Multitude of molecules in busy star factory

Astronomers have detected over a hundred different types of molecules, when observing a "starburst" galaxy where stars are forming at a very high rate. That’s the richest molecular diversity yet found outside the Milky Way, offering unprecedented insights into the complex processes driving star formation in galaxies.

In the Universe, some galaxies are known as “starburst” galaxies, where stars are forming at a much faster rate than our galaxy, the Milky Way. How easily stars are made depends on the properties of the raw material from which stars are born. Molecular gas — gas with high proportion of different molecules — is such material. Stars form from dense regions within molecular clouds, under the influence of gravity. But it’s not known how such abundant formation of stars can take place in starburst galaxies – and how this phase in the life cycle of a galaxy ends is also a mystery.

An international research team has observed the center of a galaxy, NGC 253, that is known to be producing many new stars, using the ALMA telescope (Atacama Large Millimeter/submillimeter Array) in Chile. They detected more than one hundred molecular species, far more than previous studies outside our own galaxy have detected. The molecular gas in the center of NGC 253 is more than ten times as dense as the gas found in the centre of our own galaxy. This chemical feedstock is the richest found outside the Milky Way, and it also includes molecules that have been detected for the first time outside our own galaxy, such as ethanol and the phosphorus-bearing species PN (phosphorus nitride). The wealth of data has allowed astronomers to better understand the physics and chemistry of this kind of galaxy.

Because each molecule emits at certain characteristic frequencies, observations over a wide frequency range enable analysis of the physical properties and provides insights into the mechanism of starbursts. In the near future, ALMA will be upgraded as a part of the ALMA 2030 Development roadmap, making wide-frequency observations like this study even more efficient.

About the study

This survey was conducted as an ALMA Large Program named the ALMA Comprehensive High-resolution Extragalactic Molecular Inventory (ALCHEMI), led by Sergio Martín of the European Southern Observatory/Joint ALMA Observatory, Nanase Harada of the National Astronomical Observatory of Japan, and Jeff Mangum of the National Radio Astronomy Observatory.