Dark Energy Survey Catalogs 226 Million Galaxies

By: Govert Schilling May 28, 2021 19

The latest release from the Dark Energy Survey catalogs millions of galaxies, mapping the history of galaxy clustering across space and time.

In one of the biggest sky surveys ever, astronomers have captured 226 million galaxies up to 7 billion light-years away in an area covering about one-eighth of the entire sky. This treasure trove of data provides scientists with the best-ever probe of cosmic evolution and illuminates the role of dark matter and dark energy in shaping the large-scale structure of the universe.

The Dark Energy Survey (DES) started back in August 2013. On May 27th, the international collaboration published its second data release, covering the first three years of observations. The results are described in 30 scientific papers, available on the DES website. “It’s a beautiful dataset,” says René Laureijs, project scientist of the European Space Agency’s Euclid mission.

The new results support the scenario in which mysterious dark energy and slow-moving dark matter particles vastly overshadow the remaining ~5% of “normal” matter in galaxies, stars, planets, and people. There’s one nagging discrepancy, though: just like other surveys, DES found that the current universe is a few percent less “clumpy” than the ΛCDM model would predict. Nobody knows why.

The real star of the survey is the massive 570-megapixel Dark Energy Camera, built by the Department of Energy at Fermilab in Chicago, and mounted at the prime focus of the 4-meter Blanco Telescope at the Cerro Tololo Inter-American Observatory in Chile. Night after night, it has captured hundreds of 90-second exposures, each as wide as four full Moons. Over the years, the whole 5,000-square-degree survey area was imaged at least 10 times down to a limiting magnitude of 23.3, while ten deep fields were studied repeatedly in even more detail.

Based on a galaxy’s brightness in five wavelength bands in visible and near-infrared light, the DES team can determine its “photometric redshift,” which yields a rough but reliable distance estimate. Thus, astronomers are able to discern the evolution of galaxy clustering across the history of the universe, which sheds light on the actions of dark matter and dark energy. Estimates of so-called cosmic shear — minute shape distortions due to weak gravitational lensing — provide additional information on the distribution of dark matter. The elaborate data analysis was carried out at the National Center for Supercomputer Applications at the University of Illinois.

Although the Dark Energy Survey was completed in early 2019, the last three years of data are still being processed; results may not be published until a few years from now. Meanwhile, an equally impressive spectroscopic galaxy survey officially took off a few weeks ago at the 4-meter Mayall telescope at Kitt Peak National Observatory in Arizona. The similarly named Dark Energy Spectroscopic Instrument aims to capture real spectra of tens of millions of galaxies and quasars over the next five years.

Slated for launch in late 2022, the Euclid space mission will carry out an even larger and deeper survey with similar cosmological goals. According to project scientist Laureijs, Euclid will study about 15 times more galaxies than the Dark Energy Survey has done, out to distances of 10 billion light-years, both by measuring their brightness (focusing on the infrared) and by taking their spectrum. “We really need a higher precision to definitely validate the ΛCDM model,” he says.

Comments

Peter Wilson

May 28, 2021 at 3:02 pm

Q. A train is heading west at 50 mph. How long will it take to reach Denver?

Most people recognize the above problem to be “causally incomplete.” It is missing a key parameter: the distance to Denver. But what if the problem is more complicated, like our universe? Lost in all the “dark” discussion is the fact that the ΛCDM model contains no distance-term. Could this be a problem? Yes. Most gravitational problems cannot be solved without specifying distance-between.

Perhaps: Λ = η/(R_i)^2 , where η (“eta”) is cosmic reaction to local action, as in Newtonian action/reaction, and R_i is the distance over which the reaction takes place, roughly that between galaxy clusters, about 10^23 m. The equation yields the observed value of Λ, 10^-52/m^2 , sans mystery or fanfare. The ΛCDM model, on the other hand, offers bewilderment.

Can’t we do better that that?

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Andrew James

May 28, 2021 at 8:59 pm

Oh dear, oh dear. What is truly bewildering is thinking that repeating this fiction again and again makes it come true. I've already highlighted why with multiple posts to the site, but you keep coming back with silly premise and whingeing that no one will listen to you.

Again. Comparisons of Newtonian cosmology and general relativity have been discussed ad nausum for decades. Newtonian cosmology has lots of flaws that you continue to ignored. I see absolutely no theoretical nor observational evidence this is even remotely related any current cosmological model. That you fail to incorporate the vacuum energy at all is enough to your notions are utterly false. As this article rightly says: "The new results support the popular ΛCDM model,..."

Instead of me yet again tearing down your gross errors, readers might prefer looking at the 2021 arXiv pdf article by Leandros Perivolaropoulos and Foteini Skara "Challenges for ΛCDM: An update" here [1]. As there is nothing resembling your notions, and no observational evidence or existence of actual proofs. I'd think that 1455 reference papers in this article carry more 'gravity' than one lonely lost and confused voice.

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Andrew James

May 28, 2021 at 11:02 pm

Saying "Can’t we do better that that?" Why yes we can! For one. Forget the limiting notions of Newtonian physics and start embracing General Relativity and Quantum mechanics!

As for "Most gravitational problems cannot be solved without specifying distance-between." Why then galaxy redshifts and an apparent accelerating expanding universe? How do you explain the observed rotation curves of galaxies? Newtonian notions alone don't cut the mustard, does it.

As for: "... is the fact that the ΛCDM model contains no distance-term." Why should it? It is an additional correction based on other parameters that can be tested and verified by observation. e.g. Energy density. As the Universe is not static, a correction term is adopted.

You then say: "The equation yields the observed value of Λ, 10^-52/m^2..."

Wow how darn convenient!! Nice cherry picking! All you've done is deliberately pluck out he distance where: "roughly that between galaxy clusters, about 10^23 m" so that it amazingly just happens to match the same ΛCDM model predicted value. That's plainly dodgy and deceptive. [Why not use the average distance of galaxies or even the size of the Universe?]

You plainly have realised that ΛCDM model predicts having Λ=10^-52/m^2 but have fail to notice it is based on measuring the vacuum energy density, which you just happen to want to also ignore? Frankly anyone can access Wikipedia page on the Cosmological constant e.g. See under heading 'Positive value.'

But Gosh. Your own words now actually validates the exact ΛCDM model prediction!!! Better still, the ΛCDM model predicts it without a 'distance-term' at all!

Seriously. Reverse engineering problems (like in this example) with any academic institution would end your scientific career for good. Here it now just diminishes any credibility that you may of had. You have no argument.

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Andrew James

May 28, 2021 at 11:32 pm

Q. A train is heading west at 50 mph. How long will it take to reach Denver?

A. Does anyone in the history of the Universe ever really want to go to Denver? Umm... Where is Denver anyway? (Its northwest and in another hemisphere from where I live. If I went by train, I'd drown. Also 12 billion years ago I think it was much closer!) 😉

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Andrew James

May 30, 2021 at 4:33 am

OK. You've also said a year ago that : "It is in reference to the Friedmann equations, not our universe. In these equations, the basis of the lambda-CDM model, there are no stars nor galaxies. Only a uniformly expanding, ideal gas."

Any gas has mass, density and energy, but now you are saying it has no distance term either? If Λ=10^-52.m^-2, then what unit is it actually measuring?

If a mathematical constant is a key number/ whose value is fixed by an unambiguous definition. eg. pi. Is the cosmological constant invariant or scale-invariant, then?

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Peter Wilson

May 31, 2021 at 12:34 pm

Good question. In cosmology, any force beyond gravity has to have dimensions of per-unit-area (1/m^2 , or m^-2). Why? One of Friedmann’s equations is for acceleration (m/s^2). In it, Λ is multiplied by c-squared. The result has dimensions of per-second-squared [(m^-2)*(m/s)^2=1/s^2]. Multiply this by the distance, r, as long as r > R_i, and you get acceleration (m/s^2). So whatever its true nature, an anti-gravity force has to manifest as per-unit-area.

Pressure, by contrast, is divided by c-squared, then subtracted, not added. This means that, counterintuitively, pressure works against expansion; it is “pro-gravity,” and acts to slow the expansion. Pressure is small, today, especially after being divided by c^2, and can be safely ignored. If Λ is greater than about 10^-53/m^2, however, it must be included in the calculations. It is.

Now that we have that clear, we can resume the debate about what it is. Does the observed Λ, a positive 10^-52/m^2, represent a mysterious energy, that makes more of itself as the universe expands? Or is a reaction-term? Since the ΛCDM model comes with no reaction-term, my bet is on the latter. It is a much simpler explanation.

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Andrew James

May 31, 2021 at 8:50 pm

Simple. Science does not recognise bets. Also. There is "no reaction" term except in a static universe. If you think it is static, you'll be pretty lonely methinks.

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Andrew James

May 31, 2021 at 9:04 pm

Eh? That's nuts. If "Pressure, by contrast, is divided by c-squared, then subtracted, not added. This means that, counterintuitively, pressure works against expansion; it is “pro-gravity,” and acts to slow the expansion"

Then why do we physically observe an acceleration in the expansion?

That single premise is just dead wrong! (Are you a static cruncher then?)

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Peter Wilson

May 31, 2021 at 12:45 pm

P.S. I’ll confess: the paper includes at least one mistake/point-of-confusion.

In Newtonian mechanics, velocity has zero gravitational effect. In GR, velocity has almost zero effect...unless v is a substantial fraction of c. This means that a relativistic model is always at least one variable more complicated than its Newtonian counterpart. In the paper, it is asserted that the simplest possible model that incorporates “reaction” requires four (4) variables. In the video, it is asserted that the simplest possible model that incorporates “reaction” requires five (5) variables. The video was made later, and is correct.

You are not the first to argue that “reaction” is a Newtonian concept; therefore, it need not be included in a relativistic model. This is incorrect. A relativistic model is always more complicated than the corresponding Newtonian. Never simpler.

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Andrew James

May 31, 2021 at 8:41 pm

As for "You are not the first to argue that “reaction” is a Newtonian concept; therefore, it need not be included in a relativistic model. This is incorrect. A relativistic model is always more complicated than the corresponding Newtonian. Never simpler."

Occum's razor is only a guide to an absolute fact. "Never simpler" is an just an unsupported assumption. To insist on such faith is actual delusional, and this is why no one takes you seriously. Also 'Newtonian concept' does not equate to Newtonian cosmology.

Simple. Why has Newtonian cosmology been mostly discarded? General relativity explains the expansion, Quantum Mechanics explains the origin of the Universe and its behaviour via the Big Bang. That the Universe does not appear static, means that Newtonian physics is inadequate to account for evidence via observation of the Universe.

No one is fooled. Adaptation of this ultimately fails because the prediction does not match reality. Egocentricity will not change this .

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Andrew James

May 31, 2021 at 8:56 pm

Sorry. The issue here is your deceptive tactics promote a wrong premise. You use the ΛCDM model result not your equation to validate your ideas. its all just smoke and mirrors.

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Andrew James

June 1, 2021 at 4:44 am

"I’ll confess: the paper includes at least one mistake/point-of-confusion."

Perhaps that's why arXiv wasn't interested?

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Randy Schmid

May 31, 2021 at 9:02 pm

I'm a retired aerospace engineer, not a physicist, but Mr. Wilson's arguments seem to make sense. In engineering lingo, the system appears to be "under-specified.

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Andrew James

June 1, 2021 at 9:30 pm

"...Mr. Wilson's arguments seem to make sense." How exactly?

No. The failure is the basic premise is flawed. He expects us to ignore general relativity (and quantum mechanics) because he thinks it unnecessary, when in fact, they are the core tenets of modern cosmology. These effects are already predictable, and indeed we can test hypotheses via actual observation. Deleting or ignoring knowns just for expediency or belief is nuts - especially when they not trivial. That he doesn't seem to have a good grasp about Newtonian cosmology in context or why the current ΛCDM model is held by most cosmologists, certainly indicates a lack of understanding. (I wonder if there is a religious motivation somewhere in the mix. e.g. An indeterminate solution to explain the universe or its creation is just abhorrent.) But somehow this novice knows better, and that all cosmologists wrong and will not bend until it is proven to him.

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Peter Wilson

June 2, 2021 at 7:55 pm

“...and will not bend until it is proven to him.”

True, but you can prove me wrong faster than I can microwave dinner. All it would take is a link to the Wikipedia cosmology page, or a published paper, in which the cosmic reaction terms, η and R_i, have been weighed, mathematically, and found to contribute much less to expansion than the observed value of Λ, 10^-52/m^2 . Since you haven’t done that, let’s ask the audience.

Which is easier to believe, A or B?

A) The equation, Λ = η/(R_i)^2 , yields the observed value of dark energy, but it is still wrong...for some reason. Probably a coincidence. Anyway, the “theory” it is derived from—authorities have overlooked something important—is hopelessly flawed. Mr. Wilson doesn’t understand quantum mechanics or General Relativity.
B) The equation is correct...because its premise is.

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Andrew James

June 3, 2021 at 12:26 am

"Which is easier to believe, A or B?" C

"The equation, Λ = η/(R_i)^2 , yields the observed value of dark energy, but it is still Ummm... Finally something absolutely true. That is why no one is listening.

"Anyway, the “theory” it is derived from—authorities have overlooked something important—is hopelessly flawed." At least that better than being dead wrong.

"Mr. Wilson doesn’t understand quantum mechanics or General Relativity." That's why most ignore what you say.

"The equation is correct...because its premise is." Umm... Unproven and it makes no sense.

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Andrew James

June 3, 2021 at 12:28 am

Correction : "The equation, Λ = η/(R_i)^2 , yields the observed value of dark energy, but it is still wrong. Umm... Finally something absolutely true. That is why no one is listening.

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Andrew James

June 4, 2021 at 10:20 pm

Are you a snake oil saleman here? "Actual saying "The equation, Λ = η/(R_i)^2 , yields the observed value of dark energy, but it is still wrong...for some reason." is just outragous. You've just just picked about 10^23 m just to match a Λ value of 10^-52 that was determined by the measuring the vacuum energy density. It does not "...yields the observed value of dark energy..." That is just completely untrue.

Quantum mechanical effects are real and not theoritical. e.g. Casimir effect. Marcus Sparnaay measured it first in 1958. It's observable. That is why such QM effects are needed in any cosmological models. Same with GR. Discarding General Relativity and Quantum Mechanics makes your words look like science fiction!

Sorry. You've been caught out fudgeing and manipulating data to suit some easily proven wrong premise. That's the whole point of my response.

Note. Perhaps if you read that 2021 arXiv pdf article by Leandros Perivolaropoulos and Foteini Skara "Challenges for ΛCDM: An update." Then you might come up with better contentions. Do so.

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Andrew James

June 10, 2021 at 8:23 pm

"True, but you can prove me wrong faster than I can microwave dinner."

Actually prophetic. Newton didn't know of 3K CBR either - a caveman only with fire. So why was the universe hotter in the past and what evidence do you have that the expansion is constant? Real observational data says otherwise.

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