ALMA obtains a privileged view of dueling opposing forces in the Large Magellanic Cloud nursery

New observations of 30 Doradus were made using the highly-sensitive Band 6 receivers on ALMA, an observatory co-operated by the U.S. National Science Foundation’s National Radio Astronomy Observatory (NRAO), and led to a surprising revelation about the molecular cloud. “Stars form when dense clouds of gas become unable to resist the pull of gravity. Our new observations reveal clear evidence that gravity is shaping the thickest parts of the clouds, while also revealing many lower-density cloud fragments which are too turbulent for gravity to exert much influence,” said Tony Wong, a professor at the University of Illinois at Urbana-Champaign and the lead author on the new research. “We were expecting to find that the parts of the cloud closest to the young, massive stars would show the clearest signs of gravity being overwhelmed by feedback, and as a result, a lower rate of star formation. Instead, these observations confirmed that even in a region with extremely active feedback, gravity’s presence is still strongly felt, and star formation is likely to continue.”

“ALMA’s extraordinary resolution and sensitivity allowed us to map the entire 30 Doradus region from the southern skies,” says Mónica Rubio, professor at the University of Chile and associate researcher at the Center for Astrophysics and Related Technologies (CATA), Chile, a specialist in Magellanic Clouds and co-author of this study. “It was a surprise to confirm that dense regions existed and survived in such a violent environment, where ultraviolet radiation and wind from hundreds of massive stars should scatter and photoionize most of the gas. We are confident that the excellent conditions of the skies over northern Chile for millimeter-wave observations, and the power of ALMA, will continue to amaze us with important discoveries in the coming years.”

To form a clearer picture of what was happening in 30 Doradus, the team divided the cloud into clumps to measure how one part of the cloud differs from another. Since stars typically form in the densest parts of molecular clouds, distinguishing between the less-dense and more-dense clumps was critical to building a clear understanding of what is happening in 30 Doradus. The novel approach revealed a pattern. “We used to think of interstellar gas clouds as puffy or roundish structures, but it’s increasingly clear that they are string-like or filamentary,” said Wong. “When we divided the cloud into clumps to measure differences in density we observed that the densest clumps are not randomly placed but are highly organized onto these filaments. The filaments themselves appear to be shaped by gravity, so are probably an important step in the process of star formation.” 

Unlike the Milky Way, which experiences a relatively slow and steady star formation rate of roughly seven stars— or the equivalent of four solar masses— each year, 30 Doradus’ home galaxy, the LMC, and its star-forming regions go through “boom and bust” cycles, which often results in periods of intensely paced star formation. The team hopes that the new findings, as well as additional future research, will shed light on the differences between the Milky Way and other, more active star-forming galaxies, including how the competition between gravity and feedback shapes molecular clouds and impacts stellar birth rates. 

Remy Indebetouw, an astronomer at NRAO and a co-author of the research said, “30 Doradus contains the nearest massive stellar cluster to Earth. Clusters like this one can act like bombs in galaxies, blowing out gas and even changing their long-term evolution. We want to understand how molecular clouds turn into stars, in detail— how long does it take, how quickly do newly formed stars start to affect their natal cloud, and over what distances, things that are currently not well understood. Observing these clusters will get us one step closer to an answer.”

Wong added that the observations are both helping scientists to understand the broad scientific implications of star formation and revealing the history and future of galaxies. “One of the biggest mysteries of astronomy is why we are able to witness stars forming today. Why didn’t all of the available gas collapse in a huge fireworks show long ago? What we’re learning now can help us to shine a light on what is happening deep within molecular clouds so that we can better understand how galaxies sustain star formation over time.”

Additional information.

The research paper titled “The 30 Doradus Molecular Cloud at 0.4 Parsec Resolution with ALMA: Physical Properties and the Boundedness of CO Emitting Structures,” by Wong et al. (2022) appeared in The Astrophysical Journal.

The original press release was issued by the U.S. National Radio Astronomy Observatory (NRAO), ALMA’s partner on behalf of North America.

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership between the European Southern Observatory (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences of Japan (NINS) in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its member states, by NSF in cooperation with the National Research Council of Canada (NRC) and the Ministry of Science and Technology of Taiwan (MOST), and by NINS in cooperation with the Academia Sinica (AS) of Taiwan and the Korea Astronomy and Space Science Institute of South Korea (KASI).

ALMA construction and operations are conducted by ESO on behalf of its member states; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) is responsible for the overall direction and management of construction, commissioning and operations of ALMA.