4 ms·

> No, there shouldn't be any rouge planets moving fast enough. For comparison's sake, the only rouge planet that we know of is Mars, which moves around 24 km/s

> No, there shouldn't be any rouge planets moving fast enough. For comparison's sake, the only rouge planet that we know of is Mars, which moves around 24 km/s. :)

sova 12y ago
24 km/s relative to whom/what? =)
mirimir 12y ago
The discovery of hypervelocity stars (HVS) leaving our galaxy with speeds of nearly $10^{3}$ km s$^{-1}$ has provided strong evidence towards the existence of a massive compact object at the galaxy's center. HVS ejected via the disruption of stellar binaries can occasionally yield a star with $v_{\infty} \lesssim 10^4$ km s$^{-1}$, here we show that this mechanism can be extended to massive black hole (MBH) mergers, where the secondary star is replaced by a MBH with mass $M_2 \gtrsim 10^5 M_{\odot}$. We find that stars that are originally bound to the secondary MBH are frequently ejected with $v_{\infty} > 10^4$ km s$^{-1}$, and occasionally with velocities $\sim 10^5$ km s$^{-1}$ (one third the speed of light), for this reason we refer to stars ejected from these systems as "semi-relativistic" hypervelocity stars (SHS). http://arxiv.org/abs/1411.5022 http://arxiv.org/abs/1411.5022 There could also be hypervelocity planets, right? Catching up to them would be hard, though.
- jessriedel 12y ago
  > There could also be hypervelocity planets, right? There could definitely be hypervelocity planets just like planets. However, the density of these drops dramatically as you increase the speed you're looking for above the "typical" speed at our galactic radius (~230 km/s), simply because they are created by chance events. I believe the density of rouge planets is supposed to be of order the average density of normal planets in the galaxy (i.e., there might be 3 times as many rouge planets, but not 100 times as many). So finding a relativistic rouge planet nearby enough to be useful has negligible probability. (They are created by close encounters with black holes, after all.) > Catching up to them would be hard, though. Well, if you're thinking about using them as "space ships", you need to get up to speed anyways (since the alternative is to just travel on your own).
  - mirimir 12y ago
    Yes, that's a good point about density. If you could catch one, your itinerant colony would have resources at speed for interstellar travel. You'd only need to accelerate a relatively small ship. And those resources would include mass for decelerating your ship at destination. But you couldn't stop for very long, without losing your ride.

> No, there shouldn't be any rouge planets moving fast enough. For comparison's sake, the only rouge planet that we know of is Mars, which moves around 24 km/s. :)

sova 12y ago

24 km/s relative to whom/what? =)

mirimir 12y ago

The discovery of hypervelocity stars (HVS) leaving our galaxy with speeds of nearly $10^{3}$ km s$^{-1}$ has provided strong evidence towards the existence of a massive compact object at the galaxy's center. HVS ejected via the disruption of stellar binaries can occasionally yield a star with $v_{\infty} \lesssim 10^4$ km s$^{-1}$, here we show that this mechanism can be extended to massive black hole (MBH) mergers, where the secondary star is replaced by a MBH with mass $M_2 \gtrsim 10^5 M_{\odot}$. We find that stars that are originally bound to the secondary MBH are frequently ejected with $v_{\infty} > 10^4$ km s$^{-1}$, and occasionally with velocities $\sim 10^5$ km s$^{-1}$ (one third the speed of light), for this reason we refer to stars ejected from these systems as "semi-relativistic" hypervelocity stars (SHS). http://arxiv.org/abs/1411.5022 http://arxiv.org/abs/1411.5022 There could also be hypervelocity planets, right? Catching up to them would be hard, though.

jessriedel 12y ago
> There could also be hypervelocity planets, right? There could definitely be hypervelocity planets just like planets. However, the density of these drops dramatically as you increase the speed you're looking for above the "typical" speed at our galactic radius (~230 km/s), simply because they are created by chance events. I believe the density of rouge planets is supposed to be of order the average density of normal planets in the galaxy (i.e., there might be 3 times as many rouge planets, but not 100 times as many). So finding a relativistic rouge planet nearby enough to be useful has negligible probability. (They are created by close encounters with black holes, after all.) > Catching up to them would be hard, though. Well, if you're thinking about using them as "space ships", you need to get up to speed anyways (since the alternative is to just travel on your own).
- mirimir 12y ago
  Yes, that's a good point about density. If you could catch one, your itinerant colony would have resources at speed for interstellar travel. You'd only need to accelerate a relatively small ship. And those resources would include mass for decelerating your ship at destination. But you couldn't stop for very long, without losing your ride.