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Webb captures iconic Horsehead Nebula in unprecedented detail

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Re: Webb captures iconic Horsehead Nebula in unprecedented detail

#81

Post by injidup »

sandworm101 wrote: post #71
markus_zhang wrote: post #69

Earlier quoted context omitted.

Is 2,000 billion some theoretical limit or something else? Thanks.

Yes. Take the age of the universe, multiple by the rate of expansion to get the total size of the universe, then multiple by the average density of galaxies in the observable universe. There are some further complications, but at the root it is basic algebra.

So if the universe has a size then what do you see if you are on the edge of it? Do you see stars to the left and nothing to the right? I mean given the speed of light and the age of the universe and the rate of expansion there are regions inaccessible to us but that doesn't quite mean the universe has a finite size.

Re: Webb captures iconic Horsehead Nebula in unprecedented detail

#82

Post by causal »

sandworm101 wrote: post #71
markus_zhang wrote: post #69

Earlier quoted context omitted.

Is 2,000 billion some theoretical limit or something else? Thanks.

Yes. Take the age of the universe, multiple by the rate of expansion to get the total size of the universe, then multiple by the average density of galaxies in the observable universe. There are some further complications, but at the root it is basic algebra.

Replying to the other replies here - this regards the observable universe. Speed of light limits and all that. Of course we have no reason to believe the universe just stops at the point where we happen to lack the ability to observe.

Re: Webb captures iconic Horsehead Nebula in unprecedented detail

#83

Post by dragonwriter »

injidup wrote: post #81
sandworm101 wrote: post #71

Earlier quoted context omitted.

Yes. Take the age of the universe, multiple by the rate of expansion to get the total size of the universe, then multiple by the average density of galaxies in the observable universe. There are some further complications, but at the root it is basic algebra.

So if the universe has a size then what do you see if you are on the edge of it? Do you see stars to the left and nothing to the right? I mean given the speed of light and the age of the universe and the rate of expansion there are regions inaccessible to us but that doesn't quite mean the universe has a finite size.

Finite size doesn’t require an edge. Consider the surface of a balloon for a 2-D case (or the perimeter of a sphere, for a 1-D case): it has finite extent, but no edge.

Re: Webb captures iconic Horsehead Nebula in unprecedented detail

#85

Post by fooker »

madradavid wrote: post #84

Total noob question here and I apologize in advance. Are these the “actual” pictures or are they “touched up” by an artist ? If they the real pictures then this is truly impressive …

It's the intensity of infrared(-ish) light hitting multiple sensors with different wavelength filters.

If you were to look at it in person it would be a fairly smooth white patch. The colors are artificially assigned, but not by an artist. You pick a specific color for each wavelength. The Hubble palette is spelled out here: https://www.astronomymark.com/hubble_palette.htm

Re: Webb captures iconic Horsehead Nebula in unprecedented detail

#86

Post by whatshisface »

madradavid wrote: post #84

Total noob question here and I apologize in advance. Are these the “actual” pictures or are they “touched up” by an artist ? If they the real pictures then this is truly impressive …

They're "touched up" in a scientific way to remove flaws in the telescope (light leaking in from the sides, some distracting aspects of the diffraction patterns that from around stars). The colors come from combining several black-and-white images, taken at different frequencies. You can explore the subjectivity of infrared images by opening them in GIMP and playing with the hue slider.

Re: Webb captures iconic Horsehead Nebula in unprecedented detail

#87

Post by reactordev »

sandworm101 wrote: post #71
markus_zhang wrote: post #69

Earlier quoted context omitted.

Is 2,000 billion some theoretical limit or something else? Thanks.

Yes. Take the age of the universe, multiple by the rate of expansion to get the total size of the universe, then multiple by the average density of galaxies in the observable universe. There are some further complications, but at the root it is basic algebra.

What about the big ring [0]? Or other mega structures of galaxies outside that “bubble”?

[0] https://en.m.wikipedia.org/wiki/Big_Ring

Re: Webb captures iconic Horsehead Nebula in unprecedented detail

#88

Post by dotnet00 »

injidup wrote: post #81
sandworm101 wrote: post #71

Earlier quoted context omitted.

Yes. Take the age of the universe, multiple by the rate of expansion to get the total size of the universe, then multiple by the average density of galaxies in the observable universe. There are some further complications, but at the root it is basic algebra.

So if the universe has a size then what do you see if you are on the edge of it? Do you see stars to the left and nothing to the right? I mean given the speed of light and the age of the universe and the rate of expansion there are regions inaccessible to us but that doesn't quite mean the universe has a finite size.

The observable universe has a size, the cosmic microwave background is what we 'see' at the 'edge' in terms of photons (~400k years after the big bang). We could see further if we could map out the gravitational wave or neutrino backgrounds (1 sec after the big bang).

But for now we can't really say if the universe in its entirety has a finite size.

Re: Webb captures iconic Horsehead Nebula in unprecedented detail

#89

Post by reactordev »

worldsayshi wrote: post #80
sandworm101 wrote: post #71

Earlier quoted context omitted.

Yes. Take the age of the universe, multiple by the rate of expansion to get the total size of the universe, then multiple by the average density of galaxies in the observable universe. There are some further complications, but at the root it is basic algebra.

Is that really the way to see it? As I understand it, the Big Bang didn't happen in "one place". The Universe is expanding from an compressed state - the Big Bang state. But there is no center point. We can only see that there's expansion but it's not from a single point. The only known "center point" is us. And the only reason it's a center point is because we can only see as far away as light has traveled since the…

This theory of multiple points supports the big ring and other structures outside the “this shouldn’t exist” bubble. The bubble is the Big Bang + rate of expansion. It was thought that there was nothing outside of the farthest point… but there is!

Re: Webb captures iconic Horsehead Nebula in unprecedented detail

#90

Post by lupire »

dragonwriter wrote: post #83
injidup wrote: post #81

Earlier quoted context omitted.

So if the universe has a size then what do you see if you are on the edge of it? Do you see stars to the left and nothing to the right? I mean given the speed of light and the age of the universe and the rate of expansion there are regions inaccessible to us but that doesn't quite mean the universe has a finite size.

Finite size doesn’t require an edge. Consider the surface of a balloon for a 2-D case (or the perimeter of a sphere, for a 1-D case): it has finite extent, but no edge.

It has a surface, though, which is what PP was asking about.An answer to the question is, yes, nesr the edge/face, one side is dark. But relativity and expansion makes the situation a bit more complicated.
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