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Have researchers imaged dark matter, as per a recent claim? Rob Sheldon comments

April 27, 2017
Cosmology, Intelligent Design, Physics
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Hubble image captures what dark matter is supposed to be.

From Nancy Atkinson at LiveScience:

Now, researchers have produced what they say is the first composite image of a dark matter filament that connects galaxies together.

…

In their paper, they explained that in order to study the weak lensing signal of the dark matter filaments, they required two sets of data: a catalog of galaxy cluster pairs that were lensed, and a catalog of background source galaxies with accurate distance measurements.

They combined lensing data from a multi-year sky survey at the Canada-France-Hawaii Telescope with information from the Sloan Digital Sky Survey that mapped luminous red galaxies (LRGs), which are massive, distant, and very old galaxies.

…

Hudson and Epps combined or “stacked” more than 23,000 galaxy pairs, all located about 4.5 billion light-years away. This allowed them to create a composite image or map that shows the presence of dark matter between galaxies. Hudson told Seeker that the filament in their “image” is the average of all 23,000 pairs. More.

Why wouldn’t this be bigger news?

Our physics colour commentator Rob Sheldon, who thinks dark matter definitely exists, writes to say,

… this “first image” is a composite of 23,000 different galaxy pairs, where they would scale and rotate each of the 23,000 images before overlaying them. So it isn’t exactly an image of anything in particular, and could very easily be an image of the scaling algorithm. Suppose every image was of a circular galaxy, but when they scaled the images it became elliptical, so the “bridge” is just the infrequent appearance of two circular galaxies that nearly touch, now scaled to ellipses and stretched to fit the superposition.

This happens all the time in these statistical surveys, and even happened to me in my PhD thesis. All the exciting “bridge” data in my 3-week superposition data set came from a single day, an observation which I tried to bury on page 100. I still find it miraculous that no one called me out on it, and I got my PhD anyway. But then I didn’t exactly call a press conference to advertise it either.

I don’t know whether they actually believe their massaged data set shows a bridge, or whether they just want everyone else to believe it and reap the fame. But in either case, it shows how far astronomy has fallen. I think I will propose to superpose 1,000,000,000 stellar images to show that for the first time I found a star that wasn’t round.

Nice try though.

See also: Dark matter: What if gravity just doesn’t stick to the rules?

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Comments
You can't turn a circle into an ellipse by translating, rotating and scaling it. If the effect was spurious, it would also appear when they analysed random galaxy pairs. But it doesn't. The dark matter bridge only shows itself when they analyse physically adjacent pairs. See figure 3 of the paper: "The weak-lensing masses of filaments between luminous red galaxies" lukebarnes
PaV:
The “90% of the mass of the universe” is mostly “dark energy,” and not “dark matter.” I forget the breakdown, but it’s something like 75 to 25%, dark energy to dark matter.
Ahhh, ok. Whoops.
I know what they’re looking for, but the images they present look like some entirely different kind of phenomena; not dark matter. Rob Sheldon is saying that they are possibly dealing with distortions of some kind. If you want my guess, I think what they’ve done will turn out to be completely worthless in terms of ‘dark matter.’ It might prove of value somewhere else.
Yeah, I've got to be more careful on this blog to not step on the toes of the informed with my offerings of "expertise"; quite a few people here actually know stuff. A lot of stuff, even. Dr. Sheldon's comment of "could very easily be an image of the scaling algorithm" is pretty funny. Just photo manipulate the universe until your combined transformation artifacts grow into headline worthy "phenomena". LocalMinimum
LocalMinimum: The “90% of the mass of the universe” is mostly "dark energy," and not "dark matter." I forget the breakdown, but it's something like 75 to 25%, dark energy to dark matter. I know what they're looking for, but the images they present look like some entirely different kind of phenomena; not dark matter. Rob Sheldon is saying that they are possibly dealing with distortions of some kind. If you want my guess, I think what they've done will turn out to be completely worthless in terms of 'dark matter.' It might prove of value somewhere else. PaV
PaV: They're looking for distortions of light due to gravity, as gravity is really what they need out of dark matter; and lots of it it would seem from that "90% of the mass of the universe" figure floating about. LocalMinimum
When I looked at the image, my first impression was that they didn't really know what they were looking at. I think that's what Rob Sheldon is cautioning. I appreciate his take on it. Isn't "imaging" dark matter an oxymoron? PaV

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