background preloader

Dark Matter (Wikipedia)

Dark Matter (Wikipedia)
Dark matter is invisible. Based on the effect of gravitational lensing, a ring of dark matter has been detected in this image of a galaxy cluster (CL0024+17) and has been represented in blue.[1] Dark matter is a hypothetical kind of matter that cannot be seen with telescopes but accounts for most of the matter in the universe. The existence and properties of dark matter are inferred from its gravitational effects on visible matter, radiation, and the large-scale structure of the universe. Other than neutrinos, a form of hot dark matter, it has not been detected directly, making it one of the greatest mysteries in modern astrophysics. Astrophysicists hypothesized dark matter because of discrepancies between the mass of large astronomical objects determined from their gravitational effects and the mass calculated from the observable matter (stars, gas, and dust) that they can be seen to contain. Overview[edit] Baryonic and nonbaryonic dark matter[edit] Observational evidence[edit]

Dark Energy (Wikipedia) Adding the cosmological constant to cosmology's standard FLRW metric leads to the Lambda-CDM model, which has been referred to as the "standard model" of cosmology because of its precise agreement with observations. Dark energy has been used as a crucial ingredient in a recent attempt to formulate a cyclic model for the universe.[8] Nature of dark energy[edit] Many things about the nature of dark energy remain matters of speculation. The evidence for dark energy is indirect but comes from three independent sources: Distance measurements and their relation to redshift, which suggest the universe has expanded more in the last half of its life.[9]The theoretical need for a type of additional energy that is not matter or dark matter to form our observationally flat universe (absence of any detectable global curvature).It can be inferred from measures of large scale wave-patterns of mass density in the universe. Effect of dark energy: a small constant negative pressure of vacuum[edit] .

Inflation (Wikipedia) In physical cosmology, cosmic inflation, cosmological inflation, or just inflation is a theory of exponential expansion of space in the early universe. The inflationary epoch lasted from 10−36 seconds after the Big Bang to sometime between 10−33 and 10−32 seconds. Following the inflationary period, the Universe continues to expand, but at a less rapid rate.[1] Inflation was developed in the early 1980s. In 2002, three of the original architects of the theory were recognized for their major contributions; physicists Alan Guth of M.I.T., Andrei Linde of Stanford and Paul Steinhardt of Princeton shared the prestigious Dirac Prize "for development of the concept of inflation in cosmology".[5] Overview An expanding universe generally has a cosmological horizon, which, by analogy with the more familiar horizon caused by the curvature of the Earth's surface, marks the boundary of the part of the Universe that an observer can see. Space expands . . Few inhomogeneities remain Duration Reheating Notes

Black Hole (Wikipedia) A black hole is defined as a region of spacetime from which gravity prevents anything, including light, from escaping.[1] The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole.[2] Around a black hole, there is a mathematically defined surface called an event horizon that marks the point of no return. The hole is called "black" because it absorbs all the light that hits the horizon, reflecting nothing, just like a perfect black body in thermodynamics.[3][4] Quantum field theory in curved spacetime predicts that event horizons emit radiation like a black body with a finite temperature. This temperature is inversely proportional to the mass of the black hole, making it difficult to observe this radiation for black holes of stellar mass or greater. Objects whose gravity fields are too strong for light to escape were first considered in the 18th century by John Michell and Pierre-Simon Laplace. History General relativity

Neutron Star (Wikipedia) Neutron stars contain 500,000 times the mass of the Earth in a sphere with a diameter no larger than that of Brooklyn, United States A neutron star is a type of stellar remnant that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event. Neutron stars are the densest and tiniest stars known to exist in the universe; although having only the diameter of about 10 km (6 mi), they may have a mass of several times that of the Sun. Neutron stars probably appear white to the naked eye. Neutron stars are the end points of stars whose inert core's mass after nuclear burning is greater than the Chandrasekhar limit for white dwarfs, but whose mass is not great enough to overcome the neutron degeneracy pressure to become black holes. The discovery of pulsars in 1967 suggested that neutron stars exist. Neutron star collision Formation[edit] Properties[edit] Gravitational light deflection at a neutron star. Given current values Structure[edit]

Dark Photons It’s humbling to think that ordinary matter, including all of the elementary particles we’ve ever detected in laboratory experiments, only makes up about 5% of the energy density of the universe. The rest, of course, comes in the form of a dark sector: some form of energy density that can be reliably inferred through the gravitational fields it creates, but which we haven’t been able to make or touch directly ourselves. It’s irresistible to imagine that the dark sector might be interesting. In other words, thinking like a physicist, it’s natural to wonder whether the dark sector might be complicated, with a rich phenomenology all its own. But so far, there’s no evidence of anything interesting beyond that. Still — all we have are upper limits, not firm conclusions. Dark Matter and Dark Radiation Authors: Lotty Ackerman, Matthew R. Just to translate that a bit, here is the idea. However, we know a little more about the dark matter than “it doesn’t annhilate.”

Dark Matter may Shine with Invisible 'Dark Light' Mysterious dark matter could be shining with its own private kind of light. This "dark radiation" would be invisible to us, but could still have visible effects. Astronomers usually assume that dark matter particles barely interact with each other. Lotty Ackerman and colleagues at Caltech in Pasadena decided to test this assumption by supposing there is a force between dark matter particles that behaves in the same way as the electromagnetic force. Their calculations showed that it could have as much as 1% of the strength of the electromagnetic force and not conflict with any observations. If the force is close to this strength, its effects might be detectable, as it should affect how dark matter clumps together. "It might even help with some niggling problems we have now," says team member Sean Carroll. Carroll even speculates that more complex dark matter might exist, forming dark matter atoms with their own chemistry - and maybe biology. More From New Scientist More from the web (YouTube)

Is Dark Matter a Wimp or a Champ? The mysterious dark matter that makes up most of the material in the universe may actually have an electric charge, a new study suggests. If so, it might help explain why astronomers see so few dwarf galaxies in orbit around larger ones. Dark matter is detected by its tug on light and visible matter, so astrophysicists have largely assumed that it interacts mostly through the force of gravity - and not electromagnetism, for example. Indeed, the leading dark matter candidates, known as weakly interacting massive particles, or WIMPs, are electrically neutral. But theorists Leonid Chuzhoy and Rocky Kolb of the University of Chicago say it may be time to consider the possibility that dark matter is actually composed of charged massive particles, or CHAMPs. The idea for CHAMPs is not new - it was actually discarded more than a decade ago, after underground particle detectors failed to pick up any sign of such candidates. 'Prematurely rejected' Massive particles and MACS J0025. Missing dwarfs

Could Dark Photons & Dark Atoms Exist? A little over a year ago, Sean Carroll over at Cosmic Variance brought up the idea of Dark Photons, a mysterious analog to dark matter and dark energy that would have created a sort of shadow version of electromagnetism. (The photon is the gauge boson of electromagnetism, meaning that it's the particle that mediates the electromagnetic force. A dark photon would, by analogy, give rise to some similar interaction. See Particle Physics Fundamentals for a brief introduction to this concept ... more to come on this soon, I think.) Anyway, back to dark photons. The goal of the original paper (written by Carroll and others) was to propose a mechanism by which dark matter and dark energy could be part of a larger, more rich (and interesting) set of physical behaviors in their own right. The problem, of course, is that so far we haven't actually observed either dark matter or dark energy directly, but know about them only by their gravitational interactions with other matter.

Magnetar (Wikipedia) Artist's conception of a magnetar, with magnetic field lines. Description[edit] Like other neutron stars, magnetars are around 20 kilometres (10 mi) in diameter and have a greater mass than the Sun. The density of the interior of a magnetar is such that a thimble full of its substance would have a mass of over 100 million tons.[1] Magnetars are differentiated from other neutron stars by having even stronger magnetic fields, and rotating comparatively slowly, with most magnetars completing a rotation once every one to ten seconds,[7] compared to less than one second for a typical neutron star. Magnetic field[edit] As described in the February 2003 Scientific American cover story, remarkable things happen within a magnetic field of magnetar strength. Origins of magnetic fields[edit] Formation[edit] Magnetar SGR 1900+14 is in the exact center of the image, which shows a surrounding ring of gas seven light-years across in infrared light, as seen by the Spitzer Space Telescope. See also[edit]

Magnetic Reconnection (Wikipedia) Magnetic Reconnection: This view is a cross-section through four magnetic domains undergoing separator reconnection. Two separatrices (see text) divide space into four magnetic domains with a separator at the center of the figure. Field lines (and associated plasma) flow inward from above and below the separator, reconnect, and spring outward horizontally. A current sheet (as shown) may be present but is not required for reconnection to occur. This process is not well understood: once started, it proceeds many orders of magnitude faster than predicted by standard models. A magnetic reconnection event on the sun. The resistivity of the current layer allows magnetic flux from either side to diffuse through the current layer, cancelling out flux from the other side of the boundary. Theoretical descriptions of magnetic reconnection[edit] The Sweet-Parker Model[edit] where is the out-of-plane electric field, is the characteristic inflow velocity, and , gives the relation . is the outflow velocity.