Most stars in the universe –including our life-giving Population 1, main-sequence Sun, one of more than 100 billion stars in the Milky Way, that formed approximately 4.6 billion years ago–are formed a massive star clusters created from the violent gravitational collapse of matter within a region of a large molecular cloud. These clusters are the building blocks of galaxies, but their actual formation from these dense clouds is a mystery.
The outskirts of our Milky Way Galaxy are orbited by about 150 globular star clusters, among the oldest objects in the galaxy, formed about 11.5 billion years ago, 2.3 billion years after the Big Bang and shortly before the rate of cosmic star formation reached its peak, 10 billion years ago –a period known as “cosmic high noon.” A globular cluster might be the first place in which intelligent life is identified in our galaxy,” according to Rosanne DiStefano of the Harvard-Smithsonian Center for Astrophysics (CfA).
Stars in these ancient clusters contain fewer of the heavy elements needed to construct planets, since those elements (like iron and silicon) must be created in younger generations of stars. In contrast to DiStefano, some scientists have argued that this makes globular cluster population 11 stars less likely to host planets. Only one planet has been found in a globular cluster to date.
The image of cluster G286.21+0.17, caught in the act of formation, is a multi-wavelength mosaic made out of more than 750 individual radio observations with the Atacama Large Millimeter/submillimeter Array (ALMA) and 9 infrared images from the NASA/ESA Hubble Space Telescope. The cluster is located in the Carina region of our galaxy, about 8000 light-years away.
Dense clouds made of molecular gas (purple ‘fireworks streamers’) are revealed by ALMA. The telescope observed the motions of turbulent gas falling into the cluster, forming dense cores that ultimately create individual stars.
The stars in the image are revealed by their infrared light, as seen by Hubble, including a large group of stars bursting out from one side of the cloud. The powerful winds and radiation from the most massive of these stars are blasting away the molecular clouds, leaving faint wisps of glowing, hot dust (shown in yellow and red).
“This image shows stars in various stages of formation within this single cluster,” said Yu Cheng of the University of Virginia in Charlottesville, Virginia, and lead author of two papers published in The Astrophysical Journal.
Hubble revealed about a thousand newly-formed stars with a wide range of masses. Additionally, ALMA showed that there is a lot more mass present in dense gas that still has to undergo collapse. “Overall the process may take at least a million years to complete,” Cheng added.
“This illustrates how dynamic and chaotic the process of star birth is,” said co-author Jonathan Tan of Chalmers University in Sweden and the University of Virginia and principal investigator of the project. “We see competing forces in action: gravity and turbulence from the cloud on one side, and stellar winds and radiation pressure from the young stars on the other. This process sculpts the region. It is amazing to think that our own Sun and planets were once part of such a cosmic dance.”
“The phenomenal resolution and sensitivity of ALMA are evident in this stunning image of star formation,” said Joe Pesce, NSF Program Officer for NRAO/ALMA. “Combined with the Hubble Space Telescope data we can clearly see the power of multiwavelength observations to help us understand these fundamental universal processes.”
Source: “Gas Kinematics of the Massive Protocluster G286.21+0.17 Revealed by ALMA”, Yu Cheng et. al., The Astrophysical Journal. https://doi.org/10.3847/1538-4357/ab879f “Stellar Variability in a Forming Massive Star Cluster”, Yu Cheng et. al., The Astrophysical Journal. https://doi.org/10.3847/1538-4357/ab93bc
The Daily Galaxy, Max Goldberg, via The National Radio Astronomy Observatory
Image at the top of the page shows star cluster G286.21+0.17, caught in the act of formation. This is a multiwavelength mosaic of more than 750 ALMA radio images, and 9 Hubble infrared images. ALMA shows molecular clouds (purple) and Hubble shows stars and glowing dust (yellow and red). ALMA (ESO/NAOJ/NRAO), Y. Cheng et al.; NRAO/AUI/NSF, S. Dagnello; NASA/ESA Hubble.