Is the density of interstellar space too high for relativistic flight?

It occurred to me that if we are able to travel at relativistic velocities, then interstellar gas and dust will (a) be denser because of relativistic length contraction, and (b) be hitting the space ship with a lot of energy, which might heat it unacceptably, or even blow it up.

There is also the risk of hitting even a small piece of dust, which because of the high velocities will be like a small bomb.

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