They say that when we look up to see stars, we’re actually seeing the light from dead stars. So technically, we can’t see what’s out there in the present? What do you think is out there now? is it just new, modern stars or we don’t get to see anything at all? (since by now, everything has expanded billions of miles apart from each other that light is far from anything to reach)
In: Planetary Science
Stars you see by naked eye are rather close. Like, few hundred light years close, and pretty much not dead.
The universe is highly homogeneous which means that on the largest scales we see the same thing everywhere. Galaxies are not too dissimilar from one another. (Even though there is plenty of variety there are also lots of galaxies to sample.) So looking at very distant galaxies and ones closer is like looking at one sort of average galaxy at different points in time.
So we don’t know exactly what is going on “right now” but we roughly know. Maybe very massive stars we see in a galaxy 2-3 billion light years away are long gone, we have a good idea how that galaxy looks now by looking at galaxies a bit closer. Or rather we can only see a specific galaxy at a specific point in time but given a large number of similar galaxies we can easily piece together possible “screenplays” for galaxy formation and development.
None of the stars you can see with the naked eye are dead, except maybe (one in a million chance) Betelgeuse, an appropriate star to name a living-dead demon after.
For us to be seeing stars that have been dead for billions of years, the stars would have to be more than a billion light years away. None of the stars you can see without a telescope are even close to that far away. They’re all within a few thousand light years of us.
No they aren’t.
The stars we can see with out naked eyes aren’t that far away.
Most stars we can see are less than a 1000 light years away.
Our entire galaxy is only 100,000 light years across.
The shortest lived stars are very rare blue super giants which last for 10 million years.
Our own sun is 5 billion years old and will last for maybe 9 or 10 more billion years.
Red dwarfs, which are the most common type of star can last for trillions of years.
So in terms of how long stars last the delay of us seeing them of a few years, decades, centuries or even millennia is nothing.
The farthest object we can see with our eyes is the Andromeda Galaxy, we can only see it under ideal conditions like out in the country where the air is clean and there isn’t much light pollution and even then we can’t make out any details, but the distance is large enough that some of the shorter lived stars we see in there are almost certainly dead by “now”.
For object farther away viewed big telescopes and other instruments the certainty is much bigger. Especially since the brightest things tend to be the most short lived (in general if not in ever individual case).
Of course “now” or “at the same time” are not really concepts that hold any really meaning on these scales. Relativity means that such things don’t really work the way we normally think of them.
So yes keeping in mind that “now” is not really a thing, a few of the nearer objects and many of the more distant objects no longer exist “now”.
However we do have a good understanding of how stars live and move and die. We know their lifecycle and can make pretty good guesses how stars and larger objects have changed over time since they emitted the light we see.
I just want to add that the vast vast vast majority of stars you see with your naked eye are within like a few hundred light years. So their light left a ~hundred years ago, not billions. Even the Andromeda galaxy, which is perhaps the farthest thing you can see without a telescope, is only 2.5 million light years away.
So almost everything you see without a telescope is still there, just a little bit older than what we see.
When you are looking at the stars with your unaided eyes, 75% of them are within 500 light years. 90% of them are within 1100 light years. So unaided, what you see is younger than the Roman empire and most is younger than the oldest university in the english speaking world.
As for what we can see with a telescope… Stars have lifecycles and we can estimate where stars are on this (by size, emission spectrum, etc). We can also observe how they are moving and, along with all the other gravitational sources, predict their path. Thus we can and do make pretty good models of what distant galaxies look like now. In fact one thing we do to test theories is to model young ( far away ) galaxies we see, simulate their temporal evolution, and see if they look like the closer, older galaxies. (Simplified for eil5).
They’re not all dead. Only the extremely far ones that appear to be older may have expired.
But what’s left depends on the star type.
Very large ones likely died as they burn fast for stars. It could have left a black hole, or just blew apart into its parts, which may have enough material to form another, smaller star like our sun and planets. Right “now” it could be lit and planets still cooling. Life could be starting in its early proto- life state like it did here.
But we won’t see that. We still see the large star as it was however many years ago.
White dwarfs are what our sun would leave. They expand and fire off the outer layers, cooking the planets nearby. Then the center is a dead husk of a star, still glowing from risidule heat for a certain amount of time. We would see a nubula. Large area of gas lit up by the dead core, and if you look close, you might still see some planets if they survived and stayed in orbit.
Yeah i like to think that a ten thousand years ago a giant space civilization started growing and had taken up a lot of our sky but we haven’t seen it yet because the light hasn’t arrived
Some of the light is only tens of years old. many more stars we see as they were hundred of years ago. All of the stars you can see as separate points of light with your un-aided eyes are maybe a few hundred thousand years old, within our local galaxy. We can see other galaxies that are millions of light-years away, but they are mainly just fuzzy blurs in the night sky. The vast majority of all these stars that we can see, in our local and nearby galaxies, are still there now.
When astronomers look at the deep sky, up to billions of light-years away, they see ancient galaxies containing stars that may well have mostly exploded into novas or burned out into dwarfs since then, but there are always new stars being formed from the dust and debris of other stars. So we’d expect new stars to still be there, if we could jump there (or where they’ve moved to) today.
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