Not quite sure what the intended question was - - - which star are you asking about?
The sun IS a star - the one our planet orbits.
It happens all the time. What happens to the Sun? Nothing at all.
I think that it would be to hot to live on earth and we would have never existed
Convert into a dwarf white star which is really hot, then a neutron star, and finally, a black hole.
The earth would only rotate the sun because the sun is a star so only stars and meteors would be left.
That's not possible a star is a sun, planets revolve around a star, and the planet would be destroyed far far far far far before the star reached it, if that was even possible
Please note that the Sun IS a star. If some OTHER star replaced the Sun... Well, the result would depend on what star you are talking about. A few stars are so big that they would engulf Earth - Earth would be gobbled up by the star. The majority of stars are smaller and fainter than our Sun (our Sun is approximately in the top 90 percentile with respect to brightness and size); in this case, Earth would simply not receive enough light to maintain life as we know it. If you chose a random star, it would likely be either too faint or too bright for us.
If Betelgeuse replaced our Sun, it would likely cause drastic changes in our solar system. Betelgeuse is a red supergiant star, much larger and hotter than our Sun, so Earth would be too close to it and would likely be engulfed by the star's expanded outer layers. The intense radiation and heat would also have significant effects on the other planets in our solar system.
A star 100 times the mass of Jupiter would barely be massive enough to be a star at all. However, the collision would probably be bad for the Earth and us, its inhabitants.
it goes boom
If the sun were to undergo a nova event, it would expel its outer layers into space, creating a bright explosion. This would not result in the complete destruction of the sun, but it would significantly alter its appearance and affect the surrounding planets in the solar system.
The question makes no sense. The sun is a star, if it were to "enter" another star it would be destroyed (or at least lose its identity as a separate object) in the process. There is essentially no chance this will happen during the expected lifetime of the Sun as a main sequence star anyway.
Our Sun is not a secondary star. See related question.