DARK MATTER!


Jan Oort (1900 - 92) [left] and Fritz Zwicky (1898 - 1974) [above] Zwicky invented the terms "dark matter," "supernova," and "neutron star"!  He was also the first to propose using galactic clusters as gravitational lenses to view very distant objects.


Vera Rubin (1928 - 2016).   Note her calculator, the same kind I used in my first theoretical calculations around 1962!


Jan Oort and Fritz Zwicky in the early 1930s independently noticed problems when the virial theorem was applied to stars in galaxies, or galaxies in clusters. Zwicky coined the term “dark matter.” Vera Rubin addressed the question of invisible mass in a long series of careful measurements beginning in the 1960s. In 1975 she reported that the speeds of stars in each of the galaxies that she had studied were independent of the distance from the core of the galaxy, rather than depending on the inverse square root of the distance to the central condensation. Many other studies confirmed this result and indicated consistently that about 95% of the mass of most galaxies is in an invisible cloud extending out to typically more than 10 galactic radii.
Since then, a few galaxies have been found that have no dark matter, and there is a hint of a galaxy or two consisting almost entirely of dark matter. In clusters of galaxies, the dark matter distributions tend to merge and blend. A number of possible culprits have been eliminated from consideration over the years, and the only surviving good candidate for dark matter is massive particles that interact gravitationally, and (very unlikely) weakly, but not electromagnetically or via the strong interaction. No particle in the Standard Model has the characteristics that detailed observations require for dark matter particles. The currently accepted best cosmological model is known as the ΛCDM model, where Λ is the Einsteinian cosmological constant (dark energy) and CDM means "cold dark matter."


Ways to Study Dark Matter:

• Rotation curves for stars in individual galaxies,
• Gravitational micro-lensing (LSST),
• Speeds of galaxies in large clusters,
• X-ray emission by hot gas in clusters,
• Power spectrum of temperature variations in the Big Flash,
• Study of baryonic acoustic oscillations in the Big Flash, as they survive in the present universe.
• Direct detection of Dark Matter particles on earth. [Here are the two largest facilities with underground DM detectors, LNGS, and SURF.]






The last scattering surface is currently more than 40 billion light years away.





The power spectrum of temperature variations observed in the Big Flash at high resolution is extraordinarily sensitive to the precise composition of the early universe, and gives us what is probably our most accurate look at the actual, measurable composition of the universe at a temperature of 3000 K.




Old results

Latest results

A quote from the literature: “On sub-degree scales, the rich structure in the anisotropy spectrum is the consequence of gravity-driven acoustic oscillations occurring before the atoms in the universe became neutral.  The frozen-in phases of these sound waves imprint a dependence on the cosmological parameters, which gives CMB anisotropies their great constraining power."

“After the Universe recombined, the baryons and radiation decoupled, and the radiation could travel freely towards us. At that point the phases of the oscillations were frozen-in, and projected on the sky as a harmonic series of peaks."


Baryonic acoustic oscillations are turning into a major and important tool in determining precise distances to the most remote galactic clusters and systems.




A search for dark matter particles produced in collisions was asserted to be the number one priority of the previous run cycles of the LHC.  The masses of the particles could be anywhere from 10 to 1000 GeV, and their signature would be processes where a good part of the final energy and momentum seem to be missing.  So far, as of spring 2025, no trace of dark matter is seen. 

[Presumably, galaxies, stars and planets may have dark matter cores. Does this matter??]


One sadly likely explanation for why dark matter is not present in the Standard Model is that the dark matter particles feel only the gravitational force. If this is true, there may be no possibility whatsoever of detecting dark matter particles directly, so that we can study them only via the gravitational effects of large assemblies of such particles. Thus, dark matter particles would be an entirely new category of pointlike fermions, neither quarks nor leptons. And their detailed understanding would presumably require a quantum theory of gravity. The vital role of dark matter in our universe is, of course, to stamp the density variations caused by quantum fluctuations in the very early universe onto the expanding later universe, and therefore to provide the seeds of all large-scale structure that now exists!
Final reports on the results of the Planck Satellite observations have been released.

The oldest known galaxies, based on red shifts, were previously said to have existed about 480 million years after the Big Bang. Astronomers had previously though the so-called Cosmic Dark Ages ended about 450 million years after the Big Bang, but final results from the Planck satellite indicate that they did not end until about 550 million years afterward. Before that the universe should supposedly have been too dense, turbulent and hot for significant amounts of star formation. The earliest galaxies should supposedly not have appeared much before 550 million years. However, a galaxy was already known (GN-z11) which is seen as it appeared at 400 million years, and it looks “surprisingly mature.” The new, hard-working James Webb Space Telescope is our best hope for studying the First Galaxies.  The James Webb Space Telescope (JWST) has identified JADES-GS-z14-0 as (so far) the earliest and most distant galaxy observed, appearing as it existed 290 million years after the Big Bang  All the very early galaxies seen by Webb seem remarkably mature to have formed so soon. That's just the kind of thing we wanted to learn!  By the way, observation of these very early galaxies would be impossible without using gravitational lensing. 

GRAVITATIONAL LENSING

EXAMPLE OF DARK MATTER MAPPING

COSMIC INFLATION (355)

MORE ON THE POWER SPECTRUM OF LAMBDA-CDM

COMPUTER SIMULATIONS OF EARLY UNIVERSE!

LOCAL EXPERTS!

DARK ENERGY

MAKING MATTER?