have we ever seen a galaxy or star form

[AlphaBeta]

hi, it seems as though I have read claims that we can see a galaxy or star form, but how deceptive is it to say that when it takes tens of millions of years at the very least for an event like this to happen, yes?

 

so, how would we have any idea what we are actually looking at, that is to say if we have never seen a star being born how do we know we are looking at one of the stages in the birth of a star when the amount of time we have to view the process wouldn't even be equivalent to watching one still frame of a movie.

 

they say we have seen a star being formed as if it's like watching a video of the event, but as I just explained we are basically watching a still picture of an event that occurs over millions of years so it's not actually possible to say we know what we are watching or that in 50 million years this event will produce a star.

 

we can't even predict the weather more than a week away but we are to believe that we can predict cosmological events millions of years into the future.

 

please explain.

[insane_alien]

well, when we look really far away we are seeing the way things were billions of years ago since the light has taken that long to reach us.

 

so, by looking at various distances we can see various slices of time. also, there are a lot of stars and galaxies out there, look at any part of the sky and chances are you can find a star and whole galaxies in various stages of formation.

 

it is true that we have never seen the complete formation of a single star but we have seen many stars at various stages of formation and death.

 

this is also how we can predict cosmological events a few billion years in advance(well, major ones that are easy to predict anyway)

[AlphaBeta]

saying that we are looking back in time, makes no sense when talking about events that are going forward from present day and into the future... sure, if you are talking about a supernova than, it really doesn't matter... because we are talking about something coming apart.

 

but, I still don't understand how we can claim to know what we are looking at... you agree it is highly theoretical, yea? meaning we can't actually verify it 100% directly, we are just taking educated guesses based on observations but we can never know if we are actually right or not wouldn't you agree.

[insane_alien]

no it is not highly theoretical. we are making direct observations.

 

we can look at star at various stages in their lifecycles and piece together the whole process from there.

 

Assume you knew nothing about humans. not how they grow, not how they change and so on.

 

if i lined up a number of humans, from new borns to the elderly, say one from every year( a newborn, a one year old a two year old and so on) you would be able to detail the human aging process even though you are not watching an individual age from cradle to grave. this is basically what astronomy does with stars. there are billions of stars up there at various stages of their life so we have been able to deduce various things about their formation, main sequence life and death.

 

as fopr the looking back in time thing, i have never been completely comfortable with that analogy myself, but i cannot think of anything better. if we look at alpha centauri, it is 4 light years away from earth. this means we see it now as it was 4 years ago. when we look at the sun we see it as it was 8 minutes ago, when we look at the moon we see it as it was 1 second ago. when we look really far away, to other galaxies we see millions of years ago. when we look at the cosmic microwave background radiation we see the very moment when the universe became transparent to photons, about 13billion years ago.

 

perhaps martin will swing by and explain it. he is very good with this stuff and i have only a passing interest in it.

[AlphaBeta]

i don't think the human analogy works because it's always teh form of a human just at difference sizes... a star being formed means stages where it is in no way a star or resembles a star - it might just be a gas cloud.

 

so, i still want to know - how we can claim something is the formation of a star, at a point where it in no way resembles a star.

 

but, if martin replies - I would rather know how we can tell a galaxy is forming, because I am incredulous that we can see anything like this... I think that it's just educated guesses, but there is no way to verify it or falsify the claim.

 

if something resembles a galaxy, that's one thing - I'm talking about viewing something that in no way is a galaxy and saying this is a step in the formation of a galaxy and this will eventually be a galaxy - I'm referring to claims like that.

[insane_alien]

Alpha, if you want to take the analogy that far, then do i need to remind you that humans do not alyways look human. we resemble tadpoles when we are still sperm. and we don't look all that human in the early stages of embryonic development. same with stars, but once they start looking like stars, they look like stars till they die.

 

also, the change from a cloud of gas to a star is not a clean cut transition. there are examples of stars partway through the transition from gas cloud to fusing star. we have a pretty good number of snapshots of various stages of star formation.

 

you seems to be asking what about halfway between the stages we have observed, well, there is always going to be a situation halfway between observed stages, but it is not much of a leap to figure out what goes on in there.

[AlphaBeta]

yea, but we have directly observed the entire process of an zygote developing into a human - so it's still a false analogy... we haven't directly observed the entire process of a star, because that is basically impossible given the time it would take... so what I'm saying is that it's not directly observable like the claims would lead you to believe... there is a lot of inference and filling in the gaps... and I'm just not too convinced that these claims can be substantiated in any scientific way... the gaps are simply too big in my opinion, to say we know what sequences of a star formation looks like since we never actually directly observed gases turning into a star... because it doesn't happen overnight - so it's really just educated guesses to me... even though they might be correct - I think it's deceptive to say we have observed the formation of a star... but I'm more interested in galaxy formation at this point.

[insane_alien]

i think you are pushing the analogy to far and in the wrong direction.

 

the point of the analogy is that you do not have to observe one individual to determine how something changes over time as long as it is a similar thing be it a human, star, galaxy, whatever. as long as you can see examples from various stages of its existance.

 

and we have observered the transition form gas cloud to fusing star(or its effects anyway as the star is still masked by the gas cloud at this time)

 

it sounds to me like there are always going to be too many gaps for you to believe it.

[AlphaBeta]

"as long as you can see examples from various stages of its existance."

 

that's my entire question - how do we know what the stages look like, since we've never seen a full process carried out... like we have with a human - how do we actually know what the beginning stages of a star formation looks like, we have nothing to compare it to - and we'll never see this stage develop into a star... so, how could you confirm the claim - see... it's circumstantial. it's not a direct oberservation and I think maybe they are making claims they can't really put to the test, but that's why I'm here to find out what others say about it.

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to further clarify, if we had a time lapse video of the entire process of a star formation from start to finish than we would have the ability to recognize intermiediate stages before something is to become a star... but since we have never seen anything close to an entire start to finish formation of a star, how could we ever know what the first steps look like or some of the intermediate stages... it just seems like they are working from a conclusion backwards to me.

 

they are using very superficial, circumstantial evidence to try and piece together the stages, but that doesn't seem all that scientific to me.

[Martin]

... I am incredulous that we can see anything like this... I think that it's just educated guesses, but there is no way to verify it or falsify the claim.

 

if something resembles a galaxy, that's one thing - I'm talking about viewing something that in no way is a galaxy and saying this is a step in the formation of a galaxy and this will eventually be a galaxy - I'm referring to claims like that.

 

Alien and AlphaBeta, thanks for getting this discussion going. I'm glad you thought I could contribute--actually there are several people around that know something about star and galaxy formation (the general term astronomers use is "structure formation", in this context the word structure covers stars, galaxies, galaxy clusters, filaments, voids etc, the formation of all this structure is a challenge to explain.)

 

The best talk about structure formation that I know is the one given by George Smoot to the TED club, he shows movies and has very good slides.

We humans are just at the beginning of understanding structure formation.

 

Evidence is building up that dark matter is real and that it plays an important role in starting the processes of structure formation.

 

It's a good time for scientists to be humble about our understanding, although they can be proud of the progress that has been made (in a modest way) towards comprehending this wonderful process.

 

Clouds of dark matter can actually be "seen" by their optical distortion of more distant objects, even though the clouds themselves are transparent. The way you can tell a curved lens of glass is there even though it is transparent by how it affects the images of what's behind.

 

I'm not exactly sure what Alpha is asking about. Certainly we have seen a lot of pictures of proto stars and proto galaxies, embryonic early stages of these things. And they resemble what they will eventually become, in certain ways. There are star-forming regions even nearby, in Orion, where we can see gas clouds condensing around proto-stars. When gas falls together it has to radiate away extra energy as heat and we can see the heat given off---this is even before any fusion, any ordinary hydrogen burning, has begun. It is not a star yet but it is beginning to look like one.

So we have "baby pictures" of young structure. Fuzzy proto galaxies too.

 

But Alpha isn't asking about baby pictures that already RESEMBLE in some way, like being more concentrated blobs. He is asking about how we model the very beginning of concentration and condensation, before you can even see a distinct blob.

 

How does the process proceed before there is any visible resemblance, before any fuzzy blob-ness that you can distinguish with a telescope. This is a very interesting question where some modest progress has been made and which George Smoot talks about. One great tool that is being used to attack this problem is computer modeling.

 

You set up a simplified universe with no ordinary matter in it, only dark matter---because most matter is the transparent kind we call "dark". And you start out with the DM almost perfectly even distributed. Just a few slight ripples caused by quantum fluctuation around the bang time. Just a very very slight "waviness" left over from start of expansion.

 

And you let normal gravity operate, and you see what happens and how long it takes.

 

The falsifiability aspect, at this early stage, is that if doesn't produce structure like what we see, within a reasonable time, then it must be based on wrong premise, and you can rule the model out.

 

This is "seeing" with a computer model.

 

You have to realize that the cosmic structure is more than just individual stars and galaxies. there are huge cobweb wisps comprising clusters of galaxies, and huge voids. It is very beautiful. Delicate and grand. It is not just random speckles splattered about. There are aspects of organic pattern.

Have you ever admired cobwebs? Or the way hairy mold grows on bread? Or the wrinkles on someone's face when they are very old? It isn't just random. Or the veins in a piece of rock. Or the smoke rising from a cigarette, from the days when some of us used to smoke them. It's very lovely and not just random. So getting a computer model that just implements the law of gravity to produce something similar is very challenging.

 

The dark matter has to fall together by its own gravity and make just the right pictures.

 

This is something that astronomers are having fun with now. A young grad student or postdoc would quite likely consider getting into structure formation research, as a specialty. And that is what George Smoot was describing in that video lecture to the TED club. Alpha you might enjoy it.

Just google "Smoot TED" if you want to watch and listen to the talk.

[AlphaBeta]

Thanks for the post, Martin - I'll google that ted talk - and also... you edited my last post at 7:37 and you posted your reply at 7:39... world's fastest typer?!!! lol

[insane_alien]

he didn't edit your post, the auto merger did.

[AlphaBeta]

Hey, I've been upgraded to quark status... cooooooooooooooooooool.

[insane_alien]

all that means is that you have over 10 posts.

[Law]

well, when we look really far away we are seeing the way things were billions of years ago since the light has taken that long to reach us.

 

geez...that is SO depressing...theres no possible way to communicate with outside life then...

[insane_alien]

i wouldn't call it depressing, and communication is perfectly possible, it just takes a longer time than usual. think of it as having a friend on the otherside of the world and you only communicate using letters and the postal system is still where it was in 1850. it's going to take months, maybe even a year for a reply to get back to you. thats a similar sort of scale.

[Blue Fire]

The fact of the matter is that we have never observed the complete evolution of a star or galaxy. Thus we cannot know with 100 percent certainty what that process is. But, there are sooooo many stars in varying stages of development, and there are soooooo many galaxies in varying stages of development, and therefore we have had soooooooooooo many observations that we are pretty darned sure about what the whole story is. Sooooo sure that most astronomers are willing to accept it as fact.

 

Even a child who has not witnessed the entire life cycle of a tree and who has not been educated about it either can look at a forest and be pretty darned sure that he sees seedlings, saplings, young trees, old trees and dead trees - after, of course he has seen a bunch of them in a bunch of forests.

Edited July 20, 2009 by Blue Fire
typo