Comment Re:I don't understand this ... (Score 3, Interesting) 184
Not all supermassive black holes are actively accreting. In fact, the fraction of time their accretion disks actually output massive amounts of radiation is ~10%, on patches of ~ hundred million years timescales.
A planetary system could form outside the center of the galaxy and travel close to the galactic center. You have to keep in mind that the distances between stars are enormous when compared to distances between planets. For example, our nearest star is 270 000 earth-sun distances (4 lightyears) away, while Jupiter is only 5 earth-sun distances from the Sun. So a "stripping" of planets, due to tidal forces, is extremely small, even when it comes close to the supermassive black hole in the center of the galaxy. It is true however that for the closest orbits, such as 120 earth-sun distances for S2 (S2 reaches speeds of 5000 km/s), this effect will be important. However, I suspect that while a single, quick swing-by will alter the orbits of planets (generally increasing ellipticity), that effect leads to the immediate destruction of the entire system. Normal planetary systems are also not stable systems. Changes in the orbits, interactions between planets, etc. are common; Only when stable oscillations are reached, the orbits remain the same for a few million years. So I suspect that the planets can re-arrange into a stable system (perhaps under ejection of one of the planets).
I think the changes are better if the system is a newly born star, where planetoids are still forming in a thick disk of gas and dust. Then, the partially destroyed disk can re-arrange quickly and form planets after swing-by. That would not necessarily be a problem for "spreading of life", if this process occurs e.g. via comets.