Formation of a Spiral Galaxy (ver. 3)

How is a galaxy formed? This is one of the big questions in the field of current astrophysics. Here, we show a numerical simulation of the formation process of a galaxy based on a hierarchical scenario of structure formation. In this scenario, a galaxy is formed via the mergers of smaller galaxies.

The Universe is initially very smooth. However, tiny fluctuations are imprinted in the matter distribution and the gravitational pull forms small galaxies based on these fluctuations. First, the dark matter dominating the mass of the Universe clumps together through its own gravity and then gases, such as hydrogen and helium, are attracted by the gravity of the dark matter clumps. In this movie we show the gas in blue, but we do not show the dark matter.
Stars, which are shown as yellow points, form from regions of dense gas. One second in this movie corresponds to tens of millions of years.
A large galaxy is built via mergers of small galaxies. Not just stars, but also gas is accreted during this phase. The gas accreted onto the galaxy forms a disk and then stars form in this disk.
When a small galaxy passes through the disk, its gravitational force enhances the spiral structures in the disk.
This is an edge-on view of the resulting thin disk galaxy.
This image captures the full extent of the spiral galaxy that was formed in the super computer.

640x360, Flash Video Streaming

Click Here (SIGGRAPH2007 version, with sound)

640x360, Windows Media Video (no-sound version)( zip file : 81.7 MB)

320x180, mpeg1 (no-sound version)( zip file : 26.0 MB)

Details of the Numerical Simulation

Physics ModelStandard Cold Dark Matter Model
PurposeTo Understand of the Formation Process of a Spiral Galaxy; the co-evolution of a galaxy, the central region of the galaxy and its super-massive black hole; and the origin of globular clusters.
Calculation ModelMethods:
Gravity Calculations (TREE-GRAPE method)
Gas Interaction(SPH)
Radiative Cooling, Star Formation
Number of Particles:
Dark Matter 1×106 particles, Baryons 1×106 particles
Initial Conditions:
Time Scale~ 13.5 billion years
Spatial Scale~ 0.3 million light years
ResearcherTakayuki R. Saitoh (NAOJ)
ReferencesSaitoh & Wada, 2004, ApJ, 615, L93.
Kawakatu, Saitoh & Wada, 2005, ApJ, 628, 129.
Saitoh, Koda, Okamoto, Wada & Habe, 2006, ApJ, 640, 22.

Details of the Visualization

This simulation calculates the kinematics (motions) of three kinds particles: stars, gas and dark matter. In this movie, only the stars and gas are visualized.
Observed galaxies have a hundred billion stars, but only one million particles were considered in this simulation. Each particle represents more than hundred thousand stars. So this simulation probably doesn't have enough resolution.
In the future, a high-resolution simulation with more particles will provide a more detailed scenario of galaxy formation.

Credits of the SIGGRAPH Version Video

The streaming video was edited for screening at the SIGGRAPH2007 Electronic Theater, with music and narration added. The credits of this version are given below (the affiliations given are for the time when this video was produced):

  • Simulation: Takayuki R. Saitoh (NAOJ)
  • Visualization: Takaaki Takeda (NAOJ), Sorahiko Nukatani (RIKEN)
  • Programing for Vasiallization: Takaaki Takeda (NAOJ), Toshiyuki Takahei (RIKEN)
  • Scenario: Eiichiro Kokubo, Catherine Ishida (NAOJ),
    Caroline Collins Petersen (Loch Ness Productions)
  • Narration: Catherine Ishida (NAOJ)
  • Recording: Masayuki Yamamoto, Hiroyuki Hatano (S.C.ALLIANCE Inc.)
  • Music: Asako Miyaki
  • Produce: Eiichiro Kokubo, Shoken Miyama (NAOJ)

Release Date