Dark Matter

When astronomers encountered some difficulties with what they were seeing in the universe, the only answer they could come up with was that there must be dark matter out there – lots of it.  Dark matter is matter that cannot be seen but which still exerts tremendous gravitational attraction.  As a result, there have been a number of concerted efforts to find out what dark matter actually is. Two important articles about this appeared in the scientific press in September and November of 2016. Surprisingly, both articles actually called into question the existence of “dark matter.” So many have questioned what is going on.

September news article -- Acceleration relation found among spiral and irregular galaxies challenges current understanding of dark matter

The original research paper by Stacy McGaugh, et al

November news article -- Unexpected interaction between dark matter and ordinary matter in mini-spiral galaxies

The original research paper by E.V. Karukes  and  P. Salucci

Both these studies involved the role of so-called “dark matter” in maintaining the observed rotation rates of galaxies. It is these galaxy rotation rates which caused the whole idea of dark matter to be introduced in the first place.  This is because the outside spiral arms of galaxies were rotating as fast around the inner core as the insides of the galaxy were.  Gravitationally, it was to be expected they would be rotating much more slowly, just like our outside planets rotate more slowly around the sun than the inside planets do.  One professor of astronomy independently concluded about the September research article regarding the rotation rates of galaxies that: “Nothing in the standard cosmological model predicts this [result], and it is almost impossible to imagine how that model could be modified to explain it, without discarding the dark matter hypothesis completely." More recently, one of the authors of the November article, Paolo Salucci, concluded that their results: “… make it clear to scientists that there is another sort of physics yet to be discovered and explored.” So, these two articles suggest that the dark matter idea might have to be questioned or, perhaps, a new sort of physics awaits discovery, or both.

When Sir Isaac Newton mathematically encapsulated the way that massive bodies behave under the influence of gravity, it allowed the behavior of all objects in the solar system to be described exactly. Ever since, astronomers have been using those equations in order to explain the behavior of everything that we see in the universe from comets to galaxy clusters.

The rate at which the individual planets circle the sun was thus neatly described by Newton’s laws, and was shown to be reliable over many years. By way of illustration, a planetarium uses these gravitational laws to show what solar system events occurred at a given time in the past or will occur at a given time in the future. Archaeologists rely on eclipse information based on these gravitational laws to date historical events.

In essence Newton’s Laws stated that the further away a body is from the central object it is orbiting, the more slowly it will travel. Thus, the planet closest to our sun, Mercury, has an orbital speed around the sun of about 30 miles per second. In contrast our earth, the ‘third rock from the sun’, travels at a speed of 18.75 miles per second, while the distant and tiny Pluto only travels at 3 miles per second. If the Law of Gravity was being followed, it was expected that the rotation or orbit speeds of stars around the nucleus of their parent galaxy should fall off in a very similar manner to the planets around the sun.

In the late 1970’s, Vera Rubin and Albert Bosma independently discovered something unusual about the way that galaxies rotate. They didn't behave the way that gravitational laws said they should. Instead, what was found was that, outside the region of the core of a galaxy, the speed of the stars in their orbits was approximately the same all the way to the galaxy’s outer edge. There was no slowing, no drop-off, in the orbit speed. Once this fact had been fully established, the necessity for an explanation became obvious. It is in this context that the Dark Matter concept developed.  The problem can be seen in the diagram below of the expected and then observed rotation curve of the Andromeda Galaxy.

Andromeda rotation rate

The rotation curve of the Andromeda Galaxy. The expected curve, as determined by gravity, is shown by the red line. What was actually seen is shown by the white line. Other galaxies show similar results. Due to these observations, astronomers concluded that up to 90% of the mass of the universe must be in the form of dark matter.

Newtonian gravity did not predict these observational results; so something was evidently not being taken into account. If these “flat rotation curves,” as they are called, were to be explained by gravitational action, then it was only possible if there was a huge amount of matter in an immense halo around the entire visible galaxy and beyond. This huge halo had to extend way beyond the stars that made up the visible edge of the galaxy for the proposition to work. Since this halo of material was not visible, and did not appear to emit any light, it eventually came to be called “Dark Matter”. In November of 2016, Dr. Andreas Ringwald defined dark matter this way: "Dark matter is an invisible form of matter which until now has only revealed itself through its gravitational effects. What it consists of remains a complete mystery."

Though it still remains a mystery, various forms of dark matter have been nonetheless proposed, such as hot dark matter – like plasma; cold dark matter – like cold hydrogen gas; Massive Compact Halo Objects (MACHO’s) - like swarms of planet or moon-sized objects wandering aimlessly throughout the galaxy. Extensive observations have ruled out all three of those particular options, however. Furthermore, by late October of 2013, studies by the Kepler Space Telescope had ruled out any possibility of dark matter being made up of black holes of any size. The possibility of it being in the form of “strange” or exotic matter was proposed in November of 2014 because of the unsuccessful search for a likely candidate. This is currently considered quite unlikely.

The current favorite explanation lies with WIMPs. WIMPs are proposed to be Weakly Interacting Massive Particles - something like neutrinos. In recent scientific history, much time, money and research effort has been expended in looking for WIMPs. They appear to be the only possible explanation left. But WIMPs in the form of neutrinos, and a slew of other possible particles, have all been ruled out by experiment and observation. It was hoped the Large Hadron Collider at CERN was going to discover the key elusive dark matter particle that could be labelled as the WIMP. To date, it hasn’t. Neither is it interacting as predicted.

Getting back to the two articles mentioned in the introduction, Ekatarina Karukes, the lead author of the November paper, put it this way. "Most dark matter, according to the most credible hypotheses, would be … WIMP’s. It would not interact with ordinary matter except through gravitational force … Our observations, however, disagree with this notion.” If that is the case, then the original proposition is false since it was expected that dark matter would interact with matter via gravity and so govern the galaxy rotation rate. The November study goes further. It shows that the distribution of matter and dark matter must be closely related if dark matter is really there. The authors state that “we found a link between the structure of ordinary, or luminous matter like stars, dust and gas, with dark matter." In other words, these observations show that, if dark matter really does exist, it can only be in those locations where ordinary matter is present. It means that there cannot be a massive halo of dark matter extending beyond the visible limits of galaxies. The reason, according to this study, is that those visible limits mark where ordinary matter comes to an end, and so dark matter must end there as well. In fact, in February of 2015, a specific search for dark matter halos beyond the visible limit to galaxies gave a negative result for the galaxies that were specifically studied for such an effect. So the conclusion is that dark matter can only occur in those locations where ordinary matter is found – not out on its own elsewhere. This negates the idea of dark matter halos existing at all.

The September 2016 paper came to similar conclusions using a sample of 2693 data points in 153 galaxies. David Merritt, professor of physics and astronomy at Rochester Institute of Technology, did not take part in either study but came to these conclusions from these scientific papers. He said: Galaxy rotation curves have traditionally been explained via an ad hoc hypothesis: that galaxies are surrounded by dark matter. The relation [or law] discovered by McGaugh et al. is a serious, and possibly fatal, challenge to this hypothesis, since it shows that rotation curves are precisely determined by the distribution of the normal matter alone. Nothing in the standard cosmological model predicts this, and it is almost impossible to imagine how that model could be modified to explain it, without discarding the dark matter hypothesis completely."

However, that is not all. The September 2016 paper determined that there was a precise mathematical relationship between the visible matter present and the acceleration that the stars in galaxies undergo. It is an almost exact relationship or law with very little room for error in galaxies of all varieties. The source of the acceleration or force is not identified, except that is not normal gravity. The paper’s lead author, Stacy McGaugh, said: "The natural inference is that this law stems from a universal force such as a modification of gravity like MOND, the hypothesis of Modified Newtonian Dynamics proposed by Israeli physicist Moti Milgrom.”  

The MOND approach by Milgrom tries to explain the rotation curves by adding a small acceleration term to the normal Newtonian gravitational equations. This term has little effect on small scales, such as in our solar system, but it becomes effective on the larger scale of galaxies. While other gravitational phenomena cannot be accounted for by the MOND proposal, McGaugh’s study does not discount the validity of Milgrom’s approach. In fact it is in line with it. It is a purely mathematical device that gives us the right answer to some observations.  But that’s the problem.  It is only a mathematical device.  There is no actual physical reason for the additional term or the new Law. This in itself might caution us that we should look at other options where other accelerating forces exist apart from gravity.

In the earliest years of the 20th century, Kristian Birkeland was studying the behavior of plasmas, and proposed that the auroras – the northern and southern lights – were the result of electric currents from the sun exciting the plasma in our upper atmosphere.  He assumed the plasma was there, but that is as far as he could get.  His lab experiments appeared to be showing the same thing the auroras were demonstrating.  (A plasma is created when an atom is stripped of one or more electrons.)  It was only in the 1970’s that it was discovered that the upper atmosphere is a plasma and the current from the sun is a stream of protons known as the solar wind. It was at this time we discovered Birkeland had been correct all along. 

Birkeland’s work was the beginning of something now known as plasma physics.  However, almost immediately a mathematician and physicist, Sydney Chapman, well-respected for his work, decried any idea of plasma physics.  His opinions blocked the progress of plasma physics until his death in the 1970’s.  At that time, in conjunction with new discoveries in space, plasma physics became much more widely studied.  What has been found is that over 99% of the material in the universe exists in a plasma form.  Thus, studying how plasma filaments behave in the lab can give us some clues as to what is going on in space. 

Plasma currents are electric currents.  They are surrounded by constricting magnetic fields, and thus the term electromagnetism is the term used for their effects.   It is in this context that Anthony Peratt of Los Alamos National Laboratories pointed out in 1992, the electromagnetic force can be up to 1039 times stronger than gravity out in space. His experiments and simulations show that the answer to the dark matter dilemma lies along this line of investigation. In a series of articles in the IEEE Journal for December 1986, he discussed his experiments and computer simulations with intertwining plasma filaments acting under the forces of electricity and magnetism. He pointed out that, at the cross-section of interaction between the filaments, miniature spiral galaxies were formed. These galaxies actually included all known types. The number of interacting filaments ranged up to 12 experimentally and up to 6 in simulations. However, when using just two or three filaments, galaxies of all types were formed by their interaction. Peratt pointed out that these lab results can be linearly up-scaled to cosmic proportions as a result of known plasma behavior.  Thus, the key candidate for an accelerating force is electricity and/or magnetism, which to date has largely been ignored by gravitational astronomers.

lab filaments

The illustration above shows what happens in the lab when two plasma filaments interact. Looking down on them at their point of interaction, we can see the formation of a radio galaxy, then an elliptical galaxy, a barred spiral, and finally a full-fledged spiral galaxy. These form very quickly and the outer arms of these miniature galaxies are spinning as fast as the inner sections of the arms around the core.

For this present discussion, one important point emerges from these experiments of Peratt. These lab-generated miniature galaxies, whether spiral or elliptical or whatever form they took, all had rotation curves which are exact replicas of their cosmic counterparts. The “flat” rotation curves resulted because galaxies were not acting under gravitational forces, but were rather controlled by electro-magnetic interactions, which act in a different way, as well as being much faster and stronger than gravity. Thus the forces involved in plasma interactions alone are capable of producing flat rotation curves in galaxies without any extra mathematical terms or exotic physics or the necessity for dark matter. Peratt’s research therefore deserves much wider publicity among astronomers, physicists and cosmologists than it has received to date. So, too, does the answer to the dark matter conundrum that he found from plasma physics by reproducible experiments in the lab. It is a complete solution to this puzzle and, what is more, it is reliable science.

Barry Setterfield, December, 2016