Member
Quick question about distance and time.
Hey, this has been on my mind for a while, but I'll make this quick and simple.
Say you look up at Proxima Centuri at ~4.22 LY away and see it's light was being emitted 4.22 years ago. Now if one was to aim the Hubble or equivalent at Proxima and took a few snaps of it would the photos of it record the light emitted as it was 4.22 years ago or would the photos represent a more recent state of the star?
Order of Kilopi
The photons that are recorded by the camera, departed Proxima Centauri ca. 4.22 years ago. The image is as it was.
Imaging it through a telescope won't make the photons travel any faster.
If you want an image as it is at this moment, then take a picture of it in 4.22 years.
Member
That's the idea I had in mind... Thanks for confirming it. The Deep Field Hubble photos left that afterthought in my head for some reason.
Established Member
The fact that we see objects as they were when the light left them has been a tremendous boon. It means that we can study the way the universe was millions and even billions of years ago. Thus we can study its development over time.
Established Member
But if you can't see what it looks like right now, how do you know how it developed?Originally Posted by Fortunate
Order of Kilopi
Established Member
I did not mean that we could study the development of a particular object over time. I meant that we could study the devlopment of the universe over time by comparing the objects from one time period with those from different time periods. This assumes a certain degree of homogeneity.
Established Member
Ok. I see what you mean. oops
Established Member
Stellar evolution models
For sun like stars, most main sequence stars, or objects already in place, like planetary nebulae, we use stellar evolution models. Tools like the Hertzsprung-Russell diagram are really important for that. But a lot of things in the sky can be seen to change. Variable stars, the sudden appearance of McNeil's Nebula, and the ability to see objects like planetary nebulae in various stages of development give us plenty of opportunities to study how things develop over time (i.e., the Egg Nebula is a "proto-planetary nebula", meaning it has not quitge yet made it to planetary nebula status, but it's on the way).
Established Member
But what kind of time frame are we talking about? 100 years, 100,000 years... How long does it take for a noticable difference to appear?
Established Member
A very interesting recent article discusses the discovery of "light echoes" from old, nearby supernovae. These echoes may allow us to "see" the original burst of light while also viewing the remnant centuries afterwards.
http://spaceflightnow.com/news/n0512/25echolight/
Established Member
Minutes to years to centuries to millenia
Variable stars change with periods ranging from minutes to days. The various episodes of eruption around Eta Carinae generally last on the order of a year. The various concentric rings of the Egg Nebula represent thermal pulses roughly 100 years apart. Changes in main sequence stars probably don't become evident on time scales less than a few million years.
Order of Kilopi
If you haven't already seen this dynamic change cited in the BA Blog :: Crabby Hubble, you might enjoy it:
Crab Nebula 28-year animation
Order of Kilopi
And of course, the granddaddy of them all is the cosmological evolution of galaxies that we see when we look at quasars. Those we see billions of years ago! Thus we have a full accounting of what galaxies in general have done since their inception. We do have to look farther away to see back in time, but there is good (indirect) evidence that nothing much changes as you go farther away.
Banned
How does looking at Quasars, billions of years ago, give us a "Full" accounting of galaxy evolution???
Order of Kilopi
Because quasars are one of the earliest stages of galaxy evolution. True, before that there's the initial formation, so that's what I meant by "since their inception". The inception part is certainly of great importance, and that piece is getting filled in as well. As for the phases since the quasars, we can see those quite well in the Hubble deep field, though I presume there are some gaps there that need filling in as well. Probably after one more generation of telescopes, there won't be anything missing at all. Thank goodness for the Cosmological Principle, which implies that it doesn't matter where we see the galaxies, only when.
Banned
Ken G
I thought that when they relooked at many (But not all) "Quasars", they found that they were in already formed galaxies. Quasars were just so bright, it was very difficult many times to see the stars of the galaxy.
Order of Kilopi
That's EXACTLY, What he's Saying ...
Quasars Form, In Galaxies, As they Finish, their Final Collapse ...
Ya' Know, When The Infalling Matter, Turns The Central Black Hole, On Brighter, than The Las Vegas Strip!
Order of Kilopi
You said it better than I could've!
Order of Kilopi
That's What, I'm Here for ...
Speaking of Which, I've Gotta Head To Las Vegas, Some Time Soon ...
My Father, Just Taught me, a Mathematically, Sound Way, to Play CRAPS!
Order of Kilopi
Just remember the casinos are not in the business of giving away money, somebody's got to pay for all those flashing lights!
Established Member
one form of study that hasn't been mentioned is a "cross sectional study".
This looks at an entire population of objects, as a whole, and uses the data to outline how the objects evolve in time.
This is like looking at human developement. You don't have to take a single individual and track them for 70 years to understand the general life of a person. You lose some depth (can't study significant effects of ethnicity, location, social class, etc) but you can still get quite a few details.
The trick is, of course, proper classification (if we accidentally included apes in our study, we'd skew our observations of the human life).
Order of Kilopi
That's Why, we Play Craps ...
High Odds ...
Especially, If you Bet WITH, The House!
Order of Kilopi
He said he had a mathematically sound way to play, not to win.
Order of Kilopi
Stay in the game as long as you can, eh? Just like life itself.
Order of Kilopi
And note that any cross sectional study mixes in information about how the overall population is changing with time, in addition to age-related issues. This same problem holds in astronomy, such as with Population I, II, and III objects confusing the issue of evolutionary effects.
Established Member
as I said, the trick is in proper classification (often done before, during and after cross sectional studies)
Banned
ZaphodBeeblebrox
Senior Member
Above is how Ken actually started his statement...
I am saying that the earliest stage of galaxy evolution would not have a galaxy worth of stars around a voraciously feeding SMBH!!!
I said the above...so, if you want to dispute that they found galaxies around the Quasars...to say that the voracious feeding SMBH is the begining of a galaxies evolution, ie the feeding SMBH promotes star production to form the galaxy, thats one thing. However, if there are galaxies already in existence around the Quasars, then Quasars are not the initial stage of galaxy developement!
Order of Kilopi
The buzzword you find these days is "coevolution", which means that SMBH and galaxy formation are a kind of chicken and egg problem. All I'm saying is, at some point you have a very young galaxy, and it's a quasar, and we can follow the evolution pretty well by looking at different distances. The actual formation process is still under study, but will probably make steady progress as telescopes get better and better at unveiling the mystery.
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