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According to Nebula Theory, stars and their systems of planets form when a massive cloud of gas and dust (a nebula) undergoes gravitational collapse at the center, forming a new star. The remaining material from the nebula then forms a disk around the star from which planets, moons, and other bodies will eventually accrete (a protoplanetary disk). This is how Earth and the many bodies that make up the Solar System came together roughly 4.5 billion years ago, eventually settling into their current orbits (after a few migrations and collisions).<\/p>\n
However, there is still debate regarding certain details of the planet formation process. On the one hand, there are those who subscribe to the traditional \u201cbottom-up\u201d model, where dust grains gradually collect into larger and larger conglomerations over tens of millions of years. Conversely, you have the \u201ctop-down\u201d model, where circumstellar disk material in spiral arms fragments due to gravitational instability. Using the Atacama Large Millimeter\/submillimeter Array (ALMA), an international team of astronomers found evidence of the \u201ctop-down\u201d model when observing a protoplanetary disk over 500 light-years away.<\/p>\n
<\/p>\n The team was led by Jessica Speedie, an astronomy and astrophysics Ph.D. candidate at the University of Victoria. She was joined by colleagues from the Kavli Institute for Astronomy and Astrophysics (KIAA-PKU), the Center for Simulational Physics (CSP-UGA), the Cambridge Institute of Astronomy, the Centre de Recherche Astrophysique de Lyon (CNSA-CRAL), the Institute of Astronomy and Astrophysics (ASIAA), the Department of Earth, Atmospheric, and Planetary Sciences (MIT EAPS), the National Astronomical Observatory of Japan (NAOJ), the European Southern Observatory (ESO), and multiple universities and observatories. <\/p>\n \n