Stars expand enormously as they age into red giants. When they eventually burn through their vast stores of hydrogen, stars shrink and become extremely hot. Scorched by the burning core, the outer layers of the star then balloon.
This behemoth expansion leaves the star hundreds of times its original size, but thinly spread. This particular red giant is 350 times larger than the sun, but has only 1.5 times the mass.
I have a question. the hadith probably mentioned one of the signs of the judgment day but it is quite obvious the life will become extinct long before anything like that literally happening. then what is the purpose of mentioning such a sign when no one will be there to witness it.