Question

I was told that a star that I am seeing today would have died long back. Then how am I able to still see it? It will not be possible? If it is, then why?

Answer 1

You always see past in the night-sky. The light emitted by that star millions of years away will reach us after a million years, and in theory you could see the star as long as it emitted radiation in its entire lifetime and until the light directed towards us has dissipated, as already mentioned in another answer.

When you're seeing the star, it might actually be dead. But what you're observing is the light emitted by that star millions of years ago , and not now, i.e. you're looking into the past. The astronomers would witness the entire lifespan of the star as long as it emitted radiation continuously until it dies in a supernovae. It wouldn't simple disappear in the nightsky.

If a star, visible to us today, about 2 billion light years away, dies now. We would come to know of its death only when the light from its supernovae reaches us, after 2 billion years .

Consider a star in one of the farthest known galaxies in the observable universe some 13 billion light years away. Assuming a star is born in this galaxy now, and a static universe, we would witness its birth after 13 billion years and the star would have already died by the time we witness its birth. Though after 13 billion years the star would appear in our nightsky and remain until its entire lifespan for as long as it had emitted radiation. If the star lived for 5 billion years, we would see the star for 5 billion years in the sky and know of its death after 18 billion years.