DURHAM, United Kingdom — Orbiting our home galaxy, the Milky Way, is a vast number of satellite galaxies that surround us in a rather strange pattern. Now, however, astronomers say they are getting closer to understanding why they are in a strange formation.
Researchers at Durham University have a new theory as to why the faint satellite galaxies surrounding the Milky Way are arranged in a thin rotating plane called the ‘plane of satellites’. The alignment looks like a thin plane that cuts through the galaxy while, at the same time, circling a coherent and long-lived disk.
The strange alignment has puzzled scientists for years since its discovery in the 1970s. There is no physical mechanism for creating the satellite plane. It was thought that the satellite galaxies should be arranged in a roughly circular configuration that would detect the dark matter of the universe. However, the plane’s supercomputer simulations failed to recreate similar structures that could trace the evolution of the universe since the beginning of the Big Bang. Without concrete or tangible proof, some researchers began to question the cold dark matter theory of galaxy formation.
Is this alignment just a fluke?
Similar to the way star constellations change, the international research team suggests that the level of satellites is simply a cosmological quirk that will decay over time. Their model also explains how the galaxies we see now form gradually with clumps of cool dark matter. Although never seen by the human eye, dark matter is thought to make up about 27 percent of the universe.
The conclusion of the current study came from new data from the European Space Agency’s GAIA space observatory. GAIA draws a six-dimensional map of our Galaxy and includes precise positions and measurements for about a billion stars in the galaxy — one percent of the total — along with companion systems.
The data gave scientists orbital projections of the galaxy’s past and future satellite. Their predictions showed that the plane would form and dissolve in a few hundred million years. Although it sounds like a lot, it is a glimpse into cosmic time.
“The plane of the satellites was really shocking,” says lead study author Till Sawala, a professor at the University of Helsinki, in a media release. “It is not surprising that a puzzle that has endured for nearly fifty years required a combination of methods to solve it – and an international team to assemble.”
Our neighboring galaxies are in the ‘right place at the right time’
The scientists also searched new tailored cosmological simulations for evidence of satellite levels. Previous simulation research has failed to include the satellites’ distances from the galactic center, making the virtual satellite systems appear much rounder than the real ones.
In the current study, they created several simulations of the Milky Way, all containing a layer of satellite galaxies similar to those seen in telescopes. The tailored virtual simulations are proposed to give more validity to the Standard Model of cosmology and the theory that dark matter is the foundation behind the formation of our universe.
“Thanks to amazing data from the GAIA satellite and the laws of physics, we now know that the plane is just an alignment of chance, a matter of being in the right place at the right time, just like the constellations of stars in the sky,” says Carlos Frenk, professor of fundamental physics at Durham University’s Institute for Computational Cosmology. “Come back in a billion years and the plane will have disintegrated, just like today’s constellations. It continues to provide an extremely faithful account of the evolution of our Universe.”
The study is published in the journal Astronomy of Nature.
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