Large Jupiters have their own Energy sources, planetary systems, and their own world populated by their kind. They can become Suns or a planet, even a binary companion Let's see what they actually are? Hello and welcome to this post, I'm your friend K*. Today we will be learning about Brown dwarfs, a fascinating class of objects and they are interesting in every aspect.
Introduction:
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| Brown Dwarf : Midst of Debris Disk |
Many decades ago, the scientists had planets, Moons, Stars, Nebulae, Galaxies, Black holes and other objects. at that time, they were aware of how a star forms and evolves but there was a missing point. what actually happens when a Star is forming We know this can't be done in some years; instead, it takes several million years. So in our post about stellar Birth mentions a point If a forming star aka protostar never reaches the point required for Hydrogen Fusion, it becomes a Failed Star or Brown dwarf. Don't be confused by its name, which is misleading because Brown dwarfs don't appear Brown. In this post, we'll keep discussing such points and facts. Keep in mind this is an episode taking an account what happens when a Protostar fails to get enough temperature and pressure.
We see planets orbiting their stars, we're also certain all these entities form in one nebula typically. many years ago, Scientists had the same problem; they were not able to establish a connecting link between stars and planets if they formed from the same Giant gas cloud. The Population I entities with less than 0.07 Solar masses and below 0.09 Solar masses (Population II) are never able to fuse Hydrogen. So they are larger than the largest Gas giant planets and many times Smaller than the Smallest stars. They are called Brown dwarfs.
Let's see their general characteristics:
Mass and radius:
These objects are so massive than Common Jupiter-like Planets, usually they are 13 (Mj) Jovian mass times heavier and can't be more massive than 80 Mj because at this mass range, Hydrogen Fusion can be ignited. This is also how small a star can be if it fuses Hydrogen, of course. You may wonder no matter how much mass a Brown Dwarf holds, its Radius will always be around 1 Jupiter radius. when they are forming, they do accumulate gas and dust. it increases mass but Gravity compresses, making them denser rather than larger.
Fusion Method:
They fuse Deuterium which is a type of hydrogen. Imagine Normal Hydrogen has 1 proton and 1 electron but with these, Deuterium has 1 neutron also, which makes it heavier than common hydrogen and Easily Fusable in low temperatures and pressures. For this fusion, the core's Temperature must be over 1 to 3 million Kelvin and around 1 Million Kg per cubic meter density, meaning If you create a 1-meter cube of this material, it would weigh a million kilograms. Now you can imagine how badly gravity packs such things.
In deuterium Fusion, Deuteron (particle of Deuterium) Collides with a proton (Ionized Hydrogen), creating Helium-3 and releasing a Gamma ray photon. Its energy is sufficient to cope with the Gravity's compression. It creates a pressure that stops the compression of gravity therefore, they are Balanced.
Temperature and Luminosity:
It is said that Brown dwarfs can have extremely low temperatures, you may wonder. The coolest brown dwarfs have a temperature less than the Freezing point of water. Their Luminosity is very low sometimes they can hardly glow in Visible light if they do it will be in their Earlier stages. Later on, when they create Degenerate Helium - 3 they gradually lose their brightness as they spend their time. The majority of Brown dwarfs emit their radiation in the Infrared part, which means they won't be visible to human eyes.
Their temperature can vary from 600 Kelvin to 3500 Kelvin We'll also discuss on their types like we do for stars.
Formation and Life Cycle:
Now this is the most interesting part, we know that Stars form in dense molecular clouds or Stellar Nurseries. The cloud starts to collapse once the Jeans mass is exceeded, which lets gravity compress the cloud and bring its particles closer and closer after some million years. At a point where the Center of the gas cloud generates heat by gravity and the outer layers of the cloud are dense enough to trap heat inside.
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| Protostar : Creating Brown Dwarf |
When the Central temperature and Density reach, respectively, around 1 million K and 1 Million Kg per cubic meter, it begins to fuse Deuterium, producing helium-3 nuclei which accumulate inside where this fusion is going on. we also said in this process, gamma rays are also released in the form of Energy. All these events try to stop the gravity and make the system stable where it neither collapses nor explodes. The most important step in their lives is failing to reach the appropriate Temperatures and densities of Hydrogen Fusion. So they keep fusing Deuterium while a Massive Brown dwarf (65 Mj) can fuse lithium, which is still not enough to become a star.
In this period, The Brown dwarfs look like mini stars in many ways. they have Relativistic jets and Accretion disks. However, their gas-dust feeding process is much slower than the Stars. Remember, if we see a protostar with the same features, we can't tell its future until we know its disk turbulence, mass accumulation and ejection rate. For normal human eyes, we can't tell whether the protostar will create a Star or a Brown dwarf, even though scientists often say star formation is a violent process, while Brown dwarf formation is relatively calm, but they both come into existence from Cosmic tornadoes or Storms. all these are violent processes for us humans.
We see that Gravity was trying to compress the sphere of gas and increase the Temperature As a result, the fusion ignites, which halts the collapse and now the star will spend some time in this stage. Some million years later, it does accumulate gas and dust, but at a slower rate, which will make the star weaker if there is no increment in mass-acquiring rate. It keeps fusing deuterium and creates degenerate helium-3. Since gravity is not aggressive and fusion is also appropriate, It will remain in this stage otherwise Normal stars would go beyond this stage when gravity becomes more powerful so it has to find a new way to fight the gravity but Brown dwarf never enter that phase So it will remain Jupiter sized deuterium fusing Gas giant which is 13 to 80 times massive than Jupiter.
The Deuterium fusion only occurs at the early stages of the Brown dwarfs but after some million years, it starts to cease gradually due to the degeneracy of helium-3, so the brown dwarf is completely balanced. it will slowly cool down and become Black. it won't emit any visible radiation. however, it will remain a Stormy Jupiter-like planet. Brown dwarfs don't die they will remain at this stage, like a completely dark hell. Some theories tell us Brown dwarfs expel some of their material as the Gas giants do, in this way they can lose their mass, but it won't be significant. As the Time will pass, they will become colder and colder, changing their color and They go through M to Y class in their lives. Keep in mind, a 65 Mj Mass Brown dwarf, may not lose its material to become 13 Mj Object So They will only change their color like Y dwarfs.
Like Stars, they have their own worlds. Let's see their Types.
Classification of Brown Dwarfs :
Their Classification is based on (a) Spectral studies, on the
basis of Chemical signatures. (b) Mass, because a
15 Jupiter mass BD (Brown dwarf) will be completely
different than a 70 Jupiter mass BD. (c) Temperature,
which varies greatly in Brown dwarfs and decides their
evolutionary stages. So those 3 contribute to their classification
mainly along with other minor factors. Keep in mind, The Brown dwarfs
are not the original part of
The MK System, they were added to fill the gaps between planets and Stars. In MK
system, Brown dwarfs are categorized as M, L, T, Y, From
Hottest to coolest. Let's know more about them But first,
you can look at this table below showing Mass, Temperature and their
important feature in the spectra.
M Type )
In the original MK system, M Class Represents is devoted to Stars but Modern discoveries have shown that Many of the M-Main Sequence Stars or Red dwarfs do not behave like normal stars. Instead, there were signs of other molecules in their spectra, which raised doubts among Scientists. Later on, it was found that later than the M5.5 class was abnormal than the rest of the stars. However, not all late M dwarfs (Later than M5.5) show this anomaly. Now, they are categorized as Brown dwarfs. Their main feature is that they fuse Lithium instead of Hydrogen, which is the key feature of Objects around 65 times heavier than Jupiter. All M Brown dwarfs are in their early period of their lives; they have recently left the protostar phase around some million years ago. they will eventually cool down and be categorized as later and cooler groups in Brown dwarfs. you can see and compare in the image below.
L Type )
These dwarfs are a little bit older than the previous group as they have cooled down, lost some of their luminosity and will spend some billion years here in this class. their key feature is that 13 Mj dwarfs can Start Deuterium Fusion, hence they are balanced. All the entities we are talking about originated from the Gas cloud collapse process, which gives birth to stars.
We are discussing the objects that have failed to become a star, meaning they failed to Start Hydrogen Burning. In human eyes, L dwarfs will look truly Red and Brown; in some respects, they are true Brown dwarfs by color. You can look at the table below.
T Type )
These Brown dwarfs are so old, meaning they formed earlier than previous categories, due to the temperature loss they have reached in this group. This kind of Brown dwarfs are very hard to detect due to their low luminosity.
The Infrared is a widely used method to detect them. Their mass is very low, like Gas giant planets. Their blue-magenta look comes from Methane Absorption. We'll discuss their similarities and differences in this post ahead. for now you can look at the chart here.
Y Type )
These are the coolest brown dwarfs, They may have the temperature of the common room, just around 20 to 30 degrees Celsius. At this point, it is very hard to distinguish between a planet and a Brown dwarf with the same mass. Since they are cool and emit little to no visible light, their appearance will be Dark grey or completely black. Someone might call them a black dwarf but that is a totally another thing. For more info you can check in this image below.
The Dual Nature
Since Brown dwarfs sit between Stars and planets, they share many
features of both as well as their own properties. Let's see their
Stellar and Planetary Features. Mind it! These properties can only be
found in Brown dwarfs.
Stellar Features
First, they are born like Stars, meaning the gas cloud collapses and creates a protostellar object but never achieves the required condition to Burn Hydrogen. We have repeated it many times. Sometimes, an Accretion disk around a brown dwarf triggers the Dust and gas collapse process in its various spots and creates Planets.
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| Brown Dwarf - In Proto-star Stage, Showing Star like Features. |
It's too common for Brown dwarfs to be orbited by Planets, like Stars. If there were two independent gas clouds compressed by gravity, they could create Two Brown dwarfs, and they would behave like Binary partners or Substellar Siblings. Just like Stars, where most of the stars are Binary, trinary or multiple star systems the majority of brown dwarfs are also Binary components. They can become Binary partners in some star systems as well. During their formation, they can eject Jets or Outflows like solar wind or Stellar winds.
Planetary Features
If a Brown dwarf is captured by the Gravity of another Star it can also orbit the parent star just like planets. Scientists have found that so many brown dwarfs behave like planets when they are trapped in the powerful gravitational field of common star, White dwarf or Neutron Star. Sometimes a Brown dwarf can have rings like Saturn. Low mass Brown dwarfs like T and Y dwarfs have an atmosphere and weather as we see in our Jupiter or Saturn. It is so hard to differentiate between Star, Brown dwarf and planet in this condition. Only well-detailed observations can distinguish it. They may create Aurorae or polar lights in their poles, which is the main feature of the planet.
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| Brown Dwarf as a planet with Two Large Moons |
T and Y class Brown dwarfs, sometimes also referred to as Rogue planets, meaning they don't have any star or stellar remnant to orbit but they directly orbit the Galactic Center by themselves. Our Earth and the entire solar system orbit the Galactic center indirectly Because Everything in the solar system orbits the Sun, which is itself moving around the Central part of our Galaxy Milky Way. Just like our Moon Orbits Both the Earth and the Sun, since the Moon orbits the Earth and it is revolving around the Sun. This Feature may or may not exist in brown dwarfs, depending on their presence of the parent object.
Brown dwarfs like other Objects :
You now know that Collapsing clouds can create the ingredients of the Universe but it starts with atoms and molecules like ultramicroscopic particles. In any such Stellar formation zones, it will collect sub-atomic particles, after many thousands of years, it creates somewhat larger Micron or millimeter-sized particles and this process continues until a star is born completely. However, this process is delicate and long-lasting; numerous obstacles may prevent or corrupt the actual rate of growth or sometimes change the fate of the stellar nursery. It is like if a Caterpillar Larva hatches from the egg, it has to face unnumbered difficulties and challenges that we're not gonna talk about; instead, you can imagine by yourself.
Imagine, in a stellar nursery, Things didn't go right What happens? There is one outcome, which is that it may create a planetary mass object if their dust and gas eating is interrupted by Immense radiation from O or B-type Stars, feels a shock wave of the Supernova Explosion or some powerful energetic events like Jets from Black holes, Gamma ray bursts or any powerful event. Such objects' growth will be stopped for some time or forever.
They will become planetary mass objects and not be bound gravitationally by a massive object. They will start orbiting the galactic center slowly or ejected from their birthplace because O and B-type Stars can cut the cloud into many pieces through their immense radiation or the proto-stellar core we described earlier can lose its outer layer by a process called photo erosion. in which, Primitive core loses its outer layers and heavy radiation prevents the further Evolution and such object will now stop its growth getting a size of Asteroid, planet or Gas giant or a brown dwarf depending on which point it faced interruption.
That's why we have so many Rogue planets, many of them were ejected by their fellow planets' gravitational effect or formed in accretion disks and now kicked from their place like orphans. If they are caught by a massive object's gravitational field, they become its planet or sometimes crash into another planet or object. We should not say they are orphans, they choose to orbit the Central region of the Galaxy instead of joining a Stellar system. It is also one of the reasons why some brown dwarfs behave like planets, while some remain in the interstellar medium acting like a complete system where they have their own planets, Asteroids, meteors, and Moons like an entire mini or Dark Solar system. while some become binary partners.
JuMBO :
We've stated that if any object's formation is interrupted when it has the mass of a planet, it behaves like a Rogue planet. Scientists classify such objects in Class P, which is dedicated to Interstellar planetary Mass objects. You Remember Dumbo Jumbo from old cartoon? It may sound funny, right?
In 2022, our beloved James Webb Telescope found some 540 objects near the Orion nebula and 42 of them were Binary. Their masses ranged between 0.7 to 13 Jupiter masses, meaning many of them are rocky planets or moons and Jupiter-Saturn-like gas giants. They called these Binaries "Jupiter Mass Binary Objects or JuMBO".
Their formation theory is similar to what we've discussed in the last Section. We should not forget that the entire Orion constellation is a center of Stellar Activity where Massive Stars like the O and B groups reside there and it is an active stellar nursery where around 180 Stellar forming zones have been discovered so far. They may have faced the same consequences as in the Previous Section. They are different from Brown dwarfs because they are planets and Brown dwarfs can be anything from a Planet to Failed Star. They are objects with bad fortune but still they are fine, which tells that no matter the situation and consequences, stay happy and bold.
Imaginary Scenarios :
We always think theoretically on Unreal Scenarios in our posts. It's good to discuss on Some interesting phenomena which increase our Critical thinking abilities. There are two possibilities in this situation first the sun would formed as a Brown dwarf or Later become one.