How long does it take for stars to be visible? see Details.?

Question

I heard once that the stars we see (or at least some of them) are not active anymore but we still see them due to the rate at which light travels. If this is true (though I cant seem to finy anything online about it), how long on average does it take us on Earth to see a new star that has been "born"?

Answer 1

This depends on the distance from the earth the star was formed, if the star was formed say 4 light years away (a light year is the distance light travels in a year) it would take 4 yrs before we on earth see it, if the star forms 1000 light years away it will be 1000 years before we see it, as if it dies we will still see it for a 1000yrs before we witness its death.

Answer 2

A star is born inside a cloud that collapses onto itself. When the density and temperature are sufficient to trigger the fusion reaction at the centre, there is still a lot of dust surrounding the new born star; this dust prevents us from seeing the star.

Eventually, the stellar wind will push away the dust that has not managed to collapse into the stable central sphere that becomes the star.

The big lumps (that may, with time, form planets) are too massive to be shoved away by the pressure of light and charged particles. But, with time, gets thinned out sufficiently for the star's light to "escape".

And, of course, once light can escape, it can only travel at the speed of light so that we have to wait some more before the star becomes visible from Earth.

PS: A good portion of the dust is cleared away at the protostar stage (the star shines from the gravitational energy, not yet from fusion), so that the final clearing, after the onset of fusion, does not last very long.

However, most stars are born in clusters, inside very large clouds. The star does clear a sphere around itself, but his sphere may be embedded in a much larger cloud which takes a lot longer to be cleared.

PS#2: One mechanism to clear the dust around them is called bipolar flow (the dust is ejected along the polar axes of the star, because most of the matter is along the equatorial plane, where it blocks the way out). "These bipolar outflows are very short-lived by astronomical standards, a mere 10,000 to 100,000 years, but they are so energetic that they typically eject into space more mass than ends up in the final protostar." (Universe)

Answer 3

It depends on the distance of that star. The light from a star being born "x" light years away would take "x" years to reach your eyes. There are no nearby molecular clouds of new star formations. The great nebula in Orion shows new stars but it is hundreds of light years away. The Pleiades, also a few hundred light years away, are new stars ("only" about 120 million years old) -- the dinosaurs (60 million years ago) would have seen those new stars forming.

Answer 4

It depends on how far away it is from us. The speed of light is constant in a vacuum, which is what space is. These distances are measured in light years (the distance light travels in a year, almost 6 Trillion miles)If a new star was born close to us, like 25 light-years, then we would see it 25 years after it was born. If it were 1000 light years away, it would be visible from here in 1000 yrs.

Answer 5

From the moment at which a new-born star starts to shine, i.e. from the moment when nuclear fusion processes turning hydrogen to helium in its core have started, the further time it would take for a new-born star to be seen from earth depends entirely on its distance from us.

If it was a mere 10 light years away it would take 10 years. If it were a million light years away it would take a million years. Of course in the latter case we would need a telescope.

Answer 6

The universe is about 6000 years old, which means the light from the stars less than halfway across our own galaxy will not be visible yet. Every night new stars appear in the sky as their light finally reaches earth and the light from the nearest galaxy to ours (Andromeda) will not arrive for another almost 2.2 million years. Ain't religion great?

Answer 7

One such "stellar nursery" that's closest to Earth is in the Orion Nebula. Called the Trapezium, this new-born group of stars first "turned on" no more than 300,000 years ago and are some 1,500 light years away.