The age of a star is directly related to its mass. Stars are stabilized by the balance of outward radiation pressure and inward attraction generated by internal nuclear fusion reaction. The greater the mass of the star, the stronger the inward attraction, and the stronger the outward radiation pressure needed to maintain stability. The stronger the radiation pressure, the greater the intensity of nuclear fusion reaction, the greater the consumption of nuclear fusion raw materials and the shorter the service life. Therefore, the greater the mass of a star, the shorter its life span; The smaller the mass, the longer the life.

The lifetime of a star like the sun is about 1000 billion years. A red dwarf with a mass of110 solar mass can live for 30-50 billion years, while a star with a mass of10 times that of the sun can only live for tens of millions of years.

As can be seen from the above picture, the life span of a star with twice the mass of the sun is only 300-400 million years; A star with three times the mass of the sun has a life span of only about 1 100 million years. Therefore, the age of cluster B and cluster C will not exceed several hundred million years. And cluster a may be billions of years old. Is the oldest cluster a.