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PlaidBastard t1_itpz0pq wrote

So, a little googling got me this: https://astronomy.com/magazine/ask-astro/2006/01/how-close-can-stars-get-to-each-other-in-galaxy-cores

TLDR; stars only 860 AU (Earth-Sun distances) apart instead of 5 lightyears (360 times further) means probably no planets in the first place, but pretending there were, the night sky would ABSOLUTELY be brighter! The daytime sky would be bright! Unless someone can show the math otherwise, I think you can bluntly estimate 360^2 = ~130k times brighter, all other things being equal.

That's fun to think about. I don't think I've seen a good visualization of what that visual environment would look like in the visible spectrum in human dynamic range. Could be more watts per square exposed meter than anything organic can exist at...

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glurth t1_itqjd1c wrote

Lemme riff some math off this data:

Luminosity Of Star / distance from star squared = apparent brightness of star

Let's pick a star with Luminosity: L

apparent brightness at avg EARTH star distance = Eb = L / (30k AU^2)

apparent brightness at avg galactic center star distance = GCb = L / (850 AU^2)

solve both for L

L= Eb/(30k AU^2)

L=GCb / (850 AU^2)

two terms for L: set expressions to equal each other

Eb/(30k AU^2) = GCb / (850 AU^2)

Gcb/Eb = Ratio of apparent brightness between star seen from earth and from the galactic center

Gcb/Eb = 30k^2/850^2 = 722.5K

So that one star will be 722k brighter at avg galactic center star distances, than at earth avg star distance.

(For comparison- our sun is 1AU from earth, using the same formula, it is 900 million times brighter than an avg earth distance star (of the same luminosity), and .... 722.5K times brighter than an avg galactic center distance star (of the same luminosity): the same number we computed earlier - what an odd coincidence- somebody better check my math!)

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incarnuim t1_its895u wrote

I'm imagining aliens with very small eyes telling ghost stories:

"Don't mess with humans. They're invisible ninjas that evolved in total blackness. They move through the night killing and pillaging at will. If you don't eat your vegetables, we will send you to the land of Living Nightmares, Earth....

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incarnuim t1_itqkxt6 wrote

Why would stars 860 AU away preclude planets? For comparison, Jupiter is 4-6 AU from Earth and 1e-3M(•). Jupiter gives Earth a little bit of a wiggle, but obviously doesn't preclude stable orbits. A body with M=1 M(•) only needs to be ~32 times further out to have the same gravitational effect, so 130 AU or so. Red Dwarf stars with M=0.1 or even 0.05 M(•) could be closer, roughly at the orbit of Neptune, and have little gravitational effect on a planet 1 AU from a parent star (this would technically be a binary star system, but a Far Binary, as opposed to a Close Binary system which would be more like Tatooine....)

A star 860AU away would produce practically no wiggle on a planet 1 AU from a parent star.

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cbusalex t1_itr53i5 wrote

> Why would stars 860 AU away preclude planets?

If 860 AU is the average distance between stars, and the stars are moving relative to each other, then over a long enough timeline most stars will have much closer encounters than that.

Gliese 710 is projected to pass within 0.1663 light-years of the sun within the next couple million years, 30 times closer than the 5 light-year average distance between stars in this neighborhood. If that sort of thing is typical, then you'd expect stars with an average distance of 860 AU to have occasional passes at only a few dozen AU.

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incarnuim t1_itrh0jj wrote

Possibly, but I personally don't know enough to posit the effects of that on planetary systems. Have any other stars passed that close to us over the past several million years? If not, then Gliese 710 may be an atypical event...

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Allarius1 t1_itqmko1 wrote

Isn’t that just considering the impact after planets have formed and stable orbits have already occurred?

How would the presence of the extra stars affect the formation to begin with?

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incarnuim t1_itrhaxo wrote

That's a good question, to which I have no idea.

For that matter, we could talk about capture of rogue planets too. A dense network of stars might act like something of a net for rogue planets...

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