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IS DARK MATTER REAL??

Blog#385

Wednesday, March 20th, 2024.

Welcome back,

Astrophysicists have piled up observations that are difficult to explain with dark matter. It is time to consider that there may be more to gravity than Einstein taught us

The stars still have secrets. we know why they shine, and we know why they twinkle, but we still do not know why they move the way they move. The problem has been with us for the better part of a century. In the 1930s Swiss astronomer Fritz Zwicky observed that some galaxies in a cluster of about 1,000 fly surprisingly fast around their common center of mass.

Even with generous estimates of the individual galaxies’ masses, they did not add up enough to account for this motion. Zwicky fixed the mismatch by conjecturing the existence of a new kind of matter: “dark matter.”

In the 1970s American astronomer Vera Rubin, who died in 2016, saw the same thing happening in single galaxies. The velocities of stars far out from the center of a galaxy remained roughly the same as those closer in, when astronomers would have expected them to slow down because of the dwindling gravity at the galaxy’s far reaches. Again, the visible mass alone was not sufficient to explain the observations.

Rubin concluded that in galaxies, too, dark matter must be present.

Since then, even more evidence has accumulated that we must be missing something. The tiny temperature fluctuations in the cosmic background radiation astronomers see pervading space, as well as the gravitational bending of light around galaxies and galaxy clusters and the formation of the cosmic web of large-scale structure throughout space, confirm that normal matter alone cannot explain what we see.

For many decades the most popular hypothesis has been that dark matter is composed of new, so far undetected particles that do not interact with light. The alternative explanation that we have the right particles but the wrong laws of gravity has received little attention.

Thirty years ago this stance was justified. The idea of particle dark matter gained traction because back then physicists had other reasons to believe in the existence of new particles. Around the 1950s and 1960s physicists realized that the protons, neutrons and electrons that make up atoms are not the only particles out there.

Over the next decades particle accelerators started turning up new particles left and right; these came to make up the Standard Model of particle physics and opened theorists’ minds to even more possibilities. For instance, efforts to unify the fundamental forces of nature into a single force required theorizing a set of new particles, and the concept of supersymmetry, developed in the 1970s, predicted a mirror particle for every known particle in the universe.

Some of these theorized particles would make good dark matter candidates. Another suspect for the role was a particle called the axion, invented to explain the smallness of a parameter in the Standard Model.

But after three decades of failed attempts to detect any of these particles, ignoring alternative hypotheses is no longer reasonable.

Originally published on www.scientificamerican.com

COMING UP!!

(Saturday, March 23rd, 2024)

"WHAT IS MIRROR UNIVERSE THEORY??"

The Penrose process:

Via Wikipedia

Animation:  © Eugene Pylinsky

Throat singing: The Gyuto Monks of Tibet

Our Galaxy is Caught Up in a Giant Cosmic Cobweb! 🕸️

If we could zoom waaaay out, we would see that galaxies and galaxy clusters make up large, fuzzy threads, like the strands of a giant cobweb. But we'll work our way out to that. First let's start at home and look at our planet's different cosmic communities.

Our home star system

Earth is one of eight planets — Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune — that orbit the Sun. But our solar system is more than just planets; it also has a lot of smaller objects.

An asteroid belt circles the Sun between Mars and Jupiter. Beyond Neptune is a doughnut-shaped region of icy objects called the Kuiper Belt. This is where dwarf planets like Pluto and Makemake are found and is likely the source of short-period comets (like Haley’s comet), which orbit the Sun in less than 200 years.

Scientists think that even farther out lies the Oort Cloud, also a likely source of comets. This most distant region of our solar system is a giant spherical shell storing additional icy space debris the size of mountains, or larger! The outer edge of the Oort Cloud extends to about 1.5 light-years from the Sun — that’s the distance light travels in a year and a half (over 9 trillion miles).

Sometimes asteroids or comets get ejected from these regions and end up sharing an orbit with planets like Jupiter or even crossing Earth’s orbit. There are even interstellar objects that have entered the inner solar system from even farther than the Oort Cloud, perhaps coming all the way from another star!

Our home galaxy

Let's zoom out to look at the whole Milky Way galaxy, which contains more than 100 billion stars. Many are found in the galaxy’s disk — the pancake-shaped part of a spiral galaxy where the spiral arms lie. The brightest and most massive stars are found in the spiral arms, close to their birth places. Dimmer, less massive stars can be found sprinkled throughout the disk. Also found throughout the spiral arms are dense clouds of gas and dust called nebulae. The Sun lies in a small spiral arm called the Orion Spur.

The Milky Way’s disk is embedded in a spherical “halo” about 120,000 light-years across. The halo is dotted with globular clusters of old stars and filled with dark matter. Dark matter doesn’t emit enough light for us to directly detect it, but we know it’s there because without its mass our galaxy doesn’t have enough gravity to hold together!

Our galaxy also has several orbiting companion galaxies ranging from about 25,000 to 1.4 million light-years away. The best known of these are the Large and Small Magellanic Clouds, which are visible to the unaided eye from Earth’s Southern Hemisphere.

Our galactic neighborhood

The Milky Way and Andromeda, our nearest neighboring spiral galaxy, are just two members of a small group of galaxies called the Local Group. They and the other members of the group, 50 to 80 smaller galaxies, spread across about 10 million light-years.

The Local Group lies at the outskirts of an even larger structure. It is just one of at least 100 groups and clusters of galaxies that make up the Virgo Supercluster. This cluster of clusters spans about 110 million light-years!

Galaxies aren’t the only thing found in a galaxy cluster, though. We also find hot gas, as shown above in the bright X-ray light (in pink) that surrounds the galaxies (in optical light) of cluster Abell 1413, which is a picturesque member of a different supercluster. Plus, there is dark matter throughout the cluster that is only detectable through its gravitational interactions with other objects.

The Cosmic Web

The Virgo Supercluster is just one of many, many other groups of galaxies. But the universe’s structure is more than just galaxies, clusters, and the stuff contained within them.

For more than two decades, astronomers have been mapping out the locations of galaxies, revealing a filamentary, web-like structure. This large-scale backbone of the cosmos consists of dark matter laced with gas. Galaxies and clusters form along this structure, and there are large voids in between.

The scientific visualizations of this “cosmic web” look a little like a spider web, but that would be one colossal spider! <shudder>

And there you have the different communities that define Earth’s place in the universe. Our tiny planet is a small speck on a crumb of that giant cosmic web!

Want to learn even more about the structures in the universe? Check out our Cosmic Distance Scale!

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