Hot answers tagged galaxies
22
Not quite like in the photo above, which shows more than what the naked eye can see, but yes, absolutely! Our galaxy (well, the chunk of it visible from these parts) is a naked-eye object. The fact that your question even exists shows how much time is now spent by people under light-polluted skies.
It will not be visible from the city, however. You need to ...
19
The material (gas and stars) in the outer part of a galaxy move with roughly the same velocity as the inner part (for example, see this paper), which means that the inner portions do indeed have a faster angular speed; this is sometimes referred to as the "winding problem."
One important feature of spiral arms is that they are bright more because they have ...
16
The estimates I've read are similar to yours: 200 to 400 billion stars. Counting the stars in the galaxy is inherently difficult because, well, we can't see all of them.
We don't really count the stars, though. That would take ages: instead we measure the orbit of the stars we can see. By doing this, we find the angular velocity of the stars and can ...
14
Asimov's description is pretty much correct. There aren't many stars out there, so the night sky away from the galactic disk would be fairly dark. Toward the galaxy you you have an edge on view of the galactic disk.
As for a sky full of galaxies, you might see a few but probably not. They are intrinsically very faint and moving a few tens of thousands of ...
14
Short answer
The question is a bit ambiguous.
If the question is
why do star velocity increase with distance close to the galactic centre ?
the answer is
because their orbit encompass more mass, and this corresponds to a stronger gravity pull.
If the question is
why does their velocity stays constant and does not decrease at big radii, ...
14
To some extent the universe exhibits something called self-organized criticality where a dynamic, non-linear system with many degrees of freedom (the gas after the Big Bang but before the emergence of structure) eventually forms a system with a notable degree of scale invariance (moons orbiting planets, planets orbiting stars, stars orbiting galactic ...
13
No one has discovered it. Dark matter is a proposed explanation to some observed phenomena.
In particular,
Galaxies rotate at a speed that implies they are quite heavy, especially towards the outer edges - but when we look at the mass from stars and interstellar gas, there isn't enough to make them spin the way they do.
Gravitational lensing is a ...
11
There are two elements to why the universe appears to be so orderly: the physical laws of that govern the universe are the same everywhere, and astronomical objects are very, very, very far from each other.
Consider two objects, one much larger than the other, and both very far from anything else. Because of gravity (which works the same everywhere), the ...
11
If you have a properly aligned telescope with good setting circles, you can easily use the RA and Dec of the galaxy to locate it (or any other deep space object you have the coordinates for). However, many times you don't have those properly dialed in or you're using an alt-az telescope mount (like a Dobsonian telescope) and need another way to find your ...
10
The idea of the existence of galaxies is certainly not new, and quite a bit older than the field of modern astrophysics.
In 1750, Thomas Wright, an English astronomer correctly speculated that the Milky Way was a flattened disk of stars and that some of the nebulae astronomers viewed in their telescopes were separate "Milky Ways".
In 1755 Immanuel Kant ...
10
The simple answer is that the average galaxy spacing is around a few megaparsecs, while the biggest galaxies are around 0.1 megaparsecs in size. So the average spacing is somewhere in the range of 10 - 100 times the size of the biggest galaxies. The peas I had for lunch today were (at a guess - I didn't measure them!) 5mm in diameter so the interpea spacing ...
9
I was giving a talk about the galactic black hole at the center, Sagittarius A*, back in 1998. At that time, it was already clear to enlightened people that it had to be a black hole. An analysis of a two-temperature plasma helped to bring some new evidence that the object had a real event horizon.
The black hole is huge but it is not "galactically" huge. ...
9
Look at the question a different way: will the Earth get "sucking into" the sun? Answer: no, it's in orbit.
Now, black holes are a little different because inside 3/2 of the Schwartchild radius there are no stable orbits, but at very large distances gravity is gravity and orbits are orbits.
8
"The Milky Way Galaxy" is indeed the correct name for our Galaxy in western culture, the name "Milky Way" comes from the Latin Via Lactea (translated from Greek).
The name varies from culture to culture, for example the Chinese use "Silver River" to represent our Galaxy.
Wikipedia has a good list of name for the Milky Way.
8
Yes. Since the gravitational force is long-range, one star traveling through a star field tends to leave behind a slightly denser "wake" of stars that moved slightly towards its previous locations. This increased density acts to pull backwards on the fast-moving star, creating a sort of fluid friction, or viscosity. The Virial Theorem is based on a ...
8
According to this link (now dead):
In the solar neighborhood, the stellar density is about one star per
cubic parsec (one parsec is 3.26 light-years). At the Galactic core,
around 100 parsecs from the Galactic center, the stellar density has
risen to 100 per cubic parsec, crowded together because of gravity.
So we'd see about 100 times as many ...
8
One interesting fact is that there are some revolving structures in space that aren't mostly flat - they're known as elliptical galaxies. And the difference here is that elliptical galaxies usually don't have much gas or dust in them. Interestingly enough, the orbits of objects in the inner solar system also tend to be coplanar, whereas the orbits of the ...
7
It takes millions of years for galaxies to collide so even though they're mainly gas and dust they have a weak force of attraction. Also as you mentioned in your question they have a super massive black hole in the middle that pulls them together and drags the rest of the galaxy with them.
It's also incredibly unlikely that even one of the stars will ...
7
There's a strong consensus among astrophysicists that there is a supermassive black hole at the center of our Galaxy (as there are in most large galaxies, apparently). But as cool as that fact is, it's possible to make too much of it. The black hole at the center of our Galaxy has a mass of a few million times that of the Sun, which is a tiny fraction of ...
7
I think the important thing, as Patrick brought out, is that the name "Milky Way" is what the galaxy is called in Western culture. Names change between cultures and between languages. As far as astronomical objects go, often they will have ties to ancient cultures (e.g. Mercury, Jupiter). In English, the name of our galaxy is The Milky Way Galaxy. Sometimes, ...
7
Yes all the stars you can see belong to the Milky Way galaxy. The Sun is located about two-thirds of the way out from the galactic center. Thus the band across the sky known as the "Milky Way" (from whence the galaxy name came) is the main disk of the galaxy. However, all the individual stars we see are still inside that disk, we just happen to be closer ...
7
most of the astronomy images we find online have some color modification
How close to the false color images would they be
This is a common misconception, that the pictures you see of galaxies and nebulae are necessarily "false color", "modified color", or "photoshopped". Some of them, yes. But a lot of them are quite simply true color, but taken ...
7
Unfortunately, it's highly highly unlikely. We're barely even capable of identifying individual stars within the Andromeda galaxy (and the ones we can identify, if any, are almost all supergiants - these are pretty much the only stars we can identify in the Local Magellanic Clouds, which are closer than Andromeda). Even if we were able to identify individual ...
6
Welcome to the mystery of Dark Matter. The gravitational influence of an undetected (aside from its gravitational influence) amount of matter is what is causing the irregular rotation of stars in the galaxy as you noted (not black holes). And solar systems behave much more classically, which again gave us the clue to dark matter's influence.
Wikipedia has ...
6
The Milky Way has prominent dust lanes that can obscure a significant portion of it. As seen in the various pictures in this article, there are parts where the dust lanes are so thick that it might actually appear to be two bands. I used to teach an astronomy lab where plastic celestial spheres (like world globes, but for the sky) were used. They had the ...
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