Astronomers have unveiled a surprising new view of the center of the Milky Way galaxy, revealing the cosmic complex network of gas filaments in unprecedented detail. This image was generated using the Atacama Large Millimeter/Submillimeter Array (ALMA) and forms the largest ALMA dataset ever collected. This giant map will help scientists investigate how stars form and evolve in the most extreme regions of galaxies: near supermassive black holes.
“It’s an extreme place, invisible to us, but now it’s revealed in amazing detail,” said Ashley Burns, an astronomer at Germany’s European Southern Observatory (ESO) and a member of the research team. The observations provide a rare look at the cold gas, the fundamental building blocks of stars, across a region known as the central molecular zone (CMZ). This is the first time that cold gas across this region has been mapped so precisely.
Mapping of the central molecular zone
The area captured in the image spans more than 650 light years. It contains a dense cloud of gas and dust surrounding the supermassive black hole at the center of the Milky Way. “This is the only galactic nucleus close enough to Earth that we can study it in such detail,” Burns explains. The new dataset reveals the structure of the entire CMZ at a variety of scales, from giant gas layers spanning tens of light years to tiny clouds surrounding individual stars.
The survey responsible for this work is called ACES, which stands for ALMA CMZ Exploration Survey. ACES focuses specifically on cold molecular gases, the materials that fuel star formation. By analyzing the signals from this gas, researchers uncovered a surprisingly complex chemical environment. The study detected dozens of molecules, ranging from relatively simple molecules such as silicon monoxide to more complex organic compounds such as methanol, acetone, and ethanol.
Extreme star formation near the galactic center
In the CMZ, cold molecular gas moves along elongated filaments, funneling material into dense clumps where stars can form. Astronomers understand this process fairly well in quiet parts of the Milky Way, but the situation near the galactic center is much more intense.
“The CMZ is home to some of the most massive stars known in our galaxy, many of which live early and die young, ending their lives in powerful supernovae or even supernova explosions,” says ACES leader Steve Longmore, professor of astrophysics at Liverpool John Moores University in the UK. Through the ACES study, researchers hope to learn how such violent environments affect the birth of stars, and whether current theories about star formation hold true under these extreme conditions.
“Studying how stars are born in the CMZ also gives us a clearer picture of how galaxies grow and evolve,” Longmore added. “We think this region shares many characteristics with galaxies in the early universe, where stars formed in chaotic, extreme environments.”
Building the largest ALMA mosaic
To collect this huge data set, astronomers used ALMA. ALMA is a powerful observatory operated by ESO and its partners in the Atacama Desert, Chile. This is the first time that such a large part of the galaxy’s center has been investigated with ALMA, and it provides the observatory’s largest images to date. The final mosaic was created by combining many individual observations, like putting together pieces of a puzzle. The finished image is the length of three full moons in the sky.
“When designing the survey, we expected a high level of detail, and we were genuinely surprised by the complexity and richness revealed in the final mosaic,” says Katharina Immer, an ALMA astronomer at ESO who is also involved in the project. The results of the ACES program are described in five papers accepted for publication in June 2016. Royal Astronomical Society Monthly Noticesthe sixth one is currently in final review.
Future observations will reveal more
“With upcoming broadband sensitivity upgrades to ALMA and ESO’s Very Large Telescope, we will soon be able to reach even deeper into this region. We will be able to resolve finer structures, track more complex chemistry, and explore interactions between stars, gas, and black holes with unprecedented clarity,” Burns said. “In many ways, this is just the beginning.”
Availability of research papers and data
This research will be presented in a series of papers describing ACES data. Royal Astronomical Society Monthly Notices:
Paper I — ALMA Central Molecular Zone Survey (ACES) I: Overview paper Paper II — ALMA Central Molecular Zone Survey (ACES) II: 3mm continuum images Paper III — ALMA Central Molecular Zone Survey (ACES) III: Molecular beam data reduction and HNCO & HCO+ data Paper IV — ALMA Central Molecular Zone Survey (ACES) IV: Data from two intermediate-width spectral windows Paper V — ALMA Central Molecular Zone Exploration Survey (ACES) V: Data from CS(2-1), SO 2_3-1_2, CH3CHO 5_(1,4)-4_(1,3), HC3N(11-10) and H40A lines Paper VI — ALMA Central Molecular Zone Exploration Survey (ACES) VI: ALMA’s large-scale program reveals highly fibrous central molecular zone (under minor revision)
The complete dataset is available on the ALMA Science Portal (https://almascience.org/alma-data/lp/aces).
Global collaboration supporting the ACES project
The ACES collaboration includes more than 160 scientists, ranging from master’s students to retired researchers, representing more than 70 institutions across Europe, the Americas, Asia, and Australia. The project was initiated and led by principal investigator Stephen Longmore (Liverpool John Moores University, UK) and co-leads Ashley Burns (European Southern Observatory, Germany), Carla Battersby (University of Connecticut, CT, USA), John Barry (University of Colorado Boulder, USA), and Laura Corzi (Centre for Astrobiology, Madrid, Spain). (CdA)), Adam Pinsburg (University of Florida, USA (Florida)), Jonathan Henshaw (Max Planck Institute for Astronomy, Heidelberg, Germany), Paul Ho (Academia Sinica, Taiwan), Izaskun Jiménez-Serra (CdA), JM Diederik Kruijssen (COOL Research DAO), Elisabeth Mills (University of Kansas, USA), Maya Petkova (Chalmers University of Technology, Sweden), Mattia Sormani (Dipartimento di Scienza e Alta Tecnologia (DiSAT), Insubria University, Italy), Robin Tress (Swiss Federal Institute of Technology Lausanne, Universität Institute for Theoretical Astrophysics, Heidelberg, Germany), Daniel Walker (University of Manchester, UK Alma Regional Center Node), Jennifer Wallace (Connecticut).
The ALMA Data Reduction Working Group within ACES is coordinated by Adam Ginsburg, Daniel Walker, and Ashley Burns. Contributors include Nazar Budaiev (Florida), Laura Colzi (CdA), Savannah Gramze (Florida), Pei-Ying Hsieh (National Astronomical Observatory of Japan, Mitaka, Tokyo), Desmond Jeff (Florida), Xing Lu (Chinese Academy of Sciences, Shanghai Observatory), and Jaime Pineda. (Max-Planck-Institut für extraterrestrische Physik, Germany), Marc Pound (University of Maryland, USA), and Álvaro Sánchez-Monge (Institut de Ciències de l’Espai, CSIC, Bella Terra, Spain; Institut d’Estudis Espacials de Catalunya, Castelldefels, Spain), and 30 More than one additional researcher who helped with data reduction.
