You don't even need "a few times the Earth's radius." Assuming identical density, mass is proportional to the cube of radius. Earth already has the highest den

You don't even need "a few times the Earth's radius." Assuming identical density, mass is proportional to the cube of radius. Earth already has the highest density of all the large objects in the solar system, at about 70% of the density of solid iron. An object that has the same density as Earth, but with 2x the radius, will have the mass of 8 Earths. If the object was made of solid iron, it will have the mass of over 11 Earths. That's a lot of mass in a small area.