Question

How can you determine the age of a star cluster in which all stars formed at the same time? (hint: think about the main sequence of stars and which stars evolve how quickly)

 

Does the expanding universe expand into something? Is there a center from which the universe expands?

Answer 1

(1) Stars in a cluster formed at approximately the same time, it can be easier to determine their overall age by determining the size and luminosity of a range of stars in one cluster. Most stars spend about 90% of their lives in the main sequence phase where nuclear reactions are converting hydrogen to helium in the star's center, releasing vast amounts of energy.The more massive a star, the brighter and the hotter the star is in this stable stage of its life.The most massive stars are “blue-hot” and extremely bright, whereas the least massive stars are “red-hot” and quite faint. For example, we can look at the hottest, bluest, and most massive star in the star cluster that hasn’t left the main sequence, and calculate precisely how hot and bright it is. The mass of the star tells us how much fuel it had, while the brightness tells us how fast it is burning that fuel. Therefore, it is possible to roughly calculate the age of the star, and subsequently, the age of the other stars in the cluster.

(2) Expanding universe means it has been growing ever since its beginning with the Big Bang.It is not expanding into something rather it is growing in space and time.We know that galaxies are moving away from each other. However, the galaxies are not moving through space, they are moving in space, because space is also moving. In other words, the universe has no center; everything is moving away from everything else. A good way to help visualise the expanding universe is to compare space with the surface of an expanding balloon(famous ballon analogy). Imagine that you are on one of many dots on a spherical balloon, suppose your balloon world is being inflated with air. All the other dots will be getting farther and farther away from you as the balloon gets bigger. In fact, all dots get farther from each other, so no matter where you are, it looks as if you are at the center of the expansion. The expansion of three-dimensional space is similar. Like the surface of the balloon, there is no center in the universe.