Are Deep Space Objects Still There?

[Edeff]

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The light by which we see distant deep space objects left those objects thousands, millions, even billions of years ago, yet we speak of them in the present tense, Perhaps this is just a convenience; they may be more accurately referred to in the past tense. In any event, given that the light forming the images we see actually left the objects so long ago, how do we know they still exist?

 

[lomidrevo]

basically all stars we can resolve individually are located in our own galaxy, so none of them is further than approximately 150 000 light years, so for those farest away we see them as they appeared 150 000 years ago. This is quite short period comparing to lifecycle of most of stars, so almost all of them still exist in the same stage as we see them, but a small part might have evolved meanwhile to another stages of their life, including stellar remnants. But we have models of stellar evolution so we can predict their current stage.

 

[lomidrevo]

For the objects further away, we talk about galaxies. They would still exist, evolved however (depending on their observed distance), some of them merged. Anyway we have models for that as well, so we can predict that.

 

[lomidrevo]

btw I think astronomers are probably not so interested in the "current" status of the farest objects. Any information originated at those object cannot travel faster than light, including any gravitational influence, they might have on us. If astronomers want know how the galaxies in the universe looks right now, they just observe our close neighborhood.

 

[mathman]

Individual stars in neighboring galaxies can be seen by telescope. The Cepheid variables give the information needed for distance. In distant galaxies, type Ia supernovae are visible - their observation led to the observation that expansion of the universe is speeding up.

 

[lomidrevo]

Individual stars in neighboring galaxies can be seen by telescope. The Cepheid variables give the information needed for distance. In distant galaxies, type Ia supernovae are visible - their observation led to the observation that expansion of the universe is speeding up.

Correct, I should have added "by naked eye" in my first post to be clear. I assumed (perhaps incorrectly) that OP's thoughts emerged when looking at the night sky with all its beauty and majesty, as usually is my case :)

 

[Grinkle]

If astronomers want know how the galaxies in the universe looks right now, they just observe our close neighborhood.

I sometimes fall into the trap of forgetting that objects at the edge of the observable universe, per the hypothetical co-moving clock, are not actually older than objects right next door. A comment like the one you made is a great anchor for my intuition.