Astronomers discover mysterious 500-light-year-wide 'cavity' in our Milky Way


Oct 22, 2019
My observation. The reference paper, The Per-Tau Shell: A Giant Star-forming Spherical Shell Revealed by 3D Dust Observations,, 22-Sep-2021. "Abstract A major question in the field of star formation is how molecular clouds form out of the diffuse interstellar medium (ISM). Recent advances in 3D dust mapping are revolutionizing our view of the structure of the ISM..."

More reports on stars forming from molecular gas clouds in the galaxy. Young ages reported too here, some 6 to 22 million years old. Spiral arms are short lived, and there is a limited number of molecular gas clouds observed today in the galaxy, e.g. M42 in Orion. The molecular gas clouds are also short lived. Other reports indicate about 72 large molecular gas clouds studied recently within 2 kpc from earth. Bird's eye view of molecular clouds in the Milky Way. I. Column density and star formation from sub-parsec to kiloparsec scales,

My observation. Molecular gas clouds within 2 kpc of the Sun number about 72 according to this survey. Masses used indicate the survey gas clouds contain some 10,000 solar masses or so. All molecular gas clouds are young and so too is the lifetime of the MW spiral arms. Over billions of years, the MW must regenerate these molecular clouds observed because they are all of a recent origin and young, typical ages 10 million years or so. What we do observe today in astronomy is a limited number of the large, molecular gas clouds and all very young ages compared to age of the solar system, MW galaxy, and universe postulated age of 13.8 billion years old.
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