Brown Dwarfs Challenge our View of the Universe. Here's How.

thanks to brilliant for helping support this episode hey crazies you've probably heard of white dwarves black dwarves and red dwarfs they're all types of stars or at least the remnants of stars but there are also these strange objects out there called Brown dwarfs they're a little big for a planet but a little small for a star so which category do they fall into planets or stars are they actually Brown what are they made of here's everything you need to know about brand Dwarfs thank you full dis

closure Brown dwarves are a relatively new object of interest for astronomers they were first hypothesized in 1962 but we didn't discover one until 1988 and that wasn't confirmed until 1995. so the study of brown dwarves is only like 10 years old uh what I would do that math again 2023 minus 1995 borrow the one borrow the one oh God that was 28 years ago still though it's still very recent for astronomy we discovered black holes first not only are brown dwarves very dim and very small most of th

e light they're emitting is in the infrared range thankfully humans are really good at solving problems when we want to our infrared telescopes have allowed us to find over 3 000 Brown dwarves this image was taken with the very large telescope in Chile in 2004 is it orbiting that white star right there no that's the brown dwarf then what's the reddish brown thing in exoplanet orbiting the brown dwarf this is the first picture ever taken of an exoplanet we had to overexpose the image to see the e

xoplanets so the brown dwarf looks White so they're actually Brown well no stars come in many colors and we can sort them by surface temperature you'll find Brown dwarves over here below the red Dwarfs they're like subred Dwarfs of course Brown isn't dark red it's dark orange it would have made more sense to call them Crimson Dwarfs but I don't get to name things okay don't at me these Brown dwarves would be mostly a deep red color but depending on how you see color it might come across a bit ma

genta that's just the really hot ones though the cooler ones would actually be black only becoming visible due to reflection like planets and they wouldn't be much larger than a planet either the largest planet in our solar system is Jupiter it's about 11 Earths across and contains almost 318 Earth's worth of mass but if you add any more mass to Jupiter it wouldn't get much bigger it would just get denser so the next time you hear about some exoplanet that has the mass of 10 Jupiters yeah that l

ooks like this all objects in this Mass range have roughly the same volume Brown dwarves started about 13 Jupiter masses and go up to about 80 Jupiter masses but they're all about the same size we don't see any dramatic size differences until you start looking at actual Stars our brown dwarf stars no they're sub Stars you mean like planets also know on the mass scale they're sandwiched between planets and stars they're like the cosmic middle child properties of both but belonging to neither clas

sification is difficult work but we do eventually figure the shirt out did I hear someone say shirt no I I said shirt science Asylum merch is always available just like this awesome we need better nonsense shirt Link in the doobly-doo unbelievable stars have an incredible amount of mass I mean our sun has a mass of 333 000 Earths that's a lot of mass without nuclear fusion Stars would collapse in on themselves inward gravity raises the temperature of the Stellar core the fusion from that core pr

ovides an outward counter Force to balance it but the less mass of the star the lower the gravity which means the lower the temperature which means less outward force from Fusion so lower Mass Stars find equilibrium at a smaller size but there's a limit long-term sustained hydrogen Fusion isn't possible below a certain temperature somewhere around 1.6 million Kelvin which sure is incredibly hot by human standards but for some perspective our own Sun's core is 10 times hotter than that anyway a c

ore temperature of 1.6 million Kelvin corresponds to a surface temperature of about two or three thousand Kelvin and a mass of about eight percent our own Sun's mass that's equivalent to the 80 Jupiters we mentioned earlier all objects Above This limit are considered stars and can be plotted on an HR diagram for anyone new to these diagrams they're nothing fancy it's just brightness graphed against surface temperature AKA surface color our sun is Right smack in the middle it's a small white star

aside from allowing our existence it's fairly unremarkable it's currently in a region of this graph called the main sequence All Stars in this region are primarily fueled by sustained hydrogen fusion and they'll be here for most of their lives but if we look at lower Mass Stars we can see they're dimmer and cooler eventually we get down to the red dwarfs they're the coolest Stars they could sit on the main sequence for trillions of years round dwarves are below that if we go cooler than red dwa

rfs we step off the main sequence none of the objects down here can sustain hydrogen Fusion at least long term brown dwarfs are essentially failed Stars you mean like Jupiter absolutely not I'm so tired of this myth yes Jupiter is incredibly massive it contains half the mass orbiting the Sun but don't let anyone convince you it's a failed star Jupiter is not a failed star Brown to dwarfs are failed Stars Jupiter is definitely a planet the distinction at low masses might be vague but Jupiter is n

owhere near that boundary while the upper Bound for brown dwarves is clearly defined by hydrogen Fusion the lower bound is a bit undecided oh man do I really want to bring up this internet discourse again okay the official definition for all astronomical words is decided by the international astronomical Union or iau they've been around since 1919 but they Rose to infamy in 2006 because of the Pluto decision we're not going to get into that today that decision was for the lower bound on what it

means to be a planet we're looking for the upper bound the iau has a definition for this too but it's messy at best it's just a placeholder it was never meant to be the final answer so let's start by taking a look at how stars and planets form it all begins as a giant cloud of cold gas and dust both planets and stars will form from this Cloud but in very different ways stars form quickly from the gas and dust itself usually near the center of the cloud this consumes the vast majority of the Clou

d's Mass all the leftovers form into small rocks first those rocks then vary gradually combine to form things like planets it takes hundreds of millions of years longer even gas giants like Jupiter form this way there's a rocky core somewhere in there that's the distinction I think makes the most sense Brown dwarfs should be defined as objects that form like stars but aren't massive enough to become Stars if it forms like a planet then it's a planet simple distinct and clear unfortunately we don

't have direct access to formation history without a time machine and the last time I used one of those things went very badly we don't even know if each brown dwarf formed in the star system we found it in or if it formed by itself and was captured later or if it was ejected from some other star system so while my preference makes the most sense theoretically it's probably not that useful to astronomers I'm guessing that's why the iau definition hasn't been updated since the mid-oughts or as th

e Brits would apparently say the mid-notties anyway let's go through that iau definition item number one objects with true masses below the limiting mass for thermonuclear Fusion of deuterium currently calculated to be 13 Jupiter masses for objects of solar metallicity that orbit stars or Stellar remnants are planets no matter how they formed jargon alert jargon alert jargon alert I'm gonna explain it calm down deuterium is just the fancy name for heavy hydrogen that's hydrogen with an extra Neu

tron fusing deuterium is a lot easier because it requires one less step to be clear Fusion always requires that we overcome the natural repulsion of atomic nuclei that can be done either with ungodly temperatures or through Quantum tunneling ideally both but with regular hydrogen that's still not enough to make it stick we also need a weak interaction that turns one of the protons into a neutron otherwise they'll just push themselves apart again deuterium doesn't require that extra weak interact

ion so it fuses at a lower temperature temperatures you might find in a sub Stellar object like brown dwarfs side note technically deuterium Fusion happens in All Stars before they get to the main sequence you know before they're hot enough for hydrogen Fusion Brown dwarfs just don't ever make it to the main sequence end of side note alright back to the working definition item number one says objects below 13 Jupiter masses are definitely planets because they can't fuse deuterium item number two

says any substellar objects above 13 Jupiter masses are definitely Brown to wharfs it doesn't matter how or where the object formed how is that message sure it sounds simple and clean until you try to categorize objects say you've got two objects with a mass of I don't know 20 Jupiters by the iau definition these are both clearly Brown dwarfs but then we look a little closer and notice quite a few differences maybe this one has a rocky core and behaves more like a gas giant planet some brown dw

arf Spectra match up quite well with gas giants but maybe this other one behaves more like a star it's gas or plasma all the way down in that case calling them both Brown dwarves doesn't really tell us much about them the only thing they have in common is their Mass it could just be that brown dwarf is too broad a category to be useful these objects actually span three spectral classes on the HR diagram LT and Y the l-class dwarves are the hottest so they're mostly plasma the t-class dwarves are

a little cooler so they'd likely be a mix of plasma and gas the y-class dwarves are the coolest so they'd be mostly gas assuming they all form like stars they'll all start the same way as a protostar they'll fuse deuterium into helium during the initial collapse but that deuterium Supply will run out after several million years or so after that it will collapse further in an attempt to become a star but alas there's not enough Mass mechanical forces can halt the collapse before it gets hot enou

gh kinda like gas giants the Ronda Wharf will eventually settle and its appearance will depend on its temperature with such a low mass and no Fusion to speak of these objects are Immortal full-blown stars become black holes neutron stars or white dwarfs they end Estella remnants Brown dwarfs will be brown dwarfs forever forever well unless they get eaten by a more massive object at some point during their lives if left to their own devices though they will cool off over time so the spectral clas

s depends on more than just Mass each y-class dwarf might be young with a lower Mass or it could be old with a higher Mass we have to measure the mass separately to know for sure some of them are so cold that there's talk of adding a fourth spectral class z-class dwarfs but that's a problem for data-driven astronomers we'll let them figure that one out in simplest terms Brown dwarfs are just sub Stellar objects too cool to have any long-term Fusion reactions but hot enough that there might be a

few short-term ones if the brown to wharf is still fresh enough to shine it might appear a deep red color but its thermal Spectrum will actually peak in the infrared we've been able to find thousands of these objects so far and thanks to some citizen science thousands more have been identified for a review even jwst is on the job now in the end though Brown dewarf might just be a temporary name I mean classification is one of my favorite parts of science but it's difficult to do us humans we nee

d to split reality into metaphorical boxes to understand it but the universe resists true reality has no lines No Boundaries it just is and until next time remember it's okay to be a little crazy if you want to understand reality a bit better brilliant.org is a great way to do just that YouTube may be interactive through the comments section especially on my channel but if you really want to understand this stuff you need to do it yourself brilliant has thousands of interactive lessons on many d

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complex Square to get probability density the wave motion disappears anyway thanks for watching