Something to note about the brown dwarfs we looked at yesterday: Our views on how they would appear to someone nearby in visible light are changing. It’s an interesting issue because these brown dwarfs exist in more than a single type. If you’ll have a look at the image below, you’ll see a NASA artist conception of the three classes of brown dwarf, all of these being objects that lack the mass to burn with sustained fusion.
Image: This artist’s conception illustrates what brown dwarfs of different types might look like to a hypothetical interstellar traveler who has flown a spaceship to each one. Brown dwarfs are like stars, but they aren’t massive enough to fuse atoms steadily and shine with starlight — as our sun does so well. Our thoughts on how these objects appear are evolving quickly, as witness yesterday’s discussion, and we’re likely to need another visual rendering of brown dwarf classes soon. Credit: NASA/JPL-Caltech.
One thing should jump out to anyone who read yesterday’s post on the appearance of Luhman 16 B: The artist here does not depict bands of clouds/weather on the object, but rather localized storms of the kind that some researchers believed would characterize brown dwarfs. We know that Luhman 16 A (33 times Jupiter’s mass) is of spectral type L7.5, while Luhman 16 B is categorized as T0.5, putting it near the transition between types L and T. And Luhman 16 B shows strong evidence of banding.
That’s according to Daniel Apai and team, as discussed yesterday, in an analysis based on data from TESS. Looking further at the image above, it’s clear we’re going to be re-working our depictions going forward as we analyze more brown dwarfs. If we should expect a banded object at the L-T transition, then at least the L dwarf and the T dwarf shown here will likely show the same atmospheric pattern (obviously, we’ll need to confirm these speculations with hard data). That would leave the Y dwarf as yet undetermined, and for good reason, as these objects are vanishingly hard to see.
Atmospheric temperatures drop as we move across the types of brown dwarfs here, with the L dwarf being the brightest and hottest in the image; its typical temperatures are in the range of 1400 degrees Celsius. The magenta T dwarf takes us down to about 900 degrees Celsius, but the Y dwarf really drops the reading, with the coldest yet identified having a temperature of a mere 25 degrees Celsius. That’s not all that far off what my thermostat is set on — 72 ℉ — as I try to take the chill off this morning.
All three of the brown dwarfs shown above appear at the same size, a reminder that all types of this object have the same dimension, which is roughly that of Jupiter, despite wide variations in their mass. Same radius, major disparity in mass, in other words. My hopes that we would find one of these fascinating objects at no more than, say, 1 light year seem to have been dashed, although it’s certainly true that Y dwarfs are so cool that finding them is going to be difficult even for the best infrared observatories.
As we keep looking, we can now refer to the updated map of L, T and Y dwarfs in the vicinity of the Solar System that the Backyard Worlds: Planet 9 project has produced. You’ll recall from earlier posts here that Backyard Worlds: Planet 9 is funded by NASA as a collaboration between professional scientists and the public.
All those non-professional but often highly adept astronomers and volunteers have produced a map with a radius of about 65 light years. The work of 150,000 volunteers has been going on since 2017 using data from the WISE mission under its Near-Earth Object Wide-Field Infrared Survey Explorer (NEOWISE) incarnation. The study was presented at the ongoing virtual meeting of the American Astronomical Society.
Dozens of new brown dwarfs turned up in this work, which drew on data from the now retired Spitzer Space Telescope. Using the Backyard Worlds: Planet 9 results, astronomers consulted data from the space telescope to observe 361 local brown dwarfs of types L, T and Y and combined the results with previously known dwarfs, many of them catalogued by CatWise, the catalog of objects from WISE and NEOWISE.
The result: a 3D map of 525 brown dwarfs.
Image: In this artist’s rendering, the small white orb represents a white dwarf (a remnant of a long-dead Sun-like star), while the purple foreground object is a newly discovered brown dwarf companion, confirmed by NASA’s Spitzer Space Telescope. This faint brown dwarf was previously overlooked until being spotted by citizen scientists working with Backyard Worlds: Planet 9, a NASA-funded citizen science project. Credits: NOIRLab/NSF/AURA/P. Marenfeld/Acknowledgement: William Pendrill.
The galaxy’s coldest known Y dwarf is a neighbor (not surprising, given that more distant dwarfs should be below the level of detection), but it turns out that it is comparatively rare, a bit of an anomaly given our expectations of brown dwarf distribution. Of the seven objects nearest to our Solar System, three are brown dwarfs. And the Sun’s position within this cluster of nearby objects is a bit unusual as well, says Aaron Meisner (National Science Foundation NOIRLab), a co-author of the study:
“If you were to put the Sun at a random place within our 3D map and you were to ask, ‘Typically, what do its neighbors look like?’ We find that they would look very different from what our actual neighbors are.”
Again, we have to weigh this outcome against the difficulty in observing Y dwarfs, so conclusions shouldn’t be drawn too hastily. With brown dwarfs having exoplanet dimensions but no companion main sequence star (in most cases), they become useful objects as we refine the tools of exoplanet characterization. The James Webb Space Telescope should be able to tell us more about nearby brown dwarfs, as will the upcoming SPHEREx mission, an all-sky infrared survey scheduled for a 2024 launch.
The paper is Marocco et al., “The CatWISE2020 Catalog,” accepted for publication in the Astrophysical Journal Supplement Series (abstract/preprint).
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While the equilibrium configuration of a brown dwarf (radius and temperature) is going to be influenced highly by mass ( 13 to 80 Jupiters),
there is undoubtedly as well the startoff conditions based on the analog to the “hydrogen” main sequence: the “deuterium” one. Generally speaking, the deuterium burning phase in these less massive objects is not a direct interpolation from the lowest mass red dwarfs – which go on forever. A rough order of magnitude I remember was a period of
300,000 years vs. hundreds of billions or trillions. But the full mechanics of it, I seldom see in text or literature. So, depending on
whether a brown dwarf was recently formed, or has been around for long time, there ought to be a hump of high temperature for a period of
deuterium consumption in the interior. My guess is that the duration probably varies a couple of magnitudes ( 3 million, 30 million…) but the mass sensitivity and energy rate associated with it, I hesitate to guess. Then, in addition, the formation of clouds or storms at the surface could be affected by internal convection, So could we just be scratching the surface on this question?
I think you mean light year or parsec … as bad as the last year has been, most of us aren’t quite hoping for a brown dwarf inside of 1 AU yet. (But wait, think of the data we could collect on the Jupiter flyby…)
Yes, am having to thank those who caught this — inexplicable typo.
A brown dwarf within 1 AU would be quite exciting. Was the intended distance 1 light year?
I was wondering how a brown dwarf would appear to the naked eye at, say, 01. AU? What would the absolute magnitude be in visible light? Would it provide enough infrared radiation to warm a moon to a comfortable level (assuming a pretty good greenhouse atmosphere)?
The moons could really hug its brown dwarf companion without fear of blasts of UV radiation and other atmosphere-stripping factors.
Since it seems that there is undisputed proof (via neutrino emissions) that a fission reactor is percolating at the earth’s core, would not it be possible for something similar at the core of a brown dwarf? I realize that its not that simple given the radically different core environments but it might be worth trying to model.
Just idle speculation by a a YouTube astronomer:)
I seem destined to swap 1 AU for 1 LY every six months or so. Thanks for flagging that — I just fixed it!
Like the artistic imagery created with the word ‘palette’.
No romance have modern astronomers . I mean ‘brown’ simply cos black was already spoken for ! Shame on you Jill Tarter.
Might just as well called them ‘mud dwarfs’.
If Galileo had discovered them we would have been ‘burnt Sienna’.
If it helps, apparently there is no such color as “brown”. The color of “brown” is simply a darker shade of orange.
Perhaps “burnt orange” dwarfs would be a more artistic term for these sub-stellar objectives. While we are at it, “dwarf” is not a pleasant term. How about burnt orange stellarino?
Be careful with that definition. Following the same primary color mixing methodology there is no such color as black since it’s merely a darker shade of white. I am happy to call brown brown.
Y dwarf with a 20C surface temperature could make a potential habitat for life – from bacteria to larger, floating planktonic life.
Need a bioreactor to process gazillions of tonnes of hydrogen? Look no further. Add enough CONP and trace elements, spice with engineered bacteria, and voilà.
As a colonization target, the living room on the surface of a Y dwarf would put Venus to shame. The number of floating cloud cities and supported populations could be vast by comparison. The cities would need to draw heat from the interior to heat their hydrogen floatation balloons, but that is a “trivial” engineering issue. Mastering hydrogen isotope fusion for energy would offer insanely long colonization periods.
[Has anyone written a SciFi story around the possibilities?]
If they have, I haven’t seen it. Absolutely a great plot device, Alex!
Saturn has similar zones of liquid water in their atmospheres, and very high temperatures deeper down. The only difference is that you need to go to 10-50 atm of pressure to reach them. Fortunately, the ingredients of “hydrox” or “hydroheliox” breathing gas are close at hand, though I don’t know how long our Robinsons could tolerate them in reality. Some genetic engineering is needed for the ammonia and hydrogen sulfide exposure anyway. The vast membranous organisms made of polythiazyl that capture mineral-rich soil from the ring material are rather less likely. :) I’m afraid I’ve started and abandoned this story three times over again… someday…
A big difference from brown dwarfs is Saturn has nearly the same surface gravity as Earth, while these brown dwarfs would have gravity an order of magnitude higher than Jupiter.
Charlie Stross has humans living around Saturn (floating cities, I think) at the end of Accelerando. As long as biological beings live inside airtight bubbles, the exterior temperature is not really an issue and can be easily solved, compared to gravity which we cannot negate. As with any planet with permanent world-girdling storms, wind power for energy and propulsion is almost a steam-punkish technology to use, but it could define how people would live under such conditions, rather like Polynesians, or the the various people in Costner’s “Waterworld” as analogs.
Kim Stanley Robinson, as memory recalls, does the same thing in his early The Memory of Whiteness, putting tiny habitats around rocks orbiting Uranus.
I feel like you can put a bubble anywhere and it is the same. I want the humans out of their shell. The way I was thinking of going about this would pay homage to the first book of fiction I remember reading as a child, one of the many versions of the Swiss Family Robinson. Every guide to writing says fiction is about conflict, yet that story was essentially about exploring, describing some new wonder, and figuring out ways to use it. I don’t think I could sustain a pure lack of conflict throughout a story, but perhaps there is a way to create a sense of innocence regarding some of the action on Saturn.
The story begins with some of the last Americans working out of a museum-embassy in West Canada, organizing refugees into an expedition to claim some of the ice-caves of Callisto by terms of an old treaty. They are sabotaged and forced down into the atmosphere of Saturn. Refusing to surrender to futility, they improvise an aerofoil and hold altitude as long as they can, until one of the children … spots land! It turns out that Saturn has representatives of both geneses – small, strange descendants of Earth, and descendants of the vast filamentous carbon organisms previously known from subduction zones of Mars. On Saturn, these have adapted to polymerize sulfur and nitrogen from the atmosphere as well, forming immense membranes, and have evolved not only to navigate the regular bands of rising air, but to extract energy by spinning and stopping in turbulent flows. We put all of these life forms deep in the liquid water zone of Saturn, partly for biochemistry but more to shield them from the harsh light of observational contradiction.
Now adapting humans to Saturn with limited equipment and 50 years of genetic engineering advances is a tall order. Can we reprogram the cells of a human cornea to be as resistant to alkali as a flamingo’s toes? Can humans resist poisoning by hydrogen sulfide and ammonia? Is it too much to distribute oxygen directly to capillaries by electrical connections for hydrolysis? I imagine there could at least be terahertz sequencing and terahertz-directed mutagenesis. I would argue, thinly, there are a limited number of extracellular proteins that account for most vulnerabilities, while the interior of the cells can be guarded with robust membrane transport. The only way to really know is to try and see!
Vague memories of a sci-fi novel about a solar system fully colonized via a revolutionary space drive. The planets, moons and asteroids were divided along the (then) political blocks on earth. The US got Jupiter with a moon of Jupiter (Callistro?) given to Cuba. The Soviet Union got Saturn. The story telling was pretty good with a lot of great imagery. Bubbles of some sort were used for human habitation on Jupiter. Intra-planetary transport used a kind of steam train traveling through the clouds of Jupiter form bubble to bubble. I don’t recall how Jupiter’s strong gravity was dealt with – perhaps that space drive could moderate the strength of gravity. Given the psychedelic/lurid imagery, the book was probably written in the 70’s or 80’s.
That might have been a Piers Anthony, although he’s likely not the only one to use “future planets of the Solar System” = “20th century nations of Earth”.
In the shadow of the Outer Space Treaty such plots briefly seemed passe, but with the current Scramble for the Moon (or more properly, the lunar pole; also I don’t think they capitalize it yet) I think it is due for a comeback. Unfortunately.
Yes, it was likely Bio of a Space Tyrant” by Piers Anthony. He was a very prolific and, in my opinion, a very imaginative and entertaining author.
Well, Jupiter “surface” gravity is ~2.5x Earth’s. Brown dwarfs are the same size but 13-80x as massive => gravity would be 30-200x Earth’s on the cloud’s top!
It doesn’t sound like a nice place to live :-)
Unlike gas giants, whose gravitational contraction is counteracted by weaker coulomb pressure , brown dwarfs reach an equilibrium similar to white dwarfs – with electron degeneracy pressure finally equalising their gravity ( even the most massive brown dwarfs are thus only 10-15% larger than Jupiter ) . This makes them much denser per unit mass with consequently much greater gravity.
Of course, gravity would pose a problem for colonists – humans 1.0 – colonists. I don’t for a moment think that we will be the colonists, any more than Devonian fish could colonize the continents. Post-human colonists will be very different species [plural usage here] or machines. Gravity will still be an important environmental feature, but if Clement could write about Mesklinites, Forward about the cheela, and Baxter about the flux, there should be plenty of room for beings of some type to live in the surface layers of the atmosphere of a Y type BD. Conditions should be almost clement by comparison. Warm, windy with a chance of…
That’s not bad. I had initially been thinking that with such gravity and a hydrogen atmosphere, there would be no way for anything to remain aloft, but the preprint speaks of wind speeds around 4.5 *km*/s. If there are bands of updraft as on Saturn, I suppose canny flyers might remain aloft. How they would evolve is a bit dicey; at a guess the smallest microbes might remain viable due to the sheer volume and turbulence of the atmosphere? Also, speaking of “chance of…” are there enough heavier elements to maintain an ecosystem?
My initial comment had suggested adding the needed heavier elements except for hydrogen. But Ashley’s comment in the previous post indicates that there are TiO/CO clouds, so that suggests to me that C and O are present in sufficient abundance. So N, P, and perhaps S are needed, as well as Fe, Mg for terrestrial life. But we are talking alien life I presume?
meh … a paltry few hundred Gs perhaps? Robert Forward’s Dragon’s Egg told a story of intelligent life at 67 billion G’s on the surface of a neutron star. That guy took things to the limit.
Great idea Alex, but only for machines or cyborgs. Perhaps aquatic creatures they bring along might tolerate 30 plus gees at the surface of Brown Dwarf at the lower end of the mass range:
At the size of Jupiter, a minimum mass BD(13 Mj) would have a surface gravity of 13 times greater(scales directly as the mass):
13 x 24.8 = 322.8 ms^-2 or 13 x 2.53 g = 32.89 g.
I don’t think we’d survive more than a few crushing minutes at 33 Gees. Yikes:).
Intelligent creatures that evolved on such a BD would of course be fine. But if they wanted to become spacefaring, they would have a tremendous problem:
The escape velocity would scale as the square root of the mass, so approx 3.6 times that of Jupiter:
3.6 x 60 = 216 km/s
So we are talking something like Orion pulse propulsion to get off the surface:).
Those calculations are for a minimum mass BD. I assume that a maximum mass BD(80 Mj) would be at the hotter end of the spectrum(pun intended), so uninhabitable.
Stay safe in the age of plague.
It does now seem the probability of a brown dwarf closer than Alpha Centauri is now slim. However, there are still cooler objects that might be relatively nearby and as yet undetected- the planetary-mass objects.
The link below argues that the space density increases as the brown dwarf temperature decreases, and if this trend continues there should be a lot of PMOs out there.
“Preliminary Trigonometric Parallaxes of 184 Late-T and Y Dwarfs and an Analysis of the Field Substellar Mass Function into the “Planetary” Mass Regime”
Well, Iain M Banks’ ‘The Algebraist’ did feature a stealthy galaxy-spanning high tech culture lurking quietly in gas giants, not much different from Y class brown dwarfs really. A lovely, whimsical story.
I still think there’s hope for more brown dwarfs and even ultracool M dwarfs to be found in the 5pc volume, especially in the crowded Milky Way plane and bulge. They could be lurking there in the clutter waiting for the next, and better WISE type mission, especially if they don’t have high proper motion.
On that idea of living on a brown dwarf with its open vistas:
Gravitational force is proportional to GM/r^2, just for the record.
Why I bring that up is that most brown dwarfs are about the same
radius as Jupiter, with the more massive ones dropping in radius.
Jupiter’s surface gravity is about 2.5 or more relative to Earth.
So, when you get on board at 13 and rise to 80, you are talking serious loads on any vertical structure.
If I recall the first brown dwarf to be verified ,in 1994, was 120 million years old Teide-1 . With a temperature of around 2600 K it has a spectral class of M8 despite having a mass of just 55 X that of Jupiter.
The illustrations of the different types of brown dwarfs may be correct. I am intuiting that the higher temperature of the L dwarfs atmosphere disrupts any banding effect which is the result of a fast rotation and Coriolis deflection of winds? Venus only has a single Hadley cell and very slow rotation.
Ashley Baldwin, there is no electron degeneracy in a brown dwarf because pressure ionization is not great enough. The core has to reach a pressure high enough to get the atoms to move and collide fast enough to reach fusion like in a red dwarf. The next step needed is the triple alpha process which fuses helium into carbon and it makes a white dwarf where the electron degeneracy was defined as I recall reading in Astronomy magazine that every electron shell has to be completely full to be considered electron degeneracy pressure. In other words, a white dwarf is more dense that the center of the largest brown dwarfs.
White dwarfs aside, ‘unbound’ electron degeneracy applies to brown dwarfs too and indeed less massive objects too in a related ‘bound degeneracy ‘ guise . Pauli nailed it.
‘Unbound’ electron degeneracy pressure , free electrons . As opposed to the weaker but closely related ‘bound electron’ degeneracy pressure seen in the molecules of smaller bodies such as terrestrial planets and everyday objects like you, me – and gas giants like Jupiter. Hence Jupiter’s comparable ( or larger) size compared to even the most massive brown dwarfs. Adding more mass simply increases the outward resistance to gravity .
Unbound electron degeneracy is what ultimately prevents the onset of persistent nuclear fusion in the more/most massive brown dwarfs. It is much more efficient at lower masses in resisting gravitational collapse than the thermal push back induced by nuclear fusion . Even that of hydrogen in borderline cases. Which is why some of the most massive brown dwarfs temporarily undergo this sort of fusion ( as opposed to deuterium and lithium ) before fizzling out to become L or as with Teide-1, M brown dwarfs.
But don’t take my word for it . Check out the evidence I’m citing .
Does this mean drip feeding more mass into a brown dwarf may not necessarily initiate proton-proton fusion until mass is significantly higher than would otherwise be typical in star formation?
The idea here is that “drip feed” mass addition would minimize heating from release of gravitational potential energy thereby keeping the core relatively cool. Could the brown dwarf go directly to a neutron star scenario without passing through a fusion phase? That transition to a neutron dwarf would release enormous energy I think; perhaps enough to blow up the whole shebang. I don’t know why I ask these questions other than pure curiosity.
Ashley Baldwin, I think you are using the term degeneracy pressure different than what I’ve heard, It is the Pauli exclusion principle which prevents further collapse in a white dwarf star in the electron degeneracy. Two electrons can’t occupy the same energy state, so an electron is forced up into a higher energy level. It is the mass of the star which determines electron degeneracy. For example, in a white dwarf the electron degeneracy or Pauli exclusion principle between electrons keeps the white dwarf from collapsing further, but if the star is more massive, like in a super nova explosion, the Pauli exclusion principle between the electrons is over powered, the electrons are forced to combine with protons to become neutrons. http://hyperphysics.phy-astr.gsu.edu/hbase/Astro/whdwar.html
Also the size of the star inner core temperature is determine by the mass and gravity, so it is the speed of the particle collision and movement there that determine fusion, so they have to be moving fast enough for the electric forces between light helium and the strong nuclear force grabs them and combines two light helium them into helium.
The only thing I am using is the published astrophysical literature in relation to brown dwarfs. Which are kept from collapsing by unbound electron degeneracy a la Pauli . At least whilst not fusing.
It’s this degeneracy that reduces gravitational collapse and so core temperature rise – thus limiting persistent fusion in a way not seen in the more massive molecular clouds that become normal stars. . It seems that Coulomb pressure is now also considered a variant of electron degeneracy – but occurring in the bound electrons in molecules.
Feel free to check up. It’s a good read . Both the extended literature and online lectures from experts in the field .
The most controversial thing about brown dwarfs currently is that there are those that think they qualify as stars – at least whilst fusing . For anything from 10-100 million years . Longer than O2 and O3 stars. And deuterium is after all just an isotope of hydrogen .
This *is* an interesting topic – maybe https://astrophysicsspectator.org/topics/degeneracy/DegeneracyPressure.html is a reasonable thing to start with. The Wikipedia article on white dwarfs gives useful math. Apparently the degeneracy pressure starts with metallic hydrogen in the cores of planets as small as Saturn. I guess if hydrogen is metallic, that pretty much means all the electrons are mobile and delocalized relative to the nuclei, so that makes it like the plasma of a star, but under enough pressure to fill all the available states? Still, even at the size of the smallest brown dwarfs, the size is apparently still more a matter of Coulomb pressure, and it only transitions to degenerate electron pressure as the mass increases.
I don’t really understand the reason for a near-constant radius for planets over Jupiter, but there’s some basic sense to it: planets get bigger the more mass is added, but white dwarfs get *smaller* with increasing mass. Because the gradient of gravitational potential energy within the compressed star increases, the range of kinetic energy and so the velocities the electrons can have under the Pauli principle increases. Brown dwarfs have less mass per nucleus than white dwarfs, but a feather-light object of any composition wouldn’t increase in size without limit based on the degeneracy pressure of cold unbound electrons. Are these simply limited to fill the radius they can cover without forming a non-degenerate material?
I think the Coulomb or electric forces is not the same thing as the Pauli exclusion principle which only applies when all the electron shells are full as inside a white dwarf. So we don’t disagree on that?
Brown dwarfs do have a limited fusion. It is the electric forces which keep a star from collapsing, or better, cause the particles to repel each other and like charges repel each other as in the proton repulsion of light helium. Also above the 10 million kelvin needed to for fusion burning, stars have another process called the CNO cycle or carbon cycle which helps keep the fusion burning. and also the carbon cycle which I recall reading works above ten million Kelvin. The carbon cycle is interesting because protons quantumly tunnel into the carbon 12, nitrogen and oxygen atoms and the cycle ends or returns to the original carbon 12 which which is started is energy saving.
There is another type of degeneracy, the neutron degeneracy where the Pauli exclusion principle between the neutrons keeps the neutron star from collapsing into a black hole, but a larger mass star is needed to pass the Schwarzschild radius.
The first link above used the term “Coulomb pressure”. I should never have followed suit because now I have to try to *understand* it. I mean, what I meant was “regular old pressure of rocks piled on top of each other”. Van der Waals repulsion, from the Pauli exclusion principle, but with particles separated by position rather than difference in momentum. There is quite a bit of math about it at https://web.pa.msu.edu/people/ebrown/docs/stellar-notes.pdf (p.61-63) While I doubt Coulomb ever tackled that math, they are indeed adding up individual Coulomb interactions between electrons and nuclei. Why they are doing this in a charge-neutral sphere centered on an ion, and what that has to do with pressure or how it answers Exercise 5.9.3 … yikes. That is going to take more than a few minutes to figure out!
The Chandrasekhar limit has its own set of physics guard dogs. The Wikipedia article on white dwarfs gives you all the math you need, but understanding it *intuitively* is another matter. Part of it is that when electrons become relativistic, a difference in momentum sufficient to escape the Pauli exclusion means that they gain a proportional amount of energy (not the square root) because the relativistic mass increases in proportion to the velocity.
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The electrons escape the Pauli exclusion principle when it is over powered by the gravitational collapse of the iron core in a type 2 supernova explosion. It is a process called the neutronization of protons. Ingles 2015. The electrons are forced to combine with protons and they turn into neutrons. This is beta plus decay. The proton needs to emit a neutrino and a positron to carry away it’s positive charge The proton turns into a neutron due to the extreme gravitational collapse. The result is neutron star when the Chandrasekhar limit is passed.
There is a radiation pressure in the core of a brown dwarf as well as repulsion from like charges like electrons repulsing each other and protons repulsion of each other. There is deuterium fusion which is part of the proton proton chain in stars. The first stage is when two protons collude fast enough to have the energy to turn one of the protons into a neutron. The positive charge of the proton is carried away by the emission of a positron and neutrino. The neutral particle is the neutron without any charge. The making of deuterium emits positrons and the deuterium which combines with a hydrogen atom to fuses into helium 3 with the emission of emission of gamma rays is the radiation pressure that balances the gravity. It’s the final state of the proton proton change the fusing or combing two helium three into helium four is not in the core of a brown dwarf
According to Wikipedia, Brown dwarf star electron degeneracy pressure is needed for the fusion of helium three into helium four to sustain fusion in the core. I did not know that electron degeneracy pressure was needed until I looked it up on Wikipedia and Ashley Baldwin mentioned it. https://en.wikipedia.org/wiki/Brown_dwarf
I don’t think they actually say that – their point is more that the degeneracy pressure holds the nuclei far enough apart that they don’t fuse. Fusion also depends on the thermal energy of the nuclei, but the kinetic energy associated with degenerate electrons isn’t thermal because they’re not able to get rid of it. (Which means they can’t get rid of it by agitating nuclei, I assume … though I don’t understand what is on hand locally to tell the electron it’s not allowed to do a Rutherford against any nuclei it encounters unless it clears its flight plan with Stellar Central Command.)
Brown dwarfs are something like 1.2% to 7.6% the mass of the Sun, with about the radius of Jupiter = 10% the radius of the Sun. Above this mass you have red dwarfs, which expand in mass and radius roughly in direct proportion until you get to the Sun. The lowest-mass white dwarf I know of ( https://tinyurl.com/y5rlaz9a ) is 30% the mass of the Sun but 3% the radius of the Sun. If we could find one that had been stripped down to a quarter that size, by the inverse cube root relation it would still be less than 5% the radius of the Sun. I assume this is because white dwarfs have double the mass per degenerate electron because elements other than H are half neutrons.
The big difference is red dwarfs reach a low mass threshold where the core of the star can undergo an exothermic fusion reaction, preventing contraction. White dwarfs start heavier and have an endothermic reaction only at a high mass to produce neutrons. But given the role of degeneracy pressure in all these objects, why is the carbon detonation or even the helium flash of a white dwarf so much more dramatic (nova/supernova) compared to lithium burning in a brown dwarf also supported to some degree by degeneracy pressure? Is it just a matter of having less lithium to work with?
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