Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I'm not referring to phenomena such as galaxies or clusters but rather, what is the largest discrete celestial body that has been observed in the universe?

share|cite|improve this question

Depends on your definition. Do you count hydrogen clouds and other wispy things? I'm guessing no. So that pretty much leaves us with stars, dense things, and black holes...

If you're looking at objects' diameters, it appears NML Cygni has the largest radius. R136a1 is the most massive of ordinary, discrete objects. Supermassive black holes are of course much more massive than that. The heaviest discovered seems to change frequently but the largest I found was OJ287, at 18 billion solar masses, listed in the Wikipedia article.

That being said, I think the question is a little unfair. What holds stars together? Gravity. What are stars, and even black holes if you include their whole event horizons, mostly composed of? Empty space. Can you see through a hydrogen cloud? Yes. These are all identical to galaxies and superclusters of galaxies, so if the former things are really to be considered "objects," the latter should be, as well.

share|cite|improve this answer

There is a "Giant Blob" out there that may vie for the largest "thing". It is actually comprised of giant galaxies connected by Lyman alpha blobs. Probably not exactly what you were looking for, but perhaps the Lyman alpha blob may meet your criteria. If not that, then there is the mysterious Hanny's Voorwerp. There is still a lot of stuff out there that defies classification.

share|cite|improve this answer
If wisps count and clusters don't, I'd say the Giant Blob probably takes the cake. – Andrew Jul 20 '11 at 16:53
@Andrew, fair enough. The question itself is a bit unclear as to what really counts. :) – Larian LeQuella Jul 20 '11 at 22:47
Also, bonus points to you for turning up objects with such wonderful names. Hanny's Voorwerp really sounds like it came straight from a Star Trek script. I love it. – Andrew Jul 21 '11 at 13:36
Actually, Hanny's Voorwerp sounds like it came straight from the Hitchhiker's Guide to the Galaxy. – ghoppe Jul 22 '11 at 21:15
If you are interested in this particular story: – Larian LeQuella Jul 23 '11 at 1:15

protected by David Z Mar 4 at 17:57

Thank you for your interest in this question. Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site (the association bonus does not count).

Would you like to answer one of these unanswered questions instead?

Not the answer you're looking for? Browse other questions tagged or ask your own question.