APOD: Dark Matter in a Simulated Universe (2021 Oct 31)

Comments and questions about the APOD on the main view screen.
User avatar
APOD Robot
Otto Posterman
Posts: 4527
Joined: Fri Dec 04, 2009 3:27 am

APOD: Dark Matter in a Simulated Universe (2021 Oct 31)

Post by APOD Robot » Sun Oct 31, 2021 4:05 am

Image Dark Matter in a Simulated Universe

Explanation: Is our universe haunted? It might look that way on this dark matter map. The gravity of unseen dark matter is the leading explanation for why galaxies rotate so fast, why galaxies orbit clusters so fast, why gravitational lenses so strongly deflect light, and why visible matter is distributed as it is both in the local universe and on the cosmic microwave background. The featured image from the American Museum of Natural History's Hayden Planetarium Space Show Dark Universe highlights one example of how pervasive dark matter might haunt our universe. In this frame from a detailed computer simulation, complex filaments of dark matter, shown in black, are strewn about the universe like spider webs, while the relatively rare clumps of familiar baryonic matter are colored orange. These simulations are good statistical matches to astronomical observations. In what is perhaps a scarier turn of events, dark matter -- although quite strange and in an unknown form -- is no longer thought to be the strangest source of gravity in the universe. That honor now falls to dark energy, a more uniform source of repulsive gravity that seems to now dominate the expansion of the entire universe.

<< Previous APOD This Day in APOD Next APOD >>

User avatar
Ann
4725 Å
Posts: 11715
Joined: Sat May 29, 2010 5:33 am

Re: APOD: Dark Matter in a Simulated Universe (2021 Oct 31)

Post by Ann » Sun Oct 31, 2021 6:22 am


That's a striking illustration of dark matter and baryonic matter in the Universe. I like it!

A fun thing about the map is that dark matter is very appropriately shown as dark▮, but the parts where there is not a lot of dark matter shown as light gray. But we all know that the Universe is pretty dark, because the night sky is dark. Do you remember why it is dark? What is the correct answer?

1) It's dark because the Universe is young, and the speed of light is slow compared with the size of the Universe, which means that much of the light that the Universe has produced has not had time to reach us.

2) It's dark because the Universe is expanding, and the wavelengths of light are stretched along with it, so that much of the light of the Universe has been stretched far beyond the visible part of the spectrum.

3) It's dark because the Universe is not just expanding but accelerating, so that the ever-growing size of the Universe is really outrunning the speed of light, which means that much of the light of the Universe will never reach us!

4) It's dark because there is not an infinite number of stars in the Universe. Come on, people. What makes anyone think that there are so many stars in the Universe that there is not a single point along any arbitrary line of sight in the Universe that wouldn't eventually "hit a star"?


Surely there isn't a star along every line of sight in the Hubble Deep Field? Of course there are more stars in the parts of the Universe that are not observable. But, no, we can't see them.

Small Big Bad Wolf.png
Anyway, take a look at the APOD again and note how the light gray stuff behind the dark filaments of dark matter almost looks like expanding bubbles, huffing and puffing like the Big Bad Wolf. Maybe that's where the dark energy is??

Ann
You do not have the required permissions to view the files attached to this post.
Color Commentator

User avatar
orin stepanek
Plutopian
Posts: 7101
Joined: Wed Jul 27, 2005 3:41 pm
Location: Nebraska

Re: APOD: Dark Matter in a Simulated Universe (2021 Oct 31)

Post by orin stepanek » Sun Oct 31, 2021 11:55 am

DarkMatter_KipacAmnh_1200.jpg
I skimmed through today's APOD! Very interesting; and took about
an hour! Wow; it seems there are more things that we can''t see and
feel than we can see and feel! :shock: If all that dark matter is
making the universe grow; it'll get a lot larger than it already is!
You do not have the required permissions to view the files attached to this post.
Orin

Smile today; tomorrow's another day!

jmhaas@bellsouth.net

Re: APOD: Dark Matter in a Simulated Universe (2021 Oct 31)

Post by jmhaas@bellsouth.net » Sun Oct 31, 2021 1:10 pm

Looks like the neural pathways in the human brain.

User avatar
Chris Peterson
Abominable Snowman
Posts: 16313
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: APOD: Dark Matter in a Simulated Universe (2021 Oct 31)

Post by Chris Peterson » Sun Oct 31, 2021 2:38 pm

Ann wrote:
Sun Oct 31, 2021 6:22 am
4) It's dark because there is not an infinite number of stars in the Universe. Come on, people. What makes anyone think that there are so many stars in the Universe that there is not a single point along any arbitrary line of sight in the Universe that wouldn't eventually "hit a star"?
That one is arguable (not necessarily wrong, just not certain). It is possible that the extent of the Universe is infinite, and if so, contains an infinite number of stars. Of course, this poses no problem for a dark sky, given that we only need consider the observable universe for that (related to your #3), and there is certainly only a finite star count in any finite volume.
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

ta152h0
Schooled
Posts: 1398
Joined: Mon Aug 29, 2005 12:46 am
Location: Auburn, Washington, USA

Re: APOD: Dark Matter in a Simulated Universe (2021 Oct 31)

Post by ta152h0 » Sun Oct 31, 2021 3:15 pm

Does that mean the Universe will never collapse? pass the ice cold one
Wolf Kotenberg

User avatar
Chris Peterson
Abominable Snowman
Posts: 16313
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: APOD: Dark Matter in a Simulated Universe (2021 Oct 31)

Post by Chris Peterson » Sun Oct 31, 2021 3:19 pm

ta152h0 wrote:
Sun Oct 31, 2021 3:15 pm
Does that mean the Universe will never collapse? pass the ice cold one
The current evidence suggests that dark energy now dominates gravity, and therefore for the last few billion years (and for the infinite future) its expansion rate has been increasing. So it will head towards some variation of heat death, not a collapse or bounce.
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

User avatar
neufer
Vacationer at Tralfamadore
Posts: 18734
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: Dark Matter in a Simulated Universe (2021 Oct 31)

Post by neufer » Sun Oct 31, 2021 5:30 pm

https://en.wikipedia.org/wiki/Cold_dark_matter wrote:
<<In the cold dark matter theory, structure grows hierarchically, with small objects collapsing under their self-gravity first and merging in a continuous hierarchy to form larger and more massive objects. Predictions of the cold dark matter paradigm are in general agreement with observations of cosmological large-scale structure.

In the hot dark matter paradigm, popular in the early 1980s and less so now, structure does not form hierarchically (bottom-up), but forms by fragmentation (top-down), with the largest superclusters forming first in flat pancake-like sheets and subsequently fragmenting into smaller pieces like our galaxy the Milky Way.

Since the late 1980s or 1990s, most cosmologists favor the cold dark matter theory (specifically the modern Lambda-CDM model) as a description of how the universe went from a smooth initial state at early times (as shown by the cosmic microwave background radiation) to the lumpy distribution of galaxies and their clusters we see today—the large-scale structure of the universe. Dwarf galaxies are crucial to this theory, having been created by small-scale density fluctuations in the early universe; they have now become natural building blocks that form larger structures.
..................................................
Several discrepancies between the predictions of the particle cold dark matter paradigm and observations of galaxies and their clustering have arisen:
  • The cuspy halo problem: The density distributions of dark matter halos in cold dark matter simulations (at least those that do not include the impact of baryonic feedback) are much more peaked than what is observed in galaxies by investigating their rotation curves.

    The missing satellites problem: Cold dark matter simulations predict large numbers of small dark matter halos, more numerous than the number of small dwarf galaxies that are observed around galaxies like the Milky Way.

    The disk of satellites problem: Dwarf galaxies around the Milky Way and Andromeda galaxies are observed to be orbiting in thin, planar structures whereas the simulations predict that they should be distributed randomly about their parent galaxies.

    Galaxy morphology problem: If galaxies grew hierarchically, then massive galaxies required many mergers. Major mergers inevitably create a classical bulge. On the contrary, about 80% of observed galaxies give evidence of no such bulges, and giant pure-disc galaxies are commonplace. That bulgeless fraction was nearly constant for 8 billion years.
Some of these problems have proposed solutions, but it remains unclear whether they can be solved without abandoning the CDM paradigm.>>
Art Neuendorffer

zendae1

Re: APOD: Dark Matter in a Simulated Universe (2021 Oct 31)

Post by zendae1 » Mon Nov 01, 2021 12:25 am

I tried viewing it 3D in case there was a teapot but it was turtles.

User avatar
johnnydeep
Captain
Posts: 1041
Joined: Sun Feb 20, 2011 8:57 pm

Re: APOD: Dark Matter in a Simulated Universe (2021 Oct 31)

Post by johnnydeep » Mon Nov 01, 2021 1:15 pm

zendae1 wrote:
Mon Nov 01, 2021 12:25 am
I tried viewing it 3D in case there was a teapot but it was turtles.
"Turtles all the way down!" From https://en.wikipedia.org/wiki/Turtles_all_the_way_down
"Turtles all the way down" is an expression of the problem of infinite regress. The saying alludes to the mythological idea of a World Turtle that supports a flat Earth on its back. It suggests that this turtle rests on the back of an even larger turtle, which itself is part of a column of increasingly large turtles that continues indefinitely.

The exact origin of the phrase is uncertain. In the form "rocks all the way down", the saying appears as early as 1838.[1] References to the saying's mythological antecedents, the World Turtle and its counterpart the World Elephant, were made by a number of authors in the 17th and 18th centuries.[2][3]
--
"To B̬̻̋̚o̞̮̚̚l̘̲̀᷾d̫͓᷅ͩḷ̯᷁ͮȳ͙᷊͠ Go......Beyond The F͇̤i̙̖e̤̟l̡͓d͈̹s̙͚ We Know."

Nukeit

Re: APOD: Dark Matter in a Simulated Universe (2021 Oct 31)

Post by Nukeit » Tue Nov 02, 2021 5:00 pm

Resembles a neurolink or even possibly mycorrhiza. "to be belittled" at best.

User avatar
neufer
Vacationer at Tralfamadore
Posts: 18734
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: Dark Matter in a Simulated Universe (2021 Oct 31)

Post by neufer » Tue Nov 02, 2021 6:10 pm

Nukeit wrote:
Tue Nov 02, 2021 5:00 pm

Resembles a neurolink or even possibly mycorrhiza.

"to be belittled" at best.
Last edited by bystander on Wed Nov 03, 2021 3:50 am, edited 1 time in total.
Reason: Please, no hot links to images > 500 kb. Substituted a smaller image.
Art Neuendorffer