Gaia spots stars flying between galaxies
sciencedaily.com
sciencedaily.com
Basically, the void between galaxies isn't actually that much of a void. It's just in intergalactic space stars tend to be hundreds or thousands of light years apart rather than the 5-10 (where we are in the Milky Way) or, say, in light weeks or less in the galactic center.
It's known (and he talks about) stars being ejected from galaxies. This is important because a lot of intergalactic stars have high metallicity and are likely to at least some of the time still have their planetary systems.
It is interesting to consider where these stars came from. A nearby galaxy being the obvious candidate. I wonder if the 3D velocity measurements can be precise enough to ever determine this to a high degree of likelihood. It would be cool to find some intergalactic visitors in our own galaxy.
The idea of having thousands's of light years of empty space with the same approximate black hole density as the galactic disk, but without the dust, gas, or stars to see their effects is rather a horrifying barrier to exploring the halo stars.
[1] This is a possibly theory. It is counter to axion theory (massive weakly interactive particles) as Axions require CPT violations we can't create experimentally, and LIGO is seeing collisions of black holes in the correct mass range, and which can't be created via stellar collapse (as they're just too big). Which lends some credibility to this mass range (also it wouldn't impact the CMB so the theory holds a fair amount of water).
https://medium.com/starts-with-a-bang/ask-ethan-can-stars-es...
[1]: https://www.goodreads.com/book/show/13554058-the-wandering-e...
We'd see this amazing group of stars and planets, going away from us knowing the more we wait for space travel to less likely our species would to reach any other star system.
Just wow.
At some point in time (past or future, or magically also present), a star passed in very close vicinity to our sun. It had a habitable planet in its system, full of alien plant and animal life. For the brief moment it was Δv-accessible, it was studied, and eventually colonized. The people going there knew it was going to be a one-way trip, as the star eventually moved further away. Possible stories to set before, during, or after encounter (or even long, long after).
(This works for no-FTL, hard sci-fi setting. By "very close vicinity" I mean, close enough for us to reach it via sublight propulsion, but still far enough not to mess up the inner Solar System gravitationally.)
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EDIT: Wow, turns out this isn't even that implausible - https://news.ycombinator.com/item?id=18123098.
"Are there others out there? Yes. And they're like us. We should try to meet again some day."
It's almost like a modern day Atlantis myth, but true.
If you want a really interesting setting for a game/book, imagine a major regression on Earth (standard post-apocalypse trope), and the colonists finally find a way to visit again...
By the time we managed to meet them again, there would be no reason to expect them to be like us.
> If you want a really interesting setting for a game/book, imagine a major regression on Earth (standard post-apocalypse trope), and the colonists finally find a way to visit again...
This is a regular feature of Motie civilization in the series beginning with The Mote in God's Eye.
Depending on technological advancements and how "hard" you want to consider your sci-fi or future science (purely based on likely developments of current technology, etc), how close to Earth conditions you want to assume the other planet was, how much you believe humans are still evolving, whether you think humans are likely to evolve along similar paths if segregated, whether we are considering mental models only or physical likeness...
So yes, no reason necessarily to expect them to be, but some small chance depending on a lot of factors lining up.
> This is a regular feature of Motie civilization in the series beginning with The Mote in God's Eye.
Yes, it's not an original trope. The rogue star explanation is one of the more feasible I've heard though.
It could easily be the origin of a story of the first interstellar star-ship from Earth traveling across the cosmos, only to reach a planet already inhabited by a human civilisation. (This would presume that knowledge of the traveler world was lost at some point)
Possibly easy to address... maybe, it was small and dim, and in line with a bright star, so we'd interpreted it wrongly.
What's a reasonable ∆v? We get some free ∆v from Earth's orbital velocity of 107,000 km/h, or 29.7 km/s. Our fastest spaceship (which is around sun, https://wikipedia.org/wiki/List_of_vehicle_speed_records#Spa...) is 252,792 km/h, or 70.22 km/s - which isn't including the ∆v to cancel that, ∆v to return to Earth, cancel again.
This 70.22 km/s is about 2 ten thousandths of the speed of light (70.22/299,792). It would take about 20,000 years for alpha centuri (4 ly) to arrive at that speed, and 200,000 years to travel 40 ly, 2,000,000 years for 400 ly.
Of course, maybe we can go faster in future. but propellant is a problem, you have to come back, and a manned mission is orders of magnitude heavier.
Space is big.
funexercise: propose a means of propulsion that could do this.
EDIT a new one is going 692,000 km/h, over twice as fast. At that rate of improvement, maybe we'll get closer to it sooner than I thought. https://www.space.com/41447-parker-solar-probe-fastest-space...
Along that point, what does the heliosphere of such a star look like - a giant comet?
Lastly, were a life-bearing planet sent into space this way have any chance of maintaining that life without a parent star to heat and magnetically shield it?
The heliosphere would look normal because there would be no drag on it. A comet has a tail because the sun is both melting and pushing material away from it.
Lastly, we could probably heat our homes with the core of the planet for a little while, but everything would be dead within a few years. I think the Twilight Zone covered this scenario in an episode! In it the Earth started moving away from the sun for no good reason.
Damned if I remember what it's called, or who wrote it, though...
I wish that Banks had expanded on the idea with further novels as I really enjoyed reading about the cyclical rise and fall of societies while humanity explored different social/political structures, hoping to achieve some form of long-term stability.
We are tantalized with so many possibilities to be explored, without being able to go out and touch them.
I really wish humanity or at least some nations would focus on direct exploration of the cosmos. It would open up entire new industries, provide more jobs, and more beneficial side effects compared to how much we spend on war and preparing for war.
Most importantly perhaps, it could provide a collective sense of hope and purpose that seems to be increasingly missing from our species.
Space is big.
I was curious about this, so I found this source[0] via wikipedia:
"Although the galaxies will plow into each other, stars inside each galaxy are so far apart that they will not collide with other stars during the encounter. However, the stars will be thrown into different orbits around the new galactic center. Simulations show that our solar system will probably be tossed much farther from the galactic core than it is today."
Interpreted literally, it would seem this at least leaves open the idea that a star passing through any other star's solar system and, say, sending its planets into wildly different orbits or flinging some into interstellar space, is meaningfully more likely than a star actually physically hitting another star, but I haven't seen the math. I wouldn't be surprised if they're both extremely unlikely - the diameter of our solar system appears to be about 8500 times larger than the diameter of the sun, which may not change the odds in any significant way.
[0] https://www.nasa.gov/mission_pages/hubble/science/milky-way-...