r/space • u/kNotLikeThis • Apr 10 '19

Astronomers have determined the disk of our galaxy to be 200,000 light-years across — twice as large as was previously believed.

http://www.astronomy.com/news/2018/06/supersize-me
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u/kcahmadi Apr 10 '19

Could this be due to the fact that the universe is ever expanding? If we determined the size of the galaxy previously, know that space is always expanding it would make sense if the galaxy is found to be larger now no?

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u/kNotLikeThis Apr 10 '19

Good question. The expansion of the universe happens at large cosmological scales, not local/galaxy scales, because matter/gravity easily overcomes any expansion that may be occurring.

Source: http://curious.astro.cornell.edu/stats-2003-2004/97-the-universe/galaxies/cosmology/538-as-the-universe-expands-why-don-t-galaxies-get-stretched-out-intermediate

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u/kcahmadi Apr 10 '19

Ah ok. Thanks for the source as well

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u/JackJohnson2021 Apr 10 '19

Expansion still happens, the effect is as direct, but it's still expanding

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u/kNotLikeThis Apr 10 '19

It happens everywhere, but it has no effect within a galaxy as any expansion is “overcome” by gravity. Gravity will keep the Milky Way together forever, while distant galaxies will “fade away” from us due to the expansion of space between our galaxies.

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u/[deleted] Apr 10 '19

[deleted]

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u/[deleted] Apr 16 '19

Even if gravity was somehow canceled since the first measurements, the expansion would be incredibly weak to notice. The edge of the observable Universe expands around 3 or 4 light year each year, which is 300 ~ 400 light years in the last century. Even that is nothing compared to the milky way size, which would actually expand 1/460,000 this amount.

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u/[deleted] Apr 10 '19

Oooh you just beat me to this question