Dark Matter Observed…
In Visualizations

A new press release from the European Southern Observatory (ESO) announces a lack of observational evidence for dark matter nearby: “New measurements show that the amount of dark matter in a large region around the Sun is far smaller than predicted and have indicated that there is no significant dark matter at all in our neighbourhood.”

Pretty significant stuff, but let’s take a look at the accompanying images…

I admire their simplicity, but hey, with dark matter, what choice does a visualizer have? The depiction of the dark matter halo around the Milky Way looks a little clumpy to me, but again, what else can you do? A uniform blob of blue around a galaxy image doesn’t communicate much…

(Admittedly, at the scale of this image, simulations reveal the Milky Way’s dark matter environment to be somewhat clumpy, albeit not in the way depicted in the animation. It’d be keen to use computational data in a visualization such as this one, but I suppose limited time and resources prevent that.)

Anyway, I like the annotated version of the image above; in particular, the indication of the volume of space relevant to the survey.

The accompanying video (available in ESO’s typical plethora of formats) is also an exercise in simplicity, offering a straightforward revolution around the three-dimensional model used to produce the still above. I kinda wish they included the sphere around the Sun once again, just to convey the scale of the survey, but I can guess why they avoided it… Then you have to think about labels, and labels mean language, and it is the European Southern Observatory, after all. Gotta make good b-roll for Hungarian nightly news, I suppose.

And on a final note, not that I would ever nitpick, but… Are those actual galaxy locations in the background? I’ve flown around the Local Group quite a bit, and although adjusting the brightness of the nearby galaxies can change the appearance considerably, I don’t recognize anything in the background. Just curious.

Nice work from ESO, understated but effective. And maybe someday, these kind of press images can be more data-driven.

Dark Matter Blobs!

Reporting from the American Astronomical Society meeting in Seattle, Washington… In a brand spankin’ new press release from Hubble, we have the first-ever “3D map of the Universe’s Dark Matter scaffolding.”

First off, the result is quite kewl. We’re beginning to map the stuff that “outweighs” ordinary matter by a factor of six to one. Great work, COSMOS team!

The above image isn’t the primary image released, but it’s the one with which I find the greatest fault. By abstracting the blobs of dark matter without any reference to scale whatsoever, we’re left with no sense of how large the object is that we’re looking at. The primary image that accompanies the press release improves on the problem by labelling slices at 3.5, 5.0, and 6.5 billion years ago, but the size of the image on the plane of the sky is left undescribed—although the caption does clarify that “Each panel represents an area of sky nine times the angular diameter of the full Moon.”

Images such as the one above do a disservice to public understanding of astronomers’ work by abstracting the result completely from reality. The lack of scale I already complained about, but I have other issues as well“ The use of isosurfaces is non-intuitive for the vast number of people. The inclusion of half a box around the data provides a sense of dimension but could also confuse people. And a meaningless background haze does nothing in service of the rest of the image.

Great science, bad picture.

Visualizing Dark Matter

So I’d just finished writing my previous post, and lo and behold, a press release from Hawaii arrives in my email inbox. The image above shows gravitational lensing in a group of galaxies—which is to say, not a cluster of galaxies but a structure much smaller and less massive. This is the first time lensing has been observed resulting from such low-mass collections of galaxies.

Coincidentally, the discovery of the first gravitational lens was published exactly twenty years previous—in January 1987—also by the Canada-France-Hawaii Telescope (CFHT). The original image can be found on the page of images that accompanies the new announcement.

The image lacks much meaning for the uninitiated, although an accompanying image that shows how lensing works can clarify the concept greatly. (Unfortunately, those vary widely in quality and ability to induce or reduce confusion, but that’s a subject for a lengthier post.) Even better, you can connect research images with, say, an animation (with appropriate descriptive elements) that shows lensing, along the lines of one available on the Wikipedia site.

As an aside, I should mention that the light gets bent more by dark matter than the luminous matter in the galaxies. So in a sense, gravitational lenses allow us to visualize dark matter… (That’s my excuse for the subject of this post.)