Australian National University
It's a pattern that repeats on celestial levels. Our planet has the moon, but also a host of other artificial satellites that we've used to boost Earth's follower count. The sun has planets, moons, asteroids, and comets.
But neither can compare
to galaxies like our Milky Way, which not only hosts hundreds of
billions of stars but also has additional satellites, entire
galaxies that chill in our galaxy's neighborhood.
If the dwarf galaxies were following the standard model of cosmology - a theory which underpins most of our understandings of how the universe was formed - they should have been all over the place, scattered around our galaxy's perimeter like autograph seekers mobbing a TV star, not arrayed in an orderly line, like a string of bodyguards.
Then researchers noticed that Andromeda also had dwarf galaxies arrayed in a plane around its center. Still weird, they thought, but maybe these two were just outliers.
But now, a study (A Whirling Plane of Satellite Galaxies around 'Centaurus A' challenges Cold Dark Matter Cosmology) published in Science suggests that these patterns might not be as odd as they first appeared.
A similar row of dwarf galaxies was discovered in 2015 around Centaurus A, a galaxy 13 million light years away.
With three galaxies all showing signs of a similar pattern, cosmologists are trying to figure out how to reconcile new observations with established theories.
There are a few ideas being tossed around trying to understand what might be happening around these larger galaxies.
Some of the theories focus on the idea of tidal forces in the formless void of space.
The resulting dwarf galaxies would orbit the larger ones in a plane and along the same direction, similar to what Oliver Müller and colleagues observed.
But researchers have no idea how long these tidal dwarf galaxies would last after a collision, and that does have implications for cosmology.
Going from building block to afterthought is a lot to reconcile.
Dark matter is a critical component of the standard model, helping to explain the gravitational pull between objects in the universe, which can't be explained by the visible matter in the universe.
This study isn't a death knell for the standard cosmological model, which can explain what happened in the universe moments after the Big Bang, calculate the number of atoms that were present in the universe minutes after it started, explain the presence of cosmic background radiation, and explain how matter is distributed in the universe today.
It's a greatest hits list that's hard to beat.
How to reconcile the observations with the theory? More calculations, more thinking, and more data.
For this study, Muller and colleagues looked at the velocities of the satellite galaxies in relation to our perspective here on Earth to extrapolate more detail about their movement around Centaurus A.
There are ways to answer that question.
The upcoming James Webb Space Telescope, in addition to the stalwart Hubble, could help astrophysicists study more galaxies and their satellites.
By comparing images of the same galaxy taken months or years apart, Michael Boylan-Kolchin says, researchers might be able to get a better sense of how dwarf galaxies are orbiting their hosts, especially if researchers want to take a look at the nearby Andromeda.
But it won't be easy.
At the very least, these new observations will let people take a closer look at how our galaxies formed.