Astrophysics - SpeedyLook encyclopedia

Disciplines of astrophysics

There exist various disciplines in astrophysics:

Cosmology
Planetology
stellar Exobiologie
Instrumentation
Physical
Héliosismologie and Physical Astérosismologie
of the interstellar Environment
astrophysical Plasmas
Physical galactic
Technologies of propulsion (space)

Propulsion by the antimatter
Propulsion plasma

Astrophysics being a very vast subject, the astrophysicists generally use several disciplines of the physics, of which mechanics, electromagnetism, statistical mechanics, thermodynamics, quantum mechanics, relativity, the nuclear physics, the physics of the particles, atomic and molecular physics.

History

See also: Cosmologist

Also far that the historical data go up, one finds of the evidence of the existence of astronomy. For a long time, astronomy was a discipline quite distinct from physics. In the thought aristotelician, the celestial world tended to perfection, with the celestial bodies which seemed to be perfect spheres circulating on perfectly circular orbits, whereas the terrestrial world seems condemned to the imperfection. These two worlds could not thus be dependant.

Aristarque de Samos (310 av. J. - C.) - 250 av. J. - C.) was the first to propose the idea according to which the movement of the celestial bodies could be explained by the rotation of planets of the solar system (of which Earth) around the Sun. Unfortunately, at the time, the geocentric vision of the universe prevailed and the heliocentric theory of Aristarque was declared eccentric and heretic. This vision remained in place until an astronomer named Nicolas Copernic ressuscita the heliocentric model at the 16th century. In 1609, thanks to the telescope that he had invented, Galileo discovered the four most brilliant Jupiter moons, and showed that they turned all around this planet. This discovery was in complete contradiction with the dogma of the Catholic church of the time. He escaped a severe sorrow only by claiming that its work was only pure mathematical and thus purely abstract work, contrary to natural philosophy (physics).

Starting from the precise data of observations (mainly coming from the observatory of Tycho Brahe), of research were carried out to find an explanation theoretical to the behavior observed. Initially, only of the empirical laws were formulated, such as the Lois of Kepler on the planetary movement at the beginning of the 17th century. A few years later, Isaac Newton succeeds in establishing the link between the laws of Kepler and the dynamics of Galileo. He discovered indeed that the same laws governed the dynamics of the objects on Earth and the movement of the stars in the solar system. The celestial mechanics, application of Newtonian gravity and the laws of Newton to explain the laws of Kepler on the movements of planets, was the first unification of astronomy and physics.

After Isaac Newton had published his book, Philosophiae Naturalis Principia Mathematica , sea transport changed radically. As from 1670, the whole world was measured starting from modern instruments giving the latitude and of clock. The needs for the Navy pushed with the progressive improvement of the instruments and the astronomical observations, giving thus more data to the scientists.

At the end of the 19th century, one discovered that the sunlight could break up into a spectrum of coloured lines. Experiments with heated gases showed thereafter that the same lines were present in their spectrum. These specific lines corresponded to a single chemical element. This was the proof that the chemical elements present in the Sun could be found on Earth. Indeed, helium was initially discovered in the spectrum of the Sun, from where its name, and only then on the Earth. At the 20th century, the Spectroscopie (the study of these spectral lines) developed, in particular thanks to the projections of the quantum physics which could explain the experimental and astronomical observations.

Observational physics

The majority of the observations in astrophysics are carried out by using the electromagnetic Specter.

the Radioastronomie studies cosmic radiations which have a wavelength higher than a few millimetres. The waves radios are generally emitted by the cold objects, like the interstellar gases or the clouds of dust. Radiation microwave of the cosmological diffuse Fond comes from the light of the Big-Bang which undergoes a Décalage towards the red. The Pulsar S were detected in first by the frequencies Micro-onde S. the study of these frequencies requires very large Radiotélescope S.
astronomy Infrarouge studies radiations of which the wavelength is too large to be visible and smaller than the radio waves. The observations in infra-red are generally made with telescopes similar to the optical telescopes. The objects studied with the infra-red are more cold than stars, like planets for example.
optical astronomy is the oldest form of astronomy. The most current instruments are the telescopes associated with a sensor with coupled load or spectroscopes. As the terrestrial atmosphere interferes somewhat with the made observations, the adaptive Optique and the space telescopes made their appearance in order to obtain the best quality of possible image. On this scale, the stars are very visible, and much of chemical spectra can be observed in the chemical composition of stars, of Galaxie S or of Nébuleuse S.
astronomy with Ultraviolet, x-rays or Gamma ray studies the very energy phenomena such as the binary pulsars, the black holes or the Magnétar S. These radiations penetrate the atmosphere of the Earth with difficulty, it thus has only two possibilities there to exploit them, the atmospheric space telescopes and Cherenkov telescopes. RXTE, the telescope with x-rays Chandra and the observatory with gamma rays Compton are of the observatories of the first type. The stereoscopic system of high energy (HESS) and telescopes it MAGIC belong to the second category.

Put aside electromagnetic radiations, only very few things located at long distance can be observed since the Earth. Some observatories of gravitational waves were built but these waves are very difficult to detect. One also finds some observatories of Neutrino S for the study of the Sun, mainly. The cosmic rays are particles of high energy which are observed when they run up against the terrestrial atmosphere.

The observations also differ on the scale from time that they consider. The majority of the optical observations are spread out over several minutes, even over several hours, so that the phenomena which evolve/move more quickly than this time interval are not visible. However, the historical data of some objects extend over centuries or millenia. In addition, the radio observations are focused on events on the scale of the millisecond (Pulsar millisecond) or combines the data of several years (studies of the deceleration of pulsars). The information obtained on these various scales gives access different results.

The study of our own Sun holds a particular place in observational astrophysics. Because of enormous distance to which the other stars are, the details which one can acquire on the Sun are without common measurement with what one could observe on other stars. The comprehension of our Sun is used thus as guide to our knowledge of other stars.

The stellar evolution, the subject which studies how the stars change, is often modelled while placing the various types of stars to their position on the Diagramme of Hertzsprung-Russell. This diagram represents the state of a stellar object, of its birth to its disappearance. The material composition of the astronomical objects can often be studied while using:

the Spectroscopy
the Radioastronomy
astronomy neutrino

Theoretical astrophysics

The astrophysicists use a large variety of tools like the analytical model (such as the polytropes to obtain the approximate behavior of a star) or the digital simulation on Ordinateur. Each tool has its advantages. The analytical models of a process are generally better to obtain the inner working. The digital models, them, can reveal the existence of phenomena and effects which could not be seen differently.

The theorists in astrophysics try to create ideal models and to include/understand the observable consequences of these models. This helps the observers to seek the data which can refute a model or help in the choice between several contradictory alternatives or models.

The theorists also try to produce or modify models to take account of new data. In the event of contradiction, the general tendency is to try to make tiny modifications of the model to adapt it to the data. In certain cases, a great quantity of incoherent data to repetition can lead to the total abandonment of a model.

The subjects studied by the theorists in astrophysics include the evolution and stellar dynamics, the formation of the galaxies, the material structures with large scales of the Universe, the origin of the cosmic rays, the General relativity and the physical cosmology, with the assistance of the Théorie of the cords and the Physique of the particles. Relativistic astrophysics is used as tools to evaluate the properties of the structures with large scales. For these structures, the gravitation plays a big role in the studied physical phenomena and is used as a basis for physics of the black holes and the study of the gravitational waves.

Among the studied theories and the models recognized in astrophysics, one can find the model lambda-CDM which included the Big-bang, cosmic inflation, the black Matière and fundamental theories of physics.

Some examples of process:

The energy sinks and the black Matière is currently the main subjects of research in astrophysics, being given that their discovery and the controversy on their existence is resulting from the study of the galaxies.

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