How Would Galaxies Form in a Universe Without Dark Matter? Researchers Find Out

Galaxy Formation Without Dark Matter

1.5 billion years after the start of the simulation. The lighter the color, the higher the density of the gas. The light blue dots show young stars. Credit: © AG Kroupa/Uni Bonn

A study by the University of Bonn simulates a universe in which Newton’s laws are only valid to a limited extent.

For the first time, researchers from the Universities of Bonn and Strasbourg have simulated the formation of galaxies in a universe without dark matter. To replicate this process on the computer, they have instead modified Newton’s laws of gravity. The galaxies that were created in the computer calculations are similar to those we actually see today. According to the scientists, their assumptions could solve many mysteries of modern cosmology. The results are published in the Astrophysical Journal.

“Perhaps the gravitational forces themselves simply behave differently than previously thought.” — Prof. Dr. Pavel Kroupa

Cosmologists nowadays assume that matter was not distributed entirely evenly after the Big Bang. The denser places attracted more and more matter from their surroundings due to their stronger gravitational forces. Over the course of several billion years, these accumulations of gas eventually formed the galaxies we see today.

An important ingredient of this theory is the so-called dark matter. On the one hand, it is said to be responsible for the initial uneven distribution that led to the agglomeration of the gas clouds. It also explains some puzzling observations. For instance, stars in rotating galaxies often move so fast that they should actually be ejected. It appears that there is an additional source of gravity in the galaxies that prevents this — a kind of “star putty” that cannot be seen with telescopes: dark matter.

However, there is still no direct proof of its existence. “Perhaps the gravitational forces themselves simply behave differently than previously thought,” explains Prof. Dr. Pavel Kroupa from the Helmholtz Institute for Radiation and Nuclear Physics at the University of Bonn and the Astronomical Institute of Charles University in Prague. This theory bears the abbreviation MOND (MOdified Newtonian Dynamics); it was discovered by the Israeli physicist Prof. Dr. Mordehai Milgrom. According to the theory, the attraction between two masses obeys Newton’s laws only up to a certain point. Under very low accelerations, as is the case in galaxies, it becomes considerably stronger. This is why galaxies do not break apart as a result of their rotational speed.

Results close to reality

“In cooperation with Dr. Benoit Famaey in Strasbourg, we have now simulated for the first time whether galaxies would form in a MOND universe and if so, which ones,” says Kroupa’s doctoral student Nils Wittenburg. To do this he used a computer program for complex gravitational calculations which was developed in Kroupa’s group. Because with MOND, the attraction of a body depends not only on its own mass, but also on whether other objects are in its vicinity.

The scientists then used this software to simulate the formation of stars and galaxies, starting from a gas cloud several hundred thousand years after the Big Bang. “In many aspects, our results are remarkably close to what we actually observe with telescopes,” explains Kroupa. For instance, the distribution and velocity of the stars in the computer-generated galaxies follow the same pattern that can be seen in the night sky. “Furthermore, our simulation resulted mostly in the formation of rotating disk galaxies like the Milky Way and almost all other large galaxies we know,” says the scientist. “Dark matter simulations, on the other hand, predominantly create galaxies without distinct matter disks — a discrepancy to the observations that is difficult to explain.”

Calculations based on the existence of dark matter are also very sensitive to changes in certain parameters, such as the frequency of supernovae and their effect on the distribution of matter in galaxies. In the MOND simulation, however, these factors hardly played a role.

Yet the recently published results from Bonn, Prague and Strasbourg do not correspond to reality in all points. “Our simulation is only a first step,” emphasizes Kroupa. For example, the scientists have so far only made very simple assumptions about the original distribution of matter and the conditions in the young universe. “We now have to repeat the calculations and include more complex influencing factors. Then we will see if the MOND theory actually explains reality.”

Reference: “The formation of exponential disk galaxies in MOND” by Nils Wittenburg, Pavel Kroupa and Benoit Famaey, 5 February 2020, Astrophysical Journal.
arXiv: 2002.01941

3 Comments on "How Would Galaxies Form in a Universe Without Dark Matter? Researchers Find Out"

  1. Howard Jeffrey Bender | February 9, 2020 at 6:10 am | Reply

    There are two questions in this article – galaxy development and Dark Matter. Here are two answers relating to String Theory.

    The question of galaxy development is a troubling one. How in the world did a minuscule force like gravity ever attract particles flying apart from the massive force of the Big Bang to form anything, never mind galaxy cores! And the universe continues to expand at about 67 km (41 mi) per second, even now. And, BTW, where did all this matter and energy come from in the first place? Surely you don’t think it all just happened to be there, from nothing, at the Big Bang?

    Perhaps String Theory offers a way.

    According to String Theory, a brane (dimensional membrane) surrounds our universe. What if such branes, rather than Black Holes, are also the centers of galaxies? Superheated gas would also form around branes, and they would explain how the matter in the universe became concentrated as galaxies even as the universe was, and still is, flying apart from the Big Bang at a rate that absolutely won’t allow any matter (quarks, even) to gravitationally attract each other to form anything. It would also explain those low-mass stars at the center of the Milky Way and the Andromeda galaxy, and other curious phenomena seen at those centers. Specifics about the physical creation of galaxies using the quantum foam and similar to Hawking radiation are described in my YouTube https://www.youtube.com/watch?v=cQUMq2Z11Jc&t=3s

    Regarding Dark Matter, there may be a String Theory explanation. As you may know, quantum mechanics requires that strings must be formed as pairs in the quantum foam – a string and an anti-string – that immediately annihilate each other. Quantum mechanics also requires both the string and anti-string to be surrounded by “jitters” that reduce their monstrous vibrating energies. What if this jitter remains for a fraction of an instant after their string/anti-string annihilations? This temporary jitter would be seen by us as matter for that instant before it too returns to the foam. That’s why we never see it – the “mass” lasts only for that instant but is repeated over and over and over, all over. Specifics on this can be found in my YouTube at https://www.youtube.com/watch?v=24WyRKT8t4w

  2. Torbjörn Larsson | February 9, 2020 at 6:17 am | Reply

    MOND is dead; we know it does not explain reality.

    Of course MOND explains galaxies, that is the only purpose of its ad hoc fit. But it does so worse than general relativity, it does not explain everything that general relativity explains, and we now know it is not a physics of gravity:

    “Then there is TeVeS (tensor-vector-scalar), MOND’s relativistic cousin. While MOND is a modification of Newtonian gravity, TeVeS is an attempt to take the general idea of MOND and make it into a full mathematical theory that can be applied to the universe as a whole … These nearly simultaneous observations “brutally and pitilessly murdered” TeVeS theories, said Paulo Freire, an astrophysicist at the Max Planck Institute for Radio Astronomy in Bonn, Germany. “Gravity and gravitational waves propagate at the speed of light, with extremely high precision — which is not at all what was predicted by those [alternative] theories.””

    [ https://www.quantamagazine.org/troubled-times-for-alternatives-to-einsteins-theory-of-gravity-20180430/ ].

  3. Basically there would be no universe without dark matter. All matter is a marriage of ordinary matter (positive density mass) and dark matter (negative density mass). Where dark matter acts as the insulating cushion for ordinary matter from the expanding effects of dark energy, it provides an embrace that instantiate the force of gravity.
    This consideration is better understood by thinking of gravity a bit differently. Where the universe’s total energy is broken down to as 68% dark energy, 27% mass-energy via dark matter, and 5% mass-energy via ordinary matter, the percentage of energy distribution suggests a differing evolution. If we assume that dark energy, being the largest distribution of total energy, represents the foundation for space-time and provides for a net zero inclusion of matter as a whole, then it starts as 100% of the total energy. Upon the advent of matter, as a whole, the distribution of total energy is shared among the universal components. It is a process that maintains the concept of retaining a zero sum net gain, by redistributing this total energy with the complementarily paired positive and negative density matter. This evolutionary distribution also takes on other aspects of universal purpose: dark energy being responsible for the increasing universal expansion of the newly created matter, dark matter insulating the ordinary matter from being torn apart within its dark energy medium, and ordinary matter building and evolving into whatever it can. In effect, dark matter is the ‘force’ created to insulate ordinary matter, or positive density mass, by warping the space-time fabric of dark energy away from its complementary partner, ordinary matter.
    So if dark matter is what engenders a force of gravity for ordinary matter to bond, then the accretion and accumulation of ordinary matter is just the resultant consequence of this force. And if the black holes are nothing but dark matter, then it would also follow that dark matter can be accumulated, separate of ordinary matter. It would therefore also follow that the gravitational force is more representative of negative density mass than positive density mass.
    If you’re interested in exploring this concept more, please review the alternative theories presented in the book, ‘The Evolutioning of Creation: Volume 2’, or even the ramifications of these concepts in the sci-fi fantasy adventure, ‘Shadow-Forge Revelations’. The theoretical presentation brings forth a variety of alternative perspectives on the aspects of existence that form our reality. #shadowforgerevelations

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