It is natural for astronomers to focus their telescopes on the parts of the universe that are closest to us, because these stars and galaxies can be examined in the most detail. But astrophysicists sometimes have trouble balancing the population of our galaxy’s neighborhood with dark matter theory. For example, early models predicted more nearby galaxies than were actually found in the real universe, a problem known as the “missing satellite” problem.

The chunks of dark matter should have enough gravity to pull the gas into the stars and then form galaxies.But another problem is that some simulations end up producing large, orbiting clumps of dark matter that look like should Host satellite galaxies – but they don’t seem to have any real cosmic counterparts. This is known as the “too big to fail” problem, because massive dark matter clusters are thought to be too large to form galaxies in them.

A third challenge arises from the fact that the satellite galaxies orbiting the Milky Way and Andromeda appear to orbit in a plane, rather than spread out—something dark matter physicists didn’t expect.

There are also cosmological questions that Frank and his colleagues want to solve. Astronomers who use nearby supernova explosions and other local phenomena to measure the current rate of the universe’s expansion get different answers than those exploring the early universe. If the dark matter model is correct, then there must be a way to resolve the troubling and persistent discrepancies between past and current observations.

But a simulation like SIBELIUS might help. It may turn out that where galaxies live on the cosmic dark matter web does have an impact on measuring the expansion rate of the universe. What if the Milky Way was in a “hole” in the web—if it was more of a rural area between dark matter metropolises? If our universe isn’t actually representative, our local measurements of how fast the universe is blowing out may be a little off.

Priyamvada Natarajan, an astrophysicist and dark matter expert at Yale University, said the Milky Way could happen to be in a region where dark matter is fairly dense or sparse. “The cool thing about this simulation is that they can solve: How typical or unusual is our local volume? How rare is the distribution of matter we see around us? Are we on a mountain or in a valley?” she said.

Comparing apples to apples is necessary when comparing galaxies observed with telescopes to those seen in simulations, said Jenny Sorce, an astrophysicist at the Orsay Institute for Astrophysics in France who helped design a similar The simulation, called CLONE, focused on galaxies in the Virgo cluster. “You can’t compare one type of cluster to another if they don’t have the same history or the same environment,” she said.

Frenk and his team did extensive initial testing at low resolution on their own computers. But time on a supercomputer, like on a telescope, is limited. They have only one chance to run a full simulation, which requires millions of computing hours on thousands of computer cores. But based on their simulations, they found that the Milky Way neighborhood does look atypical: We live in a region of the universe with fewer galaxies than average, but also more large galaxy clusters than average. It’s like living in a low-elevation city like Los Angeles, but with mountains in the distance.

Frenk and Boylan-Kolchin speculate that if the Milky Way is indeed an oddball, it might help explain some of the dark matter mysteries. If we are in a sparse part of the universe, this may explain why local measurements of the expansion rate differ from those expected based on measurements of the distant universe.

If our Milky Way is in the middle of an atypical region, that might explain why these moons are in unusual configurations — maybe they’re pulled into the Milky Way’s orbit in a particular way.

In other words, if the Milky Way’s vicinity is indeed unusual, it means that cold dark matter theory will survive these challenges — for now.