when looking at what appears to be a spherical globular object, how do we know we're not looking down a cylindrical object? With maybe a rounded end? A pencil would look circular from that perspective.
by Budgieye moderator
An interesting point. A "round, smooth" galaxy might be more elongated if it were viewed from the side. In our galaxy, similar supernova remnants are spherical or cylindrical, depending on our viewpoint.
Great question! 😃
For a particular object, with just an SDSS image ... you can't.
Which leads to the question of what is the distribution of intrinsic shapes, of elliptical galaxies?
With a sufficiently large sample, and making the assumption that we are not in a highly peculiar place in the universe (where all elliptical galaxies are oriented so we see a non-random distribution), then the distribution of observed shapes points to the distribution of intrinsic shapes (with perhaps some degeneracy).
It turns out that 'big' ellipticals cannot be more 'cylindrical' than mildly oval (when viewed 'side on'), while dwarf ellipticals can be somewhat more oval.