Research Highlight

How colliding galaxies shape star formation

doi:10.1038/nindia.2015.170 Published online 21 December 2015

By analysing images captured by space telescopes, researchers have gained new insights into how star formation is affected in a pair of interacting galaxies that will eventually collide with each other1. These insights may help clarify how major tidal interactions between galaxies contribute to star formation and galaxy evolution.

When two galaxies are about to collide, many stars and large amounts of gas are often disturbed or displaced as tidal debris. This debris then evolves, sometimes forming stars but occasionally forming tidal dwarf galaxies.

To analyse star formation in a pair of interacting galaxies, the researchers mapped the abundance of neutral hydrogen atoms in regions between a pair of massive interacting galaxies ― NGC  90 and NGC  93. Analysis of infrared and ultraviolet images from space telescopes revealed that interactions between these two galaxies seem to have displaced a large fraction of hydrogen atoms in NGC 90.

The scientists detected extended on-going star formation in the outer disk of NGC  90 and identified a lower density of hydrogen atoms in the major star-forming regions of this galaxy. However, no signatures of star formation were found in regions with the highest hydrogen atom density, indicating that debris containing the highest density of hydrogen atoms is hostile to star formation.

The findings confirm that high hydrogen atom densities may be a necessary but not sufficient criterion for star formation, the researchers say.


1. Sengupta, C. et al. Arp 65 interaction debris: massive HI displacement and star formation. Astron. Astrophys. 584, A114 (2015) doi: 10.1051/0004-6361/201425149