Undergrad Practical cosmic speed limit for macroscopic objects?

[BWV]

as far as I can find, the rotational velocity of neutron stars is the fastest observed speed of a macroscopic object

Wondering about an upper limit to the velocity of macroscopic (say 1 gram or more) projectiles based on known physical processes. I.e. it’s not physically impossible for an asteroid-size object to travel at .9c, but guessing no known process could accelerate it to that speed - a burst of energy like a supernova would just obliterate it.

 

[oz93666]

Interesting thought .... I think we have to invoke the help of an advanced ET race who could construct a linear accelerator many light years long electromagnetically accelerating an object , but then there's the issue of drag from "vacum " of space , which is not a complete vacum... even so should get to about .99c

 

[pinball1970]

as far as I can find, the rotational velocity of neutron stars is the fastest observed speed of a macroscopic object

Wondering about an upper limit to the velocity of macroscopic (say 1 gram or more) projectiles based on known physical processes. I.e. it’s not physically impossible for an asteroid-size object to travel at .9c, but guessing no known process could accelerate it to that speed - a burst of energy like a supernova would just obliterate it.

Sling shot? If the star was large enough that could accelerate an object, more so for a black hole, I am guessing you would already have to travelling at a very high velocity to reach significant % of c.

 

[pinball1970]

IIRC it would take a year to accelerate 1kg at 1g to 0.9C. There is a calculator on line for this.

 

[BWV]

Sling shot? If the star was large enough that could accelerate an object, more so for a black hole, I am guessing you would already have to travelling at a very high velocity to reach significant % of c.

It looks like an upper limit for the slingshot is 2x the orbital velocity, messing around with Gemini and the vis-viva equation it does look possible for a massive object orbiting just outside of the event horizon of a black hole to reach relativistic speeds - as high as .05C then an object slingshotted off of it could reach an even higher velocity

 

[Filip Larsen]

Note you need at least two orbiting massive objects for a (normal) gravitational slingshot, not just one, in order for a test particle to gain speed relative to the common center of mass.

For maximum effect, one could image a pebble falling with high relative speed towards a pair of black holes orbiting each other very close (nearly at contact), but I am not aware if there is an easy way to quantify the speed change which would include relevant (i.e. significant) relativistic effects.