11
$\begingroup$

I've read that an object colliding with a black hole will move it, as it would any other object. Could a laser continuously fired into a black hole move it?

$\endgroup$
25
$\begingroup$

A laser carries linear momentum, so when a laser is fired into a black hole, this linear momentum is transferred to the black hole, causing it to accelerate.

Of course, for a realistic astrophysical black hole you'd need an unrealistically powerful laser for this to make a significant impact on the motion of the black hole.

$\endgroup$
5
  • 27
    $\begingroup$ FWIW, the Sun's luminosity is $\approx 3.828×10^{26}$ watts. We can use $E=pc$ to calculate the light's momentum, and equate it to $p=mv$ for the change in momentum of the black hole (this ignores the small change in mass of the BH due to absorbing the light). If we blast a small 3 solar mass BH with the entire solar output for 1 million years, we increase its speed by ~6.75 m/s. $\endgroup$
    – PM 2Ring
    Nov 9 '21 at 13:52
  • 2
    $\begingroup$ @PM2Ring That's actually...more than I was expecting, honestly. $\endgroup$
    – KEY_ABRADE
    Nov 10 '21 at 0:52
  • 1
    $\begingroup$ Would a micro black hole be moved more or less? $\endgroup$
    – Ben Warner
    Nov 10 '21 at 3:05
  • 3
    $\begingroup$ You could fire the laser to just skim the hole such that the light did a 180 and came back at you. That would double the momentum transfer. $\endgroup$
    – Keith
    Nov 10 '21 at 3:45
  • 1
    $\begingroup$ @Keith and then you could set up a mirror so that after the light does a 180 you can bounce it back and do it again, reusing the light an arbitrary number of times. (Still not realistic.) $\endgroup$
    – DMPalmer
    Nov 10 '21 at 4:40

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.