Stockholm university

Observations of Dramatic Galactic Collision Unlock Clues to the Reionization of the Universe

An international team, led by Dr. Alexandra Le Reste from Stockholm University and the Oskar Klein Centre, used the MeerKAT radio telescope to investigate processes at the origin of the Epoch of Reionization, a crucial period occurring a billion years after the Big Bang. The study, made possible by MeerKAT's increased sensitivity relative to older telescopes, reveals how galaxy mergers might have influenced the transformation of the Universe during this epoch.

Caption: Image of the galaxy Haro 11. The stars in the galaxy, shown in white, is surrounded by a halo of ionized gas in red. The newly imaged neutral Hydrogen gas, shown in blue, has been displaced during an interaction between two galaxies that resulted in the creation of Haro 11.


The study focused on Haro 11, a galaxy in our local universe that is emitting strong ultraviolet radiation, and discovered an unusual distribution of neutral Hydrogen gas, primarily concentrated on one side due to a past galaxy merger. This observation suggests that galaxy mergers could play a significant role in the escape of ultraviolet radiation by moving gas away from galaxies. This study marks a key discovery, because the escape of strong ultraviolet radiation a few million years after the Big Bang is what caused the Epoch of Reionization.

“It is not unreasonable to think that the mechanism we identified, with the gas being ejected far
from the center of galaxies during galaxy mergers, could play an important role during the Epoch
of Reionization”

says Le Reste.

MeerKAT is a precursor to the Square Kilometer Array (SKA), which will allow researchers to peer directly into the Epoch of Reionization in the future. Other members from the Department of Astronomy at Stockholm University that were a part of the study include Matthew Hayes, Jens  Melinder, Veronica Menacho, Angela Adamo, Arjan Bik, Timmy Ejdetjärn and Göran Östlin.

The study is published in the journal Monthly Notices of the Royal Astronomical Society the 19th of January 2024 and can be found here: