Here’s an interesting one on
the state-of-the-art in Spiral Galaxy formation modelling.
The following words caught my eye:
Quote:
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Being able to simulate a complex system like the formation of the Milky Way realistically is the ultimate proof that the underlying theories of astrophysics are correct.
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Hmmm ... when it comes to theory in science, there is no ‘proof’, so we can dispense with that statement pretty quickly, but what does this exercise really then represent ?
In their simulation, the spiral galaxy shape forms on its own. In the model, they're tracking the behaviours of individual components of a galaxy comprising 790 billion solar masses and 18.6 million particles .. a huge number crunching task !
Principles Used (Inputs):
- cold dark matter paradigm;
- physical laws of gravity;
- fluid dynamics;
- radiophysics.
Model Outputs (Results):
- stars form in giant high density cold molecular gas clouds;
- star formation and distribution not uniform - clumped, clustered;
- heat build up by supernova explosions;
- visible matter accelerated to high redshifts by these explosions;
- removal of this matter from the core results in a concave disk;
- this results in the correct stellar mass as per observations;
- at the end, a thin curved disk forms corresponding to measured mass, angular momentum and rotational velocity ratios.
General Litmus/Reality Tests:
- can’t have too many stars at the centre;
- the overall stellar mass can’t be several times bigger than observed.
Predictions:
- distributions of stars and hot gases for the outer halos of the Milky Way (currently technologically, beyond detection).
There’s also a whole lot of extra ‘tweaks’ they’ve recommended going forward (of course).
Coming back to answer my original question though, to me, what it is they’ve actually shown, is that from the known individual component behaviours, a spiral shape forms which matches fairly closely to what we observe at the macro-scales .. which in itself, is amazing! That this happens, shows us that the universe is capable of forming galaxy shapes, which are not immediate directly relatable (in quantifiable terms), with the known individual component behaviours. (Ie: the whole is different from the sum of its parts).
If this is the way the universe behaves overall, then why should we ever expect the behaviours at any given level of scale, to necessarily be the same at the next level up or down ?
Cheers
PS: For anyone interested, the paper describing the model
is here.