 Now let's consider a fragment large enough to create a star the size of our sun. The primary force on the rotating fragment is gravity, pulling it towards the center. But because the subset of dust and gas that's rotating around the center of gravity follows the conservation of angular momentum laws, matter there will increase its velocity as its distance from the center decreases. This effectively slows the region's collapse into the center. In fact, if the velocity of a small piece reached orbital speeds, it would not fall into the forming star at all. The overall effect is for matter above the plane of rotation to move down and for the matter below the plane of rotation to move up. The entire fragment morphs into a disk structure around the core called a circumstellar disk. It recreates into the central object via this disk. In the early stages of the collapse into the core, the temperatures remain low because generated radiation energy is able to escape. The compression continues until the core is dense enough to hold onto the energy. This takes around 30,000 years. At that point, the core has enough mass density to capture generated photons and the temperature begins to rise. Another 100,000 years and the core temperature reaches 10,000 degrees Kelvin. At this temperature, the object begins to shine via normal non-nuclear means. It's now a protostar. So far the core has only about 1% of its final mass. Protostars develop out of these fragments in three observable phases. Protostars remain sequence stars and main sequence stars. Protostars remain shrouded in the dust and gas clouds that created them. The actual protostars can only be seen by infrared telescopes. The Eagle Nebula is a good example of this. It contains large numbers of forming stars. Some of these protostars can be seen with Hubble's near-infrared image. Here we see the trapezean cluster of four stars at the heart of the Orion Nebula. If we zoom in, we can see several protostars around one of the larger stars. They are the white object streaming material away from the central star. Here's one more example. This infrared Hubble Space Telescope image shows a protostar just 950 light years away. The protostar is the bright object with fan-like beams of light flowing from it. It's letting off flashes of light every 25.3 days. This time-lapse movie shows a pulse of light emitting from the protostar. Most, if not all, of this light is being scattered off the circumstellar disk. The observational evidence, along with computer simulations, indicate that the protostar phase can last up to a few tens of millions of years.