Questions tagged [galaxy]

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

Filter by
Sorted by
Tagged with
66 votes
5 answers
19k views

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?
user avatar
  • 693
49 votes
3 answers
29k 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 ...
user avatar
45 votes
11 answers
19k 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 ...
user avatar
  • 573
44 votes
6 answers
21k 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 ...
user avatar
  • 1,029
42 votes
3 answers
6k 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, ...
user avatar
42 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 ...
user avatar
  • 1,640
37 votes
2 answers
4k 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 ...
user avatar
  • 2,222
30 votes
3 answers
8k 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 ...
user avatar
  • 456
29 votes
3 answers
4k 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 ...
user avatar
  • 13.8k
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 ...
user avatar
  • 391
29 votes
2 answers
28k 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 ...
user avatar
28 votes
2 answers
14k 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 ...
user avatar
  • 976
24 votes
6 answers
36k 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 ...
user avatar
  • 807
24 votes
8 answers
13k 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 ...
user avatar
  • 341
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 ...
user avatar
  • 9,893
24 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 ...
user avatar
24 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 ...
user avatar
  • 431
22 votes
3 answers
3k 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 ...
user avatar
  • 1,993
22 votes
2 answers
11k 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?
user avatar
  • 416
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^...
user avatar
21 votes
4 answers
1k 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 ...
user avatar
  • 810
21 votes
1 answer
2k 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 ...
user avatar
  • 1,194
21 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 ...
user avatar
  • 681
20 votes
6 answers
3k 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 ...
user avatar
  • 3,939
19 votes
2 answers
1k 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 ...
user avatar
19 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 ...
user avatar
19 votes
4 answers
11k 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 ...
user avatar
19 votes
2 answers
693 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) ...
user avatar
  • 1,114
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 ...
user avatar
18 votes
1 answer
852 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 ...
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?
user avatar
18 votes
1 answer
419 views

Which came first: black holes or galaxies?

In other terms, did galaxies grow around black holes at their center?
user avatar
18 votes
1 answer
1k 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 ...
user avatar
18 votes
1 answer
676 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 ∼...
user avatar
  • 6,084
18 votes
1 answer
646 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 ...
user avatar
  • 281
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'...
user avatar
  • 1,166
17 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 ...
user avatar
17 votes
2 answers
14k 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 ...
user avatar
  • 1,640
17 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 ...
user avatar
  • 1,952
16 votes
2 answers
2k 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 ...
user avatar
16 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?
user avatar
  • 271
16 votes
2 answers
779 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 ...
user avatar
  • 1,114
15 votes
2 answers
2k views

What is the evidence that galaxies rotate?

Do all galaxies rotate? If so, do they rotate in the same direction? What observations have been made of galaxy rotation?
user avatar
15 votes
3 answers
1k 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 ...
user avatar
  • 427
15 votes
1 answer
1k views

How much overlap will the Andromeda galaxy and the Milky Way have when they collide?

Measurements of Andromeda's blue shift let us conclude that the distance between the Andromeda galaxy and the Milky Way is decreasing and in a few billion years they will "collide". The blue shift ...
user avatar
  • 715
15 votes
2 answers
237 views

How much greater is the star density in our galactic bar?

How much denser is it in the galactic bar than the "normal" density at the same radius? Is it just a few percent? or is it, say, "three times" as dense? Or are other factors at play: star brightness,...
user avatar
  • 1,114
15 votes
1 answer
2k views

Where is Voyager 1 (or 2) going? In which direction?

Knowing it has exited the solar system, is it traveling in the direction of the center of the galaxy, away from it, orbiting it, or maybe even going perpendicular from the disk-shaped galaxy?
user avatar
  • 479
14 votes
6 answers
7k 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 ...
user avatar
14 votes
3 answers
9k views

Can the difference between a star and a galaxy which are point sources be detected?

Obviously a star would be a point source. A galaxy should be an irregular blob if close, but if it is far away then it would seem that a galaxy too would be just a point source. Given that the star ...
user avatar
  • 336
14 votes
2 answers
11k 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 ...
user avatar
  • 1,029

1
2 3 4 5
14