ALMA Uncovers Hidden Chemistry in Milky Way Core

Normally, astronomers detect certain molecules in space by means of their so-called emission lines, which are present in the radiation they emit. These lines act as molecular "fingerprints" and also contain information about local conditions. However, the extreme conditions in the centre of the Milky Way - such as temperature and magnetic fields - make it difficult to decipher the message carried by these emission lines.

Chemical model provides insight into star formation in the galactic core

Astronomers at Leiden University, led by postdoctoral researcher Katarzyna Dutkowska, have developed a chemical model describing how emission lines are affected by the extreme conditions in the Milky Way's centre. They have now detected molecules such as HCO+, HNCO and SiO in the so-called Central Molecular Zone (CMZ), visible in the ALMA image. They have also obtained information about local velocities and temperature.

The CMZ is thought to play an important role in the formation of large-scale stellar structures, such as galactic bars and the molecular clouds from which stars form. The central regions of galaxies are essential for understanding how stars originate. The Milky Way's galactic core is the only one close enough to Earth to be studied in such detail.

Restless and extreme Milky Way centre

The CMZ stands out because it is warmer, denser, and has higher levels of radiation and ionisation than the rest of the Milky Way. The region is highly turbulent and has a strong local magnetic field. "It also appears to have the highest concentration of supernovae - exploding stars - in the Milky Way, and there is a significant influence from, for example, radiation from the supermassive black hole Sagittarius A*," says Dutkowska.

ALMA shows the heart of the Milky Way

The new ALMA image shows the centre of our galaxy with dense clouds of gas and dust tens of light-years across, as well as smaller gas clouds around individual stars. The observations provide a picture of the cold gas in the CMZ - composed mainly of hydrogen - the raw material from which stars are formed. "This region hosts some of the most massive stars known in our galaxy, many of which live short lives and die young, ending in powerful supernova or hypernova explosions," says Steve Longmore, professor of astrophysics at Liverpool John Moores University in the United Kingdom, who leads the ACES (ALMA CMZ Exploration Survey) research programme.

Research into star formation under extreme conditions

With ACES, astronomers hope to better understand how the above phenomena influence the birth of stars and whether our theories of star formation also hold in extreme environments. The researchers aim to gain a clearer picture of how galaxies have grown and evolved. The Milky Way's central region is thought to share many characteristics with galaxies in the early Universe, where stars formed in chaotic, extreme environments.

Models explain young stars

"To understand what we see in the central molecular zone, more than observations alone are needed. Our models help translate the complex chemistry of this region into a physical understanding of the environment in which young stars grow in the centre of the Milky Way," concludes Dutkowska.

This press release originally appeared on astronomie.nl.