Evolution of Sunlike Stars

Our Sun formed 4.6 billion years ago from a giant cloud of interstellar gas and dust located in the equatorial plane of our galaxy. This cloud contained mainly hydrogen and helium, with internal temperatures fluctuating just a few tens of degrees above absolute zero. An external trigger, such as the explosion of a nearby star, caused a smaller region of the gas-dust cloud to begin contracting. As this region collapsed and rotated, it formed a flat disk known as a protoplanetary disk within a few hundred thousand years. The contraction caused significant heating, especially at the center of the cloud, where material was most concentrated. From this accumulated material, the Sun was born. The remaining material in the protoplanetary disk eventually formed the planets and other bodies within the Solar System. After about 50 million years, thermonuclear reactions ignited in the young Sun's core, converting hydrogen into helium. This marked the Sun’s transition to a main-sequence star, a stage in which it remains today. The Sun will continue in this phase for another 6.5 billion years. At the end of this period, the Sun will exhaust its hydrogen fuel in the core, and nuclear reactions will shift to a surrounding layer still rich in hydrogen. In approximately 7.7 billion years, the Sun will evolve into a red giant, expanding to a diameter roughly 166 times its current size, extending beyond Earth's orbit. Over the following several hundred million years, the Sun will shed its outer layers, forming a slowly dissolving planetary nebula that will persist for tens of thousands of years. What remains of the Sun will be a small, dense, and extremely hot core known as a white dwarf.