# Current technology

1. Oct 24, 2007

### BosonJaw

Given current technology, and applicable laws, what is the greatest distance at which we can see 1 star?

2. Oct 24, 2007

### cesiumfrog

Depends how bright it is.

3. Oct 24, 2007

### BosonJaw

How about taking for instance the hottest/brightest stable star? is there a formula? Or one which must be adhered to in order to observe it correctly?

Last edited: Oct 24, 2007
4. Oct 25, 2007

### pixel01

The deep field images of Hubble are about 5 bn light years. According to the BB, we can not see anything further than 13.7 light years.

5. Oct 25, 2007

### SticksandStones

Unless I'm way off, wouldn't it be 13.7 billion light years? That is to say, the age of the universe in light years?

6. Oct 25, 2007

### Laura1013

You're forgetting about the expansion of the Universe. We can see much farther than 13.7 billion light-years.

Edit to clarify: We can theoretically see much farther than 13.7 billion light-years. Our technology and observational methods can limit us.

Last edited: Oct 25, 2007
7. Oct 25, 2007

### SticksandStones

I don't understand. If the age of the universe is 13.7 billion years, and light in a vacuum has the highest attainable velocity, then how can we see further than even light could have traveled?

8. Oct 25, 2007

### Laura1013

I don't fully understand either, to be honest. It's really easy to get confused about this. There's a lot of misinformation out there. Most introductory sources take the Universe as being flat and non-accelerating for simplicity, and use the very basic equation time x velocity = distance. So, thinking about a flat, stationary Universe that is 13.7 years old, then yes, the farthest we can theoretically see would be 13.7 years times the speed of light, or 13.7 light-years.

This previous thread may help: https://www.physicsforums.com/showthread.php?t=183924 .

But the original question asked how far away could we see a star. We can only theoretically see a star as far back as the first star that existed. That would be the theorized Population III stars, which have yet to be conclusively found.

The original question specifically asked about how far we could see with our current technology. I don't really know the answer to that question. I can say that the highest star-related redshift (not CMB) we've measured is around z = 7 to 10, which leads to distances of around 10 to 30 billion light-years, depending on which measurement you trust and which Hubble constant you use.

Last edited: Oct 25, 2007
9. Oct 25, 2007

### Staff: Mentor

The question sounds to me like it is asking how far away we can discern individual stars. That would probably be limited to our neares neighbors in our local group of galaxies - 10 million light years or so. Just a guess though.

10. Oct 25, 2007

### DaveC426913

When the light left that star, it was much closer than 13.7Gly. Space ahas expanded in that time. The star can be much farther away frim us now and yet its light (from 10Gy ago) did not have to cross all that distance.

11. Oct 25, 2007

### DaveC426913

Here is a supernova visible even in a small scope - that's 5 billion light years away.

12. Oct 25, 2007

### Staff: Mentor

I would think this would exclude supernovas, but yeah, there is no practical limit to how far away you can see them - they often outshine their host galaxies.

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