**Ask a monkey a physics question thread**

[Eric]

You wouldn't see anything for 27,000 years. Same as the time it takes to notice anything at all that is 27,000 light years away.

Right, I understand that we won't see a change in something that is 27,000 light years away for another 27,000 years. I guess the question should be, how quickly would the changes in the geography of the Milky Way happen? In other words, suppose a given star is 15,000 light years from the center of the Milky Way. Will it start drifting out more then 15,000 light years from the center the very second the black hole disappears or will it take longer for it to lose its gravitational attraction and drift out?

[MadMojoMonkey]

Right, I understand that we won't see a change in something that is 27,000 light years away for another 27,000 years. I guess the question should be, how quickly would the changes in the geography of the Milky Way happen? In other words, suppose a given star is 15,000 light years from the center of the Milky Way. Will it start drifting out more then 15,000 light years from the center the very second the black hole disappears or will it take longer for it to lose its gravitational attraction and drift out?

It will take 15,000 years for it to lose the gravitational attraction.

[Eric]

It will take 15,000 years for it to lose the gravitational attraction.

Makes sense, thanks for the clarification. Today I re-read a 2003 New Scientist article that reports on the 2002 measurement involving Jupiter:

The speed of gravity has been measured for the first time. The landmark experiment shows that it travels at the speed of light, meaning that Einstein’s general theory of relativity has passed another test with flying colours.


Ed Fomalont of the National Radio Astronomy Observatory in Charlottesville, Virginia, and Sergei Kopeikin of the University of Missouri in Columbia made the measurement, with the help of the planet Jupiter.