I understand that the Milky Way is more or less flat except for the bulge in the middle, is surrounded by a sphere of globular clusters, and has spiral arms. Now: 1) If the galaxy was ten feet in diameter, then what would be the total diameter of the spherical midbulge. (Like the radius up from the middle of the galaxy and the radius down and they two add up to the diameter)? 2) What is the diameter of the realm of the globular clusters and 3) is this glob. clust. sphere only around the bulge of the galaxy or is it around the whole thang? 4) How many spiral arms do we have, 5)and most important of all, when they say elliptic galaxy, do they mean a more or less flat ellipse, which seems proposterous, or do they mean an three-dimensional ellipse, like a football, but without points? Come to think of it, this is just as preposterous because in either case these ellipticals are turning around and around, which would turn them into spheres or discs. Therefore according to the laws of gravity, there is no such thing as an elliptical galaxy. Maybe they just mean they look elliptical in the telescpoe?
regarding the ellipticals: they would indeed be 3-dimensional “ellipses” – not so much like a football as like a peppermint lozenge, or like two Frisbees held together. A football is longer between its two ends than it is wide; elliptical galaxies flare out to their longest dimension at the point that on a football has the stitches on it (from stitches to opposite side of football), so if you imagine a very foreshortened football, say 6 inches from point to point, and a foot and a half in circumference in the vicinity of the stitches, you’ve got the general idea.
It got that way by spinning. Hold your foreshortened football so the points are aligned vertical and spin it. As you see, the spinning motion would tend to “fling out” mass towards the middle (90° away from the poles) so it becomes elliptical in that sense rather than being spherical.
Arms form after it has kept this up for awhile. Think fluids. I don’t know how many distinct arms the MW galaxy has, nor can I give you good proportional figures.
Uh, make that foreshortened football a foot and a half in CROSS-SECTIONAL DIAMETER, not circumference. From seam to the part of the football opposite the seam = 18 inches compared to 6 inches from point to point.
The milky way has two spiral arms. In fact, nearly every spiral galaxy has 2 arms (I can’t think of one that has more or fewer, but that’s not proof that they all do), for the reasons that AHunter has suggested about the formations of such galaxies. Most spiral galaxies were stretched and spun ellipsoids that grew out into long swirls
Try to imagine how a blob would have to spin to make 3 or 4 arms come out of it and you will see why (nearly) all spiral galaxies have two arms.
BTW, most galaxies are spiral galaxies, which supports the hypothesis that all galaxies eventually stretch and spin into spirals.
What “globular clusters” are you talking about? I’ve never heard anything like that in relation to a significant feature on the galactic scale. Nor have I seen anything that might fit that description in the various pictures I have seen.
Now, I’m not saying that such features do not exist, just that I’ve never heard of them. Particularly not as defining features of the shape of our galaxy.
Globular clusters are large, dense balls of stars that orbit galaxies in huge spherical orbits. They generally predate the galaxies. They’re quite beautiful through a telescope.
This from the CalTech web site:
Kevin B.
TheNerd, if you know any amateur astronomers, ask them if they can show you M15 or M2. Better yet, if you live far enough south, you can see Omega Centauris with your naked eye. All three are excellent examples.
Universally speaking, that’s quite compact. I don’t mean to get off on a hijack here, but it got me to thinking. Would planets that are circling one of those stars be more likely to have the necessary heat to support life as we know it?
Imagine living on a planet with hundreds or thousands of stars as bright as the sun in the sky at all times…I understand that’s about what the globular clusters would be like. I think that would rule out most life, and possibly planets, too.
As far as clusters orbit this galaxy, could you be referring to the Magellanic Clouds? They’re kinda like two mini-galaxies that orbit the Milky Way as satellites.
The Milky Way is 100,000 light years in diameter and 16,000 light years thick in the middle. (I may start singing Monty Python’s Galaxy Song!) So, if you scale the diameter down to 10 ft, the central bulge would be 1.6 ft thick.
No, the Magellanic Clouds are galaxies in their own right, albeit a lot smaller than the Milky Way, and gravitationally bound to it. Even little galaxies like the Magellanic Clouds are roughly 1,000 times bigger than a globular cluster.
Here’s a link to a picture of M15, one of the more famous globular clusters. The ‘M’ designation means it’s on the Messier List, which is a list of “fuzzy objects” that an astronomer named Messier came up with so he’d stop mistaking them for comets, which was what he was looking for.
Some globular clusters are regular, which means nice spheres of stars, and some are irregular. A) why aren’t they all regular, since gravity always makes things into spheres unless they are twirling too fast, and then it makes them into discs, B) do all the globular clusters rotate the say way and are their axes all in the same plane? C) does the gigantic sphere of globular clusters rotate independently of the galaxy or just as the galaxy rotates? And if the latter, is there any slippage at all?
Globular clusters and eliptical galaxies are among many subjects in astronomy covered by the Astronomy Picture of the Day site, from NASA. If you like star pictures, make it a daily visit.
Tris