Peekaboo: Once-hidden galaxy revealed to be window into cosmic history

A nearby galaxy – dubbed Peekaboo because it has long been hidden behind a star – has finally come into view enough for NASA to discover that it's more than just a tease. It offers a glance into the early universe, despite being one of the youngest galaxies ever detected. peekaboo-galaxy-zoom The Peekaboo Galaxy. Image credit …

[Mike 137]

"For now, though, the why and how of its delayed formation – billions of years behind its neighbors – will remain a mystery"

Possibly the result of a "little bang"? Why there should there have been only a single big one, except that our version of cosmology is currently based on that assumption? There may be little ones occurring all over the place all the time, but just not where we can observe them yet. We can not see the entire universe - not yet even as far as where our model of it suggests its "limits" (i.e. the distance light must travel since the notional "big bang" to reach us) might be.

[KittenHuffer]

If multiple 'little' bangs were such a thing then even if we had not seen one directly we would have observed the effects of them. So I'm afraid that you're so wrong that you're not even in the right Universe!

[Mike 137]

"even if we had not seen one directly we would have observed the effects of them"

Not if they happen beyond our observational scope (which by definition is tiny compared with the actual universe) -- or indeed if we've ascribed their effects to something else. We actually know so little about the universe in general that our theories are quite probably largely grounded in assumptions that may or may not turn out to be entirely correct. This is particularly a hazard in scientific spheres that are largely theoretical. For example, we've observed effects ascribed to Dark Matter, but does anyone actually know what it is or even whether it actually exists?

There's a growing tendency in science at large (and I've worked in various scientific disciplines and seen it in all of them) of over-confidence -- to assume much greater proximity to actuality for our theories than may be entirely justified. Science is necessarily culture bound and our culture abhors uncertainty, but the universe is full of it.

[ThatOne]

Occam's razor says it's most likely the result of a primordial hydrogen cloud, which til then minded its own business until it got stirred up because of something, and in the resulting eddies mass accumulated locally enough to start star formation. You know, it happens easily: You have a somewhat drunken night out and before you know it, a star is born...

[KittenHuffer]

So you claim that this low metal galaxy was 'Possibly the result of a "little bang"?'. Then when I say that if this were the case that we would have seen evidence. So suddenly 'Not if they happen beyond our observational scope'.

Pick one or the other, or even better, stop trying to introduce pseudo-science BS in an effort to troll a science discussion.

[that one in the corner]

> For example, we've observed effects ascribed to Dark Matter, but does anyone actually know what it is or even whether it actually exists?

No. Not at all. That is the whole point of giving it the moniker "Dark Matter".

Whatever is causing the observable effects, it is behaving as though there is a lot of matter around that we have not been able to observe, at all.

No matter what the eventual cause is found to be, even if it turns out to be modified Newtonian gravity (MOND or its relatives) it will still behave like there is Dark Matter and will very likely keep that moniker forever. Ditto Dark Energy.

Compare with the Big Bang - which was neither big nor a bang, indeed the name was deliberate British sarcasm - the moniker will likely remain even after its actual mechanism has been determined, replicated[1] and " properly" named (something sensibly polysyllabic).

[1] I recommend wearing a tin hat and ducking.

[Totally not a Cylon]

There is a theory which states that should we ever understand everything about The Universe it will promptly disappear to be replaced by a more complicated one.

There is another theory which states this has already happened. Several times!

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.

.

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All this has happened before and will happen again.....

[sitta_europea]

"There is a theory which states that should we ever understand everything about The Universe it will promptly disappear..."

Spoiler alert:

https://en.wikipedia.org/wiki/The_Nine_Billion_Names_of_God

[Totally not a Cylon]

Actually it's from:

Douglas Adams,' The Restaurant at the End of the Universe.'

[b0llchit]

Shirley, you mean Milliways.

Damn, that remark made me a bit peckish.

[Anonymous Coward]

Some day we're going to find out that the underlying universe oscillation was a simple repeating pattern of unique primes {2,3,7}, repeating at 42 iterations of the base oscillation. And everyone will imagine he's a genius, when in fact he just read it in a forgotten book.

They'll call it the "Adams number".

[Paul Hovnanian]

Age vs stellar size

Theory states that very large Pop III stars burn through their hydrogen/helium fuel very quickly generating the metallic elements. And then they go nova or supernova, distributing these components to seed newer generation stars.

The existance of this galaxy may provide evidence for a new stellar evolution route. Where smaller, old stars hang around for billions of years. Not burning through their fuel quickly and, as a result, not producing great quantities of heavy elements.

[the spectacularly refined chap]

Re: Age vs stellar size

The existance of this galaxy may provide evidence for a new stellar evolution route. Where smaller, old stars hang around for billions of years. Not burning through their fuel quickly and, as a result, not producing great quantities of heavy elements.

Theory already allows for small, slow burning stars. Small red dwarves are expected to spend trillions of years on the main sequence before they exhaust their fuel supply. The problem is that those same theories state such stars must also be metal rich.

If all stars were made of the same stuff then barring exceptional events they'd all be similar in size, the collapsing gas cloud would reach a point where the density and temperature is high enough to support nuclear fusion and bang! The star ignites, and radiation pressure and the stellar wind prevents further accumulation of material barring e.g. a collision with another star.

The first stars were devoid of metals and so they had to be HUGE, there was nothing but the gravity of the collapsing hydrogen and helium to compress them together. As a result they are believed to have come in at a couple of hundred solar masses or so. Stars that large burn quickly and brightly, we can establish that from present day observation.

The more metallic the initial material you have, the more heavy elements you have compressing the proto-core together. As a result it can ignite at a far lower mass than its metal poor cousins.

[Paul Hovnanian]

Re: Age vs stellar size

So, we are looking at a very young galaxy populated by large, young, metal poor stars. And it's much closer (20 million light years) than most of the other young, metal poor galaxies. So then it's a new point on the graph of galaxy creation dates. Galaxies in the local neighborhood are still being born.

We get a change to tweak our current understanding of galaxy birth.

[KittenHuffer]

Re: Age vs stellar size

No need to tweak the theory. This is just a 'smaller' cloud of gas that has taken longer than average to collapse gravitationally to the point where it has been able to generate stars. It may have existed 'balanced' between other galaxies, until those galaxies gave it enough space to collapse. Or it could consist of metal poor gass that was gravitationally ejected from (the outer limits of) another galaxy (or galaxies) that has now had a chance to collapse.

The bottom line is that the Universe is easily large enough that there are metal poor gas clouds sitting around in intergalactic space waiting for time (or some other event) to trigger their collapse. The 'luck' with this one is that it is so close to us, which makes for easy observation.

[DS999]

Re: Age vs stellar size

Pop III stars were able to get so large because the universe was much smaller so everything was more crowded together, allowing for quickly gathering enough mass to form stars massing thousands (some believe tens or even hundreds of thousands) of solar masses.

But nothing says that smaller Pop III stars couldn't have been born in less dense areas that weren't so massive and would have much longer lives. Theoretically some could still be around today, though AFAIK we probably have no way to tell the difference between them and stars born later in metal poor environments.

[eldakka]

Re: Age vs stellar size

> But nothing says that smaller Pop III stars couldn't have been born in less dense areas that weren't so massive and would have much longer lives.

Physics says that smaller Pop III stars couldn't have been born.

For fusion ignition to start, certain conditions are required. Those conditions can't be met such that a small Pop III star can form. The purer the star in terms of hydrogen and helium and no heavier elements, the bigger - more massive - a star has to be to meet ignition conditions. Throw in more and more impurities ('metals') the smaller and smaller the star can be to undergo ignition.

Of course, this also depends on what your individual definition of 'small' is ;)

[DS999]

Re: Age vs stellar size

So what's the minimum mass for a pure hydrogen/helium star to ignite?

[KittenHuffer]

Re: Age vs stellar size

I seem to remember that the difference is that the metals allow a collapsing gas cloud to shed heat energy much easier. So the Pop III stars could gather much more gas together prior to ignition because the heat built up in the collapse kept the proto-star inflated above the density required for fusion.

Pop II & Pop I stars are able to dump the collapse heat much more efficiently, so can reach the density required for fusion much sooner, which leaves less time for gas to be accumulated.

This doesn't exclude large Pop I stars but it does make them outliers when compared to the average size of Pop I stars. Our own Sun is larger than 90-95% of Pop I stars.

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What has not been mentioned is that if you had a small enough cloud of primordial gas, that was left undisturbed for long enough for the collapse heat to radiate, then there is no reason why it would not be able to reach the density required for fusion. So it is possible to have small Pop III, but the circumstances for them to form mean that they would likely be very lonely. And might even have to sit out in intergalactic space all on their own.

[the spectacularly refined chap]

Re: Age vs stellar size

Stellar ignition requires both pressure and temperature. It's the momentum given by the temperature that initially overcomes the repelling electromagnetic force and allows the strong force to take over. It's then the density that ensures that the fusion byproducts trigger similar interactions in nearby material to start a chain reaction.

[KittenHuffer]

Re: Age vs stellar size

I never said that you didn't need temperature as well. I just said that if the temperature is too high then it stops the required density being reached by keeping the gas cloud over-inflated. Only when the gas cloud has cooled sufficiently does it shrink to the point where the densities reach the required levels.

[Sceptic Tank]

Ok, so behind that star are ... more stars. Ho hum.

[Phil O'Sophical]

Seasonally appropriate

It's behiiiind you.

Oh, no, it isn't

[Eclectic Man]

Hiding

I do like the idea that the galaxy was 'hiding' behind a star, as if it was doing it on purpose. The best place to hide a tree is, allegedly, in a forest, but a whole galaxy? Yup, I'll just put it behind this convenient star.

[steelpillow]

You don't say?

"It offers a glance into the early universe, despite being one of the youngest..."

Uhh, can someone explain the logic of that to me, please?

[Anonymous Coward]

Re: You don't say?

Because it is so far away the light we see originated billions of years ago when the Universe was young. Therefore we see the galaxy when it was young. To us the galaxy appears to be one of the youngest because it is one of the furthest away.

[eldakka]

Re: You don't say?

> Because it is so far away the light we see originated billions of years ago when the Universe was young.

What makes this galaxy exciting is that it is an example of an extermely metal-poor galaxy that is very close, 20 million light years away. This means it can be examined in much greater detail being so close. It is not billions of light years away.

[DJ]

I must have dozed off...

...during the part where they explained how particles of matter, e.g. galaxies, etc. are increasing in velocity from the "Big Bang" instead of decreasing.

I'm no genius, but I do know when to say "I don't know".

Then again, I don't get paid to come up with ideas that make no sense at all.

Mine's the one with the number blocks in the pockets...

[KittenHuffer]

Re: I must have dozed off...

They are not increasing in velocity, the space between them and us is expanding at a fixed rate. But what this leads to is that once the space between them and us has expanded by 10% then there is 10% more space between us and them, so they appear to travel away from us 10% faster. So they are getting further away from us at a faster rate because there is more space between us, rather than them accelerating away from us. The term 'accelerating' is merely used to try to make it simpler to understand for the layperson.

If you were to go to one of these distant galaxies you would see the Milky Way galaxy 'accelerating' away from you in just the same way that we see that distant galaxy 'accelerating'. But we are here, and yet we see no effects of that acceleration.

[KittenHuffer]

Here is a good thought experiment for you

Make a straight ruler that is 13 Billion light years long. With the rate of expansion of the Universe that will mean that the ends of the ruler are travelling away from each other at (approximately) the speed of light. In theory the ruler would not be able to stay in one piece because of this expansion, so eventually the ruler would have to break into pieces. Where would you see this happening? And how long would it take?

.

Edit: I thought I was doing this as a reply to my "Re: I must have dozed off..." post above!