If I understand correctly, there are star systems that exist in space that were created outside of a galaxy (or at least the galaxy’s gravitational influence), and also others that were ejected from their respective galaxies after a cataclysmic event of some kind, like a supernova. If something like this had happened to the solar system in its early stages, would it have evolved to what it is today? I guess another way to pose this question is, are we in any way dependent on the Milky Way galaxy or could we exist in the same way without being part of a galaxy?
Right now or ab initio? The solar system could easily be ejected from the galaxy via gravitational assists from other stars, just like we use planets to accelerate up probes. It might take millions of years to exit the galaxy, of course.
If it had happened early on, then the cosmic ray flux might be important.
I’ve seen suggestions that our solar system periodically passing through the galactic disk might be the perturbation that triggers comets to fall in from the Oort cloud, leading in turn to mass extinctions.
This and Quartz’s link suggest that we might be better off with the solar system floating around in empty space, rather than the confines of the galaxy.
Those suggestions are crap. Without digging up numbers (since I’m posting from my phone right now) the difference in periodic distance from closest to furthest from the center of the galactic plane is trivial on a galactic scale–not nearly enough for there to be significant differences in density. It is the equivalent (a word my phone tried to correct into “WWII cement”) of thinking that the Earth’s varying distance from the sun causes seasons.
While we tend to think of extinction as being a bad thing, especially when human industry is the proximate cause of it, the entire class of Mammalia owes its present expansiveness to the Cretaceous–Paleogene (K–Pg) extinction event and extinction of over 70% of then-extant animals including the large dionsaurs, clearing the way for mammals (which at that point were thought to be basically a collection of small rodent-like species) to diversify into the vast array that exists today, including primates of which we are a member. Major and minor extinctions driven by environmental changes offer an impetus for rapid evolutionary change and challenge the existing order of species and connections, which drives evolution faster than ‘random’ evolution due to mutation, lateral gene transfer, or genetic drift alone. Far from being ‘better off’, a world without periodic stressors may become moribund and underdeveloped.
Our system is also formed out of the detritus of at least ten seperate stellar nucleosynthesis events, i.e. supernovas, which gives the rich distribution of elements heavier than nickel upon which we depend for industry and technology. Without being born into such a wealth of chemical elements our world would not look like it does and we would not have a dense, rocky world with a molten nickel-iron core. So, at least being from a fairly mature galaxy initially is certainly advantageous.
The News Scientist article is the typical unsubstantiated bunk that publication produces, and the density of the galactic plane at our distance is not significantly greater than our current height above it, but we are thought to pass through giant molecular clouds periodically which could disturb the Oort cloud as could random close passing of large brown dwarf or other stars that pass near enough to the Solar System to disrupt Kuiper Belt Objects (KBO) on the scale of tens of millions of years. There is also the occasional gamma ray bursts (GRB) which if even not close enough to damage Earth’s atmosphere could energize relatively dense clouds of molecular gases and cause them to accelerate and flow quasi-randomly to occassionally cut across our Solar System. We are on the inner edge of the Orion Arm at the cusp of faster and slower rotating areas so we experience some differential flow, but crucially are far enough away from dense regions that direct exposure to GRBs is very rare and usually distant enough not to be of concern, and also well shielded enough from the galactic core by gas and dust that we don’t experience the intense gamma ray flux that is thought to permiate that region.
So, we may be in a somewhat privileged location well-suited to life (or at least, our particular form of carbonaceous-nitrogeneous amino acid-based life) compared to being in more radiation-heavy or element-poor regions, but beyond that what the Earth and our Solar System would be like at a different galatic radius or outside a galaxy at all is entirely speculative, particularly given that we have yet to send a probe much outside of our heliopause and can only infer conditions and the composition of the interstellar and intergalactic media by observations and modeling.
Stranger
Apparently there are some models of dark matter, under which some fraction of the dark matter would form its own disk, rather than remaining in the spherical halo. That could result in enough of a density variation to make it work.
At a full PC now and able to dig up my links from the last time I discussed this somewhere (in the comments section.) The galaxy is 2,000 light-years thick. We are currently 50 light-years from the center of that plane, or 5 percent of the thickness. Dark matter may be more concentrated near the center of the plane, but it isn’t going to be a razor-thin disk–if there is a higher concentration, we are probably already in it. Plus, the periodic extinctions probably aren’t periodic and only one (the famous Katey) has firm evidence that it was impact-related.