The Cosmic ‘Bubble Factory’ Mystery


We don't know what caused the bubbles and arcs in NGC 2359, but the main culprit is the massive Wolf-Rayet star in the center of one of the bubbles – visible slightly below and to the right of the center. Wolf-Rayet stars are massive, highly luminous stars that continually shed material in a stellar wind – which commonly form bubbles in the interstellar medium. But the unusual structure of the NGC 2359 arcs indicate something more complex is going on. Experts wonder if the star is moving supersonically? Or, is there another energetic star in the vicinity?

The 200 Wolf-Rayet stars known in the Milky Way are considerably hotter and more luminous than our Sun. All extremely massive stars will eventually evolve though a Wolf-Rayet phase and generate bubbles (image below) because they continually eject their outer atmosphere as a stellar wind. This outgoing wind of particles typically carries away more than the mass of our Earth each year. The wind is caused by atmospheric particles absorbing outgoing starlight, although many details of this process are unknown.



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