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

Post requests, images, descriptions and reports about work in progress here.
Avatar
Hungry4info
Posts: 1133
Joined: 11.09.2005
With us: 15 years 2 months
Location: Indiana, United States

Re: New star generator for other galaxies... (work in progre

Post #41by Hungry4info » 11.09.2011, 06:06

Cham wrote:
Hungry4info wrote:? Can you elaborate on this ? Some stars are unrealistic ?
One of the examples I found was a K1V star having a radius of 2,000 R[sub]sol[/sub], and a luminosity of a few million L[sub]sol[/sub].

I can get more specific details if you want, star names, etc, when I have more time.
Current Setup:
Windows 7 64 bit. Celestia 1.6.0.
AMD Athlon Processor, 1.6 Ghz, 3 Gb RAM
ATI Radeon HD 3200 Graphics

Reiko
Posts: 1119
Joined: 05.10.2006
Age: 37
With us: 14 years 1 month
Location: Out there...

Re: New star generator for other galaxies... (work in progre

Post #42by Reiko » 11.09.2011, 07:25

YAY!!!
I look forward to test your generator. :D

Avatar
Topic author
Cham M
Posts: 4325
Joined: 14.01.2004
Age: 56
With us: 16 years 10 months
Location: Montreal

Re: New star generator for other galaxies... (work in progre

Post #43by Cham » 11.09.2011, 11:56

Hungry4info wrote:
Cham wrote:
Hungry4info wrote:? Can you elaborate on this ? Some stars are unrealistic ?
One of the examples I found was a K1V star having a radius of 2,000 R[sub]sol[/sub], and a luminosity of a few million L[sub]sol[/sub].

I can get more specific details if you want, star names, etc, when I have more time.

Yes, I need more examples.

As I said, there are a few out-of-main-sequence stars in the core. Actually, a total of 169 stars of spectral type K, which are giants. These were made on purpose to colorise a bit the central galactic core and to match the yellowish-orange part of the M31 nebula model in Celestia, and since there are very old stars in this part, in reality (stars at the end of their life).

But if there are any anomalies, I need to know.
"Well! I've often seen a cat without a grin", thought Alice; "but a grin without a cat! It's the most curious thing I ever saw in all my life!"

Avatar
t00fri
Developer
Posts: 8772
Joined: 29.03.2002
Age: 18
With us: 18 years 7 months
Location: Hamburg, Germany

Re: New star generator for other galaxies... (work in progre

Post #44by t00fri » 11.09.2011, 12:48

selden wrote:Don't forget that the density of stars in the disk is almost uniform. Spiral arms stand out because they contain bright, young stars, not because there are many more stars in them.

Selden,

this subject is much more complex than popular Web pages tend to present it. The often quoted 50 year old qualitative explanation of the spiral arm formation is based on the so-called Density Wave theory,

http://en.wikipedia.org/wiki/Density_wave_theory

It states that the spiral arm pattern we see is actually a (density) wave pattern, that rotates independently of the almost uniformly distributed stars and inter-stellar matter in the galactic disk. Typically like so:

Spiral_galaxy_arms_diagram.jpg


(Astro)physicists like myself refer usually to the much more recent quantitative results of N-body simulation of galaxy formation by means of supercomputers. The simulated dynamics among the huge number N of considered particles comprises self-gravity, hydrodynamics, radiative cooling, star formation, and supernova feedback, to follow the chemical enrichment histories of both the stars and gas.

In straight contradiction to your above statement and the Density Wave theory, let me quote the very recent results presented also on this year's international conference of the Royal Astronomical Society (NAM21). These simulations allow to separate the density of disk stars and gas:

------------------------------------------------------------------------------------
MULLARD SPACE SCIENCE LABORATORY ASTROPHYSICS
Click!
m33sim.jpg


Caption: Stellar (left) and gas (right) density maps of a simulated galaxy similar in size to M33.
(from http://www.mssl.ucl.ac.uk/theory/images.html)
-------------------------------------------------------------------------------------

Here is the corresponding press release at the Royal Astronomical Society conference NAM21 that was widely reprinted:

http://www.ras.org.uk/news-and-press/21 ... alaxy-arms

The essence lies in this simulation result together with the quoted caption from Robert Grand's NAM21 talk:


Image Caption: Snapshots of face-on view of a simulated disc galaxy. A Brighter colour indicates higher density. The Image shows two examples of star particles: the red star are travelling at the leading side of the arm, and the blue star are at the trailing side. It can be seen that the blue and red stars interchange their radial distances, with rapid migration within 40 million years. The dotted lines trace circles with radii of 4, 5 and 6 000 parsecs (1 parsec = 31 trillion kilometres), to guide the eye.

click
grand.jpg

(Image credit: Robert Grand/UCL/MSSL, Copyright© 2011 Royal Astronomical Society.)

It is evident that the stars actually rotate with the arms!

Fridger
Last edited by t00fri on 11.09.2011, 15:27, edited 4 times in total.
Image

Avatar
Topic author
Cham M
Posts: 4325
Joined: 14.01.2004
Age: 56
With us: 16 years 10 months
Location: Montreal

Re: New star generator for other galaxies... (work in progre

Post #45by Cham » 11.09.2011, 12:59

Fridger, have you tried the files I gave above ?

I need to know if there are unrealistic stars (too big ? Too luminous ?), so I can fine tune my code.

The biggest star I've found is located in the core (second STC file). It's a giant K star with a size of 2700 Rsol (this one is out of the main sequence, as I said earlier, and it shows on the HR diagram).
"Well! I've often seen a cat without a grin", thought Alice; "but a grin without a cat! It's the most curious thing I ever saw in all my life!"

Avatar
t00fri
Developer
Posts: 8772
Joined: 29.03.2002
Age: 18
With us: 18 years 7 months
Location: Hamburg, Germany

Re: New star generator for other galaxies... (work in progre

Post #46by t00fri » 11.09.2011, 13:39

Cham wrote:Fridger, have you tried the files I gave above ?

No I didn't.

Fridger
Image

Avatar
Topic author
Cham M
Posts: 4325
Joined: 14.01.2004
Age: 56
With us: 16 years 10 months
Location: Montreal

Re: New star generator for other galaxies... (work in progre

Post #47by Cham » 11.09.2011, 13:44

For everybody, here's again the link to the files :

http://fsgregs.startlogic.com/Public_Fi ... 1stars.zip (2.6 MB)
Last edited by Cham on 11.09.2011, 22:11, edited 1 time in total.
"Well! I've often seen a cat without a grin", thought Alice; "but a grin without a cat! It's the most curious thing I ever saw in all my life!"

Avatar
selden
Developer
Posts: 10138
Joined: 04.09.2002
With us: 18 years 2 months
Location: NY, USA

Re: New star generator for other galaxies... (work in progre

Post #48by selden » 11.09.2011, 15:55

Fridger,

Has a complete paper been published anywhere in addition to the news release you mention? Or is that waiting for the formal publishing of the Proceedings of the meeting?

Superficially, it looks like these results might be compatible with what's described in "Galactic spiral structure" by Francis and Anderson (2009).
Selden

Avatar
Topic author
Cham M
Posts: 4325
Joined: 14.01.2004
Age: 56
With us: 16 years 10 months
Location: Montreal

Re: New star generator for other galaxies... (work in progre

Post #49by Cham » 11.09.2011, 16:25

There's a huge problem with stars rotation period in Celestia. Many stars from the default database have ridiculous rotation period (2 days for a huge star ?). This is also very frequently occuring for the stars I generate in M31. I could add some code to define the star's rotation rate, but I may end with unrealistic values too.

Any comments on this ?

Also, what is the distance limit for stars in Celestia 1.6.1 ? I don't remember the max value.
"Well! I've often seen a cat without a grin", thought Alice; "but a grin without a cat! It's the most curious thing I ever saw in all my life!"

Avatar
t00fri
Developer
Posts: 8772
Joined: 29.03.2002
Age: 18
With us: 18 years 7 months
Location: Hamburg, Germany

Re: New star generator for other galaxies... (work in progre

Post #50by t00fri » 11.09.2011, 16:57

selden wrote:Fridger,

Has a complete paper been published anywhere in addition to the news release you mention? Or is that waiting for the formal publishing of the Proceedings of the meeting?

Superficially, it looks like these results might be compatible with what's described in "Galactic spiral structure" by Francis and Anderson (2009).

Selden,

I mainly focussed on these very recent N-body simulation results, to illustrate that the knowledge about the origin and evolution of spiral arms is still very much in motion. Mostly far from solid... I was also unable to locate a released paper about the highly acclaimed poster presentation at NAM 21 by Robert Grand. He is still a PhD student, yet a member of a research group (UCL/MSSL) specializing in these N-body simulation matters with good reputation:

http://www.ucl.ac.uk/mssl/astro/researc ... ion/mwdisk

In the scientific community, the recent detailed N-body simulations are trusted most, yet also there one has to examine critically the possibility of injected wishful thinking ;-) . A major experimental breakthrough by means of precise 3D mapping of the galactic spiral arm structure and chemical composition will come from the Gaia mission (launch 2013)

http://sci.esa.int/science-e/www/area/i ... fareaid=26

Fridger
Last edited by t00fri on 11.09.2011, 19:44, edited 2 times in total.
Image

Avatar
Topic author
Cham M
Posts: 4325
Joined: 14.01.2004
Age: 56
With us: 16 years 10 months
Location: Montreal

Re: New star generator for other galaxies... (work in progre

Post #51by Cham » 11.09.2011, 17:31

Following a suggestion from Selden, the star name could be this way (there are two alternate names for each star) :

"And K2 1c:M31 (1c):NGC 224 (1c)"
"And K1 2c:M31 (2c):NGC 224 (2c)"
"And B9 3c:M31 (3c):NGC 224 (3c)"
...

The "c" letter is used for stars located in the galactic core. But I'm unsure about its position. Is it better to place it before the number, of after, like the above examples ?

EDIT : Hmm, I think it's better without any "c" at all. Just a continuation in ordered numbers... Any comment on this ?

The numbers wont be random anymore. Just an increasing number from 1 to 75000.
"Well! I've often seen a cat without a grin", thought Alice; "but a grin without a cat! It's the most curious thing I ever saw in all my life!"

Avatar
Fenerit M
Posts: 1880
Joined: 26.03.2007
Age: 13
With us: 13 years 7 months
Location: Thyrrenian sea

Re: New star generator for other galaxies... (work in progre

Post #52by Fenerit » 11.09.2011, 18:02

Kept simple, or the filesize will increase.
Never at rest.
Massimo

Avatar
Topic author
Cham M
Posts: 4325
Joined: 14.01.2004
Age: 56
With us: 16 years 10 months
Location: Montreal

Re: New star generator for other galaxies... (work in progre

Post #53by Cham » 11.09.2011, 18:10

Fenerit wrote:Kept simple, or the filesize will increase.

I removed the "c". However, the alternate names are good. It's like real stars with various catalog numbers, and looks nice in Celestia !

I still need comments on the "realism" of the stars (luminosity, size, and what the ... with the rotation period ?)

Also, what is the distance limit for stars in Celestia ?
"Well! I've often seen a cat without a grin", thought Alice; "but a grin without a cat! It's the most curious thing I ever saw in all my life!"

Avatar
t00fri
Developer
Posts: 8772
Joined: 29.03.2002
Age: 18
With us: 18 years 7 months
Location: Hamburg, Germany

Re: New star generator for other galaxies... (work in progre

Post #54by t00fri » 11.09.2011, 19:14

Selden,

sorry, I had to cut short my preceeding post, because we had to leave for dinner...

selden wrote:Fridger,
Superficially, it looks like these results might be compatible with what's described in "Galactic spiral structure" by Francis and Anderson (2009).

Certainly, there are matches with the numerical N-body simulation results.

The paper by Francis and Anderson contains a number of interesting observations. Notably, local stellar streams for tracing the spiral arms of the MilkyWay and the connections to the map of the MilkyWay spirals via the neutral hydrogen distribution (Levine et al). The latter paper we discussed here previously, remember?

Fridger

+++++++++++++++++++++++++++++++++++++++++
Edit Most interesting stuff is also found in the data supplement of the FA paper:

http://rspa.royalsocietypublishing.org/ ... 6supp1.pdf

A complete simulation of our galaxy in terms of only two arms is derived and a video presented. Note that the whole galaxy model only uses 4500 stars and still arrives at a
viable dynamical MilkyWay model including time dependence and the central bar!

Here is the video:

http://rqgravity.net/images/spiralmotions/gss.avi

Depending on your line speed you might have to download it first.
++++++++++++++++++++++++++++++++++++++++
Last edited by t00fri on 11.09.2011, 20:58, edited 2 times in total.
Image

Avatar
Topic author
Cham M
Posts: 4325
Joined: 14.01.2004
Age: 56
With us: 16 years 10 months
Location: Montreal

Re: New star generator for other galaxies... (work in progre

Post #55by Cham » 11.09.2011, 19:18

Fridger,

please, you are off-topic. If you want to discuss these matters, start a topic in the astrophysics section.
"Well! I've often seen a cat without a grin", thought Alice; "but a grin without a cat! It's the most curious thing I ever saw in all my life!"

Avatar
t00fri
Developer
Posts: 8772
Joined: 29.03.2002
Age: 18
With us: 18 years 7 months
Location: Hamburg, Germany

Re: New star generator for other galaxies... (work in progre

Post #56by t00fri » 11.09.2011, 19:27

Cham wrote:Fridger,

please, you are off-topic. If you want to discuss these matters, start a topic in the astrophysics section.

Firstly, it was Selden who started with a more general discussion about the spiral arm structure in connection with the type of distribution of stars in the disc. I am merely answering to this above posts. Secondly, I also think this should be highly relevant for your add-on design...

If you are not interested in these issues, Selden is welcome to move the respective posts by himself and me to another thread. I can't do it obviously.

Fridger
Last edited by t00fri on 11.09.2011, 19:36, edited 2 times in total.
Image

Avatar
Topic author
Cham M
Posts: 4325
Joined: 14.01.2004
Age: 56
With us: 16 years 10 months
Location: Montreal

Re: New star generator for other galaxies... (work in progre

Post #57by Cham » 11.09.2011, 19:28

On topic : what is the current distance limit for stars in Celestia ?
"Well! I've often seen a cat without a grin", thought Alice; "but a grin without a cat! It's the most curious thing I ever saw in all my life!"

Avatar
t00fri
Developer
Posts: 8772
Joined: 29.03.2002
Age: 18
With us: 18 years 7 months
Location: Hamburg, Germany

Re: New star generator for other galaxies... (work in progre

Post #58by t00fri » 11.09.2011, 19:40

Cham wrote:On topic : what is the current distance limit for stars in Celestia ?

the maximum distance increased to 10 million light years. See
http://en.wikibooks.org/wiki/Celestia/160Features

Fridger
Image

Avatar
Topic author
Cham M
Posts: 4325
Joined: 14.01.2004
Age: 56
With us: 16 years 10 months
Location: Montreal

Re: New star generator for other galaxies... (work in progre

Post #59by Cham » 11.09.2011, 19:44

t00fri wrote:
Cham wrote:On topic : what is the current distance limit for stars in Celestia ?

the maximum distance increased to 10 million light years. See
http://en.wikibooks.org/wiki/Celestia/160Features

Thanks !

Now, what about the galactic core ? Should there be more red giants (old stars) there ?
"Well! I've often seen a cat without a grin", thought Alice; "but a grin without a cat! It's the most curious thing I ever saw in all my life!"

Avatar
Topic author
Cham M
Posts: 4325
Joined: 14.01.2004
Age: 56
With us: 16 years 10 months
Location: Montreal

Re: New star generator for other galaxies... (work in progre

Post #60by Cham » 11.09.2011, 19:51

Update : I rebuilded the STC files (still 50k stars scattered on the whole disk + 25k stars in the core).

With exagerated AbsMag (to see the whole distribution), here are two views :
front.jpg

side.jpg


With the AbsMagn set to their normal values, here's the HR diagram of two samples of 2000 stars each :
HRpop1.jpg
"Well! I've often seen a cat without a grin", thought Alice; "but a grin without a cat! It's the most curious thing I ever saw in all my life!"


Return to “Add-on development”

Who is online