- 3114 - BROWN DWARF - stars that do not shine so bright. Their brightness depends on their size. The bigger stars are the brighter they are and the shorter their lives. We are fortunate that our Sun is in the middle of the pack and should live for 10,000,000,000 years.
------------- 3114 - BROWN DWARF - stars that do not shine so bright
- Planets congeal out of debris floating around newborn stars. They are the leftover scraps of the star formation process. Recent discoveries of planetary bodies are 12 to 75 times the size of Jupiter, our biggest planet. They are not quite big enough to have enough gravity to ignite hydrogen fusion at their cores. They are called “Brown Dwarfs”.
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- Although they are not big enough to fuse hydrogen into helium they are big enough to fuse deuterium into helium. They briefly start to shine as stars with this process but quickly exhaust their supply of deuterium and start to cool down like a planet.
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- Astronomers have found hundreds of these Brown Dwarfs floating throughout our galaxy and some even orbiting other stars like planets. Brown Dwarfs are very faint and hard to find but estimates from astronomers are that they may be as numerous as the stars we see in our galaxy.
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- Planets are born in the disks of gas and dust orbiting a newborn star. It is believed that Brown Dwarfs can not form this same way that planets do. This process is limited to about 10 to 15 times Jupiter mass.
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- Most are found as independent stars not orbiting other stars. Astronomers think they are likely failed stars, no different than full blown stars at birth but for some reason get separated from the molecular cloud that feeds them. They end up stuck in the embryo stage and never mature.
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- Stars evolve depending on whatever mass they accumulate. We know stars for two distinct properties, their brightness and their color. Brightness is luminosity, or the intensity of their radiation.
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- If we us the luminosity of our Sun as the reference equal to 1, stars have luminosities form 1/10,000 that of our Sun, called Red Dwarfs; to 1,000,000 that of our Sun, called Supergiants.
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- Their brightness depends on their size. The bigger stars are the brighter they are and the shorter their lives. We are fortunate that our Sun is in the middle of the pack and should live for 10,000,000,000 years.
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- Also, the bigger the star, the more gravity that compresses it, the hotter it gets. The color of the star tells us its surface temperature.
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- Color is another word for frequency, or wavelength of electromagnetic radiation in the visible range. Our eyes detect color because of the different wavelengths that reach the cones in our retina. The temperature of a radiating body is equal to 0.0029 / wavelength.
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- For example: Our Sun is yellow light. Its maximum intensity of radiation occurs at a wavelength of about 500 nanometers. From the equation, known as Wien’s law, the temperature is .0029 / 5*10^-7 meters = 5,800 degrees Kelvin.
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- (Kelvin is the same as Centigrade but add 273 degrees because the Kelvin scale starts zero at absolute zero, -273C).
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- Using this measure of temperature stars range from 2500K to 50,000K:
- Color Maximum Temperature, K Example star
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- Blue-violet 50,000 Mintaka
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- Blue-white 30,000 Spica, Rigel
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- White 11,000 Sirius, Vega
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- Yellow-white 7,500 Canopus, Procyon
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- Yellow 5,900 Sun, Capella
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- Orange 5,200 Arcturus, Aldebaran
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- Red-orange 3,900 Antares, Beltegeuse
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- Brown less than 2,500 Brown Dwarfs
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- Brown Dwarfs were only discovered 20 years ago. Much more needs to be learned to understand their origins. Learning more will help us understand the origins of stars as well as planets.
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- These times are great for astronomy. So much is being learned every day.
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- March 31, 2021 BROWN DWARF STARS 617 3114
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--------------------- --- Wednesday, March 31, 2021 ---------------------------
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