Depending on the star's mass, we can use this growth rate to infer the star's age. However, this approach is limited to the main-sequence stage, because at later stages of a star's evolution, such as the red giant stage, this relationship no longer holds.
Nonetheless, if we observe a red giant whose mass is known, we can calculate its main sequence period and thus its minimum age. This is because red giant stars only exist for about 1% of their entire lifetime.
Field stars
The properties of different stars can also be used to determine their age. For example, the Etakarin system emits large amounts of gas and dust. These huge explosions can be speculated that this star system is approaching the end of its life and is expected to explode in the form of a supernova soon. Supermassive stars like VY Canis Majoris, as well as several others, invariably show that they have entered a very advanced stage of evolution.
Betelgeuse may explode as a supernova within hundreds of thousands of years.
In addition to very large stars, certain characteristics of stars can also reveal their age. For example, Cepheid variable stars have a characteristic light curve whose repetition rate is related to the luminosity of the star. These variable stars have relatively short life cycles. Knowing its mass can help us trace its evolutionary path and therefore its age.
Membership of a cluster or system
Stars belonging to clusters or galaxies allow us to make rough age estimates for large numbers of stars. When the age of stars can be determined by other methods, the ages of all objects in the entire system can be identified. This is particularly effective in star clusters where there is a wide variety of stellar masses, stages of evolution, and classifications.
In galaxies, stars form around the same time, so knowing the age of one star can help us estimate the ages of other stars.
However, this method cannot be applied to large structures such as the Milky Way. The formation of the Milky Way lasted billions of years. Even though the galaxy's star production process may have stopped now, the oldest stars only set a minimum age for the Milky Way, and its actual age cannot be determined.
The existence of protoplanetary disks
The presence of protoplanetary disks can set a maximum limit on the age of stars. Usually stars with protoplanetary disks are young and have just entered the main sequence stage. Over time, these disks coalesced to form planets, and the remaining material was deposited in places such as the various asteroid belts. However, the presence of pulsar planets complicates this approach.
Spin chronology
Spin chronology is a method of determining the age of a star by measuring its rotation rate and comparing it to the Sun's rotation rate, which provides us with a way to check time. This method is considered more accurate than other methods in age estimates of field stars.
Taken together, the Hertz-Sprang-Russell diagram and the various methods and tools involved have opened a window for astronomers, allowing them to peer into the age and evolution of stars. As technology advances, these methods will become more precise, allowing us to gain a deeper understanding of the universe. Have you ever thought about how many unsolved mysteries there are in the vast universe waiting for us to discover?
