About: Suns

[Christopher]

It happens regulary that someone ask for a good name for a Stellar Super Hero (sun powered theme, ex-astronaut). And of course it helps knowing how our immediate stellar neighbourhood looks like and what types of Stars are out there.

I happen to know this area a bit (read a lot about it on Wikipedia), so I though I write this down as a reference for others.

 

Gas Giants:

Practically every Gas Giant is a failed Star. Or stars are just really big Gas Giants. Every Gas Giant heavier then 13 Jupiter masses is a candidate for a Brown dwarf.

 

Brown Dwarf:

These occupy the border between "Gas Giant" and "Star". The one reason they are not your average star is that they do not fuse Hydrogen-1. They still have fusion going on, the elements being fused depending on mass:

Beginning at 13 Jupiter Masses they a thought to Fuse Deuterium (the lower limit)

Beyond 65 Jupiter Masses, they also Fuse Lithium.

Thier upper limit is around 75-80 Jupiter masses (at wich point Deuterium Fusion starts and they become Red Dwarfs; 0.075 Solar Masses)

They are still considered Stars by Astronomers, and the closest know Brown Dwarf System is Luhman 16 (Brown Dwarf Binary System, 6.5 LY).

They have four sub-classes (M, L, T, Y).

Thier Coloration tends to be Magenta or a Orange/Red (they are not actually brown). Actual luminostiy is very low, due to low temperatures and low size.

Thier radius is regardless off mass very close to Jupiters, either being held up by Cloumb force (lower mass end) or Electron Degeneracy Pressure (high end, like in White Stars).

Lifecycle: Burning off thier Fuseable Material, then cooling down to gas giant temperatures (below 1000 K). They are the only stars not able to become a White Dwarf, Neutron Star or Black Hole.

 

Red Dwarf:

Judging by thier abundance in Earths Neigbourhood they are the most common type of Star in the Milkyway (due to thier low brightness, they are hard to find at long range). Estimates asume up to 3/4 of the Stars being Red Dwarfs.

They are also incredibly long lived, with lifetimes ranging in the Trillions of years. At the current know age of the Universe, no known evolved Red Dwarfs can exist.

They are also extremely stable, though to emit the same energy amount for almost thier entire lifetime.

Despite their abudance, longelivity and stability they are not likely candidates for extraterestrial Life, since the habitable zone is very close to the star (causing it's own problems for life).

While they do produce helium it never quite gathers at the core and even if it did, they lack the mass needed to fuse helium.

Thier massrange is between 0.075 Solar Mases (needed for Hydrogen Fusion) and 0.5 Solar Masses (beyond that main Sequence Stars start).

Lifecycle: They are though to just "brun out" into helium based White Dwarfs, without any supernova or similar step. However at the curent age of the universe not one should have burned out yet.

 

Main Sequence Stars:

A large group of Star Spectral Types wich occupy a large mass range. Our Sun belongs into this group.

 

Orange Dwarf/K-Type main Sequence Star:

Mass ranges from 0.6 to 0.9 Solar Masses.

3-4 times as common as Sunlike (G-Type) stars and stable for a lot longer (15-30 Billion Years). This makes them Ideal candidates to harbor extraterestial life (in a way we can find it).

Lifecycle: Similar out Sun, but longer time before they become Red Giants.

 

Yellow Dwarf/G-Type main Sequence Star:

Our sun is one of those. It is an early third generation Star.

Mass Ranges from 0.8 to 1.2 times Solar Mass.

They are colored White to slightly Yellow (for the lower masses).

Lifecycle: They sustain for about 10 Billion Years of Hydrogen Fusion, while building up masses of Helium in thier Core. Then they enter a short 130 Million Years as a Red Giant (fusing off the Helium and expanding up to earths orbit). Eventually that Red Giant burns out into a Stelar Nebula and a White Dwarf, without any Supernova.

 

Red Giant:

Practically every Main Sequence star leaves the Main Sequenc to become a Red Giant and fuse off all that Helium

Rather shortlived and cool, but surprisingly big (and thus luminous).

They sustain mostly on Fusion of Helium, producing Oxygen and Carbon.

 

White dwarf:

The most common fnal stage of any Star out there. Up to 97% of all Stars will eventually end as White Dwarf, inculding our Sun.

Depending on the starting mass of the Star thier elemental makeup will be different:

Red Dwarf based White Dwarfs are theorethized to consist almost entirely of helium, but no red dwarf should have evolved that far yet.

Currently the most common consist of leftover Oxygen and Carbon from the Red Giant phase of main Sequence stars.

If the progenitor is between 8 and 10.5 Solar masses it will also fuse the Carbon into Magensium and Neon.

Due to massloss some heavier ones might consist of helium as well (lost so much mass they could not fuse it off as red giants, despite having enough starting mass for that).

Beyond 10 Solar mass of the Progenitor, you instead get a Neutron Star.

They do not undergo fusion and thus produce no more energy, but slowly emit thier leftover energy over incredibly long times.

Since they have no Fusion to support them they "collapse" until only Electron-degeneracy presure keeps them stable against thier own mass. It's so heavy it does not even has proper atoms anymore, but consists entirely of elemental particles (electron, proton, neutrons) kept appart only by the Pauli Principle.

Lifecycle: They are though to eventually cool of into Black Dwarfs, but due to the time it takes for them to do so no Black Dwarfs should exist at the current age of the Universe. The exact time for this to happen cannot be calculated right now.

 

Neutron Star:

They are what is left from very heavy stars (10 Solar masses or more) after they explode into a Supernova. The core colapsing to Neutron Star densities is indeed what starts the very important Type II Supernovas.

They are so heavy the Electron-degeneracy pressure cannot maintain them and the Portons and Electrons are "fused" almost entirely into Neutrons. The only thing keeping them from Collapsing further is quantum degeneracy pressure.

Thier mass ranges from 1.44 Solar Masses (the upper limit of white Dwarfs) to 10 Solar Masses (minimum limit for Black Holes). But slightly "overmassed" Neutron Stars are though possible (by later addition of mass and kept stable by other quantum physical effects).

 

Exotic Star:

A mostly theorethical subtype of a very heavy Neutron Star. In theory so heavy that the Neutrons cannot maintain themself and it instead consists of subatomic particles - Quarks, Preons, Bosons and the like - without collapsing all the way to a black hole.

 

Black hole:

What happens if a Star between 10 and 25 Solar masses ends. It is so heavy that not even Quantum Degeneracy Pressure can stop the colapse and it goes all the way into a singularity (a point in space time without any dimension), effectively making them infinitely dense.

According to general relativity they do not emit any radiation, since nothing can escape them. However, quantum physics predicts that it does emit radition (in a way that does not need anything to escape) - inversly proportional to thier mass (Hawkins radiation).

They can grow by eating other mass - including other black holes - and it is though that the supermassive black holes at the center of many universe have formed from many early black holes.

 

Primordial, small Black Holes:

There is a theory that shortly after the big bang really small black holes might have formed (anything from Plank Mass to a few hundred thousand solar masses would be possible in the early universe).

The very small ones at least might loose more energy from Hawkins radaition then they eat from cosmic background radiation. If one such black hole looses enough mass, it would explode (evaporation).

Finding a small, primordial black hole while it explodes would be the primary way to proove Hawkins Radiation.

 

 

Stellar Fusion:

In general Stellar Fusion works differently then Fusion as we atempt it for energy generation. Stars are actually way to light, big and cool for conventional Fusion, only the Quantum Tunnel Effect combined with thier incredible amounts of fuseable materials allows them to burn like they do (and is one reason they hold that long for thier mass).

Another way to look at it, is that anything heavier then a Brown Dwarf would automatically colapse into a White Dwarf, Neutron Star or Black hole if they did not have fusion to stave it off that long.

Thus ultimatively a Stars lifetime is limited by wich Elements it can fuse off. The mass defines wich elements can be fused (as higher mass means higher pressure and temperatures at the core). But even the heaviest star run into the ultimate stopgap: Iron+Nickel. Once a Star fused all the way to a Iron/Nickel core it is doomed as neither can be fused without loosing energy.

Star life shorter the bigger/more massive they are and later fusion phases last generally shorter then earlier ones.

[Lord Liaden]

I'm now wondering if I have a thick enough skin to play a size/mass-changing character called "Gas Giant."

[Cancer]

Something you omitted (because little is known): free planets, that is, planets that orbit no star.

 

There are a number of processes that must produce these, even if planets are only formed as a by-product of (i.e. with) stars. Exceedingly difficult to detect, such things have a lot of advantages for, e.g., space pirate bases.

 

I am not sure what the best guesses as to the estimated population of these things is now, but in my copious free time I'll look.

 

Another detail is that different classes of stars have different distributions in the Galaxy. If your campaign spans only a hundred parsecs or so, this doesn't matter. If it runs a thousand parsecs or more, then this could be realistically included for flavor. In general, the younger (and shorter-lived) the type of star, the more concentrated it will be toward the midplane of the Galaxy (and quite by accident, our system at this time is just about spang on the midplane).

[McCoy]

 (and quite by accident, our system at this time is just about spang on the midplane).

 

In the longer view of things, how inclined is Sol's orbit to the mid-plane?  Do we stay somewhat close to it, or at the extremes are we really far above/below it?

[Cancer]

I don't think we have the data to say. We know the magnitude of the Sun's velocity in each direction (toward the center in the plane, spinward in the plane, and perpendicular to the plane). That would be enough if the Galaxy could be adequately modeled as a point mass, or any smooth distribution of mass really, but we don't know the mass distribution well enough ... that is part of the dark matter problem. You could make assumptions and project an orbit, but I don't think anyone should pretend to believe it.

[DShomshak]

I have always seen red dwarfs listed as part of the Main Sequence.

 

Another important datum about red dwarfs: Most of them are flare stars. Every now and then they release gigantic solar flares that actually shine several times brighter than the star itself. The flare also sends out a humungous blast of hard radiation. So, even if a planet formed in the red dwarf's habitable zone, any life-as-we-know-it would get fried.

 

Which means that planets around red dwarf stars might have life as we don't know it. The ecosystem might even need periodic radiation blasts to survive.

 

Dean Shomshak

[Christopher]

I have always seen red dwarfs listed as part of the Main Sequence.

But actuall astronomical defition puts them out of it/below it.

 

And one addition I had forgotten the first time.

 

Wolf-Rayet Star:

Our sun looses about 4.2 Million Metric tons per second due to fusion (what you get when you take it's energy output and feed it into E=mc²*). It also looses about 1 Million Metric tons to solar wind.

Very big stars (around 20 Solar masses when they were early stage) have significantly stronger winds, in parts billions of time stronger. These are the so called Wolf-Rayet star. Since bigs stars also tend to have distinct "layers" of materials, this leads to them throwing away thier hydrogen (and sometimes even the helium) layer fast due to solar wind. Such stars will go up in a Type 1b or 1c supernova wich contains the higher elements, but surprosingly little Hydrogen (and Helium).

Due to thier winds they have immense brightness and radiation output, but most of that in the higher X-Ray and UV spectrum.

Not all type 1b and 1c Supernovas are from Wolf Rayet star however. A signficant part of them come from loosing stellar mass/out layersdueo other soruces, like a close companion star, a passing massive object (black hole, neutron star, other star) and similar events.

 

 

*Under ideal fusion scenarios that would still only be 0.7% of it's mass over the entire 10 billion year Yellow Dwarf phase. That is the weight difference between 4 Hydrogen and 1 Helium atom. Due to sub-ideal fusion situations, only about 1/10 of that will actually fuse off (the rest either was already heavier elements or sticks around for the later fusion phases).

[Cancer]

Red dwarfs are things that are all main sequence stars. Now, some may be given the term "subdwarf" because they are metal-poor and therefore appear below/to the left of the main sequence in an H-R diagram, but they're still fusing hydrogen into helium in their cores, which is the theory-based definition of main sequence stars.

 

Wolf-Rayet stars are very luminous and almost certainly started out much more massive than what we now observe. Not an environment you want to be in.

 

Lots of other sorts of chemically peculiar stars exist (and not all of them are in Wikipedia ) ; I hesitate to go into those.

[DShomshak]

Set aside your scruples, Cancer, and do so. Wikipedia is a good place to begin learning about a subject, but it's a terrible place to end. (And while astronomy books for laymen such as Philip's Atlas of the Universe by Patrick Moore are nice places to start, too, they have their limits, too. Give us the astrophysical freak show!)

 

Dean Shomshak

[Old Man]

Did you just call Cancer an astrophysical freak?

 

 

 

[Cancer]

No, Cancer opened up his barium-astatine star and put his head up it.