
Gaia spots stars flying between galaxies - LinuxBender
https://www.sciencedaily.com/releases/2018/10/181002103000.htm
======
cletus
Isaac Arhur touches on this subject in one of his videos, Intergalactic
Colonization [1].

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.

[1]:
[https://www.youtube.com/watch?v=xRB7a89Jh7w](https://www.youtube.com/watch?v=xRB7a89Jh7w)

~~~
valarauca1
Dealing with dark matter halo's is likely non-trivial. While the science is
still out, the most likely dark matter candidate is 15-50 solar mass black
holes [1].

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).

~~~
drjesusphd
Horrifying in what way? In the sense of being nearly impossible to navigate
taking into account their gravitational effects? If these black holes are just
as dense as in the galaxy, wouldn't that make navigating the galaxy just as
difficult? The distances are longer, but that just means corrective burns have
a stronger effect on the future trajectory.

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Ush2iaph
What better intergalactic colony ship than a whole star system accelerated to
a significant fraction of c.

~~~
Flow
But how can a civilization even start to move a star to a degree it fills a
purpose?

~~~
stcredzero
Shkadov Thrusters

[https://www.youtube.com/watch?v=_VetAm7fCS0](https://www.youtube.com/watch?v=_VetAm7fCS0)

~~~
def_ConGame
That guy's channel is awesome, but his Rhotacism drives me up the wall.

[https://en.wikipedia.org/wiki/Rhotacism_(speech_impediment)](https://en.wikipedia.org/wiki/Rhotacism_\(speech_impediment\))

~~~
stcredzero
I just imagine Elmer Fudd dressed like Carl Sagan.

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alex_duf
I wonder how we'd feel as a species if our star was one of these instead of
being the Sun.

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.

~~~
TeMPOraL
I have this science fiction writing/game backstory idea I recently came up
with. Feel free to use it, as I guess I won't get around to do anything with
it any time soon. Copying straight from my "ideas" file:

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.)

\--

EDIT: Wow, turns out this isn't even that implausible -
[https://news.ycombinator.com/item?id=18123098](https://news.ycombinator.com/item?id=18123098).

~~~
kbenson
Wow. Just the changed mindset (compared to the present, at least) would be
amazing.

"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...

~~~
thaumasiotes
> Are there others out there? Yes. And they're like us.

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_.

~~~
kbenson
> By the time we managed to meet them again, there would be no reason to
> expect them to be like us.

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.

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Razengan
Stars outside galaxies, planets without stars, asteroid clusters drifting
through nebulas, worlds orbiting black holes..

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.

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leovuyk
Surprise! Gaia satellite sees Stars flying between galaxies. Quantum-FFF
Theory suggestion: Due to still undetected Galaxy Anchor Black Hole (GABH)
gravity sources. at both sides of the spiral galaxy, in combination with Outer
HI disc black hole "slingshots" for acceleration out of the galaxy.see:
[https://bigbang-
entanglement.blogspot.com/2018/10/surprise-g...](https://bigbang-
entanglement.blogspot.com/2018/10/surprise-gaia-satellite-sees-stars.html)
see:
[https://www.sciencedaily.com/releases/2018/10/181002103000.h...](https://www.sciencedaily.com/releases/2018/10/181002103000.htm)
see also for "the origin of dead galaxies":
[http://vixra.org/pdf/1706.0490v2.pdf](http://vixra.org/pdf/1706.0490v2.pdf)

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jetrink
The abstract of the paper says that the two fastest stars are traveling at 700
km/s. For scale, at that speed, a star would take 20 million years to travel
from the outer edges of the galaxy to the center. (That ignores any
acceleration as the star falls inward, of course.)

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MichaelMoser123
Can these very fast stars bump into another solar system? Probably very
unlikely, but is it possible?

~~~
mitchty
Possible yes, likely, no. An example, the collision of the Milky Way with
Andromeda is likely to produce no collisions of solar systems.

Space is big.

~~~
graedus
> An example, the collision of the Milky Way with Andromeda is likely to
> produce no collisions of solar systems.

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-...](https://www.nasa.gov/mission_pages/hubble/science/milky-way-
collide.html)

~~~
sehugg
There used to be a relevant X screensaver ... ah, here's a port of it to JS:
[https://rtoal.github.io/galaxies/galaxies.html](https://rtoal.github.io/galaxies/galaxies.html)

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scentoni
That's no star...

~~~
stephengillie
...It's a pop culture reference.

