Using two supercomputers at Oak Ridge National Laboratory and the Swiss National Supercomputing Center, a group of researchers headed by Dr Simon Portegies Zwart of Leiden Observatory has simulated the long term evolution of the Milky Way Galaxy over a period of six billion years – from 10 to 4 billion years ago.
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If you took a photo of our Milky Way Galaxy today from a distance, it would show a spiral galaxy with a bright, central bar of dense star populations.
The Sun would be located outside this bar near one of the spiral arms composed of stars and interstellar dust; beyond the visible galaxy would be a dark matter halo.
Now, if you wanted to go back in time and take a video of our Milky Way Galaxy forming, you could go back 10 billion years, but many of the galaxy’s prominent features would not be recognizable.
You would have to wait about 5 billion years to witness the formation of our Solar System. By this point, 4.6 billion years ago, the galaxy looks almost like it does today.
This is the timeline Dr Portegies Zwart and his colleagues are seeing emerge when they use supercomputers to simulate the Milky Way’s evolution.
This image shows what the Milky Way Galaxy looked like ten billion years ago. Image credit: SURFsara / J. Bédorf / NVIDIA.
“We don’t really know how the structure of the galaxy came about. What we realized is we can use the positions, velocities, and masses of stars in three-dimensional space to allow the structure to emerge out of the self-gravity of the system,” Dr Portegies Zwart said.
The challenge of computing galactic structure on a star-by-star basis is, as you might imagine, the sheer number of stars in the Milky Way – at least 100 billion. Therefore, the team needed at least a 100 billion-particle simulation to connect all the dots.
Before the development of the team’s code, known as Bonsai, the largest galaxy simulation topped out around 100 million particles.
The team tested an early version of Bonsai on the Oak Ridge Leadership Computing Facility’s Titan – the second-most-powerful supercomputer in the world – to improve scalability in the code.
After scaling Bonsai, the scientists ran Bonsai on the Piz Daint supercomputer at the Swiss National Supercomputing Center and simulated galaxy formation over 6 billion years with 51 million particles representing the forces of stars and dark matter.
After a successful Piz Daint run, the team returned to Titan to maximize the code’s parallelism. Bonsai achieved nearly 25 petaflops of sustained single-precision, floating point performance on the Titan.
The team aims to compare simulation results to new observations coming from ESA’s Gaia satellite launched in 2013.
“One percent of the particles, or stars, in our simulated galaxy should match Gaia data,” Dr Portegies Zwart said.
Source : sci-news