Crashing Galaxies Drive Huge Shockwaves into Deep Space

Research conducted by an international team of astronomers, published in the scientific journal Nature, revealed an enormous nebula around an extreme form of a merging galaxy.

The galaxy named Makani (Hawaiian for 'wind') is pushing a large fraction of its gas into the space between galaxies called the circumgalactic medium. The team observed a wind in a glowing halo of extended oxygen out to extreme distances (one of the largest such nebulae ever observed) at different speeds and locations, corresponding to the different times at which the galaxy began rapidly forming stars. This enabled them to track the detailed energetics of the event. Seeing this expansive outflow also provides a missing link to explaining how metals can be displaced far out into the intergalactic medium (the space between galaxies).

Velocity maps of the galactic wind.
Velocity maps of the galactic wind. The velocities are from fits to Voronoi-binned [O II] data and are calculated from the red side of the cumulative velocity distribution function to specified percentiles as maximum blue shifted velocity vmax=v98% =v50% -2σ (see paper)

"What is also remarkable is that the aging and dying stars appear to be powerful enough on their own to do all of the work without the need for a supermassive black hole's help, though we expect one to be buried down in the center of the merging galaxies, maybe quite literally under a lot of dust and gas," remarked Dr. Paul Sell, who, as a member of a small collaboration, contributed to this research while a scientist at the Institute of Astrophysics of FORTH; Dr. Sell has since recently joined the faculty at the University of Florida, USA.

Though this galaxy weighs about as much as our Milky Way Galaxy, we don't see anywhere near such an extreme situation in our own Galaxy or even in other one relatively nearby. Seeing such heavy galaxies catastrophically colliding is pretty rare, especially those that have lots of cold gas from which to form new stars. The funneling and collision of the cold gas deep in the gravitational well of the merging galaxies produces a very large number of stars in a short time and in a small space. The heaviest stars formed from this burst of star formation quickly die, sending out strong winds and shockwaves that blow the gas out of the galaxy, shooting it at high speeds out into deep space.

Article: D. Rupke, … P. Sell, et al., "A 100-kiloparsec wind feeding the circumgalactic medium of a massive compact galaxy", Nature Vol. 574, pages 643–646 (2019)