So how long do galaxies last?

[Johnboy2011]

This is dangerous, I was thinking.....

When we see an image, like the Hubble deep field, of galaxies 13bn years ago, are they still there?

Do they have a life span?

John

[jkwhinfrey]

Well the stars in galaxies certainly do, and there may be many generations of them, but they won't stay the same.

On top of that galaxies often collide and merge, so I'd say they must have a life expectancy... but how long that is, I don't know.

The images Hubble sees should change over time, but I would like to sit there watching for it :-)

[ollypenrice]

I think many will have merged to form ellipticals and star formation will have ceased. As the higher mass stars burn out first the galaxies will shine only with the light of cooler, redder, lower mass stars and finally they won't shine at all - but there will be matter in there. A strange thought.

Olly

[Ptarmigan]

This is dangerous, I was thinking.....

When we see an image, like the Hubble deep field, of galaxies 13bn years ago, are they still there?

Do they have a life span?

Hmm, interesting !

When did our galaxy form and by how much has it changed since (stars, star regions, are still forming/changing)

I know there are first and second etc generation stars, our sun and planets formed from prior supernovea, hence elements higher than iron, but do galaxies form from clouds of gas ejected from preexisting galaxies ?

or are all galaxies "originals" just whizzing about and sometimes colliding ?

Is there a wee fella 13billion light years way over there looking this way thro' his orbiting telescope looking this way and thinking "gee, there's a galaxy rushing towards another, looks like they may collide " (/ andromeda and us) "I wonder if they are still there ?" !

[Ptarmigan]

I thought I remembered that globular clusters contained very old stars, so I wondered about the age of the globulars round our galaxy as an indication of the age of "us".

One of the first I googled upon

Globular cluster?ages

suggests the oldest galactic GCs have an age of 13.5 ± 2 Gyr

Only a quick read of it so far, I suppose it is talking about globulars round our galaxy, which suggests that our galaxy is about (give or take) the same age as the universe ? (unless we aquired globulars from some other older precursor galaxy)

It goes on to say that the minimum age is about 10.5Gyr and the maximum age is about 16Gyr (which would be older than current estimates for the age of the universe!)

[acey]

This is dangerous, I was thinking.....

When we see an image, like the Hubble deep field, of galaxies 13bn years ago, are they still there?

Do they have a life span?

John

They last as long as the universe itself. Some undergo mergers, but a galaxy like ours is nearly as old as the universe itself (as the globular clusters attest).

[Space Bat]

I see 2 questions here

One the galaxies observed by HST and whether they are still there?

Well as these galaxies are continuing to move away and at great speeds they are not there as the light has taken so long to reach us - that they have long gone from the location observed and well outside the Hubble Sphere of the observable universe...

2nd do they have a life span? I guess due to the large distances and expansions that there is little chance of any interaction with other galaxies unless they are clustered already....but whilst a galaxy can have some forms of regeneration where matter is redistributed...it is quite possible that the galaxy over time is consumed by its internal black hole in the centre of the galaxy which is where alot of theorist now believe is the sole source of how a galaxy is formed in the first place....so it may be that well beyond the Hubble Sphere - there are some super super massive black holes that have consumed its galaxy it helped create in the first place....

I have to say a very good question....

[JulianO]

2nd do they have a life span? I guess due to the large distances and expansions that there is little chance of any interaction with other galaxies unless they are clustered already....but whilst a galaxy can have some forms of regeneration where matter is redistributed...it is quite possible that the galaxy over time is consumed by its internal black hole in the centre of the galaxy which is where alot of theorist now believe is the sole source of how a galaxy is formed in the first place....so it may be that well beyond the Hubble Sphere - there are some super super massive black holes that have consumed its galaxy it helped create in the first place....

It's unlikely a black hole will consume a galaxy, there are a couple of things (at least) stopping it doing that. The black hole is a massive thing, and will eat up anything that goes into it.

This is also true of our Sun. However the Sun isn't eating up all the planets that orbit it, because they don't fall into it. To do that they would have to slow down, and drop out of orbit. To do that they would have to lose energy by some means, probably friction or collisions. Anyway, basically this isn't happening to a noticeable extent. The same is true for galaxies, but there the energies and distances are much much bigger. As far as we know the black hole in our galaxy is not consuming very much, otherwise we could detect it directly.

The other mechanism that stops it is as stuff falls in it heats up and produces lots of energy, which appears as light. If stuff falls in too fast, you get lots of this radiation, and this radiation flooding out can get big enough to push further stuff away, thus slowing down the rate it would consume it. So even if you can get stuff into the black hole, there is a limit to how quickly it can consume.

[Space Bat]

Hi Julian all agreeable assumptions except one...

Time

We seem to forget time has nothing to do with us??

The event of Black hole becoming galactic sized due to the ability to continue to consume matter within it's own galaxy could be a very lengthy process....but not totally far fetched as the galaxy becomes older and weaker ??

[Superewza]

I think this is relevant:

Future of an expanding universe - Wikipedia, the free encyclopedia

• 3x10^9 (Earth) years from now and the Milky Way and Andromeda will collide.
  
• 1x10^12 to 1x10^13 years from now and all the galaxies in the local group will merge into one super-galaxy due to orbital decay.

So... they don't last forever. Not as we know them at least (Jim)

Then, many trillions of years after that:

"Over time, objects in a galaxy exchange kinetic energy in a process called dynamical relaxation, making their velocity distribution approach the Maxwell-Boltzmann distribution. Dynamical relaxation can proceed either by close encounters of two stars or by less violent but more frequent distant encounters. In the case of a close encounter, two brown dwarfs or stellar remnants will pass close to each other. When this happens, the trajectories of the objects involved in the close encounter change slightly. After a large number of encounters, lighter objects tend to gain kinetic energy while the heavier objects lose it.

Because of dynamical relaxation, some objects will gain enough energy to reach galactic escape velocity and depart the galaxy, leaving behind a smaller, denser galaxy. Since encounters are more frequent in the denser galaxy, the process then accelerates. The end result is that most objects are ejected from the galaxy, leaving a small fraction (perhaps 1% to 10%) which fall into the central supermassive black hole."

Say what you will about Wikipedia, that article is well worth the read.

[badgerchap]

They last as long as the universe itself. Some undergo mergers, but a galaxy like ours is nearly as old as the universe itself (as the globular clusters attest).

Depends on what you call "The Universe" In the end, depending on who you listen to, gravity will cease to be strong enugh to keep the matter in the universe together, atoms will break apart, even black holes will evaporate. Hmmmm....