Astrophysics

Astrophysics is a hybrid of Physics and Astronomy that attempts to explain the physical workings of the celestial objects and phenomena. Astrophysics has two subdivisions: theoretical, and applied or experimental.

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Research focus

Research in astrophysics addresses a great variety of topics.

Stars

• formation and evolution
• magnetic field properties
• stellar convection

Stellar atmospheres

• nature of spectral analysis
• electron density

The Galaxy (the Milky Way)

• interstellar gas and dust

Galaxies

• formation and evolution
• modeling the environs of galactic-centre massive black holes;
• the structure and dynamics of galactic bars;
• the flow of gas into and out of galaxies;
• the role of active galactic nuclei in limiting the growth of galaxies.

Astroparticles

Astroparticles are particles that are found in the universe. The study of astroparticles, astroparticle physics, is a multidisciplinary field that involves particle physics, astronomy, astrophysics and cosmology. Particle physics studies the nature of the structure of matter and fundamental laws governing their interactions, basically astroparticle physics studies the smallest aspects of the universe. Astronomy and astrophysics study the universe on a larger scale from its origin and evolution since the Big Bang. Cosmology in turn links the theories of particle physics with theories of the Universe at its earliest moments.

Astroparticle studies employ different types of facilities and appliances. Underground laboratories to study neutrinos and dark matter are used to shield experiments from the background of cosmic muons. Land based observatories (telescopes and antennas) study very high energy gamma rays, neutrinos and very high energy cosmic rays. Satellite observatories are used to study high energy gamma rays, cosmic rays and gravitational waves.

Neutrinos

Neutrinos are the second most abundant particles in the universe. Neutrinos are produced in nuclear reactions occurring within stars. Neutrinos can also be artificially produced in high-energy collisions. Neutrinos bombard the earth constatantly in vast numbers. Each square centimetre of the human body is traversed by 60 billion neutrinos per second.

Neutrinos are not charged particles, so they don’t interact with matter through the electromagnetic force. They do not even interact through the strong force that holds together the nucleus of an atom. Neutrinos can only be affected by other particles through the weak force (e.g. in the nuclear fusion in the stars). Becasue they do not react readily, they can pass through almost any kind and thickness of matter without leaving any traces without a deviation in their direction of motion they have had since the instant of their origin.

There are three types or flavours of neutrinos: electronic, muonic or tauonic. A neutrino can oscillate from one flavour into another over long distances.

Flavour oscillation may demonstrate that neutrinos do in fact have mass. Given their abundance, it is possible that neutrinos may have been invovled in some types of symmetry changes or breaks, such as the matter-antimatter ratio, believed to be very close in the early stages of the universe but matter now has an overwhelming higher ratio to ani-matter.

Dark energy

Dark energy is a theoretical energy which exerts a negative attraction or opposes the positive attraction of matter and causes the universe to expand.

A current line of study is surveying the distribution of galaxies in the cosmos. The distribution pattern is compared to the miniscule temperature fluctuations in the cosmic microwave background. Theoretically acoustic waves moving through the early universe created temperature fluctuations, and the fluctuations are correlated to regions of the universe that had slightly higher and lower densities. These regions of varied density are believed to have influenced how matter eventually clumped together through gravitational influences and thereby formed galaxy clusters. Comparing clumping in the early universe to clumping being observed now may possibly allow researchers to ascertain the role dark energy has played in cosmic evolution.

Astrochemistry

Astrochemistry involves the study of the role of the chemical bond and organic chemistry in nature on a cosmic scale. Over 140 molecules have been identified in the interstellar gas and circumstellar shells. To date the largest is a carbon chain with 13 atoms and a molecular weight of 147.

Inflation

Inflation refers to the expansion of the universe, its velocity and whether or not it is slowing or gaining in speed. The Supernova Acceleration Probe (SNAP) is a space observtory planned for possible construction and launch by 2020. It is designed to measure the expansion of the Universe and determine the nature of Dark Energy which current theory holds is accelerating cosmological expansion.

Curvature

The curvature of space, or space-time geometry, also refers to the shape of the universe. The concept of curved space originated in the work of Albert Einstein’s Theory of General Relativity. Space is united with time in a geometric spacetime which can be curved or flat. It may be positively or negatively curved or its curvature may be zero.

Positive curvature (often depicted graphically as a spherical model) is called a closed universe: Spacetime expands from a volume of zero, reaches the maximum point of expansion and the contracts to zero volume in the Big Crunch.

Negative spacetime geometry is a pseudosphere, for example a hyperboloid which appears to curve outward from a constricted middle, like two cones end to end or a double ended funnel such as might be typical of an hour-glass shape. Negative curve spacetime has infinite volume and expands forever.

Zero curvature is a flat space and extends infinitely in any directions; it too, is an open universe that expands forever.

Einstein employed classic physics (not quantum physics) to describe the large scale of the universe. His general theory of relativity basically connotes curvature in spacetime in a given direction. That direction is determined by the energy and momentum of everything in the spacetime, i.e. not spacetime itself. He was saying, in other words, that gravity and non-gravity, geometry and non-geometry were combined. So, all types of matter and energy, everything that is involved in every type of force, exist in spacetime and also influence the shape of the spacetime.

There are some basic assumptions about the nature of the geometry of spacetime. One assumption is that space and time can be separated (though the extreme nature of such phenomena as a black hole may be an exception) and space time can be perceived as space changing with time. Another assumption in the spacetime model is that there is maximal symmetry: space is isotropic—looks the same in every direction; and space is homogenous—looks the same at every point. Curvature has to be the same at every point.

There are three posited types of energy that effect the geometry of space time: 1. Vacuum energy; 2. Radiation; 3. Matter.

One possible explanation of what determines the curvature of space time, whether the universe is open or closed, is the total energy density (designated $r$) of the universe. Vacuum energy theoretically leads to a constant energy density referred to as the cosmological constant. Energy density from radiation and matter of the universe may lead to an open, closed of flat universe.

If the universe is closed, then it has positive curvature and the total energy density has to be greater than the energy needed for a flat universe. Density for Zero curvature, flat space, is called, critical density $r_{0}\,$

Using a simple formula

$W={\frac {r}{r_{0}}}$

In a closed universe

$W>1\,$

In a flat universe

$W=1\,$

In an open universe

$W<1\,$