Massive systems held together by gravitational attraction, consisting of stellar associations, star systems, star clusters and types of interstellar clouds, stellar remnants, gasses, cosmic dust and an important but not yet completely understood component called dark matter.
16
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2answers
206 views
How would the night sky appear at the edge of the galaxy?
In Isaac Asimov's Foundation Series, there is a planet named Terminus which is believed to be the planet farthest from the galactic center.
There are almost no visible stars in its sky, only the ...
13
votes
2answers
114 views
How can a spiral galaxy exist?
A spiral arm orbiting a central mass should be dispersed quite quickly as the outer elements would move more slowly than the inner ones. The Milky Way, is about 59 Galactic Years old, which, one would ...
13
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1answer
622 views
Which way do spiral galaxies rotate?
Is it known whether spiral galaxies typically (or exclusively?) rotate with the arms trailing or facing?
Intuitively it feels weird to think of the arms as facing the direction of rotation, but ...
12
votes
1answer
2k views
How many stars are in the Milky Way galaxy, and how can we determine this?
I have heard multiple estimates on the quantity of stars within our galaxy, anything from 100 to 400 billion of them. The estimates seem to be increasing for the time being. What are the main methods ...
11
votes
4answers
211 views
What is the name of our Galaxy?
I was told that the name 'Milky Way' first came about when people observered the milky looking stretch of sky; that is, before telescopes came about and we realised it wasn't a milky cloud, but rather ...
11
votes
4answers
904 views
How to find the Andromeda galaxy without using a go-to telescope?
In other words, what is the proper technique (star-hopping or other?) in order to find and properly point a telescope to this target? Would a star atlas or other tool/reference help? Can I use the ...
10
votes
4answers
10k views
Can the “Milky Way” galaxy be seen by the naked eye in a clear sky?
Is this photo "real"? Are the stars not super-imposed in the image?
10
votes
1answer
46 views
Why is the measured distance to the Triangulum Galaxy much more uncertain than to the Andromeda Galaxy?
Why is the measured distance uncertainty for M33 (835 ± 105 kiloparsec) six times bigger than the measured distance uncertainty for M31 (778 ± 17 kiloparsec)?
They are approximately at the same ...
9
votes
1answer
716 views
How would we tell antimatter galaxies apart?
Given that antimatter galaxies are theoretically possible,
how would they be distinguishable from regular matter galaxies?
That is, antimatter is equal in atomic weight and all properties, except for ...
8
votes
4answers
323 views
What makes the stars that are farther from the nucleus of the galaxy go faster than those in the middle?
It has no sense that stars that have a bigger radius and apparently less angular speed($\omega$) goes faster than the ones near the center.
8
votes
3answers
372 views
Andromeda/Milky Way collision: How, and how accurately, can a galaxy's lateral velocity be measured?
Some sources suggest that the Andromeda Galaxy is likely to collide with our own in approximately 3 to 5 billion years.
We can estimate the distance to the Andromeda Galaxy using various techniques, ...
7
votes
3answers
72 views
What's dark matter and who discovered it?
I have heard about dark matter that's called the Master Of The Universe. What's this and is the dark matter the reason galaxies exist?
7
votes
5answers
2k views
Why are some galaxies flat?
What is the explanation for the flatness of some galaxies?
(If it's due to their rotation then why they are rotating, why some other galaxies are not flat etc., I would like to hear a nice and ...
7
votes
1answer
728 views
Why do galaxies and water going down a plug hole spin?
We all experience things spinning, whether it's water down a drain, the earth on its axis, planets round the sun, or stars in a galaxy - even electrons round an atom.
But why is spin so common in ...
6
votes
3answers
399 views
Are we capable of discovering planets in the Andromeda galaxy?
I just watched this SpaceRip video on YouTube which shows pictures taken by Hubble while looking into the disk of the Andromeda galaxy to study a certain type of variable star. It occurred to me that ...
6
votes
2answers
717 views
What happen when two galaxies collide?
As the title suggests, I know collision of galaxies happens. Questions are
Why do they collide (obviously because of gravity, but in what conditions)?
Aftermath of the collision?
If there is a super ...
6
votes
3answers
771 views
Solar system, visible stars and deep sky objects
Since I've seen that galaxies are often called "deep sky objects", as opposed to individual stars, does this mean that all visible stars in the night sky actually only belong to The Milky Way Galaxy?
...
6
votes
2answers
359 views
Mass of a galaxy via luminosity
Is there a general formula for calculating the mass of a galaxy, or even a nebula from the luminosity? Or, is there a way of calculating the total mass of a galaxy from its energy output?
Is there a ...
6
votes
3answers
84 views
What frame(s) of reference are used to measure the rotation of the Sun around the galaxy ?
I can find various speeds and estimated durations listed at numerous places but none specifically describe the frame of reference.
Possible options as example of kind of answer I expect.
Local ...
6
votes
1answer
138 views
Why doesn't my particle simulation end in a flat disc?
I've made a 3d particle simulator where particles are attracted to each other by the inverse of the square radius. The purpose of my experiment is to see if this alone would create a flat disk (like ...
6
votes
1answer
62 views
Why does Omega Centauri have a distinct chemical signature from the rest of the Milky Way?
In answering a question about the orbital path of Omega Centauri, I learned that it has a distinct chemical signature from the rest of the Milky Way. Basically, it is very rich in s-process elements, ...
6
votes
1answer
113 views
What is the frequency of occurrence of stellar classifications off the HR main-sequence?
An alternative version of this question would be: "if was to pick a star from the $10^{11}$ or so in our galaxy at random, what are the probabilities of it being various kinds of star?" (and I do mean ...
6
votes
2answers
106 views
How Scientist Came to Know the Shape of our own galaxy without going out of it?
As far as I know, scientists have been able to see a lot of differently shaped galaxies in our visible universe through modern age telescopes. But I was wondering how it was possible to know how our ...
6
votes
4answers
275 views
Why do 3d spheres and gravity tend to rotating discs on one plane?
Whether is it our solar system or a whole galaxy, there is usually a massive object (star or black hole) at the centre with gas and objects rotating around it.
The gravitational effect of the ...
5
votes
6answers
702 views
Why is the universe so organized?
If you think about the Big Bang and the flow of matter in all directions, you would think, how unorganized would this universe be? No matter how long it would take. The idea that matter or most of it ...
5
votes
3answers
45 views
What keeps galaxies united like a solar system?
Blackholes may be really strong but they act in a very short range. For example if the sun was a black having the same mass, it will be dark but we will still be revolving around it. It wont engulf ...
5
votes
1answer
66 views
How will a super massive black hole effect our galaxy?
I've recently learned that the general consensus is that several (if not, most) galaxies have super massive black holes in their center, in particular the Milky Way. This, at least to me, makes ...
5
votes
1answer
79 views
Stellar Viscosity in Galaxies
Is there such as thing as the viscosity of stars in a galaxy, along the lines of gravitational attraction between stars changing the dynamics.
If so, how is that put in terms of the Virial Theorem?
5
votes
1answer
504 views
Most accurate ways to find the average distance between stars in Milky way galaxy
I've already posted here on quora. But, I'm not totally sure if it's the most reasonable method.
Would anyone care to elaborate on how to find the average distance between stars in a given galaxy ...
5
votes
1answer
88 views
Why are there not many detectable supernovas?
Astronomers estimate that there are between 200 billion to 400 billion stars contained within the Milky Way and Andromeda Galaxy probably has 1 trillion stars. There may be around 500 billion galaxies ...
5
votes
2answers
94 views
Why is the gas halo of the Milky Way so hot?
I have read on the webpage of NASA that there is a massive hot gas halo around our galaxy. Its temperature is between 100,000 and 1 million Kelvins or more. I do not understand why is it so hot. The ...
5
votes
1answer
100 views
Galaxies seen from Earth
If we observe two galaxies from the Earth that are diametrically opposed and each 10,000 light-years from the Earth, will the separation distance between the galaxies be 20,000 light-years?
...
5
votes
3answers
207 views
Why the red-shift of distant galaxies is considered to be the effect of expanding spacetime?
Why it's not explained just by Doppler redshift caused by faster movement of those galaxies billions of years ago when that light was emitted?
Would the speeds of the galaxies necessary for Doppler ...
5
votes
2answers
164 views
NED velocity to redshift conversion?
I've done some search with the Nasa Extragalactic Database (NED) and I have a very basic question about the velocity/redshift conversion. For example, for the first object of this page, we have ...
4
votes
4answers
260 views
Are galactic stars spiraling inwards?
Are the stars in our galaxy spiraling inwards towards the center, or are they in a permanent orbit?
And if we are heading towards the center then what is the rate of this process?
I started ...
4
votes
4answers
90 views
Is dark matter around the Milky Way spread in a spiral shape (or, in a different shape)?
Dark matter doesn't interact with electromagnetic radiation, but it, at least, participates in gravitational interactions as known from the discovery of dark matter. But does dark matter exist in a ...
4
votes
1answer
163 views
How far apart are galaxies on average? If galaxies were the size of peas, how many would be in a cubic meter?
The actual number:
How far apart are galaxies on average?
An attempt to visualize such a thing:
If galaxies were the size of peas, how many would be in a cubic meter?
4
votes
3answers
59 views
What is the name of this galaxy in HCG7?
What is the name of the predominantly blue spiral galaxy at center-top of this image of Hickson Compact Group 7?
I've found a few articles mentioning the group, but they never seem to list the names ...
4
votes
1answer
638 views
Density of stars near the center of the Milky Way
At night, I can look up and see the Milky Way across the sky. My question is, supposing our solar system was, instead of way out on an 'arm' of the galaxy, if we were near the galactic center. Would ...
4
votes
2answers
423 views
How could scientists know how far a star or galaxy is from us?
How do astronomers measure how far a star (or galaxy) is away from the earth? How would they know that it has taken 13 million years for light to travel in space before it reaches us?
4
votes
4answers
353 views
What does ionization of neutral Hydrogen have to do with “transparency”?
Most accounts of the early history of the Universe make some reference to (re)ionization as being the reason that the Universe becomes transparent after a period of opacity caused by the absence of ...
4
votes
1answer
129 views
Population I and II stars
I have been thinking about the formation of the galaxy. I can easily understand that old, low-metallicity stars are in the halo, but I'm missing something when it comes to the disk.
If ...
4
votes
6answers
189 views
Why are distant galaxies not actually tiny bits of matter?
Distant galaxies are said to be moving away from the Milky Way (and us) at speeds approaching the speed of light. Since Special Relativity tells us that any object moving away from us at a velocity of ...
4
votes
1answer
168 views
Will acceleration rate of expansion of space become faster than speed of light?
From watching cosmology lectures, it seems that the space between galaxies is expanding at an accelerating rate, my question is since it is the space that is (acceleratingly expanding), the special ...
4
votes
1answer
231 views
How and why will the Milky way collide with the Andromeda?
Hubble's law says that the universe is expanding.How come the milky way and the andromeda are on a collision course?How will they end up colliding with each other?
4
votes
2answers
66 views
Galaxies that are newer than our own one
Can we see any galaxies/stars that are newer than our own galaxy?
As light takes (c) amount of times to reach us - so relatively speaking, light which would have left the newer galaxy (and far enough ...
4
votes
1answer
94 views
Does the dark matter halo rotate with the galaxy?
If the dark matter halo is stationary related to the arms of the galaxy then tidal effects should slow the galaxy rotation.
If it rotates with the normal matter in the galaxy then shouldn't it ...
4
votes
1answer
68 views
AGN accretion disk vs. torus
The torus is the donut of dust encircling the Active Galactic nucleus. The accretion disk is inside the torus. Is there a boundary between the two? At what point does a torus become an accretion ...
4
votes
1answer
118 views
Baryonic Missing Mass
A recent article from a popular astronomy website tells of discovery of missing mass (not dark matter) that has puzzled astronomers for some time. Apparently, the discovery involves enhanced electron ...
4
votes
1answer
163 views
Does conformal gravity explain the Bullet cluster lensing effects?
Conformal gravity is an "alternative" theory of gravity, where instead of using the Einstein-Hilbert action composed of the Ricci scalar, the square of the conformal Weyl tensor is used. It was ...
