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Apart from stars and galaxies, what are the most distant extended objects that we have ever seen? For example, can gas clouds or nebulae be seen in other galaxies?

In the list referred to in the link only far away galaxies are mentioned. Images of the closest galaxy, Andromeda, show separate stars. Can nebulae be observed in it? Or other non-starry objects? Stars will obviously stay point-like. I'm asking if extended objects (much bigger than stars) can be seen, with the help of time exposed photographs maybe?

By an extended object I don't mean stars or groups of stars. These are easily seen. I mean things like nebulae or other large scale structures. Can these even be observed in other galaxies?

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    $\begingroup$ en.wikipedia.org/wiki/… $\endgroup$ Commented Jun 26, 2021 at 2:26
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    $\begingroup$ @NilayGhosh Thanks for the link. Unfortunately there are only atars and galaxies and artist impressions. $\endgroup$ Commented Jun 26, 2021 at 2:34
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    $\begingroup$ @DescheleSchilder This is an interesting question! I think it will help if you clarify a little bit. If you'd like to ask about farthest resolved galaxy that's one question, the farthest galaxies observed are much farther and unresolved, do you want to exclude them by using "extended" to mean "resolved"? Of course a barely resolved galaxy will be a lot farther than "a nebula seen inside another galaxy". Those would have to be a lot closer. just fyi most of those images are from various telescopes, only a few are artists impressions. $\endgroup$
    – uhoh
    Commented Jun 26, 2021 at 6:26
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    $\begingroup$ @DescheleSchilder Although it's hard to notice this, there are at least a couple of non-stellar, extended sources in the Wiki list Nilay Ghosh pointed to -- e.g., the cluster CL J1001+0220 and the "PJ352–15 quasar jet". $\endgroup$ Commented Jun 26, 2021 at 14:29
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    $\begingroup$ @PeterErwin A quasar jet is what I meant exactly. Can it be seen directly? $\endgroup$ Commented Jun 26, 2021 at 14:50

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The Universe itself is an extended object. The earliest image of the Universe that we are able to currently obtain is the cosmic microwave background (CMB) radiation, which is more technically known as the surface of last scattering since it is when photons from the early Universe were able to decouple from the dense plasma. This occurred when the Universe was about 300,000 years old, so it's like a baby picture of the Universe. This object is more distant than any galaxy or star or other astronomical object.

Perhaps you don't like that answer, well okay. The first galaxies and stars (population III stars) have not yet been observed conclusively, but future observatories may lead the way to this. Depending on how cosmological structure formed (used to be thought to be monolithic, but nowadays we think in terms of hierarchical formation), these early galaxies could have formed before cosmic filaments. It is an open question about when the first dark matter formed, whether before or after or concurrently with these early galaxies.

The galaxy that we have observed to be furthest away, so far, is called GN-z11, which is calculated to have formed around 400 million years after the big bang.

Astrophysical jets can be seen directly and in some cases are well resolved. Sometimes they are produced by the nucleus of other galaxies, like M87, or are produced by very strong magnetic field environments, like pulsars. An example of the latter is pulsar IGR J11014-6103, also called the Lighthouse nebula. This pulsar has the largest jet so far observed in the Milky Way, and whose velocity is estimated at 0.8 times the speed of light in vacuum. From the wiki: "The jet, aligned with the pulsar rotation axis, is perpendicular to the pulsar's trajectory and extends out over 37 light-years (about nine times the distance from our sun to the nearest visible star)." The image below depicts this pulsar's jet.

For some more examples of resolved astrophysical jets, see here.

enter image description here

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  • $\begingroup$ Good answer, as usual, and find on the picture. It includes a nebula as well, which I think Deschele Schilder might also be looking for, judging from the final paragraph of his/her question, though jets certainly. The nebulae are larger than the jets, but are they as bright? Can they be resolved in other galaxies and, if so, then how far out? I think, though I hesitate to speak for others, that his/her question is asking about apparent brightness, angular diameter, distance and resolving power. What are our current limits? (My limits, at night, are about twenty feet. Old eyes.) $\endgroup$
    – JohnHunt
    Commented Jul 1, 2023 at 23:55
  • $\begingroup$ @JohnHunt Hi and thanks! Generally, most of the 'nebulae' we've observed are in other galaxies whose brightness depends on a lot - how far away, how energetic is the source, what is our viewing angle, etc. The resolvability of an object for a telescope depends strongly on the specs of that telescope. Prior to Hubble, telescopes could see to (cosmological) redshift ~1, which is not very far cosmologically. Hubble was able to see to redshift ~10 but it was very very blury. JWST can see that far but with great resolution. As long as we keep funding science, we won't have to rely on our eyes :) $\endgroup$ Commented Jul 17, 2023 at 13:08
  • $\begingroup$ This gives an idea: esahubble.org/images/heic1103e $\endgroup$ Commented Jul 17, 2023 at 13:09
  • $\begingroup$ I encourage you to ask your questions as a new post! $\endgroup$ Commented Jul 17, 2023 at 13:09

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