We Crashed The Milky Way Into Andromeda. 14 Stars Touched.

#andromeda #milkyway #math
If the Milky Way Andromeda collision happens, a trillion stars pass through a few hundred billion more and almost none touch.

If the Sun were a grain of sand, Proxima Centauri would be another grain 29 kilometers away. We built our own engine with the Milky Way, Andromeda, Triangulum and the Large Magellanic Cloud, filled it with 34,000 tracer stars, the trick Alar and Juri Toomre used in 1972, and filmed one crash. On the second pass the two disks go straight through each other and shed tidal tails.

To count star collisions, follow one star: it sweeps out a thin tube, and gravity makes the tube fatter. The expected number of hits on that pass is about a sixth. By the time the two hearts merge, about 14 stars have touched, and 12 of those hits involve a red giant. About one Milky Way star in fourteen billion gets hit.

Then we ran 100,000 futures with every distance, speed and mass drawn from its error bars. About 57 in 100 end in a merger within ten billion years, close to the 54 percent Sawala and colleagues got from Hubble and Gaia data in 2025. Andromeda's sideways drift decides whether they hit, and the small galaxies tip it: without the Large Magellanic Cloud the chance rises to 68 percent, without Triangulum it drops to 38.
Chapters:
0:00 Milky Way meets Andromeda
0:32 The Sun as a grain of sand
1:23 Our four-galaxy engine
2:41 How many stars collide
4:46 When the two hearts merge
6:05 A hundred thousand futures
7:16 The small galaxies decide
7:49 Our sky and the Sun's fate

#math #andromeda #milkyway
#universe, #perfect universe, #galaxy #Mysteries