*** Galaxy Birth *** MODEL ----- I tried to make model which is simple enough to simulate but not too much removed from reality. - at the beginning all mass is uniformly distributed through sphere - at about same time the stars form up simultaneously. They appear at random positions but are distributed uniformly through the sphere. This is the point where simulation begins - for computations stars are treated as points - movement is calculated according to Newton mechanics - mass, spectral colours and distance are chosen to correspond with real Universe metrics. Size of stars (for display) is much larger than reality, this is to make them easily visible Types of created stars: Spectrum Probability Mass(compared to Sun) M red 52.6% 0.1-0.5 K orange 24.3% 0.5-0.8 G yellow 15.8% 0.8-1.2 FA white 6.0% 1.2-4 B bright-blue 1.3% 4-20 Heavier stars are displayed in larger size and also in brighter colour. INPUT ----- At the beginning you need to enter few parameters. 1.STARS (number of stars) - more stars means prettier but slower simulation - doubling number of stars slows the simulation down four times - if simulation is too slow try smaller number - if you have strong computer or enough time try bigger number for nicer results 2.SIZE (radius of initial sphere in light years) - together with number of stars decides the average mass density - smaller value means faster gravitational collapse but also means you are watching from smaller distance so the collapse of galaxy core looks bigger (which might be just illusion because of smaller watching distance) - starting view is from distance 3xsphere radius 3.DELTA T (simulation step in years) - smaller value means more precise but slower simulation - bigger value means faster but imprecise simulation which often leads to instability of formed galaxy - when simulating very small number of stars you can use value of 1 year to get very precise simulation 4.SEED (seed for generating pseudo-random numbers) - leave empty and it will be set from time - to repeat previous simulation exactly enter the same seed (and also repeat other parameters) CONTROLS -------- Simulation can be paused at any time. While paused you can fly around the galaxy on imaginary ship to examine different parts of galaxy and views from different places. You can fly also while simulation is running but the movement will be jagged with big number of simulated stars. SPACE - pause / unpause simulation ESC - quit application ARROWS - turn the ship around A,Z - accelerate / decelerate Q,W - rotate the ship around axis MOUSE - you can turn the ship also using mouse movements RESULTS ------- Forming of galaxy usually goes through following phases: 1. Not much happens at the beginning. Few stars are thrown away as a result of gravitational slingshot. 2. After some time the sphere begins to collapse. During the collapse small clusters of stars are sometimes formed around massive stars. 3. Collapse ends in forming of extra dense concentration of stars creating the new galaxy core. Depending on parameters one of following scenarios happens: 4a. Core is stabilized and forms stable galaxy together with surrounding stars. 4b. Velocities overrule gravitation and the stars fly away in all directions. The galaxy is more or less shattered 4c. Usually some kind of compromise happens. The core expands but keeps the stars together forming the backbone of the new stable galaxy Aside from observing the galaxy as whole you can also observe the individual stars. Far enough from core you can sometimes observe star systems formed from two or more stars. Your best bet is to check solitary massive stars (blue) which have good chance to catch other lighter objects. OTHER APPLICATIONS ------------------ 1. Mechanics of star system consisting of several bodies (stars) - enter small number of stars (cca 3-10) - enter delta T = 1 year You will get very precise simulation which is also fast enough thanks to small number of simulated bodies. With bigger number of starting stars (e.g. 10) you can often observe forming of one or more 2-3 star constellations. These constellations can later meet and steal stars from each other or interfere in other ways. CRAZY UNIVERSE - WHAT IF? ------------------------- Few simulations with modified laws of gravity. 1. Gravitational constant is 10x smaller galaxy: Similar progress as in normal system but much slower. Core is shattered more perhaps because of gravity unable to hold things together. 10-star system: System is lazy, stars are getting more distance away from each other. It would be probably possible to form few-star constellation but it looks more like stars closing to each other and regrouping without forming stable structure 2. Gravitational constant is 10x bigger galaxy: System is more dynamic, more stars fly away to space at the beginning. Small star clusters are formed and there is quick gravitational collapse. The core is shattered though perhaps because of accumulated velocities and strong gravity slingshots. 10-star system: Few-star constellations have tendency to appear but are also more disturbed by nearby stars. When stars get away enough from each other stable few-star constellations are formed. 3. Gravity weakens linearly (1/r instead of 1/r^2) Gravity is so strong that conditions must be changed drastically to see anything. Objects reach velocities much bigger than light so the Newton mechanics does not anymore correspond to reality too much. 1500/100000 ly/1 year galaxy: Extreme gravity shatters anything getting too close. On bigger scale it is similar to standard model. Very rapid collapse, then shattering of core but then the stable core is formed together with stable galaxy around. 10/50000 ly/0.00001 years 10-star system: System is very dynamic but allows forming of stable few-star constellations though with different trajectories. 4. Gravity weakens cubically (1/r^3 instead of 1/r^2) Gravity is so small than nothing really moves. To see anything we have to increase star density a lot and also drastically increase delta T. The big delta T might be the reason while the simulations become very unstable. 1500/0.1 ly/20000000 years galaxy: There is no gravitational collapse. Whatever gains speed just flies away and the sphere is gradually destroyed. 10/0.1 ly/20000 years 10-star system: Doubles closest together speed each other up and fly away to space. Total destruction of system. 5. Gravity works in other direction (F=-F) galaxy: No surprise. The stars repel each other and the sphere expands. 10-star system: Stars fly away in opposing directions. LIMITATIONS ----------- This simplified model has various limitations that, to some degree, make the simulation different from reality. These are mostly: - absence of theory of relativity (however the velocities and gravitational effects mostly should not get that extreme to have serious effect) - ignoring star collisions (those are very improbable though) - static stars, no dying of old stars or creation of new ones (maybe in future versions) - no intergalactic gas and its mechanics (but its overall effect should be small enough to neglect as we consider most gas spent in creating initial stars) - limited number of stars (but it should roughly correspond to reality since the simulation does not change that much with different number of stars when density remains the same) - precision, depends a lot on delta T