Dark matter is about 5 times as abundant as ordinary matter in the universe. We see its gravitational affects on large scales – within galaxies, in groups and clusters of galaxies, and in the overall way in which galaxies are spatially distributed on the largest scales.
Galaxies on the large scale are observed to be distributed in filaments and walls of excess galaxy density, along with voids of lower galaxy densities. These filaments and walls have been discovered during the past 30 years or so.
Since galaxies themselves are primarily composed of dark matter, it makes sense that the filaments and walls and voids are reflecting the large scale distribution of matter as well.
Basically, we can think of dark matter as the scaffolding upon which the ordinary matter clumps – the luminous matter seen from galaxies’ light emission and absorption and due to stars, gas, and dust within galaxies. And when we say light, we mean radiation at all frequencies including radio waves, infrared, visible, ultraviolet, X-rays and gamma rays. Radiation sources are due to ordinary matter, since dark matter couples very poorly to electromagnetic fields – that’s why it’s dark!
Map of our Neighborhood (you are in the center) http://www.atlasoftheuniverse.com/nearsc.html, Richard Powell, CC-BY-SA-2.5
So we know that filaments and walls that we see in the distribution of galaxies reflect (deliberate pun) the underlying distribution of the gravitationally dominant dark matter. It is the gravitational field of the dark matter which has controlled the clumping of ordinary matter into galaxies and clusters and superclusters of galaxies.
Here are some of the most important known filaments discovered over the past 3 decades:
- the Coma Filament
- the Perseus-Pegasus Filament
- the Ursa Major Filament
- the Lynx-Ursa Major Filament (LUM)
- the CIG J2143-4423 Filament
Now these are mostly named after constellations, but of course they are behind the constellations and external to our Milky Way galaxy, and at large distances. The most distant known appears to be at redshift z = 2.38, which means that the light comes from a time when the universe was less than 3 billion years old. It has a linear scale of 350 million light-years.
Galaxy filaments include also structures known as walls. And here are the major walls that have been discovered:
- the CfA2 Great Wall
- the Sloan Great Wall
- the Sculptor Wall
- the Grus Wall
- the Fornax Wall
- the Hercules-Corona Borealis Great Wall
The 3-D perspective map above shows superclusters and voids in our neighborhood. It is centered on the Milky Way and extends out to 500 million light-years. Superclusters are highlighted in blue, and 3 walls are highlighted in yellow: the Coma Wall, the Centaurus Wall, and the Sculptor Wall. A number of Void regions are highlighted in red.
The CfA2 Great Wall (also known as the Coma Wall) extends from the Hercules Supercluster to the Coma Supercluster to the Leo Supercluster on the right hand side of the map. It was the first wall discovered, in 1989, by Margaret Geller and John Huchra of the Havard-Smithsonian Center for Astrophysics (CfA).
This Hercules-Corona Borealis Great Wall is much further away, at a redshift of around z = 2, which means that we are seeing it from a time when the universe was a little over 3 billion years old (more than 10 billion years ago). It has an enormous length of around 10 billion light-years. Which is incredible, since the comoving distance to the Hercules-Corona Borealis Great Wall is 17 billion light-years.
Remember, when you look at these maps, you are also in effect seeing the distribution of the underlying dark matter.
In the next blog, we will talk about possible dark matter filaments on a much, much smaller scale, on the scale of the Sun and the planets within our Solar System, including Earth.
November 27th, 2015 at 6:13 am
So, what’s in the voids? Since we’re still don’t know what dark energy (formerly known as missing mass) is, would the voids maybe be the best place to look for it? Just an odd intuition, Seems like it is dominant there ???
November 27th, 2015 at 6:52 am
Yes. Dark energy is dominant overall, and especially in the voids. The voids aren’t entirely empty, something like 1/10 it seems of typical matter density, but that’s small since on average dark energy is more than twice the energy content of matter (dark and ordinary) today.
If a region has over density of matter of more than a factor of 3 today then it will collapse on itself if it hasn’t already (since the average matter density is about 32% of critical and the dark energy density is about 68%).
In the voids the dominance of dark energy could be 10:1 or 30:1 or more. So the voids are expanding rapidly and accelerating in their expansion.
December 10th, 2015 at 6:13 pm
“Since galaxies themselves are primarily composed of dark matter …” Milgrom, McGaugh, Kroupa, Pawlowski, and others favor MOND over dark matter particles.
“I think there is a serious problem with cold, dark matter …” — McGaugh
“Dark Matter or Modified Gravity?” – Stacy McGaugh, 2015 – YouTube
December 11th, 2015 at 1:51 pm
While MOND can fit to galactic rotation curves and even our Local Group dynamics, it does a poor job of matching other observations. These include clusters of galaxies, the shape of the microwave background anisotropies and the baryon acoustic oscillations at large scale, which it can not fit at all. See http://arxiv.org/pdf/1112.1320v1.pdf
December 21st, 2015 at 6:04 pm
[…] matter in our universe, there are saber-like objects as well. In an earlier blog we talked about dark matter filaments and walls on the very large scale, at the scale of superclusters of galaxies and above. On the small scale, […]
March 15th, 2016 at 1:28 am
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