Overview: How Stars Are Made
Astronomers and physicists have theorized that stellar formation happens when clouds of gas and interstellar dust collapse, molecules of hydrogen attract one another, and nuclear fusion generates energy and heat. During the process, these young stars are very faint, with energy near the infrared spectrum. Eventually, when nuclear fusion is better established, most of the energy from conversion of hydrogen to helium generates visible light.
What Conditions Are Necessary?
In order for clouds of gas and dust to form into stars, several well-known physical characteristics need to be present. The gas cloud must be very large and dense enough to collapse under gravity. If it is too small or spread out, there won’t be enough attraction between molecules to cause the collapse. The theory is that, even for the smallest stars, the cloud must be ten thousand times the mass of our Sun. The temperature must be correct, and there must be enough dust to facilitate the process. Clouds of gas and dust like the Orion Nebula have the right conditions for young stars to form, a process that can take tens of thousands of years.
A Secret Process
Several circumstances make the process of stellar formation hard to observe. The young stars are very small and faint, and most of the energy that radiates from them is not visible. It is in the part of the spectrum that has very long waves of infrared light. Most of those waves are blocked by the atmosphere of Earth itself. As gravity spins clouds of gas and dust into stars, an opaque shell makes the process difficult to see. By the time the surrounding cloud is burned away from the protostar, ongoing nuclear fusion creates visible light.
The Role of Space Telescopes
Telescopes in space from NASA and Europe are not blocked by Earth’s atmosphere, so scientists have been able to observe many details about the universe than ever before. Some of the new observations of the Orion Nebula show many protostars at earlier stages of development. Long before nuclear fusion begins inside the cloud of gas, they contract and expand, sometimes changing size in just a few weeks. Scientists think that lumps of material form to cause short-term flares.
Spectrometers in Space
The newest observations in 2013 from space telescopes and the spectrometers aboard them show many bright infrared stars in early development. They pick up light waves that are as wide as a human hair, still in the invisible infrared range. That period of a star’s life may only last around 25,000 years, rather than the billions of years that energy comes mostly from nuclear fusion.
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