Brown dwarfs are often quite rudely called "failed stars". That's too much pressure to put on any object, even though the reason they fail to be stars is the lack of pressure in their core, I want to ask these people though, are you doing a better job of becoming a star? Anyway let's get to topic here.
Brown dwarfs are classified as celestial objects between planets and stars. Their mass can range from around 13 times the mass of Jupiter, all the way up to 80 times, however that mass puts them just under the range of stars, as it is not enough for them to forge a dense enough core during their formation to fuse Hydrogen into Helium, and sadly that reaction is what makes a star a star. They can however, in the early ages after their formation, fuse Deuterium.
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| Credit: NASA/JPL - Caltech |
Deuterium is an isotope of Hydrogen, meaning it has the same number of protons but a different number of neutrons than a 'normal' Hydrogen atom, and it has one neutron in its core whereas the common Hydrogen atoms have zero. This makes a Deuterium atom more massive than a daily Hydrogen atom, making it easier to fuse due to the stronger gravitational effect on it.
Planets cannot fuse Deuterium in their cores, giving a point to brown dwarfs. This fusion lets them emit a dim light in their early ages, making them observable in the visible spectrum of light.
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| Neptune by Voyager 2 - Credits: NASA/JPL - Caltech |
Before their discovery in 1995, brown dwarfs were theoretical objects. It's not an easy discovery to make because of their dimness, requiring powerful observations to be made in the infrared spectrum. That is what makes this measurement a big deal, it was made on a brown dwarf that is 32 light years away from the Earth. It's size is close to that of Jupiter, but it's mass is 40 times larger. The winds on the atmosphere layers of the brown dwarf were measured to be clocking up to 2290 km/h (~1450 mph), which is a couple hundred km/h faster than the winds of Neptune, which are the harshest in our solar system (at around 2000 km/h). For more comparison Jupiter's winds only range up to 370 km/h (230 mph).
On planets with solid surfaces, like ours, wind speeds are measured by observing the motion of gas particles relative to the ground. On gas giants and brown dwarfs, there is no solid surface, since they are composed almost entirely of gasses. The relative motion instead happens due to the change in pressure in different layers of the gaseous body. At a certain depth into the brown dwarf the pressures get intense enough to force the collection of gasses to behave like a solid body, rotating in unison. This interior rotation also causes the outer layers to rotate as the pressured body of gasses pull the outer layers with them. Since the atmosphere and the core rotate in near unison, measuring of the wind speeds is an approximate measurement of the rotation of the brown dwarf. There is a difference however, and the way that that's measured is very cool.
The motion of the inner gasses, caused by the rotation create strong magnetic fields around the brown dwarf. As the body rotates, its magnetic field accelerates charged particles in its atmosphere, which creates low energy electro-magnetic waves that fall into the radio wave spectrum. (The effect of accelerated charges creating electromagnetic waves is described in Maxwell's Equations of Electromagnetism.) Researchers detected these waves using the radio telescopes in the Karl G. Jansky Very Large Array in New Mexico. (Household radios unfortunately don't cut it.)
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| Credit: NASA/JPL - Caltech |
To measure the relative movement speeds of the atmosphere of the brown dwarf to its interior, they needed quite a warm one, warm enough to emit a substantial amount of infrared light. The one they observed has atmospheric temperatures around 600 degrees Celsius (~1100 deg Fahrenheit), making its infrared emissions intense enough to make the observations of its atmosphere possible through the recently 'retired' (30 Jan 2020) Spitzer Space Telescope of Caltech.
Many dim, hard-to-detect objects like brown dwarfs may still be hiding in the black of the skies. Perhaps so many, that they've got some scientists thinking these objects may be a viable solution to the trend missing gravity problem, tagged as dark matter. They are dark, they are matter, they may be a spectacular anticlimax if this turns out to be true, but they still matter.
#careforbrowndwarfs
References:
- https://www.nasa.gov/feature/jpl/in-a-first-nasa-measures-wind-speed-on-a-brown-dwarf
- http://coolcosmos.ipac.caltech.edu/cosmic_classroom/cosmic_reference/brown_dwarfs.html
- https://www.cfa.harvard.edu/research/rg/brown-dwarfs
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