April 2017
Tom Geballe
Persistence Pays Off in the Study
of Shock-heated Gas
A breakthrough has been made in a two-decade old mystery
concerning the frequently observed shock-heated gas in dense
star-forming clouds, thanks to sensitive new measurements using
Gemini North and its infrared spectrographs NIFS and GNIRS.
Shock waves in dense interstellar clouds occur when the powerful winds generated by stars
forming within the clouds ram into quiescent portions of the clouds. As a consequence
of shock heating in a previously quiescent cloud, its most abundant molecule, molecu-
lar hydrogen (H 2 ), emits numerous strong spectral lines, especially in the 2.0-2.5-micron
wavelength range, as the shocked gas cools. Measurements of the velocities and both the
absolute and relative intensities of these lines reveal much information about the nature of
the shock as well as the protostars responsible for them.
As reported in two recently published papers, Rosemary Pike (Academia Sinica, Taipei,
Taiwan), Michael Burton (Armagh Observatory, Northern Ireland), Antonio Chrysostomou
(Square Kilometer Array Office at Jodrell Bank, UK) and I have discovered lines of H 2 from
much higher energy levels than previously observed, in two shocked clouds. We have ten-
tatively linked these lines to H 2 that has recently reformed on dust particles following its de-
struction by the shock waves. If our interpretation is correct, our data are giving scientists a
first look at the spectrum of newly formed H 2 , the most abundant molecule in the Universe.
January 2018 / 2017 Year in Review
GeminiFocus
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