Dark energy interacting with dark matter

Notes on dark energy interacting with dark matter and unparticle in loop quantum cosmology

Mubasher Jamil, D. Momeni, Muneer A. Rashid

(Submitted on 8 Jul 2011 (v1), last revised 29 Jul 2011 (this version, v2))

We investigate the behavior of dark energy interacting with dark matter and unparticle in the framework of loop quantum cosmology. In four toy models, we study the interaction between the cosmic components by choosing different coupling functions representing the interaction. We found that there are only two attractor solutions namely dark energy dominated and dark matter dominated Universe. The other two models are unstable, as they predict either a dark energy filled Universe or one completely devoid of it.

Notes on dark energy interacting with dark matter and unparticle in loop quantum cosmology. (arXiv:1107.1558v1 [physics.gen-ph])

Universe by Planck's satellite

ESA's Planck satellite has delivered its first all-sky image of the Cosmic Microwave Background (CMB), bringing with it new challenges about our understanding of the origin and evolution of the cosmos. The image has provided the most precise picture of the early Universe so far. Read more.

Dark Matter Near the Sun

(Phys.org) -- Astronomers at the University of Zürich, the ETH Zurich, the University of Leicester and NAOC Beijing have found large amounts of invisible "dark matter" near the Sun. Their results are consistent with the theory that the Milky Way Galaxy is surrounded by a massive "halo" of dark matter, but this is the first study of its kind to use a method rigorously tested against mock data from high quality simulations. The authors also find tantalising hints of a new dark matter component in our Galaxy. The team's results will be published in the journal Monthly Notices of the Royal Astronomical Society.

Read more at: http://phys.org/news/2012-08-plenty-dark-sun.html#jCp

Dark Matter should not to be confused with Dark Energy, Dark Fluid (is an alternative theory to both Dark Matter and Dark Energy and attempts to explain both phenomena in a single framework), or Dark Flow (astrophysical term describing a peculiar velocity of galaxy clusters).

Source: http://www.crystalinks.com/darkmatter.html

In astronomy and cosmology, dark matter is a type of matter hypothesized to account for a large part of the total mass in the universe. Dark matter cannot be seen directly with telescopes; evidently it neither emits nor absorbs light or other electromagnetic radiation at any significant level.^[1] Instead, its existence and properties are inferred from its gravitational effects on visible matter, radiation, and the large scale structure of the universe. Dark matter is estimated to constitute 84% of the matter in the universe and 23% of the mass-energy.^[2]

Rotation curve of a typical spiral galaxy:
predicted (A) and observed (B).
Dark matter can explain the 'flat' appearance
of the velocity curve out to a large radius

Dark matter came to the attention of astrophysicists due to discrepancies between the mass of large astronomical objects determined from their gravitational effects, and the mass calculated from the "luminous matter" they contain; such as stars, gas and dust. It was first postulated by Jan Oort in 1932 to account for the orbital velocities of stars in the Milky Way and Fritz Zwicky in 1933 to account for evidence of "missing mass" in the orbital velocities of galaxies in clusters. Subsequently, other observations have indicated the presence of dark matter in the universe, including the rotational speeds of galaxies, gravitational lensing of background objects by galaxy clusters such as the Bullet Cluster, and the temperature distribution of hot gas in galaxies and clusters of galaxies.

Although the existence of dark matter is generally accepted by the mainstream scientific community, several alternative theories have been proposed to try to explain the anomalies for which dark matter is intended to account.

from: wikipedia (click the link to know more)

to know more: http://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy/

Supernova won't explode. Why?

Computer Simulation
of a spinning collapse supernova.
Credit: NASA

"Somewhere in the Milky Way, a massive old star is about to die a spectacular death. As its nuclear fuel runs out, the star begins to collapse under its own tremendous weight. Crushing pressure triggers new nuclear reactions, setting the stage for a terrifying blast. And then... nothing happens.

At least that's what supercomputers have been telling astrophysicists for decades. Many of the best computer models of supernovas fail to produce an explosion. At the end of the simulation, gravity wins the day and the star simply collapses.

Clearly, physicists are missing something." (science.NASA)

Read entire article here and watch this video:

After the Venus transit let me present you a challenge.

Transit of the planets is a way to discover another planets (exoplanets) in distant stars.

Credit: Astromic Backyard

Venus is almost the same size of our planet. So, how many Earths could be inside our Sun, if could be that possible?

Let's assume that Earth, by approximation, is a little sphere that we going to put inside a giant sphere, our Sun.

To calculate how many our Sun is large in volume than our Earth, we find the relation between both astronomical objects. So, we can establish the volume ratio between Sun and Earth:

V_Sun = X x V_Earth ↔ X = V_Sun / V_Earth    [1]

The sphere's volume can be calculated using the mathematical expression 

4/3 π R³
Thus, applied in the equation [1] brings:

X = (4/3 π R³_Sun) / (4/3 π R³_Earth) ↔  X = (R³_Sun) / (R³_Earth)     [2]

We can find the Sun and Earth radius values in Wikipedia:

R(Sun) = 6,955×10⁵ km       e        R(Earth) = 6 378,1 km

Credit: NASA

Replacing in equation [2] and solving, we obtain:

X = (R³_Sun) / (R³_Earth)   ↔   X = (6,955×10⁵)³ / (6 378,1)³   ↔  X = 1 296 634,0

That result means that our Sun is more than one million times largest than Earth. Thus, we can put about 1,3 x 10⁶ Earths inside our Sun!

Here is a playlist with videos about stars, Solar System and more.

Secrets of the Sun

Now it's time to learn about the Secrets of the Sun:

High-precision map of Milky Way's magnetic fields

The sky map of the Faraday effect caused by the magnetic fields of the Milky Way. Red and blue colors indicate regions of the sky where the magnetic field points toward and away from the observer, respectively. The band of the Milky Way (the plane of the Galactic disk) extends horizontally in this panoramic view. The center of the Milky Way lies in the middle of the image. The North celestial pole is at the top left and the South Pole is at the bottom right. Credit: Max Planck Institute for Astrophysics

(PhysOrg.com) -- Scientists at the Naval Research Laboratory (NRL) are part of an international team that has pooled their radio observations into a database, producing the highest precision map to date of the magnetic field within our own Milky Way galaxy.

Repulsive gravity as an alternative to dark energy

(PhysOrg.com) -- When scientists discovered in 1998 that the Universe is expanding at an accelerating rate, the possibility that dark energy could explain the observation was intriguing. But because there has been little progress in figuring out exactly what dark energy is, the idea has since become more of a problem than a solution for some scientists. One physicist, Massimo Villata of the National Institute for Astrophysics (INAF) in Pino Torinese, Italy, describes dark energy as “embarrassing,” saying that the concept is an ad hoc element to standard cosmology and is devoid of any physical meaning. Villata is one of many scientists who are looking for new explanations of the Universe’s accelerating expansion that involve some form of repulsive gravity. In this case, the repulsive gravity could stem from antimatter hiding in voids.

(PhysOrg.com) -- During the past few years, CERN physicist Dragan Hajdukovic has been investigating what he thinks may be a widely overlooked part of the cosmos: the quantum vacuum. He suggests that the quantum vacuum has a gravitational charge stemming from the gravitational repulsion of virtual particles and antiparticles. Previously, he has theoretically shown that this repulsive gravity can explain several observations, including effects usually attributed to dark matter. Additionally, this additional gravity suggests that we live in a cyclic Universe (with no Big Bang) and may provide insight into the nature of black holes and an estimate of the neutrino mass. In his most recent paper, published in Astrophysics and Space Science, he shows that the quantum vacuum could explain one more observation: the Universe’s accelerating expansion, without the need for dark energy. 

First Planet in Habitable Zone

(PhysOrg.com) -- NASA's Kepler mission has confirmed its first planet in the "habitable zone," the region where liquid water could exist on a planet’s surface. Kepler also has discovered more than 1,000 new planet candidates, nearly doubling its previously known count. Ten of these candidates are near-Earth-size and orbit in the habitable zone of their host star. Candidates require follow-up observations to verify they are actual planets.
Read more in PhysOrg

 Image: NASA/Ames/JPL-Caltech