You’ve probably seen them, such as the one here from Hubble, or this from JWST. If you don’t want to click through, these are just the typical deep space photographs of scores of galaxies in a single frame.
My question is, are these only visible at a specific location, or do they see this wherever they look in deep space (provided the view isn’t obscured by closer star systems and/or galaxies?
I realize it takes an incredible telescope to view these. The ones from Hubble, I believe I read, took days, if not weeks, to capture enough light to be able to resolve. I think JWST can do it in just hours. But, do they have to know where to look to find these, or are they simply anywhere they look that doesn’t have anything closer in the way?
They look anywhere that there’s not a nearby bright object in the way. Everywhere you can look, if you look long enough, you’ll see very distant galaxies.
The observed region of sky in Ursa Major was carefully selected to be as empty as possible so that Hubble would look far beyond the stars of our own Milky Way and out past nearby galaxies.
I believe that the idea is to aim at a tiny “dark” portion of sky so as not to have the image completely obscured by intervening stars. You can see in the JWST image that it still happens, but it’s minimal. It’s not in the Hubble image, but I think that’s because the Hubble image consists of several dozen different overlaid and processed images to yield that final picture.
I simple answer is that there are that many galaxies in every direction that you look, all over the sky, which is pretty mind boggling.
As noted above they get these fine pictures by looking at a dark area of the sky where other light sources aren’t interfering with the view. But the entire orb of the heavens would look like that if not for other stuff blocking the view.
Thanks for the responses. Your answers are what I was thinking.
These answers do make me wonder, though. They also say they are looking back at the big bang. That some of the galaxies in the JWST photo are 13.6 billion light years away, with the big bang occurring 13.7 billion years ago. Does that mean that anywhere you look that isn’t compromised by intervening stars (or other matter), you can see galaxies from 13.6 billion years ago? In today’s universe, those would have had to be fairly close together, correct? I know the universe is expanding, but we can’t be at the center of that expansion, can we?
Also, if some of those galaxies are 13.6 billion years old, they likely do not exist, anymore, correct? Well, the galaxies may still exist, but the stars that produced the light we are seeing no longer exist. This all seems so very strange.
It seems that from no matter where you look as far away as you can you will see galaxies like this from close to the beginning of the universe. Everywhere looks like the center of the universe, and in that sense it is. Only that the universe does not have a center, a center of mass or a center of gravity. The universe does not have any privileged place, and a center would be. There is no absolute frame of reference (see relativity), and a center would provide one.
Of course we humans cannot go anywhere to test this out, we live on Earth. But if we could go anywhere we wanted to everything we know indicates that there would be the same phenomena visible if we had also brought the right instruments.
It is, I agree. And that is only one aspect of many. I like it, btw. I believe that you don’t have to understand everthing to enjoy it.
There are a few foreground stars in that Hubble picture-- I count at least seven. The brightest is right on the right edge of the image, about 40% of the way down. You can recognize the stars by the “spiky” shape: That’s from diffraction effects from the telescope structure, on high-intensity point sources.
The Webb picture is taken of a specific, special spot in the sky. You notice how a lot of the galaxies are sort of smeared out, around sort-of-concentric-rings? Those galaxies are all gravitationally lensed, because that particular spot in the sky has a nice big massive (relatively) nearby galaxy lensing the more distant ones. That magnifies the distant galaxies, letting us get a better view of them (once we correct for the distortion, which is difficult but doable). That’s probably also why they were willing to tolerate a spot of the sky with more/brighter foreground stars, because that lensing is just too good to pass up.
Note that at a large scale, the galaxies are not uniformly distributed. Many of them are in “filaments” called the Cosmic Web. Blame Dark Matter, of course.
A straightforward picture doesn’t reveal these filaments. You have to figure out the distances involved to sort them into filaments. But there could be filaments, when viewed from Earth, that luckily line up so a pic taken along that axis will show a lot more galaxies.
A common way to visualize this kind of expansion is to compare it to dots on a balloon. Draw dots all over a balloon and then blow it up. From the perspective of any dot, it appears that all other dots are expanding away from it. No dot is truly at the center of expansion. If you think about it, the center of expansion is inside the balloon. That’s where all the dots were before the balloon was blown up. And the dots are expanding into the space outside the balloon. The inside/outside is also a way to think about time. Inside the balloon is the past, outside the balloon is the future, and the surface of the balloon is now.
Right. Just as someone in one of those galaxies looking this way would see the baby Milky Way in whatever form it had 13 billion years ag, filled with stars that no longer exist.
Thank you. That’s the best way of helping me visualize the universe that I’ve read. It doesn’t invoke some fourth spatial dimension that my brain is unable to visualize (the dreaded hypersphere ).
More of a medium scale. At the largest scales, the filaments themselves are evenly distributed. The filaments are only a couple hundred million light-years long, but the visible universe is many billions of light-years across, and the whole universe is probably much larger.
That deep field doesn’t come close to showing you all the galaxies that are in the field of view. The JWST image represents a total exposure time of 12.5 hours. If JWST does a 100 hour deep field it will see many more galaxies.
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