Hubble Space Telescope's ACS image of NGC 602 and N90. Image Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)-ESA/Hubble Collaboration.

Astronomers Use ALMA to Peer Into the SMC’s Sparkling Open Cluster

NGC 602, in the Small Magellanic Cloud (SMC) is home to AB8, the only Wolf-Rayet star in the SMC that does not belong to the nitrogen sequence, and it is the only Wolf-Rayet star that lies outside the main bar.


An open cluster, NGC 602, in the Small Magellanic Cloud (SMC), has been studied by astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA). An article published in the arXiv preprint server revealed that this cluster exhibited sequential star formation, a crucial insight into its properties.

Stars are concentrated in three main condensations in NGC 602. A compact NGC 602b lies 100 arcseconds to the NNW of the central core of NGC 602a. One of the stars in NGC 602c is WO star AB8, which is 11 arc-minutes to the NE of NGC 602c. AB8 is a binary star within the Small Magellanic Cloud, and it is the only Wolf-Rayet star in the SMC that does not belong to the nitrogen sequence, and it is the only Wolf-Rayet star that lies outside the main bar. Clusters of stars loosely gravitationally bound together formed from the same giant molecular cloud are known as open clusters (OCs). In the Milky Way, more than 1,000 open clusters have so far been found, and scientists are still looking for more.


It may be crucial for our understanding of the formation and evolution of our galaxy to expand the list of known galactic open clusters and study them in detail. The young, bright, low-metallicity NGC 602 is located about 196,000 light years from Earth in the Small Magellanic Cloud. SMC’s “Wing” includes its associated HII region N90, which contains atomic hydrogen clouds ionized by electrons. The proximity of NGC 602 and N90 allows us to examine star formation scenarios under conditions that are drastically different from those found in the solar neighborhood.

Using ALMA, astronomers led by Theo J. O’Neill of the University of Virginia examined NGC 602/N90 to determine the nature of dense gas in the region and how it evolved. In the paper, the researchers report the results of observations of molecular gas in the low-metallicity star-forming region NGC 602/N90. Over 100 molecular clumps were uncovered by carbon monoxide (CO) emissions. These clumps are clustered around the region’s border. Observations of these clumps led astronomers to estimate a total molecular gas mass of 16,600 solar masses in N90.

In the size-linewidth-surface density space, N90 clumps generally do not follow expected trends. Further, their velocity dispersion and surface densities differed from predictions derived from galactic cloud relationships. It is also suggested that intermediate-mass stars have likely formed throughout the N90 region in the last one to two million years. According to the research, NGC 602 has not directly triggered star formation along the rim of N90 but rather has formed about 130 solar masses per year in recent years. Scientists concluded that the sequential star formation history of N90 could be determined by the properties of clumps in the region. As a result, stars formed in N90 were not more efficient than those formed in solar-metallicity and higher-density environments with similar mass and density.


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Written by Ivan Petricevic

I've been writing passionately about ancient civilizations, history, alien life, and various other subjects for more than eight years. You may have seen me appear on Discovery Channel's What On Earth series, History Channel's Ancient Aliens, and Gaia's Ancient Civilizations among others.

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