My philosophic view of our universe is everything, really, everything that exists is on the spectrum of existence. I see existence as a smeared continuum vs. absolutes. An example is visible light. It’s part of the electromagnetic spectrum. Red light is part of the visible light spectrum. But is there an absolute red? We humans have an insatiable need to categorize and compartmentalize, so astronomers use 656.281 nanometers wavelength, called hydrogen-alpha (H-alpha) as a standard. H-alpha light comes from the phenomenon of hydrogen atoms emitting light at this wavelength after ionization and returning to their natural energy state. H-alpha light is abundant since hydrogen is the most abundant element in our universe. However, 656.281 nm defines one red among the infinite possible red wavelengths surrounding H-alpha.
The same goes for stuff like celestial bodies (rocks, planets, stars, etc.). They live on the continuum of existence, and we categorize/name them based on characteristics such as mass, chemical makeup, luminosity, temperature.
We define stars by their sustained ability to fuse hydrogen into helium. Never mind stars that have depleted their hydrogen and fuse helium or other, heavier elements – they were stars to begin with. Our Sun is called a yellow dwarf star. Why? It’s on the smallish side of the star size and mass spectrum and it produces a yellowish-white light. At 8% – 50% the Sun’s mass, red dwarf stars are the smallest and dimmest stars, hydrogen fusion perking along and producing reddish light.
An object with mass below 8% of our Sun’s mass (80 times Jupiter’s mass) cannot sustainably fuse hydrogen. Those whose mass is 70-80 times Jupiter’s might intermittently fuse deuterium. They’re not called stars. They are not called planets either. These objects are called brown dwarfs. They are in-between-ers. They live in an area of the existence spectrum between planets and stars. It’s a continuum. While Jupiter is cold in its clouds, -234 degrees F, objects greater than 8-10 times Jupiter’s mass are hot all the way through. An object 70 times Jupiter’s mass is hotter than a blast furnace and glows a dull red!
The process for a brown dwarf’s formation has not been nailed down. One hypothesis is that they form in the same scenario as stars, but without enough mass to fuse hydrogen. Another is they arise during planetary formation around a nascent star and escape or get flung out of the planetary system. We do know brown dwarfs with 13 to 70 times the mass of Jupiter have super-hot atmospheres, with titanium oxide, magnesium silicate and iron clouds. Without sustained fusion brown dwarfs will slowly cool over hundreds of millions of years and just go cold.
What’s in the Sky?
September 9; 30 minutes after sunset; west-southwest: A waxing crescent Moon joins Venus, Spica, and Mercury low in the sky. Use binoculars if you have them.