Complex gas motion in the center of the Milky Way

Spiral galaxy Messier 61, picture taken with the Hubble
Space Telescope. Our Milky Way might look like this galaxy.
Credit: ESA/Hubble & NASA. Acknowledgements: G.
Chapdelaine, L. Limatola, and R. Gendler

How does the gas in the centre of the Milky Way behave?
Researchers from Heidelberg University, in collaboration with
colleagues from the University of Oxford, recently
investigated the motion of gas clouds in a comprehensive
computer simulation. The new model finally makes it possible
to conclusively explain this complex gas motion.
Astrophysicists Dr Mattia C. Sormani (Heidelberg) and Matthew
Ridley (Oxford) conducted the research.

Our solar system is located in the outer regions of the Milky
Way, a disk-shaped galaxy with an approximate diameter of
100,000 light years. From the earth, its appearance can only be
observed indirectly, by measuring positions and movements of
stars and gas clouds. The Milky Way is most likely a barred
spiral galaxy, a very commonly observed type of galaxy in the
universe. A well-known example is the galaxy M61.

In addition to the luminous stars, a substantial portion of the
visible matter in our Milky Way is interstellar gas. The
distribution and motion of this gas is very complex. Especially
in the centre of the Galaxy, there are substantial
discrepancies between the measured quantities of gas and the
low rate of . “Our simulation
not only eliminates these discrepancies found in previous
models, but also allows us to reproduce the observed motion of
the gas surprisingly well,” says Prof. Dr Ralf S. Klessen, one
of the researchers at the Institute of Theoretical Astrophysics
at the Centre for Astronomy of Heidelberg University (ZAH).

The figure shows the results of the simulation of the flow
of gas at the centre of the Galaxy. The spiral structure in the
innermost region and the two arms are easily identifiable.
Credit: Matthew Ridley

In the , gas clouds in the so-called
central molecular zone (CMZ) – the innermost 1,500 light years
of the Milky Way – move on an elliptical central disk that has
two spiral arms. Gas from the surroundings flows through these
arms into the CMZ. Collisions of gas clouds create shock waves,
generating turbulence. “This turbulence could prevent the gas
from collapsing into , providing a consistent explanation for the
unexpectedly low rate of star formation in this region,” says
Dr Sormani.

The computer simulation allowed the researchers to create a
spatial image of the centre of the Galaxy and determine the
position of some known within this three-dimensional “map”
for the first time. The astrophysicists now plan to optimise
their simulation in order to improve their results and better
match observational data. They also hope to clear up any
remaining questions such as the pronounced asymmetry of the gas
distribution in the central zone of the Milky Way. Further
simulations, based on the temporal development of the chemical
composition of the gas, are intended to unravel this mystery.

“We believe that these findings will have a major impact on
future studies on the structure of our Galaxy,” says Prof.
Klessen. The research results were published in the Monthly
Notices of the Royal Astronomical Society

Explore further:
hidden galaxy

More information: Matthew G. L. Ridley et al. Nuclear
spirals in the inner Milky Way, Monthly Notices of the Royal
Astronomical Society
(2017). DOI:

Journal reference:
Monthly Notices of the Royal Astronomical Society

Provided by: Heidelberg