Martin Haehnelt

Martin Haehnelt is a German cosmologist and astrophysicist whose research focuses on the intergalactic medium, cosmic reionization, and the formation and evolution of galaxies and supermassive black holes. He is particularly known for his work using absorption features in quasar spectra—specifically the Lyman-alpha forest—to study the distribution and properties of gas in the universe. His research combines theoretical modeling with observational data from major telescopes.

The Lyman-alpha forest is a series of absorption lines seen in the spectra of distant quasars, caused by neutral hydrogen gas in the intergalactic medium along the line of sight. Martin Haehnelt uses these absorption features to probe the physical conditions, temperature, and large-scale distribution of gas between galaxies across cosmic time. This technique is one of the primary methods for studying the intergalactic medium at high redshift.

Martin Haehnelt is affiliated with the Institute of Astronomy and the Kavli Institute for Cosmology at the University of Cambridge in the United Kingdom. He has been part of the Cambridge cosmology and astrophysics community for many years. His research group works on theoretical and observational problems related to the high-redshift universe.

Cosmic reionization was the epoch in the early universe when neutral hydrogen gas, which had existed since recombination, was reionized by the first stars and galaxies. Martin Haehnelt's research investigates which sources—likely early galaxies and possibly black holes—were responsible for producing the ionizing radiation. Understanding reionization is central to understanding how the first structures in the universe formed and influenced their surroundings.