From studies of other stars which astronomers can see in many different stages of their 'life cycle', it seems pretty convincing from the data that the sun must have started out as a large collapsing cloud of gas inside some ancient interstellar cloud. This cloud was 'polluted' by a supernova several million years before the collapse phase ended, because we see certain isotopes of aluminum which could not have been a part of this cloud for very long unless they had been implanted by such an event. For example, here is such a typical dark cloud called the Lynd's Dark Nebula 1622 in Orion perhaps only 500 light-years away. At that distance, this 1 degree wide field of view would span less than 10 light-years.

The protostellar cloud collapsed for millions of years until it formed a rotating disk with a large central bulge. Out of the disk would eventually form the planets, and out of this central bulge where most of the mass wound up, formed the sun. We see such rotating disks of gas around many infant stars embedded in nebulae so this has confirmed this basic picture during the last 15 years or so. This isn't just 'theory' anymore.Astronomer Shigehisa Takakuwa and his research team used the ALMA submillimeter telescope to observe the baby-twin star L1551 NE, located in the constellation of Taurus at a distance of 460 light years. The images below show a comparison of the observed protostellar disk (left panel) and a computer simulated version with physics included (right panel). disks in simulation and observation.

The central bulge will continue to collapse under its own gravity until deep in its interior the temperatures get so high...several million degrees....that deuterium atoms begins to fuse and give off thermonuclear energy. This slows the collapse down a bit and eventually leads to a second stage where hydrogen nuclei can fuse into helium, which then starts the sun's current evolutionary phase.

While all this was happening, the surface of the sun became very active and produced a powerful wind which blew out all of the remaining gas and dust in the surrounding disk of gas which had not settled into the bodies of the new planets that had formed. This 'T-Tauri wind' also scoured clean the atmospheres of the inner planets so that they were bare rock. Those that were volcanically active, however, were able to regenerate their atmospheres from the gases ejected by volcanic activity.

With its helical appearance resembling a snail’s shell, this reflection nebula seems to spiral out from a luminous central star in this NASA/ESA Hubble Space Telescope image. The star in the center, known as V1331 Cyg and located in the dark cloud LDN 981 — or, more commonly, Lynds 981 — had previously been defined as a T Tauri star. A T Tauri is a young star — or Young Stellar Object — that is starting to contract to become a main sequence star similar to the sun.

What makes V1331Cyg special is the fact that we look almost exactly at one of its poles. Usually, the view of a young star is obscured by the dust from the circumstellar disc and the envelope that surround it. However, with V1331Cyg we are actually looking in the exact direction of a jet driven by the star that is clearing the dust and giving us this magnificent view. This view provides an almost undisturbed view of the star and its immediate surroundings allowing astronomers to study it in greater detail and look for features that might suggest the formation of a very low-mass object in the outer circumstellar disk.

From start to finish, it took something like 10 million years to form the sun and planets from a collapsing cloud of gas, and this is not very long at all!!

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