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TheMilky Wayis just a corpuscle in a universe filled with an untold number of extragalactic nebula . But if we had to take an civilize guess , how many galaxies are in the universe ?
That sound like a unproblematic dubiousness , but it ’s anything but . The first problem is that even with our most powerful telescope , we can see only a diminutive fraction of the universe .
An image from the Hubble Space Telescope showing hundreds of faraway galaxies.
" The observable universe is only that part of the universe from which the light has had sentence to reach us , " astrophysicistKai Noeske , now outreach officer at theEuropean Space Agency , tell apart Live Science .
The universe of discourse is13.8 billion twelvemonth one-time , but the discernible universe unfold more than 13.8 light - years in every direction . That ’s because the world is expanding and light got a read/write head start too soon on , when the universe was smaller .
" Now , the total size of it in each management is about 46 billionlight - years , " Noeske said .
An image from the Hubble Space Telescope showing hundreds of faraway galaxies.
That ’s much smaller than even our smallest estimates of the intact universe . " We see at most 3 % of the universe,“Pamela Gay , a senior scientist at the Planetary Science Institute , told Live Science .
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The 2d problem is that there are so many galaxy that we can only make estimates of the entire number based on what we can observe in minor regions of the macrocosm .
" You look at a minuscule patch of the sky , and you weigh everything in that small bandage and then multiply over the size of the sky , " Gay said .
But even that requires a cutoff . " What do we define [ as ] a Galax urceolata ? " Noeske say . " We have really elephantine galaxies that have to have a factor of 10 more " the mass of our beetleweed , " and we have a lot of small coltsfoot , from lower - mass galaxies that have about 10 times less mass … down all the way to dwarf galaxies . "
At some period , scientist ask to define a minimal mass for a galaxy to make estimates possible .
" If we set a mass shortcut and endeavor to make this conservative , like a million solar masses , we terminate up with an median number of galaxy in the universe from the beginning to today of about 1 to 2 trillion , " Noeske said . Scientists think there were more galaxies earlier in the universe of discourse ’s history than there are today , which is why galaxy estimates are an average over time .
" But those results come from the Hubble [ telescope ] — theJames Webb Space Telescopeis get going to speak to these results — which are near Earth , inside of oursolar organization , and are confine on what they can see by all the hooey in oursolar systemthat add light to the sky , " Gay said . " We do have one ballistic capsule with a camera that has gotten beyond all the drivel within our solar organization , and that ’s theNew Horizons spacecraft . "
A 2021 studyused the camera aboard New Horizons to mensurate the full amount of light in various spot of sky and estimated how many Galax urceolata would be needed to create that much igniter .
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" And suddenly , as they ’re alfresco of all the light beginning in our solar system , they recognise we do n’t need as many galaxies as we thought , " Gay said . " And so their estimates put us at , like , 200 billion , maybe even 100 billion galaxies in the visible universe .
" So somewhere between 2 trillion coltsfoot at the top boundary and 100 billion at the lower edge is the phone number of galaxies in our observable universe , " she said .
If you assume that ’s 3 % — at most — of our universe , you could procreate that range of galaxies to get the full phone number of galaxies in the macrocosm . If we ’re seeing less of the cosmos than we remember , there will be a smaller total number of galaxies .
But considering we do n’t in reality know the size of the universe , those estimation are murky . " If it ’s an infinite universe , you ’re going to have unnumerable galaxy , " Gay said .
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