A maser signal, an equivalent of a laser, has reached us from a distant galaxy. Its origin and intensity make it an exceptional case. The signal traveled several billion years through space before reaching us.
The emission was captured by the MeerKAT radio telescope in South Africa, after a journey of approximately eight billion light-years. Unlike conventional lasers, masers emit in the microwave and radio wave domains. The identified phenomenon is in this case a hydroxyl megamaser.
A hydroxyl megamaser corresponds to a coherent emission of microwaves produced by stimulated amplification within very dense gas clouds. In these regions, hydroxyl (OH) molecules are excited by intense radiation, often linked to vigorous star formation. When these molecules return to a lower energy state, they emit photons which in turn stimulate other identical emissions. This mechanism creates an amplified and coherent signal, observable at great distances in the radio domain.
Without a natural magnifying effect, this signal would have remained undetectable. The radiation was bent and amplified by the gravity of a galaxy located between the source and Earth. This gravitational lensing phenomenon, described by Albert Einstein, acts as a cosmic magnifying glass. It allows the observation of extremely distant objects, normally too faint to be detected.
The distance of this megamaser is a record. Its observation corresponds to an era when the Universe was only about half its current age. It thus offers direct access to the conditions that prevailed during the active phases of galaxy formation. The amplification of the signal allows for detailed analysis despite this extreme remoteness.
Illustration of the distant galaxy at 8 billion light-years (red), magnified by a lens galaxy, forming a red ring. The decomposition of the radio light reveals the hydroxyl megamaser (rainbow line top right).
Credit: Inter-University Institute for Data-Intensive Astronomy (IDIA)
These megamasers most often appear in colliding galaxies. These interactions concentrate large amounts of gas and dust, promoting intense star formation. In these environments, hydroxyl molecules naturally amplify radio emissions. The detection of such a signal therefore indicates particularly high activity in the observed galaxy.
The study of this phenomenon provides information about gas dynamics and star formation mechanisms. It can also reveal the presence of interacting supermassive black holes. These systems are likely to produce gravitational waves, which are now actively sought by astrophysicists.
Led by Thato Manamela from the University of Pretoria, this research was published in the journal Monthly Notices of the Royal Astronomical Society Letters. It paves the way for the detection of other distant megamasers, thanks to the growing capabilities of modern radio instruments.