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JWST Star Test

johninderby

By johninderby
in The Astro Lounge

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vlaiv

vlaiv

Posted
Posted

Ha! there is a thought.

Do you think JWST will suffer from light pollution issues?

I mean - multi day exposure with such aperture is bound to pick up some of the cosmic microwave background. We do call it microwave, but it is actually black body type radiation (very cold indeed) - which means some of it must be in IR part of spectrum as well.

 

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vlaiv

vlaiv

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23 minutes ago, Tomatobro said:

I was thinking about if the light of a distant galaxy has not yet reached JWST could we have a situation where two images taken say 1 month apart a distant galaxy might appear on the later image?

My first reaction was that this is not possible - but it turns out that it is - although not quite the way you said.

Problem is with expanding universe and there are bunch of galaxies that we will never see as light from them will never reach us because expansion of universe is greater and it will always be ahead of distance covered by light (and increase lead over time).

However, it turns out that our present "reach" is about 18Bly while universe is about 13.8By old and galaxies did not need much time to form - around 1By. That leaves about 3.2Bly thick shell with first galaxies that can still reach us in the future.

So there are galaxies to be seen - but will we be able to see them appear in our lifetime or maybe in future centuries (for future astronomers to compare images)? - well no.

If you think about it - our nearest star is 4 Ly away - so it takes 4 years for light to reach us.

Distance to our neighboring galaxy is 2.5Mly, and Milky way is what 100,000Ly across give or take - so depending on angle - it could take up to 100,000 years of "appearing" for a galaxy the size of milky way - not quite "popping into existence" or one moment it's not there and the next it is :D

It would also take millions of years between two consecutive appearances (remember - space expanded and the distance between galaxies that was then - is now much bigger).

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vlaiv

vlaiv

Posted
Posted
4 minutes ago, Swoop1 said:

Once again, I declare you all GIT!

I'm a computer programmer and for me, GIT is source code version control system :D - so I don't really get what you mean by that.

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Pixies

Pixies

Posted
Posted (edited)

But with the accelerating expansion of the universe, and distant objects accelerating away from  us faster than the speed of light, could  there be a point when a galaxy has moved beyond the observable limit and will just vanish to us?

 

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Pixies

Pixies

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13 minutes ago, Pixies said:

But with the accelerating expansion of the universe, and distant objects accelerating away from  us faster than the speed of light, could  there be a point when a galaxy has moved beyond the observable limit and will just vanish to us?

 

Just done some Googling - apparently in about 150 billion years, the light from these galaxies will first become so red shifted that they will appear to freeze in time.

I really need to retire and do that degree in astrophysics!

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vlaiv

vlaiv

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2 hours ago, Tomatobro said:

But could not the light from a galaxy just beyond the edge of the current observable universe be one light month away from reaching JWST?

 

Yes, but the process of them becoming visible will last couple hundred of thousand of years.

Little will change in a month - it will become roughly 1 / 12 * 100,000 brighter in the image in a course of month (if we assume uniform luminosity - and 100,000 years "appearing" period.

It won't just pop into view.

If it's bright enough - you won't see a change, if it's not - odds are that noise will be larger than change in brightness of the galaxy over the course of a month as more of it comes into view.

3 hours ago, Pixies said:

But with the accelerating expansion of the universe, and distant objects accelerating away from  us faster than the speed of light, could  there be a point when a galaxy has moved beyond the observable limit and will just vanish to us?

Yes - about 94% of galaxies that are now visible - we can't reach even if we set now off towards them with a speed of light (they are already in process of "fast" receding).

Almost all will eventually vanish from the view, but it will take couple of billion of years, so we are good for next Messier marathon :D (downside is that we can't blame expansion of universe for those galaxies that we fail to see :D ).

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Swoop1

Swoop1

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21 hours ago, vlaiv said:

I'm a computer programmer and for me, GIT is source code version control system :D - so I don't really get what you mean by that.

The term Git (or GIT if you are shouting) is a friendly derogative which I use when folk make my brain explode.

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SamAndrew

SamAndrew

Posted
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On 17/03/2022 at 11:46, vlaiv said:

Distance to our neighboring galaxy is 2.5Mly, and Milky way is what 100,000Ly across give or take - so depending on angle - it could take up to 100,000 years of "appearing" for a galaxy the size of milky way - not quite "popping into existence" or one moment it's not there and the next it is :D

My understanding is the space that becomes visible to us, appears as it was at the end of the dark age of the universe (370,000 years old), if we continue to watch that region of space we would be able to watch the stars and galaxies forming (assuming a telescope with enough resolution!) although they would continue to redshift and eventually freeze and fade from view.

As time goes on we see more and more space as it was at the end of the dark age, but we see less and less of its history before it fades out of view.

So it would actually take as long as it takes for a galaxy to form, for one to come into view, but actually it takes even longer than that because the rate of time that we see in that region of space appears much slower due to the light redshift.

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