This is interesting to learn how from an ‘almost’ homogeneous space with a very few tiny density perturbations; these big galaxies, stars, planets were made – how these first ever structures were formed. But it is tough to study that, specially because we can not observe the ‘first-ever stars’ being formed and theoretically too it’s a bit tricky – you need to take care of loads of physics and on paper it goes all messy. But we have another option – and that is to simulate the universe using numerical computations (we know how it was after inflation, we know how it looks like now, we know the forces that should be influencing the formation of structures in space, so it’s not that tough)!!
Presenting here are few snapshots of a simulation I have been running for the final project of my lab course on Numerical Simulations. This is using a cosmological code called ENZO and the following eight slices are focussing on a single region in space as time flows (from ‘then’ to ‘now’). The three sub-plots on each of these slices show the density, temperature and velocity of the matter at that point of time. The first slice was made when the universe was very young.. and as you go down the slices, you see more and more modern version of the universe, the final slice being the universe now.
At the earliest time, universe was almost homogeneous except a few regions where we had a very tiny bit of inhomogeneity in density that we term as density perturbations. Those overdense regions collapsed due to self-gravity over a period of time and finally structures were formed – halos, and then galaxies, the stars and then planets – and on one of those structures called Earth, I am sitting today and writing this blog 🙂 Well, ENZO is not a code that ‘I’ wrote, but it is something really cool to work with and the results are worth being shared.. I loved it 🙂 I hope you like it too!
This first slice as I said is when the Universe was young, almost 0.5 Gyrs after Big Bang (now it is almost 14 Gyrs). Forget the Density and Velocity sub-plots and focus on the plot in the middle i.e. the temperature plot. You see those two small greenish things on that purple background? Well, these are small perturbations on otherwise homogeneous space. Now, as they have ‘a bit’ higher density and mass, they will have a bit higher gravitational force and hence it will start attracting and accumulating more and more mass from the surrounding!!
And as you go through the next slices (from older times till today), you will see how these structures will grow. The temperature sub-plots (the purple middle plots in each slice) shows the situation most clearly – so first concentrate on that!!
This final slice shows a type of mass halo (like a big galaxy cluster) with numerous galaxies inside it! If I could go to higher resolutions, I could even show the galaxies as we see them now. And using supercomputers if this simulation could be run for days and if considerable zooming is done, it is possible to even reach the stars – the first stars that were born!!
Ohh! And you can even look at the density of individual elements at all these times – and as you can see in the following plot, whenever there is a structure being formed we have loads of electrons (the left-most slice) and ionized hydrogen (the slice at right) compared to the surrounding voids. But as at those places we have high density and temperature, neutral hydrogen can not survive there – so in the middle plot we see the neutral hydrogen density to be almost negligible (bluer = lesser density) in the structures compared to the voids:
Never thought before that I would love/want to learn programming and these numerical methods!! 🙂