Red giant or not red giant

[schlowi123]

Another conundrum.

When I hear "red giant" I imagine a star very different to a "red dwarf". But then I saw Byua Chrea YP-G d10-122 B and Byua Chrea YP-G d10-122 C.
These two are not really very different from each other. However, the first is a giant (with less than 0.5 solar radii!) and the latter is a dwarf.
And I've found several supposedly "giants" with such small size

So, again I ask: does anybody know what's going on?
Is the stellar forge trolling me?
In that case: fine, I will give up on searching things that include stars with this characteristic.

It just would be nice getting something of a "confirmation" or a "field report" from more seasoned commanders. Even it says something along the lines "Yeah, there enough of such "hickups" and it doesn't make much sense looking for them in the EDSM-data"

 

[RolloTreadway]

There are quite a lot of mini giants out there. I think - someone correct me if I'm wrong, please - that the undersized red giants are dying red dwarves, not massive enough to swell up much beyond their original size as fuel runs out.

 

[RolloTreadway]

Come to think of it, maybe I am wrong. Isn't the universe a few billion years too young for red dwarves to be dying?

I'm out of my depth here. Sorry.

 

[Sapyx]

Yes, the Stellar Forge does have some issues with "baby giants" - allegedly giant stars that are about the same size as (or even smaller than) a perfectly ordinary star of the same spectral class. You'll notice that the "heat" generated by the baby-giant star is still much greater than the regular star puts out - any planets orbiting them will be much hotter than planets orbiting a dwarfs are at the same distance, even though the luminosities ought to be identical.

As for "dying red dwarfs", Rollo's second post is correct - the universe isn't old enough for any red dwarfs to have started dying yet. According to current theories, the internal structure for red dwarfs is different to that of hotter stars like Sol. Bigger stars have a "core" where most of the fusion takes place, and a "convective layer" that slowly transfers the heat from the core out into space. Red dwarfs don't actually have a core, so the entire star is one giant "convective layer". As such, they will never attain a "giant" stage. They will simply get cooler and cooler as the hydrogen fusion fuel inside them gets more and more dilute, until after a trillion years or so, the fusion will finally cease and they'll become cold dark balls of mostly-pure helium - a "black dwarf", not entirely different in appearance to a "brown dwarf", only bigger.

 

[Heavy Johnson]

All red giants that I am aware of have radii at least ten times that of Sol.

 

[Ian Doncaster]

The key is that Byua Chrea has Sol-relative sector coordinates of -1, 45 - and this places it within the suppression cross which means that certain bright stars are not procedurally generated (believed to be a stellar forge bug where avoiding procgen of unknown bright stars near Sol got out of hand). One of the effects of this is that red "giants" end up suspiciously small. If you move a little further "west" they'll go back to normal size.

 

[RolloTreadway]

All red giants that I am aware of have radii at least ten times that of Sol.

On the contrary, of all the stars I've found that are designated in game as 'red giant' (not counting those already known about, Arcturus, Aldebaran etc), the actual giants have been a tiny minority. I get a bit of a shock now if I fly to an M class star and it turns out to be on the big side.

(EDIT: I mean, an M class that's described in game as giant. Obviously I don't expect the average red dwarf M to be very big.)

 

[Sapyx]

I had not considered that as a possibility. I knew "the cross" suppressed the formation of black holes and neutron stars, but had not considered the effect on giants.

 

[RolloTreadway]

The key is that Byua Chrea has Sol-relative sector coordinates of -1, 45 - and this places it within the suppression cross which means that certain bright stars are not procedurally generated (believed to be a stellar forge bug where avoiding procgen of unknown bright stars near Sol got out of hand). One of the effects of this is that red "giants" end up suspiciously small. If you move a little further "west" they'll go back to normal size.

Is there a map of the suppression cross anywhere? I may have been spending too much time within it.

 

[varonica]

Come to think of it, maybe I am wrong. Isn't the universe a few billion years too young for red dwarves to be dying?

I'm out of my depth here. Sorry.

Make that trillion and you would be correct, most dwarf stars have a lifetime measured in trillions of years, that's why the majority of stars in the galaxy are dwarf stars, every single dwarf star that came into existence since the beginning of the universe (well except those swallowed by black holes and etc) are still here. Eventually the proportion of dwarf stars that make up the galaxy will exceed 99%.

 

[Ian Doncaster]

There's a picture here - https://forums.frontier.co.uk/threads/mind-the-gap.373259/ - I think there are better ones made more recently, but you can see it clearly enough on this one.

EDIT: and much clearer on this one, taken about a year after the first: https://forums.frontier.co.uk/threads/neutron-star-discovery.431719/#post-6775285

 

[Interstellar Overdrive]

Confirmed. Orange giants seem to work fine though. I see plenty of procgen K giants.

 

[schlowi123]

Thank you very much for all the thoughts and prayers discussion. This was so much more than I had expected .

I take away the following: There are enough so called red giants out there, which have radii smaller then Sol. This makes my approach to a certain problem somewhat useless in this case as I suspected.

Btw. this phenomenon (tiny M (Red giant) Stars) is not restricted to "the suppression cross"; see for example Stuemiae SO-O d7-472 B.

 

[Heavy Johnson]

On the contrary, of all the stars I've found that are designated in game as 'red giant' (not counting those already known about, Arcturus, Aldebaran etc), the actual giants have been a tiny minority. I get a bit of a shock now if I fly to an M class star and it turns out to be on the big side.

(EDIT: I mean, an M class that's described in game as giant. Obviously I don't expect the average red dwarf M to be very big.)

No, I mean actual red giants not inside the game world.

 

[RolloTreadway]

No, I mean actual red giants not inside the game world.

Ah, apologies.

 

[Wobblin-Gobblin]

I've noticed such a star, too. I've opened a ticket, FD corrected it.

 

[schlowi123]

Recent events made me analyze the radii-distribution of all reported M (Red giant) stars.

So far 45,140 are reported in the EDSM database (in the bodies.json-file from 2019-05-18).
The radius distribution looks like this:

W! T! F! F!

More than 65% of all all red "giants" (!) have a radius smaller (!!) than one Sol radius!!!
Some giants these are! And the long tail is because of one real red giant with approx. 602.9 solar radii (and some other real giants in between).

So it seems we have a bifid distribution. But wait! There is more!
Let's look at the first large peak in more detail:

Wait! What? This splits into three distinct peaks! Would somebody please explain this to me?
Please take into account that the bin size is just 1/1000-th of the first picture. Thus the quantity in each bin is much smaller.

So we now have a fourfold split distribution. But wait! There is more!
Let's look at the second large peak in more detail:

Wait! What? This is an underlying broad but "shallow" distribution between ca. 10 and 120 solar radii and a sharp and steep second distribution around 30 solar radii.

So we now have a fivefold split distribution. But wait! There is more!
Let's look at this large peak in more detail:

Wait! What … the hell is going on here? This is an assymetric distribution that looks like a shoe … øhm … I mean like Sol's spectrum.

That leaves us with a fivefold++ split distribution.
I'm at a loss! The galaxy is up to something … or some kind of nepotism of the dwarfs is going on inside the stellar forge.

If anybody has an explanation for all that, please share it with me.

And apropos dwarfs, these are much more; 9,727,497 in total. Well, most of them are smaller than Sol. But more than 1,000 of those "dwarfs" have a radius more than 29 times larger than Sol's.
And their radius distribution around … … ah well, here it is

UI … looks like two overlapping peaks. And yes! the sinusoidal pattern on top is real:

I don't know what to do with that knowledge. Instead of clarity an analysis brought up more questions. That is SO typical.
But that is another issue and to come back to the topic at hand: What is a (somewhat) agreed upon radius for a M (Red) Star to be accepted as giant star? Accepted by the community that is. What FDev labels them is … øhm … different.

 

[Orvidius]

Some cool analysis there! Yeah, there are some things that I'm at a loss to explain. I never took that close of a look at the giants. Most of my data-crunching is at a more "high altitude" broad overview level, plotting them on maps.

 

[schlowi123]

I could not do these visualizations and have the utmost respect for them. They are extremely useful and were the original inspiration for many of my leisure time activities since last year November.

I've seen more patterns in other data. E.g. the distance distribution of planets that could be binaries … OMG! … no! no! NOOOOO! Please not, brain! Don't give me ideas how to waste my valuable time with the analysis of not even real data. I'll try to resist

 

[Sapyx]

But that is another issue and to come back to the topic at hand: What is a (somewhat) agreed upon radius for a M (Red) Star to be accepted as giant star? Accepted by the community that is. What FDev labels them is … øhm … different.

The link between a star's mass and its spectral class is much, um, "weaker" in ED than it is in the actual galaxy. The largest "red dwarf", the M0V class, are up to 62% of the Sun's radius. Any bigger, and the star will become too hot to classify as Class M, and instead become a class K "orange dwarf".

Note that this is for luminosity class V ("main sequence") stars. Class IV (subgiants), class III (giants), class II and I (supergiants) are larger but have evolved from smaller, hotter stars that are nearing their end-of-life cycle. However, "Class M IV red subgiants" do not exist; the universe is not yet old enough for the small stars that theorietically would form into such objects, to have done so.

There is, therefore a distinct "gap" in sizes of Class M stars, between the regular Class V red dwarfs (which end at around 0.62 solar radii) and the Class III red giants, which start at around 10 solar radii. The ED galaxy has much more of a continuum of sizes.

Finally, to addres your earlier questions about the origin or reason behind the patterning and clumping of data around certain points. It is best explained by the vagaries of the Stellar Forge, the equations ED uses to generate the stars in the galaxy. Look hard enough, at enough data, and you will see such inexplicable patterns wherever you look at the data from the ED universe.

For example, check out this graph I made of the surface conditions of Earth-like worlds, specifically, comparing the atmospheric pressure and the surface gravity:

You would not expect any kind of pattern to appear in real-universe data of thousands of Earth-like planets, but a clear pattern emerges here in this ED-erived data set: there are three distinct "groups" of ELWs, forming three separate lobes on the graph. Why? We simply don't know. It's not connected to star class, or mass code, or anything we can detect. It's "just how the Stellar Forge makes ELWs", a pattern that emerges out of the chaotic interaction of the Stellar Forge equations.