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Astronomers Discover When Galaxies Got Their Spirals
KentuckyFC writes "The universe today is filled with beautiful spiral galaxies — but it hasn't always been this way. In the early universe, there were no spiral galaxies, raising an interesting question: when did galaxies get their spirals, and how did they emerge? Now astronomers have the answer, thanks to an analysis of galaxies in an image taken by the Hubble Space Telescope known as the Ultra Deep Field. This shows some 10,000 galaxies of various ages. By ordering a subset of these by type and by age, astronomers have worked out how and when spirals must have evolved. It turns out the first spiral galaxies were simple two-armed structures and appeared when the universe was about 3.8 billion years old. But they say the universe had to wait until it was 8 billion years old before more complex multi-armed galaxies emerged, like the Milky Way and Andromeda."
Well perhaps not a Coincidence.
We are a creation of a second generation star. With our heavier elements that are assumed to be a product of the first generation stars dying process.
Assuming most Stars last an average of 10 billion years. It would be save to assume the second generation started 8 billion years after the big bang. Now creating of these heavier elements probably made gravity distribution in the galaxy a little less consistent creating new shapes too.
If something is so important that you feel the need to post it on the internet... It probably isn't that important.
The answer is obvious to anyone who likes old-style mythology:
When the gods rotate the universe to look for their next vacation spot, the resulting Coriolis force makes galaxies spin. They don't all spin in the same direction because of The Great Nebula Outing Debate of 10 000 000 000 PBB (Post-Big-Bang), when the Almighty-Mothers-In-Law kept rotating back and forth until The-So-Cute-One (then a toddler at barely 10000 years old) randomly sneezed a few more stars on Orion.
Ever since that event, people on Durandil Major have been unable to predict the way the water will flow when they flush their toilets.
If I'm remembering my astronomy correctly, first generation stars were much larger and faster rotating, but also much shorter-lived in general - some had lifespans possibly as short as a few million years.
If Japan is any indication, multiple tentacles are usually followed by bukkake.
The Elmegreens examined 269 spirals in the Hubble Ultra Deep Field and discarded all but 41 because of factors such as an inability to discern a clear spiral structure or the lack of redshift data which gives a galaxy’s age.
They divided these 41 spiral galaxies into five different types, based on features such as the number and clarity of arms, whether well-defined or clumpy and so on.
It sounds like they only found a few of each type, seems more like a good hypothesis than "the answer". It also makes you wonder if they cherry picked some of their data.
I recall a few years ago participating with a lot of others in a crowd source effort to categorize fuzzy pictures of possible galaxies. I think it was galaxy zoo.
So is this the result of our effort? Would be nice to know...
-Malakai
A Dragon Lives in my Garage
The summary says they have figured out how and when the spirals formed.
But the linked articles only say when, not how.
May the summary writer burn in hell for all eternity.
Retrospectively it could have been guessed long ago that disk galaxies need at least a few tens of rotation periods to look progressively like symmetric accretion disks in other astrophysical contexts (disks around black-holes, stars or planets). The difference between galaxies and smaller disks is mainly the number of rotations they could make, a few tens of rotations for spiral galaxies, millions or billions for smaller disks.
The guy that picked up the snowglobe and gave it a twist... Sadly that is when the great galactic disaster happened and most of the residents of Betelgeuse IV died.
Do not look at laser with remaining good eye.
I thought it was third generation? Did something new get discovered while I wasn't looking?
And as SJHillman pointed out correctly, first generation (Pop3) stars were (allegedly, we still didn't see a single one of them) almost entirely H and He, insanely huge and existed for just a few million years (compared to the billions of years that contemporary stars have ... provided they ain't too big).
So I'd say we're probably orbiting one of the first stars that have enough metal to have "rock" planets and hence support life.
We used to have a Bill of Rights. Now, with the rights gone, all we have left is the bill.
Earth formed from heavy elements produced in at least one prior generation star, but there could be more than just one prior generation (It's very, very unlikely that all or nearly all the medium weight elements above lithium, in our solar system, came from just one older star, and pretty unlikely even that all the heavies above Iron were cooked up in just one supernova).
It's not a safe assumption that stars last an average of 10 Billion years. The most numerous types, red dwarfs, make up 80-90% of all stars, last a lot longer than that, and probably stay stable on the main sequence for 100-200 billion years (American Billions). They also shouldn't spread elements around much when they finally do leave the main sequence. Stars about the size of our Sun, spectral class G2, typically live about 10 Billion years, but make up only about 2% of stars. Big stars, type O, B, and A, burn more quickly, and it's possible to get enough hydrogen together for a star to burn through all its fuel and supernova in mere hundreds of thousands of years, or possibly even a blazing fast 10's of thousands. Those stars are rare, but they are so massive that even a few produce enough heavy elements and push enough gas around when they supernova, to create hundreds of sun sized and smaller stars and all the heavy elements to give such stars the solid, rocky planets we now think are practically ubiquitous.
The supernova explosions are a common source for two effects - heavy element formation, and compressive shock waves that trigger new stars forming in nearby interstellar gas clouds. Many of these gas clouds are already enriched with heavy metals from previous supernovae, Spiral galaxies tend to get regions of new star formation, and quiet regions. But, the high and low density regions in spirals like our Milky Way exist on larger scales than the star forming "nursery" clouds, and this is largely because gas clouds are not just compressed by novae - both the dense star forming clouds and very large but more difuse clouds colide with other clouds, including clouds that were part of dwarf galaxies being captured by the big spirals. So, it's a partial coincidence - Older generation stars have some influence on the shapes of spiral galaxy features, but dwarf galaxy capture has more, and the rare colisions of spirals with other big galaxies show just how much influence the large scale objects can have, producing wildly twisted galaxys such as
If anyone wants to read up on this sort of thing, please remember, because astronomers named them before they knew anything about why there were multiple distinct types of stars in the same mass ranges, Population II stars are actually older than Population I, and Population III older than II. A given population usually includes multiple generations of stars. As an exception, the very oldest, massive stars that novaed within the first million years or so after star formation began, and produced so many heavy elements are called Population III, and most probably represent just a single generation and possibly only the largest types.
https://en.wikipedia.org/wiki/Stellar_nursery#Stellar_nurseries
https://en.wikipedia.org/wiki/Galactic_collision
https://en.wikipedia.org/wiki/Population_I_stars#Population_I_stars
and, for those people wanting more than just the Wikipedia versions, a little real source material:
http://arxiv.org/pdf/astro-ph/0012399v2.pdf
Who is John Cabal?