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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‘Monster’ Planet Discovery Challenges Formation Theory

Artist’s illustration of a "hot Jupiter". Image Credit: NASA/CXC/M. Weiss A new research presents the discovery of NGTS-1b, a hot-Jupiter transiting an early M-dwarf host in a P~2.6 days orbit discovered as part of the Next Generation Transit Survey (NGTS). The planet has a mass of M~0.8 M(jupiter) making it the most massive planet ever discovered transiting an M-dwarf. NGTS-1b is the third transiting giant planet found around an M-dwarf, reinforcing the notion that close-in gas giants can form and migrate similar to the known population of hot Jupiters around solar type stars. The existence of the 'monster' planet, 'NGTS-1b', challenges theories of planet formation which state that a planet of this size could not be formed around such a small star. According to these theories, small stars can readily form rocky planets but do not gather enough material together to form Jupiter-sized planets. Such massive planets were not thought to exist ar...

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).

CONSTRAINTS ON THE LOCATION OF A POSSIBLE 9TH PLANET

Image: The six most distant known objects in the solar system with orbits exclusively beyond Neptune (magenta) all mysteriously line up in a single direction. Such an orbital alignment can only be maintained by some outside force, Batygin and Brown say. Their paper argues that a planet with 10 times the mass of the earth in a distant eccentric orbit anti-aligned with the other six objects (orange) is required to maintain this configuration. Credit: Caltech The astronomers have noticed some of the dwarf planets and other small, icy objects tend to follow orbits that cluster together. To explain the unusual distribution of these Kuiper Belt objects, several authors have advocated the existence of a superEarth planet in the outer solar system ( planet Nine or planet X ).

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