National Astronomical Observatory of Japan

Star Formation Triggered by Cloud–Cloud Collisions

| Science

Examples of typical colliding molecular clouds (represented by the blue color and yellow contours) forming star clusters discovered by radio observations. Images of the Antennae Galaxies and the Triangulum Galaxy are shown on the left. Positions of the cluster-forming colliding clouds reported in the present research are denoted by red dots is the drawing of the Milky Way Galaxy on the right (the yellow circle denotes the position of the Sun). The inset optical images on the lower right show the Eagle Nebula and [DBS2003]179, where shining nebulae and newly born star clusters can be seen. (Credit: Nagoya University, National Astronomical Observatory of Japan, NASA, JPL-Caltech, R. Hurt (SSC/Caltech), Robert Gendler, Subaru Telescope, ESA, The Hubble Heritage Team (STScI/AURA), Hubble Collaboration, and 2MASS) Original size (39.3MB)

Japanese researchers have found that collisions of gas clouds floating in space precipitate the birth of star clusters.

Stars form by the gravitational contraction of clouds of gas in space and can have various masses. Massive stars, together with many other stars, may form huge star clusters (groups of more than 10,000 stars). The formation of such star clusters requires rapidly packing enormous amounts of gas and other materials into a small space, but the mechanism by which this occurs has yet to be clarified.

A research team led by Associate Professor Kengo Tachihara and Emeritus Professor Yasuo Fukui of Nagoya University focused on a hypothesis in which multiple gas clouds collide, allowing them to efficiently concentrate the gas and thereby form a star cluster. To verify this hypothesis, the team, in collaboration with researchers from Osaka Prefecture University and the National Astronomical Observatory of Japan, conducted observational studies of a vast amount of data obtained from more than a decade of research, as well as theoretical studies of numerical simulations based on the data. As a result, they found that collisions of gas clouds floating in space do, in fact, induce the birth of star clusters.

They observed many colliding gas clouds in our Milky Way Galaxy and also in other galaxies, suggesting that these collisions are a universal phenomenon. This suggests that it is likely that the Milky Way Galaxy collided with other galaxies soon after its birth, which caused gas clouds in the galaxies to collide frequently, resulting in the formation of many globular clusters (groups of more than one million stars). These findings have contributed to a deeper understanding of the formation of massive stars and the birth of globular clusters.

This research was published in the peer-reviewed journal Publications of the Astronomical Society of Japan in January 2021 as a special issue titled “Star Formation Triggered by Cloud–Cloud Collision II,” which contains a collection of 20 original papers based on elaborate verifications of individual astronomical bodies, as well as a review paper summarizing the latest understandings of star formation by collisions of gas clouds.

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