What do you mean they'll pass through each other.
One of my favorite factoids: if you fire a laser from the surface of the earth (and the beam magically stayed perfectly straight), you have a small but significant chance of hitting the sun or the moon, but anything beyond that, the scale is so enormous, the odds that your laser would ever hit a celestial body anywhere in the universe are effectively zero.
There are many youtube videos that try to visualize the incomprehensible scale of space. Here is one just for our solar system https://www.youtube.com/watch?v=dCSIXLIzhzk
Think of two clouds of gas colliding. The clouds as a whole collide, yes, but there's no molecular fusion happening. The molecules themselves don't collide.
"Pass through each other" is not the clearest wording.
It was not, mea culpa. :D
The Englese, she is the very hard language to speak.
Stars can only get so massive, but black holes can get much much more massive.
But even with supermassive black holes, it doesn’t change the odds of colliding solar systems that much.
There is just way too much space in between to matter.
> no difference ... gravitationally.
"practically no difference ... gravitationally, provided one is at a very large distance compared to the outer surface of an astrophysical black hole." would be more accurate.
Up close to a real black hole additional shear and tension becomes obvious, although you will generally be in the region that would be close to the surface of a star of comparable mass.
Astrophysical black holes are more complicated objects than the theoretical Vaidya-Bonnor-Kerr (VBK) black holes, especially when they are not isolated. VBK black holes absorb radiation and emit Hawking radiation (V part), including self-interacting matter (B part, although that is mostly dealing with classical electromagnetism), and they also rotate (K part). VBK breaks several symmetries: the exterior spacetime is not static, not stationary, and spherical symmetry goes to axial symmetry, including all the incoming and outgoing radiation. Real rotating black holes would break axial symmetry because real matter tends to clump (in particular theoretical VBK exterior matter does not look like accretion discs).
Small perturbations of the axial symmetry of VBK black holes tend to cause black holes to spin up as matter falls onto them. There is observational support to suggest that most real black holes are likely spinning extremely rapidly. The Kerr vacuum around a VBK is equipped with regions in which objects are dragged around in the direction of the VBK black hole's rotation. As the original angular momentum of the star may be increased by infalling material, a real black hole likely has a strong region extending well outside of where the surface of a star of comparable mass would be. While the dragging effect falls off quickly with distance outside the outermost surface of the outermost of these regions, if we replaced the sun with a real black hole which rotates at extremely high rates, all eight planets' orbits would precess compared to their orbits around the sun. Given enough observation time, this would be especially noticeable for objects on high-inclination, low-ellipticity orbits, even if they are near the outer edge of the Oort cloud. Reducing the angular momentum dramatically increases the observation time needed to distinguish gravitationally between a (growing!) solar-mass black hole and a (shrinking!) solar-mass star.
Beyond the Oort cloud things aren't gravitationally bound to our solar system anyway, so by the time you're a couple hundred thousand astronomical units away, you are on safe territory with practical gravitational indistinguishability.
In terms of light and radiation, though, swapping the sun for a solar-mass black hole would be pretty noticeable, for example https://en.wikipedia.org/wiki/Poynting%E2%80%93Robertson_eff... or https://en.wikipedia.org/wiki/Yarkovsky_effect