Question

1.What process is pushing back against gravity in the very center (the core) of sun-like stars?

2."... the length of time a star spends on the main sequence is determined almost entirely by its mass with the counterintuitive result that less massive stars live longer." What is the fundamental reason why massive stars live a much shorter time than the Sun, even though they might have 30 times as much mass – and thus more fuel – available?
3.The text discusses the build up of helium “ash” in the core of a star while it is on the main sequence. In what sense is calling it “ash” a good way to classify it?

5.Describe what will happen to the Sun’s luminosity and surface temperature as the Sun goes up the red giant branch and becomes a red giant.

6.What is the future of life on Earth based on your answer to questions 5?

Answer 1

1. Due to gravity, a immense pressure at the center of sun is created.Now, according to law of thermodynamics, PV=NKT, the temperature of the core of sun increases. When the temperature increases significantly, at the very center of sun where pressure is maximum(so is temperature), it becomes hot enough to start nuclear fusion, which fuses hydrogens together to form helium and releases a huge amount of energy. Mainly this energy counters gravitational pull and stabilizes the system.

2.More massive stars creates so much pressure at the central area that not just it's core but more layers around it hits up so much that they start to fuse together to create helium. So, in higher mass the burn of fuel(hydrogen) is much faster due to more gravitation forces. And also sometimes the temperature becomes so high it can burn is multiple ways too(helium fusion). So, though they have more fuel they burn it so fast that their life time is shorter than low mass starts.

3.When the core(very central area) burns due to helium fusion, the adjacent layer to it heats up because of the heat produced by fusion. Now, in this process hydrogen atoms burn and the core is being filled by helium and the adjucent layer starts burning. This Helium is known as Helium ash. This is referred to as 'ash' because for light mass stars this Helium remains inert. Cause Helium can also fuse, but it takes much more heat, and low mass star doesn't have that much pressure and can't produce that amount of heat. So these Helium remains as 'trash' as they can't burn, so they are called Helium ash. You may also call it inert Helium.