Specify a current technology that could accelerate to 99% light speed. Heck, specify future technology that we could conceivably build. Now, what is the exhaust

Specify a current technology that could accelerate to 99% light speed. Heck, specify future technology that we could conceivably build. Now, what is the exhaust velocity? What is the mass ratio for the starship? How big is that compared to mass of the entire solar system? How is that energy expenditure going to be not noticeable to aliens?