LONG GAMMA RAY BURSTS TO INVESTIGATE THE STAR FORMATION IN DARK MATTER HALOS

These two false-color images compare the distribution of normal matter (red, left) with dark matter (blue, right) in the universe. The brightness of clumps corresponds to the density of mass. The comparison will provide insight on how structure formed in the evolving universe under the relentless pull of gravity. Credit: NASA, ESA, CalTech

Gamma-ray bursts (GRBs) are the most luminous explosive events in the cosmos, which can be detected even out to the edge of the Universe and they can be used to probe the properties of the high-z Universe, including high-z star formation history.

Long (>2 seconds) gamma-ray bursts (LGRBs) are powered by the core collapse of massive stars, so the cosmic GRB rate should in principle trace the cosmic star formation rate. It is important to note that stars can only form in structures that are suitably dense: the star formation occurs only if the mass of the dark matter halo of the collapsed structures is greater than the minimum value M_{min}.
Structures with masses smaller than M_{min} are considered as part of the intergalactic medium and do not take part in the star formation process.
The connection of LGRBs with the collapse of massive stars has provided a good opportunity for probing star formation in dark matter halos. The value M_{min} can be constrained by directly comparing the observed and expected redshift distributions of LGRBs.
In a recent paper (Wei et al. 2016), the authors used the latest Swift GRB data to obtain a value for the minimum mass of 10^{7.7} < M_{min} < 10^{10.7} solar masses. Below this limit the star formation process should not take place.

Read more >>
http://arxiv.org/pdf/1511.04483v1.pdf
http://www.sciencedirect.com/science/article/pii/S2214404815000658

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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)?

Figure: False-Colour X-ray and infrared emission image from the core of the infrared shell. The RGB colours correspond to Chandra X-ray 0.2-10 keV (blue), IRAC infrared 8 μm (green), and HPACS 70 μm (red) data. The intensity scale is logarithmic for all channels. Overlaid are equal brightness levels from the MIPS 24 μm band. Note that around the CCO the infrared emission is suppressed in the 70 μm band and enhanced in the 24 μm band suggesting higher dust temperature. Credit: Doroshenko et al 2016 Central compact objects (CCOs) are thought to be young isolated neutron stars that were born during the preceding core-collapse supernova explosion.

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