What is Dark matter: Definition and 930 Discussions

Dark matter is believed to be a form of matter thought to account for approximately 85% of the matter in the universe and about 27% of its total mass–energy density or about 2.241×10−27 kg/m3. Its presence is implied in a variety of astrophysical observations, including gravitational effects that cannot be explained by accepted theories of gravity unless more matter is present than can be seen. For this reason, most experts think that dark matter is abundant in the universe and that it has had a strong influence on its structure and evolution. Dark matter is called dark because it does not appear to interact with the electromagnetic field, which means it does not absorb, reflect or emit electromagnetic radiation, and is therefore difficult to detect.Primary evidence for dark matter comes from calculations showing that many galaxies would fly apart, or that they would not have formed or would not move as they do, if they did not contain a large amount of unseen matter. Other lines of evidence include observations in gravitational lensing and in the cosmic microwave background, along with astronomical observations of the observable universe's current structure, the formation and evolution of galaxies, mass location during galactic collisions, and the motion of galaxies within galaxy clusters. In the standard Lambda-CDM model of cosmology, the total mass–energy of the universe contains 5% ordinary matter and energy, 27% dark matter and 68% of a form of energy known as dark energy. Thus, dark matter constitutes 85% of total mass, while dark energy plus dark matter constitute 95% of total mass–energy content.Because dark matter has not yet been observed directly, if it exists, it must barely interact with ordinary baryonic matter and radiation, except through gravity. Most dark matter is thought to be non-baryonic in nature; it may be composed of some as-yet undiscovered subatomic particles. The primary candidate for dark matter is some new kind of elementary particle that has not yet been discovered, in particular, weakly interacting massive particles (WIMPs). Many experiments to directly detect and study dark matter particles are being actively undertaken, but none have yet succeeded. Dark matter is classified as "cold", "warm", or "hot" according to its velocity (more precisely, its free streaming length). Current models favor a cold dark matter scenario, in which structures emerge by gradual accumulation of particles.
Although the existence of dark matter is generally accepted by the scientific community, some astrophysicists, intrigued by certain observations which are not well-explained by standard dark matter, argue for various modifications of the standard laws of general relativity, such as modified Newtonian dynamics, tensor–vector–scalar gravity, or entropic gravity. These models attempt to account for all observations without invoking supplemental non-baryonic matter.

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  1. tedj121

    I Vera Rubin's research

    Is it correct to say that the reason why stars at the periphery of galaxies are observed to orbit faster than can be accounted for by Newtonian physics is because they are gravitationally bound to relatively high density distributed matter also present at the periphery that must be attributed to...
  2. ShadowKraz

    I Questions about Black Holes, Hawking Radiation, and Dark Matter

    If this post should be in another forum, please advise so I can post there instead. I hope I got the right prefix. Thank you. 1) Is it possible for Hawking Radiation to be dark matter, at least in part? Do the equations rule out this possibility? 2) Are Black Holes actually spinning or is our...
  3. Mistenda

    Together, understanding the universe

    hobbyist, passionate studing of issues such as the nature of gravity, the LamdaCDM model, the dark matter, the dark energy, and the prevalence of ordinary matter over antimatter (baryogenesis)
  4. S

    I Explanation for Galaxy Rotation Curves

    The existence of dark matter was initially proposed to address discrepancies between observed galaxy rotation curves and the expected behavior dictated by our current understanding of gravity. Typically, it's argued that stars at the edges of galaxies rotate faster than expected, leading to...
  5. P

    B String theory suggests that dark matter is hiding in extra dimension

    Here is the article titled "In a ‘Dark Dimension,’ Physicists Search for the Universe’s Missing Matter" by Quanta Magazine https://www.quantamagazine.org/in-a-dark-dimension-physicists-search-for-missing-matter-20240201/
  6. M

    B Dark matter and extreme gravitational regimes

    If dark matter really lives up to it's name and truly is some form of matter, then wouldn't it feed black holes given extreme gravitational regime in a black hole?
  7. I

    B Questions about dark matter/energy

    Does the astrophysics community really think dark energy/matter is real, or that we just haven't figured out the actual physics of what is happening and this just makes it work out (to our current understanding).
  8. M

    I Rotation curves and apparent mass of a galaxy

    i am working on an alternate explanation of dark matter i am looking for data sets of rotational and the apperant mass for the same galaxy multiple data sets would be helpfull.
  9. L

    I Is Dark Matter the Key to Understanding the Pre-Visible Universe?

    Regarding the following statement: "It would appear Dark matter and dark energy are what existed BEFORE the visible universe as we know it came into being. When you look at galaxies what you're seeing could be described as "displacements" in dark matter where ordinary matter formed and took...
  10. Mahsum

    Dark Matter Density Distribution

    Hello, I have asked a similar question before, but this time I want to ask it a bit differently to be understood better. I am a physics student at a university and this semester I am going to make a term project about Dark Matter Density Distribution by using rotation curves. However, I am a...
  11. Lotto

    What is density of dark matter as a function of distance from the galactic core?

    This problem builds on my previous post, where we calculated that core's mass is ##M_1=\frac{{v_0}^2r_1}{G}##. So if we consider mass of dark matter dependent on distance ##r## to be ##M_2(r)##, we can calculated it from ##G\frac{(M_2(r)+M_1)m}{r^2}=m\frac{{v_0}^2}{r}.## So...
  12. Lotto

    What is the mass of the Galaxy's core?

    It is clear that the speed is constant because dark matter hasa gravitational effect on stars, so when a star is further from the core, gravitational force of it is smaller, but the net gravitational force of dark matter is bigger. So the net force acting on each star has to be the same. So...
  13. H

    I Role of Dark Matter in the Evolution of Large Scale Structure

    Is the basic idea behind the CDM theory regarding the production of the Universe's large scale structure simply that dark matter, being dark, doesn't interact with photons, and thus was able to coalesce gravitationally soon after the Big Bang, forming the scaffolding toward which regular matter...
  14. U

    What Are Some Common Misconceptions About Physics?

    Hello! I am a highschooler looking to learn more about physics and looking to hear a lot of feedback on my thoughts about physics.
  15. Ranku

    I Distinguishing between the effects of dark matter and MOND

    How do we distinguish between the effect of dark matter and MOND with respect to flat rotation curves in galaxies? How would the shape of the rotation curve differ between the two?
  16. F

    A Modified Gravity against Dark Matter

    I am looking for examples of Modified Gravity theories that have been developed with the aim of dispensing dark matter, besides Milgrom's [MOND][1], Bekenstein's [TeVeS][2], and the recent relativistic version of MOND ([RMOND][3]) by Skordis and Zlosnik. Are there any other examples of similar...
  17. .Scott

    B Images with CMB used to Illuminate Dark Matter

    A collaborative effort is yielding a Dark Matter picture of the universe from microwave (CMB) data collected by the Atacama Cosmology Telescope. Major sections of the sky have already been imaged. Those are shown in the image below as the red/blue speckled regions (from a University of Toronto...
  18. M

    A Photon dilemma for MOND-like dark matter

    "Superfluid dark matter in tension with weak gravitational lensing data" (Mistele, McGaugh, Hossenfelder) Regarding this paper, Sabine Hossenfelder tweets One comment summarizes this as
  19. D

    B Subatomic particles and dark matter

    I am by no means an expert in physics, but I have a question. We have recently found the particle that cause attraction (Bos-Higgs) would it not be reasonable to think the there is a particle that cause repulsion? That would lead to cluster of attraction surrounded by fields of expansion. Would...
  20. bakerjay

    A Data on galaxy rotation curves vs visible matter

    I'm after some raw data for testing theories of dark matter in galaxies. Basically what I want is table showing visible mass vs total mass within different radii (or, observed rotational velocity vs expected rotational velocity without dark matter). Plus error percentages. And ideally, for...
  21. GreenLemon

    I Exploring the Possibility of Dark Matter as Stray Exoplanets or Collapsed Stars

    I was thinking about how the dark matter theory was proposed due to inconsistencies with observed mass vs the calculated required mass for a galaxy to exist. Just wondering how we know its not just stray exoplanets or possibly even smaller collapsed stars, really any kind of mass that wouldn't...
  22. Ranku

    I What is the difference between collisionless and self-interacting dark matter?

    When dark matter is called collisionless, does it only mean that they do not collide and scatter, or does it also mean that there is no other significant non-contact interaction?
  23. Frabjous

    I Local dark matter distribution

    We do not seem to have any unexplained orbital/gravitational anomalies within the solar system. What does that imply for the local dark matter distribution?
  24. Ranku

    I CMBR Evidence for Non-Baryonic Dark Matter

    It is said that CMBR indicates that dark matter is non-baryonic. How so?
  25. F

    A Does WHIM solve the dark matter problem?

    Direct Observation of Whim (The warm–hot intergalactic medium) has known a lot progress recently. Does whim could be enough to amount to the quantity of dark matters in the universe, therefore solving the dark matter problem? If not, why?
  26. mpross

    B Dark Energy, Dark Matter and the Speed of Light

    Quote from NASA: My understanding of dark energy is based on NASA's report: https://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy; were NASA state as follows: "It turns out that roughly 68% of the universe is dark energy. Dark matter makes up about 27%. The rest - everything on...
  27. K

    I Primordial neutron star -- a new candidate for dark matter

    could this explains the 3rd peak of the CMB and dark matter cold Primordial neutron star High Energy Physics - Phenomenology [Submitted on 7 Sep 2022 (v1), last revised 12 Sep 2022 (this version, v2)] Primordial neutron star; a new candidate of dark matter M. Yoshimura Z-boson exchange...
  28. DaveC426913

    B Gravitomagnetic explanation of Dark Matter

    I was reading a thread on my phone that was reviewing a paper about DM being explainable by gravitomagnetic effects. Now I can't find it in any search. It was on its fourth page - so at least 80 posts over at least two years. Anyway, what I wanted to ask was for a description that a layperson...
  29. G

    I Data Showing Dark Matter Is Not Cold Neutrinos?

    How do we know that cold neutrinos do not make up 100% or a large percentage of the dark matter content in the universe? In my mind, the only way to prove that dark matter is not simply cold neutrinos would be to measure the density of cold neutrinos in the universe and then calculate the...
  30. Ranku

    I Identification of matter and dark matter proportions

    Is it possible to identify a volume of space, observationally/statistically, that represents the 85:15 % ratio of dark matter and matter?
  31. Ranku

    I Rotation curve and dark matter

    Do all galaxies with dark matter halo have flat rotation curve?
  32. pinball1970

    I Distant Galaxy study, dark matter and the CMBR

    The article is pop but there is a paper Pop article https://www.vice.com/en/article/g5vvjw/the-universes-oldest-light-reveals-unprecedented-dark-matter-patterns Paper. https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.129.061301 The language is a little bit click bate, I just wanted...
  33. A

    I Bullet cluster and dark matter

    Is the bullet cluster evidence for or against dark matter? I understand the explanation that it is evidence in favor of the existence of dark matter, and it convinces me. However, some argue that it is evidence against its existence? Why?
  34. ohwilleke

    A LQG Legend Writes Paper Claiming GR Explains Dark Matter Phenomena

    A new group of investigators are attempting something similar to Deur's work, which seeks to explain dark matter phenomena with general relativity corrections to Newtonian gravity is systems like galaxies. Deur's most similar publication to this one along these lines was: One thing that makes...
  35. mfb

    I Seminar: First LUX-ZEPLIN dark matter search results

    Today 16:00 UTC, in ~7.5 hours. Announcement, Link to Zoom meeting (why is this just an image on the website, not a link?) LUX-ZEPLIN (LZ) uses several tonnes of xenon to search for signals of dark matter interacting with it. It started taking data last year and it should easily set better...
  36. A

    B Rotation of Galaxies: Mass vs Dark Matter?

    Is it possible that galaxies are spinning faster than expected due to a particular configuration of the moving mass and not due to dark matter?
  37. K

    I Modified Newtonian Dynamics + dark matter sterile neutrinos or PBH?

    what about Modified Newtonian Dynamics + dark matter both right and both correct Are sterile neutrinos consistent with clusters, the CMB and MOND? Garry W. Angus arXiv:0805.4014 [ If no sterile neutrinos then Modified Newtonian Dynamics + primordial black holes Primordial Black Holes...
  38. Oldman too

    I A new concept in Low Mass Dark Matter detection

    Summary:We propose a search for low mass dark matter particles through momentum recoils caused by their scattering from trapped, nanometer-scale objects. The Paper linked details a novel concept for detecting WIMPs. I hope to see more work performed on the idea in the future...
  39. Godot_

    I Does Dark Matter Fall into Black Holes?

    Does dark matter(DM) fall into black holes(BHs)? IMHO it should... ...as it does interact with normal matter gravitationally. Once it's done so, does it add to the BH's mass? Again, IMHO it should. AFAIK it does have mass... Would that "quasi-convert" it to normal matter? ...after all, this...
  40. T

    A Which galaxies have the best studied evidence for dark matter?

    Unsurprisingly the Milky Way seems to have been studied a lot. We have really good luminous mass profiles (e.g. McMillan 2011) and increasingly accurate circular velocity observations for stars at various radiuses (e.g. Eilers 2019) meaning we can confidently infer dark matter models. So the...
  41. mollwollfumble

    I Has anyone done a PPN formalism on Dark Matter? Or other non-GR?

    This thought surprisingly came from thinking about the definition of temperature and the symmetry breaking that separated time from temperature. Which led to thoughts about symmetry breaking that separated QM from GR. Which led to to the symmetry breaking that separated dark energy from baryonic...
  42. A

    B Light and the black matter (Dark Matter)

    Originally Answered: If light reaches the Earth from the sun, why is the space between the sun and the Earth dark? Because light illuminates surfaces, objects. Space is not an object, is the lack of matter. If you turn on a flashlight in a dark room you will illuminate the floors and the walls...
  43. Zeal Faust

    B What is Dark Matter or Energy?

    I have read that almost 80 to 90% of our space is made of dark matter or Dark Energy. But what is the function of this Dark matter or energy? Is this something that binds stars, galaxies, etc? If not then what is the actual matter with Dark energy?
  44. Buckethead

    B What is the mass distribution and rotation curve of galaxy IC1101?

    I've been reading up a little on IC1101, the largest known galaxy and there is not a lot of info on it, but it seems to have an unusually large mass to light ratio according to this popular article (see half way down): According to this article at 20kpc it's got 12:1 mass to light, at 200kpc...
  45. Delisso

    I Bullet Cluster explained without 'dark substances'

    The Bullet Cluster counts as 'smoking gun' for the dark matter. But what lacks in these calculations is the super massive black holes at the center of almost every galaxy. As the most massive and most compact objects in the collision, it's expected that they are less slowed down by the collision...
  46. A

    I Dark Matter as a condensation of photons in a space

    if we assume each photon of light as a very very light piece of matter (by famous E = mc^2 and then: m = E / c^2) and sum up all photons that have been made from the creation time of a galaxy (also considering limitation of speed of light) and also photons that accidentally passing throw that...
  47. binis

    I Does Dark Matter Have a Temperature?

    A black-body absorbs and emits radiation if heated, but it does not reflect or transmit radiation.What is the temperature of dark matter?
  48. MadDog66

    I Simplification of Dark Matter effects

    What would be the distribution galactically, universally etc? How might distribution of DM change if involved forces, masses, energies or other fundamental components of DM occurred at different weights ie: Could there be less but stronger or perhaps "more but weaker" models of DM? What would...
  49. F

    Cosmology Dark Matter Textbooks: Learn Core Topics in Astrophysics & Cosmology

    Hello, could you please recommend some good introductory textbooks for studying core topics in astrophysics/cosmology, and especially dark matter? I know that 'An Introduction to Modern Astrophysics' by Caroll and Ostlie is a good book, but I 'm looking for something more concise, so to speak...