Questions tagged [galaxy]

Questions regarding systems of large numbers of stars held together by gravity.

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70 votes
5 answers
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Does the Milky Way move through space?

Does our galaxy moves through space? Or does it stay in a single location? If it does move, what causes it to move?
Mike's user avatar
  • 733
53 votes
3 answers
41k views

Does the Milky Way orbit around anything?

We know most of the objects in the Universe have a spherical or elliptical shape. The object which has less mass and gravitational pull orbits around the nearest object with more mass and ...
Zeeshan Ahmad Khalil's user avatar
49 votes
11 answers
21k views

Why do Black Holes in the middle of galaxies not suck up the whole galaxy?

As stated in several sources, it's supposed that in every galaxy there is a black hole in the middle. My question is, why do these black holes in the middle of galaxies not suck up all the ...
OiRc's user avatar
  • 613
44 votes
6 answers
23k views

How do we have photos of galaxies so far away?

A possible answer for this is that, light emitted from the galaxies travelled a billion miles all the way to earth, where the hubble space telescope picked up this light through its sensors, and was ...
K Split X's user avatar
  • 1,069
43 votes
2 answers
8k views

Why is our solar system "tipped" about 63° with respect to the plane of our galaxy?

Our own solar system is "tipped" by about 63 degrees with respect to the plane of the galaxy. Has it ever been researched or is there any scientific theory which could explain the reason why our solar ...
e-sushi's user avatar
  • 1,700
42 votes
3 answers
7k views

How did Hubble know the red shift difference between "moving away" and "old"?

My 9yo daughter is very into space at the moment and asked a question that my physics knowledge (6th form college, 20 years ago) is way too poor to answer. Her space book tells us that as stars age, ...
Whelkaholism's user avatar
37 votes
2 answers
5k views

Are there any stars that orbit perpendicular to the Milky Way's galactic plane?

Most stars orbit in the Milky Way's galactic disc. But is it possible for one to orbit perpendicular to it? Here on Earth since we're inside the galactic plane we can't get a good view of what the ...
user177107's user avatar
  • 2,689
31 votes
3 answers
12k views

What keeps galaxies together?

The super massive black hole at the centre of Milky Way has a mass of about 4 million times that of our sun. Is this enough to keep the entire galaxy together, is it this black hole which keeps the ...
O S's user avatar
  • 466
31 votes
2 answers
50k views

Is this photocomposition of Andromeda's galaxy and the Moon accurate?

I recently saw the below image circulating around twitter/Facebook/reddit. It is titled "Andromeda's actual size if it was brighter": One of the comments provides a link to another ...
Federico's user avatar
  • 395
31 votes
3 answers
18k views

How far is the Earth/Sun above/below the galactic plane, and is it heading toward/away from it?

How far is the Earth/Sun above/below the galactic plane, and is it heading toward/away from it? We know the Sun is orbiting the galactic center every 225 million years. But how far are we from the ...
jmarina's user avatar
  • 1,016
30 votes
3 answers
5k views

What are the odds that the Sun hits another star?

The Sun moves around the Milky Way disk in the same direction as most of the other stars in our galaxy (prograde). But there are a number of older stars in the galactic halo that move in retrograde ...
Connor Garcia's user avatar
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30 votes
2 answers
36k views

How many stars and galaxies can be seen by the naked eye?

How many of the luminous dots that we see naked are galaxies and not stars from our galaxy? I imagine that the majority of the luminous points that we see naked eye during the night, are actually ...
Mario Stefanutti's user avatar
29 votes
2 answers
4k views

Why does the 70-solar-mass black hole in the LB-1 system challenge current astrophysics?

Recently scientists discovered a large stellar-mass black hole, which (previously) they believed that it shouldn't be possible in our galaxy! Source An international team of scientists say they ...
Junaid S.'s user avatar
  • 391
25 votes
2 answers
1k views

Why do we believe that the super massive black holes at the centers of two merging galaxies would themselves merge?

When listening to podcasts or watching youtube videos of astronomers discussing galaxy mergers, I often hear talk about how the super massive black holes at their centers will themselves merge during ...
asgallant's user avatar
  • 561
24 votes
6 answers
39k views

What will happen to life on Earth when the Andromeda and Milky Way galaxies collide?

It is said that the Andromeda and Milky Way galaxies are coming close to each other with a speed of approximately 400000 km/hour. They will be together in the next 4 billion years. What will happen ...
AmitG's user avatar
  • 807
24 votes
8 answers
14k views

Why can't we see distant galaxies with the naked eye?

If light keeps travelling in a straight line, why can't we see distant galaxies with the naked eye? Surely if you stared long enough, the light from them would eventually hit your eye? I apologize if ...
Guit4eva's user avatar
  • 341
24 votes
4 answers
2k views

Metallicity of Celestial Objects: Why "Metal = Non-metal"?

Metallicity of objects refers to the amount of chemical elements present in it other than Hydrogen and Helium. Note: The other elements may or may not be actual ...
MycrofD's user avatar
  • 840
24 votes
1 answer
2k views

Why are there so few supernovae in M31 (Andromeda)?

Estimates of the supernova rate in the Milky Way put it at a few per century, but very few of these are visible from Earth (at least with the naked eye) because of intervening gas and dust clouds). On ...
Steve Linton's user avatar
  • 10.3k
23 votes
3 answers
4k views

How do we know Milky Way is a 'barred' spiral galaxy?

In reference to the question, "How can we tell that the milky way is a spiral galaxy?" The answers there clearly sum up the question asked. But Milky Way is not just a spiral galaxy. It is further ...
Cheeku's user avatar
  • 2,013
23 votes
1 answer
5k views

Milky Way Galaxy from Earth

I've seen a lot of beautiful pictures of the Milky Way from Earth such as this: ...but I can't understand what the cloudy ribbon at the bottom the horizon is. Is it a super-large nebula? Or is it due ...
shortstheory's user avatar
22 votes
4 answers
14k views

Why are galaxies disk shaped?

I always see galaxies in "disk" shape in pictures. It is like, there is a rotational movement on a plane and the system is balanced by the pulling-in gravitational force which prevents the stars to ...
hkBattousai's user avatar
22 votes
2 answers
12k views

Was the Milky Way ever a quasar?

Is there any evidence that the Milky Way could have been a quasar in it's early history? Is it thought that most galaxies come from quasars?
Stu's user avatar
  • 416
22 votes
1 answer
2k views

Explaining Dark Matter and Dark Energy to layman

With my little knowledge, I know this: Dark Matter The center of a galaxy controls/attracts its objects (stars, planets, comets etc.) towards itself because of gravity. But the mass of the center of ...
Farhan's user avatar
  • 701
21 votes
7 answers
4k views

Could light be dark matter?

Is it possible that light itself is dark matter? I am speaking of photons (e.g. visible light, infrared, ultraviolet, etc...). I realize light is understood to be massless, but it is obvious it at ...
Jonathan's user avatar
  • 4,375
21 votes
2 answers
3k views

How hard is it to find the Sun's "sisters?"

As @ProfRob stated in his excellent answer regarding the ejection of the Solar System's fifth gas giant, It is for similar reasons that, even though the Sun was probably born in a cluster of $\sim 10^...
WarpPrime's user avatar
  • 6,653
21 votes
2 answers
2k views

Are there any galaxies which fell out of sight horizon due to cosmic expansion?

If farthest galaxies run away from us with acceleration making them exceed speed of light, we should expect them to disappear from sky among time with increasing quantity. Did we observe this? Can we ...
Waldemar Gałęzinowski's user avatar
21 votes
1 answer
3k views

Do the axes of rotation of most stars in the Milky Way align reasonably closely with the axis of galactic rotation?

The axis of rotation of the Solar System makes a large angle of about 60 degrees relative to the axis of rotation of the Milky Way. That seems unusual - for example, most of the bodies within the ...
Roger Wood's user avatar
  • 1,359
21 votes
1 answer
3k views

What is the probability of a photon from one of these galaxies hitting the James Webb detector?

In the image of the SMACS 0723 galaxy from the James Webb space telescope can be seen distorted galaxies whose light has taken about 13 billion years to reach the telescope. On the face of it, the ...
DrMcCleod's user avatar
  • 313
20 votes
1 answer
2k views

Supermassive black holes at the center of galaxies

The fact is, many, if not most large galaxies have a supermassive black hole at their center. My question is why? Is it because when these galaxies were first formed supermassive black holes were ...
Foo Barrigno's user avatar
20 votes
1 answer
752 views

Is it "weird" that all disc galaxies rotate once every billion years?

In a recent paper (Cosmic clocks: A Tight Radius - Velocity Relationship for HI-Selected Galaxies by Meurer, et al.), it was noted in the conclusion that: [This] implies a constant orbital time of ∼...
called2voyage's user avatar
  • 6,312
20 votes
1 answer
1k views

How small can a spiral galaxy be?

The smallest observed spiral galaxies I can find are NGC 2976 and NGC 4605, both with a diameter of 20 kly, but I don't have anything like an exhaustive source to search. I've also found a mention ...
Elukka's user avatar
  • 301
19 votes
2 answers
2k views

Questions about spiral galaxy arms

I have 2 questions related to spiral galaxies. Firstly, how did the arms form? Why would the stars accumulate into those specific areas? And secondly, why are they still intact? The inner parts of ...
stanley dodds's user avatar
19 votes
2 answers
835 views

Conventional matter to dark matter ratio, outside of galaxies

Consider say this outstanding diagram from another question, To begin with galaxies have a typical density D. Intergalactic space has a much lower density d. As we know: in galaxies (with density D) ...
Fattie's user avatar
  • 1,126
18 votes
3 answers
4k views

How are constellations intact if the stars are rotating around galactic nuclei?

From what I understood, the Milky Way (or stars in the Milky Way) doesn't rotate like a collection of points in a disc due to the presence of some invisible matter. In theory, the angular velocities ...
Muhammed Roshan's user avatar
18 votes
3 answers
3k views

Where does the Milky Way end?

I was reading this article and it says the following: Researchers measured the mass of the Milky Way and found that our galaxy is approximately half the weight of a neighbouring galaxy known as ...
SpringLearner's user avatar
18 votes
3 answers
419 views

Does the rotation of galaxies precess?

Does the axis of a galaxy as a whole "wobble" the same way that the Earth does? If so do we have any idea how much or how fast the Milky Way is doing so?
smithkm's user avatar
  • 331
18 votes
1 answer
886 views

What do we know about the lifecycle of the Milky Way (or any other spiral galaxy)?

I know that the Milky Way will collide with Andromeda in the distant future but my knowledge about the lifecycle of a galaxy is very lacking. I was surprised that Wikipedia is so sparse on ...
Adam Arold's user avatar
18 votes
1 answer
2k views

Our galaxy, the Milky Way, forms part of a galaxy group called The Local Group. What are the parameters that dictate what a galaxy group is?

Are there different classifications or just the one? How does our galaxy group compare with others?
Eduardo Serra's user avatar
18 votes
1 answer
474 views

Which came first: black holes or galaxies?

In other terms, did galaxies grow around black holes at their center?
Kyriakos Kyritsis's user avatar
18 votes
1 answer
1k views

Do we get any benefit from being in a galaxy?

If our solar system were to somehow be created outside of a galaxy as a single star in the vast nothingness between galaxies, would life on Earth change any? Does being a member of a galaxy actually ...
Scottie's user avatar
  • 2,042
17 votes
2 answers
4k views

Why don't they make an image of the black hole in the M33 galaxy?

Since we see the Triangulum galaxy M33 from a quite vertical position (contrary to our Milky Way and a bit the Andromeda galaxy) it should be easy to image the black hole in the center of it, shouldn'...
user30007's user avatar
  • 1,228
17 votes
2 answers
2k views

How many galaxies have been discovered?

I know Andromeda is our nearest galaxy. But how many known galaxies have been discovered and what are they?
Unicorn's user avatar
  • 273
16 votes
2 answers
3k views

How distorted will our galaxy be if we are viewing it from several thousand light years away?

I saw this answer and read this sentence regarding the distortion of our galaxy when viewed above the galactic plane: Once you got to a point where the entire [sic] galaxy was within your vision, the ...
WarpPrime's user avatar
  • 6,653
16 votes
1 answer
3k views

How are we observing the newly discovered "dark galaxy" J0613+52, if it has no stars and is so far away from other galaxies?

I just came across a New York Times article talking about a newly found Low Surface Brightness (LSB) galaxy (also called “ultra-diffuse galaxies” or “dark galaxies”). The new galaxy, J0613+52, was ...
Curious Layman's user avatar
16 votes
2 answers
16k views

What is this bright "glow" in the center of galaxies?

It was always my belief that at the center of many galaxies, there are supermassive black holes. If this is the case, then we should not see a "light" coming out from the center since light get's ...
K Split X's user avatar
  • 1,069
16 votes
3 answers
2k views

Statistically, what would the average distance of the closest black hole be?

The closest confirmed black hole is several thousand light years away from earth. Our galaxy has about 100 billion stars. I didn't find any reliable information on the black hole count of ratio versus ...
this's user avatar
  • 437
16 votes
2 answers
21k views

How many planetary systems exist in our galaxy?

For many years scientists have studied our own solar system and modern technology allows them to look deeper and deeper into space. Knowing the Sun is only one of a few billion stars in the Milky Way ...
e-sushi's user avatar
  • 1,700
16 votes
2 answers
908 views

Boötes Void numbers, 2016

As a general science (hence Wikipedia!) reader, the latest information I have is that 60 galaxies "have been found and counted" inside the Boötes void, this of 1997. (1) What is the latest count of ...
Fattie's user avatar
  • 1,126
15 votes
6 answers
8k views

What will happen to the shape of a galaxy when a super massive black hole lying in its center dies(evaporates out)?

What's at the Center of the Milky Way? In this article it is said that a supermassive black hole lies in the center of milky way galaxy. At its center, surrounded by 200-400 billion stars and ...
Paran's user avatar
  • 904
15 votes
9 answers
6k views

How do we know we're not getting bigger?

Alright so I've been thinking a lot about how the universe expands and I've always wondered if we're getting bigger as well. Since everything would be getting larger at an equal rate (tools of ...
Landon's user avatar
  • 169

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