Free Astronomy Magazine November-December 2016

SPACE CHRONICLES over a thousand billion (10 12 ) mole- cules per cubic metre (far lower than the Earth's atmosphere, but high for an interstellar environment); warm in temperature, at over –173 degrees Cel- sius. This makes them at least 80 de- grees Celsius warmer than a standard molecular cloud, despite being of sim- ilar density. These hot cores form early on in the evolution of massive stars and they play a key role in the forma- tion of complex chemicals in space. Takashi Shimonishi, an astronomer at Tohoku University, Japan, and the pa- T his figure shows observations of the first hot core to be found outside the Milky Way with ALMA and a view of the region of sky in infrared light. Left: Distributions of molecular line emission from a hot molecular core in the Large Ma- gellanic Cloud observed with ALMA. Emissions from dust, sulfur dioxide (SO 2 ), ni- tric oxide (NO), and formaldehyde (H 2 CO) are shown as examples. Right: An infra- red image of the surrounding star-forming region (based on data from the NASA/ Spitzer Space Telescope). [T. Shimonishi/Tohoku University, ALMA (ESO/NAOJ/NRAO)] per's lead author enthused: “This is the first detection of an extraga- lactic hot molecular core, and it de- monstrates the great capability of new generation telescopes to study astrochemical phenomena beyond the Milky Way.” The ALMA observa- tions revealed that this newly dis- covered core in the LMC has a very different composition to similar ob- jects found in the Milky Way. The most prominent chemical signatures in the LMC core include familiar mol- ecules such as sulfur dioxide, nitric oxide, and formaldehyde — along- side the ubiquitous dust. But sever- al organic compounds, including methanol (the simplest alcohol mol- ecule), had remarkably low abun- dance in the newly detected hot molecular core. In contrast, cores in the Milky Way have been observed to contain a wide assortment of complex organic molecules, includ- ing methanol and ethanol. Takashi Shimonishi explains: “The observations suggest that the mo- lecular compositions of materials that form stars and planets are much more diverse than we expect- ed.” The LMC has a low abundance of elements other than hydrogen or helium. The research team suggests that this very different galactic en- vironment has affected the mole- cule-forming processes taking place surrounding the newborn star ST11. This could account for the observ- ed differences in chemical composi- tions. It is not yet clear if the large, complex molecules detected in the Milky Way exist in hot molecular cores in other galaxies. Complex organic molecules are of very special interest because some are connected to prebiotic molecules formed in space. This newly discov- ered object in one of our nearest galactic neighbours is an excellent target to help astronomers address this issue. It also raises another ques- tion: how could the chemical diver- sity of galaxies affect the develop- ment of extragalactic life? n