/sci/ - Science & Math

>>9481657
Supermassive black hole.
Actually, fairly small as SBHs go (compared to some seen in other galaxies) and it doesn't hold our galaxy together.
But we can see stars close to the centerpoint whirling about something massive at goodly fractions of lightspeed. They move visibly in photos taken months or years apart. Given that they're 33,000 light-years distant, that means they're really hustling!

>>9482025
You wouldn't want all the dark matter to be at the center of the galaxy. You may know that a hollow sphere exerts no net gravitational force on objects within it.
The orbits of stars are only affected by matter closer to the center-of-rotation than they are. I stellar velocities at various distances from the core (as measured by Doppler effect) were only due to the visible suns and dust, the rotation curve would have a particular shape; i.e. velocities would fall off steadily towards the outskirts. Stars near the rim should just crawl if most of the mass was in the central core. That's not what we see. Velocities become almost constant. It indicates that a large amount of unseen mass is distributed throughout the entire disc.