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

Comments

A SIGNIFICATIVE FRACTION OF BARYONS RESIDE IN THE FILAMENTS OF THE COSMIC WEB

(Credit: NASA, ESA, and E. Hallman (University of Colorado, Boulder) Observations of the cosmic microwave background indicate that baryons (protons, neutrons, etc., - the ordinary matter just to understand) occupies only 5% of the total energy content of the Universe (95% is dark matter and dark energy). However in the local universe approximately half of this "ordinary" matter it has never been observed.

A UNIVERSE WITHOUT A CENTER?

Image Credit: Eugenio Bianchi, Carlo Rovelli & Rocky Kolb. According to the standard theories of cosmology, there is no center of the universe. In a conventional explosion, material expand out from a central point and the instinct suggests that with the Big Bang happened something similar. But the Big Bang was not an explosion like that at all: it was an explosion of space, not an explosion in space . The Big Bang happened everywhere in the Universe.

A Sapphire Super-Earth

Twenty-one light years away, in the constellation Cassiopeia, a planet by the name of HD219134 b orbits its star with a year that is just three days long. With a mass almost five times that of Earth, it is what is known as a super-Earth. Unlike our planet, however, these super-Earths were formed at high temperatures close to their host star and contain high quantities of calcium, aluminum and their oxides – including sapphire and ruby. HD219134 b is one of three candidates likely to belong to a new, exotic class of exoplanets. These objects are completely different from the majority of Earth-like planets. They have 10 to 20 percent lower densities than Earth. Researchers looked at different scenarios to explain the observed densities. For example, a thick atmosphere could lead to a lower overall density. But two of the exoplanets studied, 55 Cancri e and WASP-47 e, orbit their star so closely that their surface temperature is almost 3,000 degrees and they would have lost this ...

SpaceTime

Search This Blog