Change in color?

[Jakelol]

Can nebulas or other deep space objects change color and if so has humans seen a color change?

I know stars can change color and i can imagen that if the explode they will change color? But how about other stuff?

[ollypenrice]

Certainly, over time - but probably over timescales far beyond a human lifespan. Examples:

The Pleiades are drifting through a region of gas and dust, lighting it with their own emission which will move as they do.

Planetary nebulae often show a greenish outer shell of doubly ionized oxygen (greenish-blue) which forms first, with an inner region of reddish ionized hydrogen forming later. When do you catch this process? Sooner or later? That will decide what you see.

As galaxies age they run out of material to create new stars, so they redden. You'll often see spiral galaxies showing Walter Baader's distinction between old 'Population 2' red stars in their central bulge with hot, young blue stars in their spiral arms....

...but old, evolved elliptical galaxies, possible created in galaxy mergers, have only the old, evolved red stars...

 

So changes in form and colour are a routine part of the evolution of the universe but a human life is trivially short in this context.  Even so, I think such evolution can sometimes be photographed.

Olly

[Jakelol]

I was almost guessing that it would be way to short time for one persons life time to notice that. Thanks for the lesson.

[vlaiv]

14 hours ago, Jakelol said:

I was almost guessing that it would be way to short time for one persons life time to notice that. Thanks for the lesson.

Yes, way too long for people to be able to notice the effect, but you can do what people that are studying galaxy evolution do - there is enough stuff out there that you can find example of each evolutionary step.

Want to know how star color changes as the star evolves over certain period of time - find similar sized stars in different stages of evolution and look at their color. Similarly you can do the same for galaxies.

Interestingly enough, things that change the fastest - Super nova remnants and planetary nebulae - are most difficult to study like that as there are not enough similar samples to be seen close by (they are small so can't be seen over large distances).

[vlaiv]

Just to add - here are a few examples where we can see the change (and potential color change) within human lifetime:

[ollypenrice]

Looking out into space at any one moment is like looking at a random crowd of people. You'll see everything from small babies, via toddlers to adolescents, the middle aged and the elderly.

Olly

[Jakelol]

1 hour ago, vlaiv said:

Just to add - here are a few examples where we can see the change (and potential color change) within human lifetime:

The last one is the most obvious i guess?

The first 2 examples what is needed for one to see that?

[vlaiv]

4 hours ago, Jakelol said:

The first 2 examples what is needed for one to see that?

Well, need to take object that changes on fast enough scales and then take few images of it at different times and compare those.

Actual imaged object is rather small - it is super nova remnant that went off recently - SN1987a, so the cloud is still small and visible by large space telescopes like Hubble.

In theory, you could observe crab pulsar like that (last image). Many amateurs take images of crab nebula, M1 and that swirl although often imaged in X-rays (way beyond amateur equipment) - can be imaged in visible, at least I think so (I think I once saw image taken at ~500nm that show inner structure).