QUASARS AND THE COSMIC REIONIZATION

Credit: NASA/ESA

Recently it has been suggested that quasars can be primarily responsible for the reionization of the universe.

A bit of history for those who do not know what is the reionization - According to the "standard theory", the universe in the early stages after the Big Bang is hot and dense and the temperature is too high for the formation of atoms (hydrogen is formed by a proton and an electron), and then protons and electrons move freely in a sea of photons.
300,000 years after the Big Bang the universe cools and protons capture electrons generating the hydrogen atoms (this stage is called recombination and it is remembered as the dark age - the neutral hydrogen does not emit radiation and the universe is completely dark).
Later stars and galaxies are generated and the light emitted from these sources ionizes the hydrogen again (the electron is separated again from the proton - ionized hydrogen). This phase, which reaches up to the present day, is that of the cosmic reionization. All these stages are studied by analyzing the cosmic microwave background.
Such analysis show that much of the reionization could have occurred at redshift z=6 (at higher redshift correspond larger distances in space and time). A recent study analyzed the number of quasars at z=6 and suggests that their population may not be enough to explain the entire cosmic reionization occurred at that time. Consequently other sources should be involved in the reionization process.
These works are important to better understand how the universe evolved from the Big Bang to the present day.

► Read more>>
http://jwst.nasa.gov/firstlight.html

► Journal reference:
http://arxiv.org/abs/1511.01585
http://iopscience.iop.org/article/10.1088/2041-8205/813/2/L35;jsessionid=9CF824AF5CCB5CA65AE592274C573018.c5.iopscience.cld.iop.org

► Image credit:
NASA/ESA

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Astrophysics collection (March 11, 2016)

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ORBITAL PERIODS OF THE PLANETS

For orbital period generally we refer to the sidereal period, that is the temporal cycle that it takes an object to make a full orbit, relative to the stars. This is the orbital period in an inertial (non-rotating) frame of reference (365,25 days for the earth).

A BINARY ORIGIN FOR A CENTRAL COMPACT OBJECT (CCO)?

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