http://stars.chromeexperiments.com/

And I also had played this game on Steam like 10 years ago and loved it. Very basic, very simple. You started out as a small speck of dust in space and as you flew threw space, your gravity would begin to absorb the elements and you would get bigger, becoming a planet, a bigger planet, a sun, a black hole... while it was mostly simuluation and you had no real enemies, gravity is always our biggest enemy and you could be ripped apart by another black hole or even a giant sun, which made the game so enjoyable. You could drift and float and control it.. you flew through space and moved the arrow keys to avoid objects. You could change your speed too.

Let me see if i can find it and i only bring it up since I can't answer your exact answer, but can show you an idea. Looks like it got a massive upgrade as it used to be 2D. https://store.steampowered.com/app/230290/Universe_Sandbox/

And CodePen can at least get you started with a simulation.

https://codepen.io/search/pens?q=universe