Globally recognised astronomical research centre, Armagh Observatory and Planetarium, has co-authored a research paper that outlines the discovery of ultra-hot hydrogen molecules in interstellar space. The groundbreaking discovery is the culmination of four decades of research.

Published in January 2023 by the journal of Astronomy and Astrophysics, the paper, titled Analysis of the first infrared spectrum of quasi-bound H2 line emission in Herbig-Haro 7,* is based on data gathered using the Gemini North telescope in Hawaii and builds on decades of research conducted using the UK Infrared Telescope (UKIRT) telescope, also in Hawaii.  It was written by astronomers from Armagh Observatory and Planetarium (AOP),Observatoire de Paris and the Gemini Observatory**

The paper describes how the research group found hydrogen molecules with temperatures of around 5,000 degrees in clouds of shocked gas in interstellar space.   This is almost as hot as the surface of the Sun.

Hydrogen molecules are normally found in the very coldest places of interstellar space, where they can be just 10 degrees above absolute zero (minus 260 degrees Centigrade).  New stars can form in such clouds from the collapse of this cold gas under gravity.

Occasionally shock waves from jets and winds produced by the newly formed young stars can heat the gas to temperatures of around 2,000 degrees. This stimulates the energy levels of the hydrogen molecules, causing them to emit at infrared wavelengths.

The temperatures of some hydrogen molecules documented in the new research paper are, however, more than twice as hot as this, at 5000 degrees.  Temperatures of 5000 degrees should tear the molecules apart.  This challenges our understanding of how interstellar shockwaves work.

While the discovery solved a long-standing puzzle about what the spectrum from the shocked molecules looked like, it has created another mystery about how molecular gas can survive at these high temperatures?

Professor Michael Burton, Director at Armagh Observatory and Planetarium, co-authored the paper. He says, “This is an incredible discovery and one that was very much unexpected.

“We have witnessed emission arising from a state that should not exist, under classical conditions, and have, in the process, created a new mystery, as we ponder what causes hydrogen molecules to become so hot and how they can survive these temperatures?

“The Armagh Observatory is the longest continuously operating astronomical research institute in the United Kingdom and Ireland and it was fantastic to collaborate with a team of global experts on this discovery, which follows four decades of research into molecular hydrogen line emission as the telescopes and technology in use for infrared astronomy has been transformed.  The recently launched infrared James Webb Space Telescope (JWST) now marks the culmination of this development.”

Armagh Observatory and Planetarium is sited in a heritage environment with a rich scientific history. The organisation delivers internationally recognised research in astronomy and related sciences and vibrant educational and outreach programmes for all ages.

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