The universe is made up of billions of galaxies, each consisting of many stars. The largest are spiral galaxies like our own galaxy. Our galaxy (the Milky Way) is surrounded by about two dozen much smaller galaxies called dwarf galaxies, which each have a much smaller number of stars. In recent years astronomers discovered that the dwarf galaxies surrounding our galaxy are found in a plane-like structure that is known as the Vast Polar Structure (or VPOS). They have also found that the dwarf galaxies surrounding the nearest nearby spiral galaxy (the Andromeda galaxy) are also found in a plane-like structure called the Great Plane of Andromeda.
Such findings have raised doubts about the prevailing theory of large-scale structure formation, the lambda cold dark matter theory. Such a theory predicts that dwarf galaxies should be located in an irregular blob around our galaxy, not in a plane-like structure.
This week a paper published in the scientific journal Nature announced two big findings. The first was that rather than being a local fluke involving only our galaxy and its biggest neighbor galaxy, the tendency of dwarf galaxies to exist in a plane (around a spiral galaxy) is apparently quite typical. The study suggested data "may indicate planes of co-rotating satellites, similar to those seen around the Andromeda galaxy, are ubiquitous." Such a finding seems to be bad news for the lambda cold dark matter theory.
The second finding of the paper may be bad news to anyone who doesn't like to hear about mysterious unexplained examples of large-scale cosmic order. The scientific paper found an astonishingly strong tendency for the motions of opposite pairs of dwarf galaxies to be anti-correlated. That phrase is quite a mouthful, so let me give a visual which explains it.
In the picture below, we see a galaxy with two much smaller dwarf galaxies next to it. (The picture is a composite image not intended to represent some particular galaxy.) The dwarf galaxies rotate around the larger galaxy. But they rotate in opposite directions, as shown by the red arrows. This is what is meant by an anti-correlated motion.
The Nature paper (by Neil Ibata, Geraint Lewis and others) first checked a huge computer model of the universe to see whether we should expect to see any difference between these two things:
- The number of dwarf galaxy pairs on opposite sides of a galaxy which have their rotation motions anti-correlated with each other.
- The number of dwarf galaxy pairs on opposite sides of a galaxy which have their rotation motions correlated with each other.
The model predicted that there should be no difference between these two. In other words, the model predicted that the type of motion labeled as A below should be as common as the type of motion labeled as B:
But the observations gave a dramatically different picture. As shown in the graph below, the study found that for every dwarf galaxy pair that had a correlated motion, there were between 2 and 4 that had an anti-correlated motion.
Dancing dwarfs? Good heavens, that sounds like something out of a Disney movie.
The paper did not suggest any mechanism for this strange choreography, nor did any of the articles about it that I read. Not surprising, as it is hard to think of any natural mechanism that could explain it.
The Sciencedaily.com article on the paper says, “The discovery may mean that our current models need to be completely revised .” So the new finding could be a paradigm buster.
This is the third time scientists have made some distant observations suggesting that the universe may behave in shocking defiance of our expectations of random behavior. One other case (discussed here) was that scientists discovered that the polarization vectors of quasars tend to be aligned in the same direction in particular regions of space. In one gigantic area of space, these vectors may be aligned in one direction, and in another huge region of space, they may be aligned in some different direction. Another comparable case (discussed here) is that scientists discovered that galaxies tend to rotate preferentially in certain directions of the sky. In some directions of the sky spiral galaxies tend to rotate as much as 7% more frequently in a left-handed rotation, even though scientists think there should be no difference between the number of left-handed rotations and the number of right-handed rotations.
At the very end of Olaf Stapledon's novel Last and First Men (available here on a single web page) are seven paragraphs that I consider to be one of the greatest passages in English literature. Below is a brief excerpt:
Throughout all his existence man has been striving to hear the music of the spheres, and has seemed to himself once and again to catch some phrase of it, or even a hint of the whole form of it. Yet he can never be sure that he has truly heard it, nor even that there is any such perfect music at all to be heard. Inevitably so, for if it exists, it is not for him in his littleness.
But perhaps the distant golden fleece to pluck is not the music of the spheres, but the dance of the spheres. And perhaps now we are starting to glimpse some of that strange and surprising cosmic dance.
Which raises the question: who or what did the choreography?