How are stars born?
Stars form deep inside vast clouds of interstellar gas and dust called nebulae. In the cores of these intensely cold regions — only 10 degrees above absolute zero — the pressure from the heat of the gas is insufficient to support the weight of the surrounding cloud, which then begins to collapse on itself.
After a few million years, the increased pressure resulting from the contraction of the core has raised the central temperature to more than 1,500 degrees Fahrenheit, and the protostar — still much larger than it will finally be — glows a cool red beneath its still-collapsing blanket of gas. When the core reaches a few million degrees, the process of hydrogen fusion begins and the collapse is finally reversed; the newly born star, stably burning its reserves of hydrogen fuel, blows away its gaseous cocoon and takes its place amongst its fellows.
Much of this process has now been directly observed, thanks primarily to the astounding power of the Hubble Space Telescope. Astronomers have actually observed gas clouds in the process of collapse, and with infrared sensors capable of peering through the thick dust and gas, they have imaged the warm glow of infant protostars — and possible proto-planetary disks in orbit around them.
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