difference between dark matter and dark energy pdf

Difference between dark matter and dark energy pdf

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The dark universe: 4 big questions

Dark Matter and Dark Energy in General Relativity and Modified Theories of Gravity

While some of these results have been noted previously, the strength here lies in that we do not assume a particular cosmological model. We incorporate Milky Way dark matter halo profile uncertainties, as well as an accounting of diffuse gamma-ray emission uncertainties in dark matter annihilation models for the Galactic Center Extended gamma-ray excess GCE detected by the Fermi Gamma Ray Space Telescope.

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Invisible dark matter makes up most of the universe — but we can only detect it from its gravitational effects. Galaxies in our universe seem to be achieving an impossible feat. They are rotating with such speed that the gravity generated by their observable matter could not possibly hold them together; they should have torn themselves apart long ago. The same is true of galaxies in clusters, which leads scientists to believe that something we cannot see is at work. They think something we have yet to detect directly is giving these galaxies extra mass, generating the extra gravity they need to stay intact. Unlike normal matter, dark matter does not interact with the electromagnetic force. This means it does not absorb, reflect or emit light, making it extremely hard to spot.

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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. 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.

We consider several cosmological models which allow for nongravitational direct couplings between dark matter and dark energy. The distinguishing cosmological features of these couplings can be probed by current cosmological observations, thus enabling us to place constraints on these specific interactions which are composed of the conformal and disformal coupling functions. We perform a global analysis in order to independently constrain the conformal, disformal, and mixed interactions between dark matter and dark energy by combining current data from: Planck observations of the cosmic microwave background radiation anisotropies, a combination of measurements of baryon acoustic oscillations, a supernova type Ia sample, a compilation of Hubble parameter measurements estimated from the cosmic chronometers approach, direct measurements of the expansion rate of the Universe today, and a compilation of growth of structure measurements. We find that in these coupled dark-energy models, the influence of the local value of the Hubble constant does not significantly alter the inferred constraints when we consider joint analyses that include all cosmological probes. Moreover, the parameter constraints are remarkably improved with the inclusion of the growth of structure data set measurements. We find no compelling evidence for an interaction within the dark sector of the Universe.


Dark energy: evidence. Page 6. The dark energy puzzle. Dark energy: what do we know? • Dark energy smoothly fills space with a roughly constant energy.


The dark universe: 4 big questions

Not a MyNAP member yet? Register for a free account to start saving and receiving special member only perks. What is the universe made of?

Both the dark matter and dark energy issues are considered essential for a deeper understanding of the evolutionary universe. According to studies, dark matter and dark energy have had a strong influence on the structure and evolution of the universe. In addition, dark matter makes up almost twenty-seven percent of the universe, with the remaining five percent being baryonic matter. It is not known exactly what dark matter is, and in order to explain the missing mass of the universe it is commonly accepted that the study of dark energy and dark matter lies at the forefront of modern research and is considered of paramount importance for the development of 21 st century physics.

Accordingly, the subject matter is quite naturally tied to other fields such as astroparticle physics, quantum physics and general relativity. Skip to main content Skip to table of contents. Advertisement Hide. This service is more advanced with JavaScript available. Front Matter.

Dark Matter and Dark Energy in General Relativity and Modified Theories of Gravity

The visible universe — including Earth, the sun, other stars , and galaxies — is made of protons, neutrons, and electrons bundled together into atoms. Perhaps one of the most surprising discoveries of the 20th century was that this ordinary, or baryonic, matter makes up less than 5 percent of the mass of the universe. The rest of the universe appears to be made of a mysterious, invisible substance called dark matter 25 percent and a force that repels gravity known as dark energy 70 percent. Scientists have not yet observed dark matter directly. It doesn't interact with baryonic matter and it's completely invisible to light and other forms of electromagnetic radiation, making dark matter impossible to detect with current instruments. But scientists are confident it exists because of the gravitational effects it appears to have on galaxies and galaxy clusters. For instance, according to standard physics, stars at the edges of a spinning, spiral galaxy should travel much slower than those near the galactic center, where a galaxy's visible matter is concentrated.

This creation of spacetime results in metric expansion around mass points in addition to the usual curvature due to stress-energy sources of the gravitational field. A recent modification of Einstein's theory of general relativity by Chadwick, Hodgkinson, and McDonald incorporating spacetime expansion around mass points, which accounts well for the observed galactic rotation curves, is adduced in support of the proposal. The hypothetical dark energy is invisible, and can be thought of as an intrinsic property of spacetime rather than usual matter stress-energy that is the source of spacetime curvature. An ostensibly separate phenomenon—the flattening of galactic rotation curves with radial distance—is also well known e.

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2 comments

  • Sarah P. 20.04.2021 at 00:24

    One idea is that it could contain "supersymmetric particles" œ hypothesized particles that are partners to those already known in the Standard. Model. Experiments.

    Reply
  • Dayanira H. 22.04.2021 at 02:50

    Expressed a fraction of the critical density it goes like this: neutrinos, between ​% and 15%; stars, %; baryons. (total), 5%; matter (total), 40%; smooth, dark.

    Reply

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