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.

 

[quencheduniversetdr]

What about pushing it with a laser?

 

[Filip Larsen]

What about pushing it with a laser?

Indeed. Breakthrough Starshot comes to mind.

 

[PeroK]

Indeed. Breakthrough Starshot comes to mind.

The project is aiming for a speed of 0.2c. Moreover, it's a one way journey, with no possibility of return to Earth. And it's a "nano probe" - the smallest probe that can do something useful like photograph an exoplanet.

Note that at that speed it would be a quick fly past with no option to settle into an orbit, a la the Enterprise!

 

[Ibix]

A freefall orbit that grazes the photon sphere of a black hole will have a peak speed relative to the hole that is extremely close to $c$.

 

[Filip Larsen]

The project is aiming for a speed of 0.2c.

The reference was meant in context of the OP question as a model-wise more simple a way to accelerate a low mass macroscopic object than using black holes.

 

[PeroK]

The reference was meant in context of the OP question as a model-wise more simple a way to accelerate a low mass macroscopic object than using black holes.

It was a good example of what is realistic. Anything resembling the Enterprise is far beyond any engineering reality.

 

[BWV]

What about pushing it with a laser?

Sure but my OP was an upper limit for projectiles from natural processes, not space travel. Looks like the only candidate that could create a relativistic macroscopic projectile is a gravitational slingshot from a black hole or maybe a neutron star. There was a typo above - the limit is around 0.5C not .05C for an object orbiting outside the event horizon - and a slingshot could get up to 2x the velocity, which presumably would exceed escape velocity and create an interstellar relativistic macroscopic object.

 

[Filip Larsen]

Sure but my OP was an upper limit for projectiles from natural processes

Right. By "known processes" I thought you meant "physical possible/feasible". So your question, I gather, is not so much large delta V but more like if there is a theoretical upper limit to the amount of kinetic energy a (naturally accelerated) micrometeorite can release on impact with Earth?

 

[BWV]

Right. By "known processes" I thought you meant "physical possible/feasible". So your question, I gather, is not so much large delta V but more like if there is a theoretical upper limit to the amount of kinetic energy a (naturally accelerated) micrometeorite can release on impact with Earth?

Yes, but not necessarily with earth, just if there is any natural processes that could impart the energy to accelerate an object to relativistic speeds without obliterating it