New star generator for other galaxies... (work in progress)

[Cham]

Easy !

What is this about ?

Okay, this is work in progress...

[Hungry4info]

M31's central binary black hole?

[Cham]

M31's central binary black hole?

It was already done, long time ago.

Guess again !

Well, here's a clue (easy !), since you're talking about this object...

This is just a prototype for now...

EDIT : I must admit that I'm pretty excited by this new toy ! Space feels soooo vast now, geez this is impressive !

[Hungry4info]

The M31 galactic core?
Yeah I know that's little different from the first guess. All I know is you're in M31, and in its inner parts, and there's a bunch of stars.

[Cham]

The M31 galactic core?
Yeah I know that's little different from the first guess. All I know is you're in M31, and in its inner parts, and there's a bunch of stars.

You're close !

EDIT : Some progress (hmmm, need more work on this, but it's going well...)

[Hungry4info]

You're populating the entire galaxy? How many stars?

[Cham]

Yes !

I'm building a full star generator. I intend to put around 50k stars in the Andromeda galaxy (and maybe some others too). I want the population to be reasonably realistic (the stars should give a proper HR diagram, in my HR LUA tool). For the moment, just main sequence stars.

On the pictures above, the magnitude is grossly exagerated, so I can see the whole distribution while tuning the parameters.

The disk distribution should also be properly oriented with the galaxy model in Celestia.

[Hungry4info]

Very nice, very nice. I've considered doing something like this before, and adding randomly generated planetary systems for them.

[Cham]

Very nice, very nice. I've considered doing something like this before, and adding randomly generated planetary systems for them.

Well, my star generator doesn't add planets. Just plenty of stars on the main sequence.

More later...

EDIT : Here's an HR diagram (from the LUA Tools) showing the distribution of a sample of 2000 stars from my new generator. Maybe the curve needs some adjustements.

Stars from other generators (the old generator from Rassilon, for example) doesn't give realistic distributions, on the HR plot.

[Cham]

Now I have a question for everyone : how should I name all these fictious stars in the Andromeda galaxy (M31) ?

Currently, they are named as "And" followed by a random number.

I could add a set of names randomly selected (with numbers), as this :

"And 124569"
"M31-34672"
"Toto 35678"
...


Suggestions ?

Once done properly, the STC files (various numbers of stars) will be published...

[Cham]

I got the orientation right, by trial and error (I still need a systematic way to do this, to ease the creation process to other galaxies in our local group).

The stars luminosity is grossly exagerated on the pictures below, so we could see the whole distribution. Currently, there are 10 000 stars in there. I could very easily change this to 50 000 stars globally (I want more in the central core). 10k stars gives an STC file of about 1.4 MB.

I have to tweak a bit the HR curve for more "realism", to change a bit the statistical distribution on the galactic thickness (especially for the central core), and to choose better star names (what are your suggestions ?).

People would have fun to add all sorts of Science-Fiction addons in-there !

[Cham]

I made some progress on the shape of the distribution. Again, the luminosity of stars shown below are greatly exagerated, so we can see the whole distribution. The AbsMag will be decreased to normal values when I'll be satisfied with the distribution) :

Front side (there are more stars on the bulge) :

Profile :

The distribution with the standard M31 galaxy :

There are 20 000 stars here. The distribution follow a classic main sequence curve on the HR diagram.

Before release, I need suggestions for the names. I don't think that it's a good idea to name all the stars "And ######" (where ###### is a random number).

[selden]

Personally I don't see any problem with using numbers as the suffix. I'd suggest using a prefix not related to the name of the constellation, though. That makes them too much like catalog designations for real stars.

[t00fri]

Cham,

I think your algorithm of generating (galaxy) stars is basically not correct, apart from their HR color distribution. There are several better attempts already in the net. In the first place, one has to take the basic inhomogeneity in star density into account that corresponds to the galaxy arms. Here is a close-up of the central quadrant of your M31 galaxy image.

Your star distribution is locally almost homogeneous, while the galaxy "arms" are still consisting of my nebula sprites blended in.

In contrast, here is e.g. an interesting site introducing a generator for (spiral) galaxies in terms of "stars only":

http://dmytry.com/galaxy/index.html
(Dmytry Lavrov's, a mathematically oriented software dev)

The galaxy generator may be downloaded freely. Unfortunately, it's not open source. A simple example thereof illustrates pretty clearly what I mean:

It's straightforward to derive a 2D probability distribution with an arm structure, such that the stars distributed according to it follows the right pattern. It can be easily coded with Von Neuman's well-known acceptance-rejection method that I have also heavily used in my galaxy (and globular) code for Celestia. A nice summary of that method is here, for example,

http://pdg.lbl.gov/2011/reviews/rpp2011 ... niques.pdf

Your star distribution might be useful, however, for modelling elliptical and irregular galaxies as well as nearby spheroidal dwarfs that all are lacking any arms. Also never forget to consider distributing your stars according to a Perlin noise function...

The best approach I can see is a blended one, depending on the actual screen resolution or -- equivalently-- the observer distance from the galaxy. As long as the observer is far away, a sprite-based rendering is fast and perfectly sufficient. Upon a closer approach, when the resolution improves a lot, a blended transition to individual stars should be done. A big advantage is that at close distance from the galaxy, one only needs to render a tiny portion thereof in terms of stars, since the rest is outside the field of view! With clever culling, this fact might make a real-time rendering possible...

Such a two-component rendering has to be set up in the core code, since it is clearly not feasible via add-ons (at least in Celestia).

Fridger

[Cham]

Fridger,

yes I agree with you, and I was also thinking about the arms structures. I may do something about it next.

However, even with 50 000 stars, once distributed on the whole Andromeda galaxy (which is even larger than the Milky Way), the density is reaaaally low ! With proper AbsMagn, we don't see much the stars (except the highly luminous O stars) while moving through M31 ! It's even a bit deceptive, actually !

Don't forget that I extremely exagerated the luminosity of these stars to see the whole distribution in Celestia, just to orient the distribution correctly relative to Celestia's model. Their luminosity (AbsMagn) will be adjusted to normal values before releasing the STC files.

From 50 000 objects on a total of a billion of stars in reality, it's just a very low sampling (a proportion of about one star for one million) ! Any structure (with or without the arms) doesn't matter at all in this case.

But I do agree that making arms would be interesting. It's a lot of work to make them fit with the model in Celestia, though !

EDIT : There's an interesting unexpected effect, while moving through the distribution : we really feel the vastness of space in Celestia with these stars. Without them, I always add the impression that the Andromeda galaxy was just a small model in Celestia (even if it's to scale !). I never had the feel of a very large space. In other words, the stars give a sense of scale which was absent before. This fact alone makes the addon really worth it !


About the names, what do you recommend, Fridger ? I'm thinking about a random selection of words, followed by a number. But which words ? Currently, it's "And ######". There's a constraint : the user should be able to select a star in M31 using the name in Celestia, while knowing by its name that it's a fictious one.