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Researchers have detected fluorine -- an element found in our bones and teeth as fluoride -- in a galaxy so far away that its light has taken over 12 billion years to reach us, a discovery that is yielding important insights into how the material is forged in the universe.

Using the Atacama Large Millimetre/submillimetre Array (ALMA), a team of astronomers from Dalhousie University and institutions in Chile, Poland, the UK, the U.S. and Spain found fluorine in the form of hydrogen fluoride in a distant star-forming galaxy for the first time.

Dr. Scott Chapman, a professor in Dalhousie’s Department of Physics and Atmospheric Science and co-author of the study, and his collaborators spotted fluorine in the large clouds of gas of the distant galaxy NGP–190387. Since stars expel the elements they form in their cores as they reach the end of their lives, this detection implies that the stars that created fluorine must have lived and died quickly.

The fluorine detection was a chance discovery made possible with the use of space and ground-based observatories. NGP–190387, originally discovered with the European Space Agency’s Herschel Space Observatory and later observed with the Chile-based ALMA, is extraordinarily bright for its distance. Using data he obtained from the Canadian Gemini-North telescope on Mauna Kea, Hawaii, Dr. Chapman realised that the exceptional luminosity of NGP–190387 was partly caused by another known massive galaxy, located between NGP–190387 and the Earth, very close to the line of sight. This massive galaxy amplified the light observed by the ALMA telescope, enabling the team to spot the faint radiation emitted billions of years ago by the fluorine in NGP–190387.

“Having identified this superb example of a lens-amplified star-forming galaxy, the stage was set to search for faint molecules like fluorine, which are such crucial indicators of the early chemical development in galaxies in the distant universe,” says Dr. Chapman.  

The team believes that fluorine is most likely produced in Wolf–Rayet stars -- massive stars that live only a few million years. Wolf–Rayet stars had been suggested as possible sources of cosmic fluorine before, but astronomers did not know until now how important they were in producing this element in the early universe. 

The discovery in NGP–190387 marks one of the first detections of fluorine beyond the Milky Way and its neighbouring galaxies. Astronomers have previously spotted this element in distant quasars -- bright objects powered by supermassive black holes at the centre of some galaxies. But never before had this element been observed in a star-forming galaxy so early in the history of the universe.

“We all know about fluorine because the toothpaste we use every day contains it in the form of fluoride,” says Maximilien Franco from the University of Hertfordshire in the UK and co-author of the study, published today in Nature Astronomy.

“Like most elements around us, fluorine is created inside stars, but until now we did not know exactly how this element was produced.”

Future studies of NGP–190387 with the Extremely Large Telescope (ELT), which is under construction in Chile and set to start operations later this decade, could reveal further secrets about this galaxy.

Links
·       Images of ALMA: https://www.eso.org/public/images/archive/category/alma/

·       Videos of ALMA: https://www.eso.org/public/videos/archive/category/alma/

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Contacts:
Scott Chapman
Dalhousie University
Tel: 1-778-678-7161
Email: scott.chapman@dal.ca

Alison Auld
Senior Research Reporter
Dalhousie University
Cell: 1-902-220-0491
Email: alison.auld@dal.ca