What are proplyds? What do they tell us about the plausibility of our model of the solar system's origin?

Proplyds, or protoplanetary disks, are rotating disks of dense gas and dust surrounding young stars. These disks are believed to be the sites where planets form in a process known as accretion, where particles in the disk come together and grow in size.

Proplyds are usually a few astronomical units (AU) in size, and they contain enough material to form planetary systems. They are composed primarily of molecular hydrogen, with traces of other molecules and elements such as helium, oxygen, and carbon. The temperature within a proplyd varies, with the central regions typically being hotter due to the proximity to the young star.

The current model of solar system formation is known as the Nebular Hypothesis. According to this model, solar systems form from clouds of interstellar gas and dust, called nebulae, which collapse and begin to rotate. Over time, the material in the rotating cloud flattens into a disk-like structure, known as a protoplanetary disk or proplyd. Within this disk, solid particles collide and stick together, eventually forming planetesimals which continue to grow and become planets.

Observations of proplyds provide strong support for the Nebular Hypothesis, as they are consistent with the expectations of a rotating disk surrounding a young star. The presence of proplyds reinforces the idea that planets form in a disk around a star through the process of accretion. Furthermore, proplyds have been observed around a variety of stars, suggesting that planet formation is a common process throughout the universe. This lends credibility to the model, as it is not just applicable to our solar system, but also to other planetary systems. In conclusion, proplyds offer strong evidence for the plausibility of the Nebular Hypothesis, our current model of solar system formation. By providing direct evidence of the protoplanetary disks where planets form, proplyds support the idea of a common process of planetary formation throughout the universe.