A "main-sequence star" is one that fuses hydrogen into helium. Eventually, the star will run out of this specific type of fuel - in other words, it won't have enough hydrogen (at least, near its core) to continue this process.
When a star "goes off the main-sequence" it generally means the star has run out of hydrogen fuel and is beginning the post-main-sequence or its end of life phase. The main sequence of a star is the time where it is no longer just a proto-star but is burning hydrogen as a primary source of fuel.
Depending on how "low" on the chart it will either be a red dwarf or a PMS (Pre-main sequence) star.
the main sequence has a limit at the lower end because as a star's mass decreases, its core temperature and pressure decrease too. This eventually causes the nuclear fusion reactions in the core to stop, leading the star to move off the main sequence.
Sirius is not a single star but a binary star system consisting of a white main sequence star and a white dwarf.
Yes Star spend most of their life span as a main sequence star. A star end will depend on its size in life the end of a start can be a red giant to supernova, a white dwarf, pulsar, or black hole.
When a star "goes off the main-sequence" it generally means the star has run out of hydrogen fuel and is beginning the post-main-sequence or its end of life phase. The main sequence of a star is the time where it is no longer just a proto-star but is burning hydrogen as a primary source of fuel.
No. Red giants are not on the main sequence.
Depending on how "low" on the chart it will either be a red dwarf or a PMS (Pre-main sequence) star.
A red main sequence star would be a red dwarf or a branch red giant. To be on the main sequence, you have to have hydrogen nuclear fusion.
The "main sequence" is the region (on the HR diagram) for stars which burn hydrogen-1. Once stars use up most of their hydrogen-1 (and have significant amounts of helium-4), they leave the main sequence.
The sun is a main sequence star, so 1 AU.
It's the size. A dwarf star has reached the end of the road and has collapsed. It's a little old star and people don't notice it, mostly.
Main-Sequence star
the main sequence has a limit at the lower end because as a star's mass decreases, its core temperature and pressure decrease too. This eventually causes the nuclear fusion reactions in the core to stop, leading the star to move off the main sequence.
None of those is a main sequence star.
Sirius is not a single star but a binary star system consisting of a white main sequence star and a white dwarf.
Yes Star spend most of their life span as a main sequence star. A star end will depend on its size in life the end of a start can be a red giant to supernova, a white dwarf, pulsar, or black hole.