What if an Earth like planet suddenly finds itself in an orbit within the "habitable zone" of its star?

The idea came to me when thinking about the classic thought experiment, "what if a golf ball sized black hole were to enter Earth's orbit". The answer depends on many factors, but it can essentially work from one of two scenarios. <br>1. It enters orbit, like a moon orbiting earth. It would likely have essentially no effect on the planet as a whole, but it could explode or "pop" into space if it were to gain enough angular velocity. <br>2. It enters orbit, but not in the same way. Instead, it enters a highly elliptical orbit, and orbits the planet at an angle. This would create a situation where once a year, the black hole would pass through the center of Earth at its widest point. This would result in catastrophe as the planet would see a massive increase in gravity with each passing year, before it would likely eventually "pop" into space, or pass harmlessly through the center of a planet. <br>But I asked myself again, "what if this black hole instead of a black hole were a star just like our own sun?"<br>What would happen if your average "habitable zone" planet were to have another star of equal mass to our own enter its orbit? And then what if it were to enter a highly elliptical orbit, and pass through our planet once a year?