Galaxies like Milky Way might be rare in our cosmic neighborhood

The Milky Way is like a twisty, maybe even fancy spiral galaxy, but it’s hard to say for sure from where we’re looking. What we do know is that there aren’t a lot of galaxies shaped like a disk in our neck of the cosmic neighborhood known as the supergalactic plane. On Earth, we pinpoint places using compass points and latitudes/longitudes, but that doesn’t cut it in space. Astronomers rely on the supergalactic coordinate system to figure out where galaxies are hanging out.

In the coordinate system, there’s this thing called the Supergalactic Plane (SGP), and it’s like the neighborhood for the Local Group of galaxies, which includes the Milky Way. The SGP is almost at a right angle to the Milky Way’s plane.

We’re not totally sure about the Supergalactic Plane (SGP)—how big it is, what it looks like, or how it fits with other space stuff. In a 2000 paper published in MNRAS, a bunch of researchers pointed out that the SGP isn’t neatly shaped like a uniform ellipsoid. They said, “The structure of the SGP is not well described by a homogeneous ellipsoid,” and mentioned that it kinda morphs between looking like a squashed pancake and a dumbbell as you move outwards.

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Supergalactic Plane (SGP) is filled with galaxies

Scientists do have the scoop on one thing: the Supergalactic Plane (SGP) is bustling with galaxies. Bright elliptical galaxies pretty much rule the SGP, and you won’t find many spirals like the Milky Way hanging around. This shortage of spiral galaxies caught the eye of some European researchers. They rolled out supercomputer simulations to figure out just how many galaxies are living it up in the SGP and where they’re throwing their cosmic parties.

You can check out the findings in the journal Nature Astronomy, in a paper titled “Distinct distributions of elliptical and disk galaxies across the Local Supercluster as a ΛCDM prediction.” The main brain behind the study is Till Sawala, hailing from the Department of Physics at the University of Helsinki in Finland. Sawala used to roll with the Institute for Computational Cosmology at Durham University in the UK.

“Galaxies of different types are not equally distributed in the Local Universe,” the researchers write in their paper. “The supergalactic plane is prominent among the brightest ellipticals but inconspicuous among the brightest disk galaxies.” 

That striking difference sets the stage for their research, which is aimed at testing our understanding of how galaxies form and evolve, and if their formation and evolution conform to the Lambda CDM model.

How small things can make a big picture

The scientists tapped into SIBELIUS, short for Simulations Beyond the Local Universe, to dig into what makes the Supergalactic Plane (SGP) tick. SIBELIUS is all about linking up the Local Group with its cosmic surroundings. One cool thing about SIBELIUS is its knack for revealing how tiny tweaks can shake up the big picture. In earlier SIBELIUS runs, they found out that having the Large Magellanic Cloud around messes with how the Milky Way and Andromeda (M31) dance around each other like a cosmic duo.

But that’s just the setup for the latest scoop. SIBELIUS has the power to play out the entire cosmic show, from the Universe’s baby steps 13 billion years ago up to the present. In this fresh batch of simulations, Sawala and the gang uncovered the secret sauce behind the arrangement of ellipticals and spirals. Turns out, it’s all about the vibe inside and outside the Supergalactic Plane (SGP). Inside the SGP, galaxies cozy up more tightly, while things are more spread out in the cosmic suburbs beyond the SGP.

In the SGP hotspot, galaxies are like social butterflies, constantly mingling and merging. This social scene transforms the lovely spirals, like our Milky Way, into ellipticals – those roundish blobs with no clear arms. However, in the chill zone outside the SGP, galactic hangouts are less frequent. That’s why the Milky Way and its cosmic buddies out there get to keep their cool spiral shapes.

“We find that SIBELIUS DARK reproduces the spatial distributions of disks and ellipticals and, in particular, the observed excess of massive ellipticals near the supergalactic equator,” the researchers write.

The SIBELIUS findings match up with what we’ve seen, giving it a thumbs-up for reliability. For disk galaxies to bulk up, like our trusty Milky Way, they crave a steady gas supply and steer clear of galaxy drama. Lucky for them, that cosmic chill spot is right outside the SGP.

“We conclude that the environment prevailing in the supergalactic plane inhibits the conditions necessary for massive disk formation: a quiet merger history and the continuous supply of cold gas,” the authors explain.

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The study aligns with Lambda Cold Dark Matter model

So, what’s the lowdown on the Lambda Cold Dark Matter (CDM) model from these findings? Well, this model is like the rock star of cosmology, the go-to standard. According to its gig, 27% of the cosmic scene is dark matter, a whopping 68% is dark energy, and we’re left with a measly 5% for the regular stuff – the baryonic matter that makes up stars, planets, and, us. “Cold” in its name means dark matter moves at a snail’s pace compared to light speed, and “dark” implies it’s basically a cosmic loner, barely rubbing elbows with regular matter or electromagnetic energy.

Sawala and the team are saying these findings give a nod to the Lambda CDM model. Why? Because SIBELIUS is built on our cosmic know-how, which includes the CDM idea. If it mimics what we observe out there, it’s like a cosmic high-five, saying, “Yep, CDM, you got it right!”

“The strikingly different distributions of bright ellipticals and disks in relation to the supergalactic plane do not require physics beyond the standard model,” they write. 

Whether we call home a spiral/disk or an elliptical galaxy doesn’t change our day-to-day, but it’s kind of cool to see where we fit in the grand cosmic picture. These findings just add more muscle to the case for the Lambda CDM model, which is pretty solid already.

Now, if only we could crack the mystery of what the heck dark matter really is.