# Why the center of our galaxy doesn't absorb us

Depending on the theories, the center of our galaxy is a super massive black hole, this is easy to accept as a truth, but what I couldn't simply devour is how the solar system is orbiting around it while not getting absorbed to the inside ? It's simple to understand how earth orbits the sun, but the black hole is something more energetic and at most pulls everything to it's center. By looking to this image for example:

If we follow the bright lines it looks like everything is really going to the true center like a vortex. If you have any simple ways to enlighten me or any references to read I will be thankful, because sometimes I don't know what topic should I search for to find answers without posting questions like this one.

And also, would our galaxy run out of stars since the black hole devours them fast while they take too long to reproduce ?

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Possible duplicate: physics.stackexchange.com/q/73705 –  Kyle Kanos Oct 18 '13 at 18:32
Hint: look up just how fast our solar system is whizzing around the galactic center. Compare it to how fast the planet goes around the sun for good measure. –  David H Oct 18 '13 at 18:34
Not to mention it looks like you put the sun in the wrong galaxy :-) Even if it were a representation of the Milky Way, we are further out than your nice-looking picture has us. So that means we have much more time to worry about being absorbed. :)) –  Howard Pautz Oct 18 '13 at 18:45
For the same reason that the Earth doesn't go whizzing into the sun. –  Pranav Hosangadi Oct 18 '13 at 18:53
Spiral arms are density waves, not streams of matter being sucked into the center. See for instance How do spiral arms form? and How can a spiral galaxy exist? –  Chris White Oct 18 '13 at 20:52

The spiral arms don't mean that the mass is getting sucked to the center. They're just wave-like density patterns.

The bodies in orbit around the center of the galaxy are in stable orbit; just like the Earth around the Sun and the Moon around the Earth. What happens is that gravity accounts for the centripetal force (in the orbiting frame, gravity is balanced by the centrifugal force), so there is no net radial acceleration "left over" to suck the body in.

The only reason things would fall into the center is if they were headed there. This can happen if two stars pass by each other and are slingshotted in opposite directions, one of which gets sent to the center of the galaxy.

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There are other ways to draw gas mass into the center, such as gas. Non-axisymmetric density patterns in galactic gas can lead to torques that draw gas into the center, and this may be part of the way that massive black holes grow. But that doesn't seem to be happening to any significant extent in our galaxy now. –  kleingordon Nov 27 '13 at 5:16
The super massive black hole is creating a force acting on the material in the galaxy, but that material still has angular momentum which needs to be conserved. In a similar way, the earth is in orbit around the sun and it is bound in its orbit by the gravitational potential from the sun's mass. If you were to naively calculate the force on the earth as $F= G m_{earth}M_{sum}/r^2$ you would conclude that the force would pull the earth in, however you would have neglected the angular momentum of the earth, for it to fall in it would need to lose its angular momentum (L) . Since $L=m_{earth} v\times d$, where d is the distance to the sun, this means the earth would need to decrease its orbital velocity to decrease L.