The universe is huge . But it is also full of stars. In our galaxy alone, it is believed that there could be several hundred billion stars . That’s a lot of zeros. Therefore, it is logical to ask if our Sun could collide with one of that incredible number of neighboring stars. After all, many cases of collisions of stars, galaxies and even black holes and neutron stars are known. Nothing prevents us from being the next protagonists of a similar apocalypse.
Without going any further, in our own solar system collisions abound. Meteorites of very different sizes are constantly falling on our planet. NASA estimates that about a hundred tons of meteorites and interplanetary dust fall to Earth every day. But we have also seen meteorites fall on other bodies, such as Jupiter or our Moon . Moon that we believe was formed by a huge collision between the early Earth and a planetesimal the size of Mars.
In short, although space is a gigantic place, clashes between different bodies are the order of the day . So could our star collide with another star in the relatively near future? Currently the closest star to the Sun is Proxima Centauri , a red dwarf located more than four light-years away . Four light years is, by definition, the distance that light travels in four years. Bearing in mind that light is the fastest thing in the universe and that a photon would be capable of going around the Earth seven and a half times in a second or traveling the distance between the Earth and the Moon in just over a second, moving four years at that speed must be an unimaginably long distance. Voyager 1 , which is one of the fastest human-made objects, would take about a hundred thousand years to travel that same distance (if only it were traveling in that direction, which it wasn’t).
However, the stars do not stand still and do not all rotate in perfect unison around the galactic center. They are moving, traveling and approaching and moving away from each other. In fact Proxima Centauri and her companions Alpha Centauri A and B (because this star system is triple) are now approaching the Sun. Not in a straight line, nor close, so there will be no collision with any of them, but enough to reduce the distance that separates us from the current 4.25 light years to the 3.1 light years that we will reach within more than twenty-eight thousand years . This distance, although smaller, will still be enormous. Proxima Centauri will still be invisible to the naked eye and Alpha Centauri A will still not be the brightest star in the sky .
We currently know of 76 different stars located less than 16 light years away (less than 5 parsecs, specifically). These stars are spread across 54 different star systems and the vast majority of them are red dwarfs and cannot be seen with the naked eye from Earth. Others are, like the pair of Alpha Centauri A and B, but also Sirius, Procyon or Tau Ceti . Sirius is the brightest of all nearby stars and also the brightest in our night sky, rivaling Venus, Jupiter and Mars in brightness. In addition to the currently nearby stars, it has been calculated, using data from the Gaia telescope, that 694 stars will pass within 16 light-years of the Sun during the next fifteen million years , that 26 of those stars have a high probability of passing less than 3 light years away and that 7 of them could pass less than a light year and a half away .
Of all the stars studied, everything indicates that Gliese 711 is the star that will pass closest to the Sun in the relatively near future (in less than 15 million years). This star, which is about half the mass of the Sun and glows an orange hue, will pass just 0.17 light-years away . This is, only in comparison with the rest of the distances mentioned, very close. It will be so close, that this star should pass through the hypothetical Oort cloud , completely disrupting the outer solar system and possibly causing a considerable increase in the visits of long period comets . This approach will not take place for more than a million years, so there is little point in worrying about it now.
When this minimum distance of just over 10,000 astronomical units (about 300 times farther from the Sun than Pluto) is reached, Gliese 711 will be the brightest star in the night sky, shining considerably brighter than Sirius. Still it will not be enough for the two stars to collide . We are not able to predict which stars will pass close to the Sun after about 15 million years, but it is very certain that before that time none will collide with our star. We believe that these collisions are so unlikely that even when the Andromeda Galaxy and our own Milky Way collide billions of years from now, very few stars will ever collide because of the incredible distances that separate them. If we see so many collisions occurring in the universe, it is not because they are very common and probable, but because there are so many stars in it that even the improbable can happen many times .
References:
A. L. Bailer-Jones et al, 2018, New stellar encounters discovered in the second Gaia data release, Astronomy & Astrophysics. 616, doi:10.1051/0004-6361/201833456
The One Hundred Nearest Star Systems, 2017, Research Consortium on Nearby Stars (RECONS)
