00:00Welcome back to the explainer today. We're diving into a massive cosmic detective story
00:04We're talking about the galaxies behind us and we're going to solve the milky way's 2 million kilometer per hour
00:10mystery
00:10We're going to map the actual invisible forces that are literally pulling our very own galaxy through the vastness of
00:16space
00:16So if you think you know your neighborhood strap in because we're about to completely shift your perspective
00:212 million that is a mind-boggling number, right?
00:25Well, right now as you sit there watching this explainer you me the earth our solar system and the entire
00:32milky way galaxy
00:34Are hurtling through space at a baffling 2 million kilometers per hour to put that into perspective
00:39That's about 600 kilometers every single second
00:42But why I mean what could possibly have enough gravitational muscle to drag an entire galaxy at that kind of
00:50speed?
00:51For decades astronomers were pretty sure they had their cosmic culprit
00:54They pointed at this thing called the great attractor. It's this massive gravitational anomaly over in the centaurus constellation
01:01And you know, it made sense at first
01:03But as our measurements got better and more precise a massive problem emerged the math just didn't add up
01:09There was this glaring mass gap the great attractor simply wasn't heavy enough on its own to pull us that
01:14incredibly fast
01:15The laws of gravity obviously weren't broken. So we knew we needed more mass to balance the cosmic equations. The
01:21question was where was it hiding?
01:23Well, it turns out the missing gravitational mass was actually right in front of us
01:28But it was completely hidden by something astronomers called the zone of avoidance or ZOA
01:32Think of it like an immense cosmic blind spot that covers up to 20 percent of our entire night sky
01:38We couldn't find the missing gravity because the center of our very own milky way is just absolutely packed with
01:44thick clouds of interstellar gas and stardust
01:47It acts exactly like a thick fog totally obscuring whatever massive structures lie directly behind our own galactic plane
01:54Basically, we were blinded by our own stardust
01:56So, how do you see through a thick cosmic fog?
02:00Well, you have to completely change how you look
02:02To crack this mystery astronomers turn to multi-wavelength astronomy
02:07Here's how it works
02:08Step 1. Infrared light
02:10Its longer wavelengths pass right through the dust clouds that normally block visible light
02:15Step 2. Radio waves
02:17These are powerful enough to punch through the absolute densest parts of the galactic plane
02:22And finally, step 3. Spectroscopy
02:25By measuring the redshift of thousands of objects
02:27Scientists could calculate exactly how far away these hidden galaxies were
02:31And more importantly, how fast they were moving
02:34And when they finally combined all these techniques to peer through that dust
02:38Boom!
02:39They found the missing heavyweight
02:41Enter the Vela supercluster
02:43Located roughly 800 million light-years away
02:46This is a massive, massive concentration of galaxies that had just been completely hidden from us this whole time
02:52It's similar in scale to the largest structures in our known universe
02:56And the most thrilling part?
02:57Its immense mass finally bridged that mathematical mass gap
03:01It exerted the exact powerful gravitational tug needed to help explain our 2 million kilometer per hour velocity
03:07Mystery solved, right?
03:08Well, actually
03:09Here's where the plot twists again
03:12Because we aren't just being pulled
03:14The crucial thing to understand here is this cosmic duality
03:18Yes, we absolutely have pulling forces
03:20Dense structures like the Great Attractor
03:22The Shapely supercluster
03:24And the newly mapped Vela supercluster located ahead of us
03:27But back in 2017
03:28Astronomers made a wild discovery
03:30We are also being pushed
03:32By what, you ask?
03:33Vast, expanding, completely empty regions of space
03:37Things like the dipole repeller and the local void
03:39Because we live in an expanding universe
03:41These empty regions of incredibly low density act as repellers
03:45Exerting this cosmic expansion pressure
03:47That literally nudges our galaxy from behind
03:50It's a cosmic push and pull
03:52To really wrap our heads around this complex push and pull
03:55We kind of need to zoom out and find our place within it all
03:58Let's quickly walk through the hierarchy of our cosmic address
04:02We start local at the solar system
04:04Then we zoom out to our home galaxy, the Milky Way
04:08Keep zooming and we find ourselves in the local group
04:11Which is basically our quiet suburban street of about 50 galaxies
04:14That whole street sits inside the Virgo supercluster
04:18Our specific cosmic branch
04:20And all of this, it's tucked away on the extreme outskirts of the massive Laniakea supercluster
04:26Which is a structure of 520 million light years wide
04:29If the Milky Way is our house, Laniakea is our home continent
04:33I absolutely love this analogy
04:36Think of Laniakea like a massive valley
04:38Any galaxy inside that valley naturally flows toward the Great Attractor at the bottom
04:43This perfectly explains the concept of a gravitational watershed
04:47Just like rain falling on a mountain ridge flows down into the same river basin
04:51All 100,000 galaxies within the borders of Laniakea are flowing downstream
04:56Toward that exact same central gravity well
04:59We are all caught in the exact same cosmic current
05:02Okay, let's snap back from that mind-bending 520 million light years scale
05:06To something hyper-local
05:08Let's look at our local group again
05:09Just 2.5 million light years away from us is Andromeda
05:13Now in the vastness of Laniakea
05:152.5 million light years means Andromeda and the Milky Way are essentially next-door neighbors
05:19We are the two undisputed heavyweights on our local suburban street
05:22Just navigating this massive gravitational flow together
05:25Our galaxy and Andromeda completely dwarf the surrounding satellite dwarf galaxies in our local group
05:31They are massive
05:32And here is an amazing fact for you
05:34While most of the universe is expanding and pushing distant galaxy clusters apart
05:38Our mutual gravity with Andromeda is actually strong enough to completely overcome cosmic expansion
05:43That's right
05:45We are gravitationally locked to one another
05:47Which leads us directly to a wildly thrilling local twist
05:51The Milka-Meta collision
05:52Because we're locked together by gravity, Andromeda isn't moving away from us with the rest of the expanding universe
05:58Nope, it is hurtling right toward us at 110 kilometers per second
06:02In about 4 to 4.5 billion years, our two heavyweight galaxies are absolutely destined to collide and merge
06:08Eventually forming one single massive elliptical galaxy nicknamed Milka-Meta
06:12Now, don't panic, because galaxies are mostly empty space
06:15It's actually highly unlikely that individual stars will physically collide
06:19But for sure, our cosmic skyline will be forever changed
06:22Now, before we completely wrap up our map of the cosmos today
06:25I have to drop the ultimate twist in this entire gravitational equation
06:29Are you ready?
06:30All the galaxies
06:31All the stars
06:32The giant Vela supercluster
06:34Andromeda
06:34The gas clouds
06:35Literally all the visible matter we've discussed throughout this explainer
06:39It only accounts for 15% of the gravitational pull moving us
06:43Just 15%
06:44The remaining 85% of the gravity required to whip us around at 2 million kilometers per hour is entirely
06:50invisible
06:51Yeah, you probably guessed it
06:53This invisible 85% is dark matter
06:56Dark matter acts as the hidden scaffolding of the entire universe
06:59It forms this massive cosmic web of filaments that literally hold these supercluster nodes together
07:04It is the true architect behind the scenes
07:07Dark matter is the dominant force shaping the gravitational watershed of Laniakia
07:11It's what holds the hidden Vela supercluster intact
07:14And it is the primary engine driving our staggering journey through space
07:18So all of this leaves us with a question that I think should really stick with you long after this
07:22is over
07:23As we continue to chart the invisible scaffolding of our cosmic watershed
07:27Peering through the galactic dust and mapping the vast voids pushing us from behind
07:30What other giant attractors are waiting to be found in the dark?
07:34I mean, we've found Vela
07:35But what else is out there, silently pulling on us from just beyond the edge of our vision?
07:40It really makes you realize just how much of our cosmic map is still waiting to be drawn
07:44Thanks so much for joining me on the explainer today
07:46Keep wondering, keep looking up, and I'll catch you next time
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