ACES survey reveals network of fibers, dozens of molecules, and complex chemistry in the central molecular region near the supermassive black hole, opening a new window into understanding star formation in extreme environments
Astronomers have captured a stunning new image of the central region of the Milky Way, revealing a complex network of filaments of cosmic gas in unprecedented detail. The data, collected using the Atacama Large Millimeter/submillimeter Array (ALMA), is the largest dataset of its kind ever created at ALMA. The dataset will allow researchers to study the lives of stars in the most extreme region of our galaxy, near the supermassive black hole at its center.
“It’s a place of extremes, invisible to our eyes, but now it’s being revealed in extraordinary detail,” says Ashley Barnes, an astronomer at the European Southern Observatory (ESO) in Germany, who was part of the team that collected the new data. The observations provide a unique look at cold gas—the raw material from which stars form—inside what’s called the galaxy’s Central Molecular Zone (CMZ). This is the first time the cold gas in this entire region has been examined in such detail.
The region shown in the image spans more than 650 light-years. It contains dense clouds of gas and dust around 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 fine detail,” Barnes says. The dataset shows the central molecular region as never before: from gas structures on the scale of tens of light-years, to small gas clouds around individual stars.
Cold molecular gas region
The gas that the ALMA CMZ Exploration Survey (ACES) is focused on is cold molecular gas. The survey breaks down the complex chemistry of the central molecular region, identifying dozens of different molecules: from simple molecules like silicon monoxide to more complex organic molecules like methanol, acetone, or ethanol.
Cold molecular gas flows along filaments that feed clumps of material, from which stars can grow. At the edge of the Milky Way, we know this mechanism well, but in the central region the events are much more extreme. “The central molecular region hosts some of the most massive stars known in our galaxy,” says ACES survey leader Steve Longmore, a professor of astrophysics at Liverpool John Moores University in the UK. “Many of them ‘live fast and die young,’ ending their lives in powerful supernova explosions, and even hypernovae.” With ACES, astronomers hope to better understand how such phenomena affect star birth, and whether our theories about star formation hold true in extreme environments.
“By studying how stars are born in the central molecular region, we can also gain a clearer picture of how galaxies grew and evolved,” adds Longmore. “We think this region shares many characteristics with galaxies in the early universe, where stars formed in chaotic and extreme environments.”
To collect the new dataset, the researchers used ALMA, operated by ESO and partners in the Atacama Desert in Chile. This is the first time such a large area has been scanned with this facility, making it the largest ALMA image ever produced. In the sky, the mosaic – created by piecing together many observations, like the pieces of a puzzle – spans an angle equivalent to three full moons side by side.
“We expected a high level of detail when we planned the survey, but we were really surprised by the complexity and richness revealed in the final mosaic,” says Katharina Immer, ALMA astronomer at ESO and a member of the project. The ACES data are presented in five papers accepted for publication in the Monthly Notices of the Royal Astronomical Society, and a sixth is in the final stages of review.
The upcoming upgrade will improve sensitivity.
“The planned broadband sensitivity upgrade for ALMA, together with ESO’s huge Extremely Large Telescope, will soon allow us to penetrate even deeper into this region – to discern finer structures, to follow more complex chemistry, and to study with unprecedented clarity the interactions between stars, gas and black holes,” says Barnes. “In many ways, this is just the beginning.”
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And I thought to myself that there is dark matter in the center of the Milky Way, like in every spiral galaxy.