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"Green peas" provide clues to the early days of the universe

This image shows Anne Verhamme, winner of the Marie Heim-Vögtlin prize 2019.

It is probable that primordial galaxies triggered the period in the history of the universe known as “cosmic reionisation”. The Geneva-based astronomer Anne Verhamme has succeeded in demonstrating this by studying green pea galaxies. In recognition of this work, the SNSF will award her this year's Marie Heim-Vögtlin prize on 16 September 2019.

Following the Big Bang some 14 billion years ago, the universe gradually cooled down, allowing electrons and protons to fuse together to form hydrogen atoms. This was the beginning of the Dark Ages of the universe, which lasted until the first stars were formed. These stars must have emitted large quantities of ultraviolet radiation that was capable of ionising the hydrogen atoms, because astronomers observed that electrons and protons separated again a billion years after the Big Bang. This is what we call the cosmic reionisation period.

Successful new measurement technique

For a long time, astronomers could not explain where the powerful UV radiation needed for reionisation had come from. The majority of observed galaxies do not emit ionising photons and the few known exceptions emit too little to keep the universe ionised.

Anne Verhamme, professor of astronomy at the University of Geneva, proposed that green pea galaxies – a new type of galaxy discovered ten years ago – probably emit large quantities of ionising photons. This assumption was based on the highly specific properties of rays emitted by the hydrogen atoms in these galaxies, known as Lyman-alpha radiation. Astronomers believe that green pea galaxies resemble primordial galaxies as they are extremely compact, are creating their first generations of stars, and are still rich in gas.

Using data from the Hubble Space Telescope, Anne Verhamme and a international team of collaborators were able to demonstrate that green pea galaxies do indeed emit large quantities of ionising photons. If green peas are analogous to primordial galaxies, it seems very likely that it was galaxies that triggered the reionisation of the universe more than 13 billion years ago.

Support from the SNSF

Anne Verhamme was able to conduct her research at the University of Geneva thanks to a Marie Heim-Vögtlin grant from the SNSF. In 2018, she was awarded an SNSF professorship and received a Starting Grant from the European Research Council (ERC). A mother of three, Verhamme will receive the Marie Heim-Vögtlin prize – which comes with prize money of CHF 25,000 – in Geneva on 16 September 2019. The event will be held as part of the welcoming ceremony for new students of the Science Faculty.

Reconciling career and family

The SNSF awarded Marie Heim-Vögtlin (MHV) grants to outstanding women researchers for 25 years. The grants enabled them to pursue their careers and raise a family at the same time. The MHV prize is awarded by the SNSF each year to honour the work of women researchers who were grantees of the MHV programme. In autumn 2017, the MHV grants were superseded by the new funding scheme PRIMA.

The MHV grant was named after Marie Heim-Vögtlin, who became the first Swiss woman to study medicine at the University of Zurich’s medical faculty in 1868. On completing her studies, she opened a gynaecological practice, where she continued practising after giving birth to two children. She is regarded as one of the pioneers in the struggle to give women access to higher education.

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