ESO: Dark Matter May be Smoother than Expected

[bystander]

Dark Matter May be Smoother than Expected
ESO Science Release | VST | KiDS | 2016 Dec 07

Careful study of large area of sky imaged by VST reveals intriguing result

---

---

Dark matter maps of KiDS survey regions G12, G9, and G15 (top to bottom) Credits: Kilo-Degree Survey Collaboration/H. Hildebrandt & B. Giblin/ESO

---

Analysis of a giant new galaxy survey, made with ESO’s VLT Survey Telescope in Chile, suggests that dark matter may be less dense and more smoothly distributed throughout space than previously thought. An international team used data from the Kilo Degree Survey (KiDS) to study how the light from about 15 million distant galaxies was affected by the gravitational influence of matter on the largest scales in the Universe. The results appear to be in disagreement with earlier results from the Planck satellite.

Hendrik Hildebrandt from the Argelander-Institut für Astronomie in Bonn, Germany and Massimo Viola from the Leiden Observatory in the Netherlands led a team of astronomers from institutions around the world who processed images from the Kilo Degree Survey (KiDS), which was made with ESO’s VLT Survey Telescope (VST) in Chile. For their analysis, they used images from the survey that covered five patches of the sky covering a total area of around 2200 times the size of the full Moon, and containing around 15 million galaxies.

By exploiting the exquisite image quality available to the VST at the Paranal site, and using innovative computer software, the team were able to carry out one of the most precise measurements ever made of an effect known as cosmic shear. This is a subtle variant of weak gravitational lensing, in which the light emitted from distant galaxies is slightly warped by the gravitational effect of large amounts of matter, such as galaxy clusters.

In cosmic shear, it is not galaxy clusters but large-scale structures in the Universe that warp the light, which produces an even smaller effect. Very wide and deep surveys, such as KiDS, are needed to ensure that the very weak cosmic shear signal is strong enough to be measured and can be used by astronomers to map the distribution of gravitating matter. This study takes in the largest total area of the sky to ever be mapped with this technique so far. ...

Galaxy Images Shed New Light on Dark Matter
University of Edinburgh | 2016 Dec 07

KiDS-450: Cosmological Parameter Constraints from Tomographic Weak Gravitational Lensing - H. Hildebrandt et al

• Monthly Notices of the RAS 465(2):1454 (2017 Feb 21) DOI: 10.1093/mnras/stw2805
  arXiv.org > astro-ph > arXiv:1606.05338 > 16 Jun 2016 (v1), 28 Oct 2016 (v2)

[neufer]

---

[Ann]

This is hot breaking news, and the pictures posted by bystander may become the APOD one of these days. If that happens, I hope the caption is going to be easier to understand than the caption that went with the ESO images. Above all, I would like to know the answer to the following questions:

• 1) How can we tell from the pictures that dark matter is smoother than expected? Are the colored "cells" smaller than expected, for example?
  
  2) How does the smoothness or the lumpiness of dark matter affect the universe? If dark matter is lumpy, does that mean that the universe is "driving along a bumpy road"? If it is smooth, does that mean that the universe is driving along a smooth freeway and perhaps picking up speed?

Ann

[rstevenson]

Not sure it's that much of a breakthrough, Ann. True, they find a significant difference in the measurement of a particular parameter when compared with the Planck 2015 data and its initial analysis, but less significant when compared with later re-analyses of Planck data. In other words, it's an incremental increase in our understanding, necessary but not startling, especially considering it came from analysis of a much better data set.

They state that they found "substantial discordance" with Planck data; they explain how they got that result, and they show how their results were not due to errors; then they suggest ways to move forward in understanding this discordance. They even suggest (if I've understood the paper fully, which I seriously doubt) that there may need to be a slight adjustment in one particular element of ΛCDM, our current best cosmological model.

The work certainly seems to be powerful and suggestive, but probably not paradigm-shaking.

Rob

[Ann]

Not sure it's that much of a breakthrough, Ann. True, they find a significant difference in the measurement of a particular parameter when compared with the Planck 2015 data and its initial analysis, but less significant when compared with later re-analyses of Planck data. In other words, it's an incremental increase in our understanding, necessary but not startling, especially considering it came from analysis of a much better data set.

They state that they found "substantial discordance" with Planck data; they explain how they got that result, and they show how their results were not due to errors; then they suggest ways to move forward in understanding this discordance. They even suggest (if I've understood the paper fully, which I seriously doubt) that there may need to be a slight adjustment in one particular element of ΛCDM, our current best cosmological model.

The work certainly seems to be powerful and suggestive, but probably not paradigm-shaking.

Rob

Thanks for reading the paper for me!

Ann

[neufer]

If dark matter is lumpy, does that mean that the universe is "driving along a bumpy road"? If it is smooth, does that mean that the universe is driving along a smooth freeway and perhaps picking up speed?[/list]

Where exactly do you think the universe is driving to

The Cosmic Background Radiation started out slightly lumpy in order that galaxies & clusters of galaxies could condense over 13.7 billion years so we'd be here to measure this stuff. I think this is simply stating that the condensation process was slower in getting started than we thought ... but I could be wrong.

[Ann]

If dark matter is lumpy, does that mean that the universe is "driving along a bumpy road"? If it is smooth, does that mean that the universe is driving along a smooth freeway and perhaps picking up speed?[/list]

Where exactly do you think the universe is driving to

To whatever it's expanding into?

Ann

[Chris Peterson]

Where exactly do you think the universe is driving to :?:

To whatever it's expanding into?

Most cosmological theories have the Universe not expanding into anything at all.

[Ann]

Where exactly do you think the universe is driving to

To whatever it's expanding into?

Most cosmological theories have the Universe not expanding into anything at all.

Well, most cosmological theories have the Universe expanding, so I guess it's expanding into nothing.

Ann

[Chris Peterson]

To whatever it's expanding into?

Most cosmological theories have the Universe not expanding into anything at all.

Well, most cosmological theories have the Universe expanding, so I guess it's expanding into nothing.

No, it's not expanding into nothing, either, as from a cosmological standpoint "nothing" actually is something.

Language is inadequate!

[Seaquest]

The universe is expanding into water .. or its expansion is driving the water outwards and away from the expansion.

[Seaquest]

The universe is expanding into water .. or its expansion is driving the water outwards and away from the expansion.

But what's beyond the water is another question.

[rstevenson]

To whatever it's expanding into?

Most cosmological theories have the Universe not expanding into anything at all.

Well, most cosmological theories have the Universe expanding, so I guess it's expanding into nothing.

Ann

Errmmmm. There is no nothing for it to expand into. The universe is all there is.

Rob

[rstevenson]

The universe is expanding into water .. or its expansion is driving the water outwards and away from the expansion.

That would explain the turtles.

Rob

[Ann]

Chris wrote:
No, it's not expanding into nothing, either, as from a cosmological standpoint "nothing" actually is something.

Language is inadequate!

Okay, Chris, point taken!

Rob wrote:
Errmmmm. There is no nothing for it to expand into. The universe is all there is.

Well put, Rob.

(And I know these things, too. I was sort of joking with Art.)

Ann

[joe mac]

The "nothing" in question would be the dimensions pre big bang, big bang imposed/created our dimension into pre existing universe,the size of which is unobservable but our dimension continues to expand into the existing. Would this be right

[bystander]

The "nothing" in question would be the dimensions pre big bang, big bang imposed/created our dimension into pre existing universe,the size of which is unobservable but our dimension continues to expand into the existing. Would this be right

According to the "big bang", space-time and everything within it began at t=0. The universe is self contained. There is no outside or pre-existence, unless you subscribe to the idea of a multiverse, in which case there are multiple self contained universes.