27 votes

Could stars form outside of galaxies?

Yes, stars can form outside galaxies if the conditions are right. An impressive example is D100, a galaxy that is moving through a cluster so fast that the ram pressure from the ambient gas forces ...
Anders Sandberg's user avatar
13 votes

Conventional matter to dark matter ratio, outside of galaxies

Let me see if I can answer at least some of this. Yes, there is dark matter between galaxies. This is demonstrated by the fact that in galaxy groups and clusters, you need more dark matter than is ...
Peter Erwin's user avatar
  • 16.7k
10 votes

Could stars form outside of galaxies?

It's quite possible for stars to form outside of galaxies, typically in environments where large amounts of gas have been stripped from a galaxy. This usually involves either a tidal interaction with ...
HDE 226868's user avatar
  • 36.3k
8 votes
Accepted

What is at the edge of the galaxy?

The short answer is: probably nothing much, because galaxies are very fuzzy objects without "edges". If you look at the stellar disk, it just fades out in density, with no evidence for a sharp cutoff ...
Peter Erwin's user avatar
  • 16.7k
7 votes
Accepted

Do any particles in AGN jets escape the galaxy?

Yes, definitely. While some matter returns to the galaxy as a so-called "galactic fountain" (e.g. Biernacki & Teyssier 2018), some material is ejected at super-escape velocity, becoming ...
pela's user avatar
  • 37.6k
7 votes

Local Bubble in space

The "local bubble" is a region of the galaxy where the density of interstellar gas is lower than average. It has about 50 thousand atoms per cubic metre, compared with 500 thousand averaged over the ...
James K's user avatar
  • 119k
6 votes

Is it likely that intergalactic stars would still retain their planets?

While near encounters with supermassive black holes are bad for the stability of solar systems [citation needed?], many intergalactic stars become intergalactic without a close encounter. They are ...
Anders Sandberg's user avatar
6 votes

Why is the Warm-Hot Intergalactic Medium (WHIM) so hot, and what is "collisionless shock heating"?

It should probably be added that the article includes a glaring error of the type you often see when the science writer apparently did not take an elementary astronomy class (this is why we have such ...
Ken G's user avatar
  • 5,320
6 votes
Accepted

Why can I see the Andromeda Galaxy despite Milky Way's rotation?

As barrycarter already pointed out, it is due to the huge time it takes for the milky way to rotate. For once, as he pointed out, the stars in an orbit similar like the sun take about 250 million ...
Adwaenyth's user avatar
  • 453
6 votes
Accepted

What differentiates a "group of rogue stars" from a galaxy?

It is just a poor choice of words. The comment refers to a discovery paper by Ferguson et al. (1998), where they used a very deep image in the Virgo cluster to establish that there were an excess of ...
ProfRob's user avatar
  • 149k
5 votes
Accepted

Why does the first measurements of the thermal Sunyaev-Zel’dovich effect from ALMA show a temperature decrease and not an increase at the cluster?

Calling it a "temperature decrease" is kind of misleading. (Possibly this is a side effect of the tendency to use "brightness temperature" in radio astronomy to mean measured ...
Peter Erwin's user avatar
  • 16.7k
5 votes
Accepted

What exactly is a "conclusive association" in Astronomy?

A "conclusive association" is an oxymoron; for example, "brawling love", "loving hate" (these first two are from Shakespeare), "act naturally", or "jumbo ...
David Hammen's user avatar
  • 33.7k
5 votes
Accepted

Conventional matter to dark matter ratio, outside of galaxies

The short answer to your question is no, there is not dark matter between galaxies, at least at any appreciable level. There is ordinary matter between galaxies, called the intergalactic medium (IGM)...
J. O'Brien Antognini's user avatar
5 votes
Accepted

Why is the Warm-Hot Intergalactic Medium (WHIM) so hot, and what is "collisionless shock heating"?

The answer is almost certainly magnetic fields. A collisionless shock occurs when you try to propagate an increase/density in pressure through a sparse plasma at faster than the sound speed. Whilst ...
ProfRob's user avatar
  • 149k
4 votes
Accepted

What would you find within a void?

The Wikipedia article on voids is pretty good (though IMO unusually awkwardly written.) The key thing is that voids are not empty, they are just large volumes which have a lower density (typically ...
Mark Olson's user avatar
  • 7,630
4 votes

What is at the edge of the galaxy?

It is argued that the edge of the galaxy has the halo of dark matter at around 100,000 light years, but there are arguments that extend the galaxy from anywhere between it being 120,000 to 200,000. ...
Durakken's user avatar
  • 397
3 votes

Why can I see the Andromeda Galaxy despite Milky Way's rotation?

It is certainly true that the galactic orbit is very slow. Yet it should be noted that even if the Sun/Earth system orbited the galaxy once every century, the Andromeda galaxy would still be seen in ...
Ken G's user avatar
  • 5,320
3 votes

What is at the edge of the galaxy?

While the Solar wind is pretty much homogenous in all directions, the galaxy puffs out stellar winds from discrete and temporary star forming regions. Protostars and giant stars which go supernova ...
LocalFluff's user avatar
  • 11.4k
3 votes

What would you find within a void?

I can address the part of the question that states "have 'few or no' galaxies, but I can't find much else". In recent years there has been a lot of work published on void galaxies. Identifying void ...
JonesTheAstronomer's user avatar
3 votes

How do we estimate the amount and distribution of Helium in interstellar and intergalactic space?

Helium in the interstellar medium is detected, and its abundance measured, essentially the same way as it is in stars: through emission or absorption lines. For example, here is a paper that observes ...
Eric Jensen's user avatar
  • 4,864
2 votes

Intergalactic Lyman-alpha absorption for high redshift quasars (Gunn-Peterson effect)

You're right that it should be possible to see the evolution of the ionization fraction of the intergalactic medium (IGM) in a single, high-redshift quasar spectrum, as you scan through the Lyman $\...
pela's user avatar
  • 37.6k
2 votes

Is our Milky Way galaxy (and its neighbors?) moving through the universe at 370 km/s (~828,000 mph) or 370 miles/sec (~1,332,000 mph)?

The two values are the peculiar velocity of the local group relative to the Cosmic microwave background The Local Group — the galaxy group that includes our own Milky Way galaxy — appears to be ...
James K's user avatar
  • 119k
1 vote

Can two neighboring galaxies move apart at steady speed?

The key word here is "eventually." The strength of the gravitation felt between two objects is inversely proportional to the square of the distance between the two bodies. As a result of ...
notovny's user avatar
  • 4,770
1 vote
Accepted

What error bar / confidence level is generally reported in galaxy distances?

The error bars are typically very large. There are several ways of determining the distance of galaxy: Cepheid Variables Cepheid variable stars have a known relationship between luminosity and period. ...
James K's user avatar
  • 119k
1 vote

Would Bussard Ramjets work in other places in or near the galaxy?

Yes it's theoretical, but on some levels, estimates can be calculated. (probably better for space-ex than here), but it's a fun design to think about. The basic design, the ship generates a magnetic ...
userLTK's user avatar
  • 23.9k

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