RELATION BETWEEN TIDAL DISRUPTION EVENTS AND HOST GALAXIES

Image: Artistic illustration of a black hole divouring a star. Credit: NASA/Goddard Space Flight Center/CI Lab

A tidal disruption event occurs when a star gets close enough to a supermassive black hole's event horizon and is pulled apart by the black hole's tidal forces.
In a recent paper (French, Arcavi & Zabludoff, 2016 ApJL) the authors show that the tidal disruption events occur more frequently in host galaxies with strong Balmer line absorption. This feature indicates low levels of current star formation.

The Balmer lines in atomic physics, is the designation of one of a set of six named series describing the spectral line emissions of the hydrogen atom. The Balmer series is characterized by the electron transitioning from n > 2 to n = 2, where n refers to the radial quantum number or principal quantum number of the electron.

In the simplified Rutherford Bohr model of the hydrogen atom, the Balmer lines result from an electron jump between the second energy level closest to the nucleus, and those levels more distant. Shown here is a photon emission. (https://en.wikipedia.org/wiki/Balmer_series)

The connection tidal-disruption/host-galaxy may be due to the fact that these host galaxies have had a recent galaxy-galaxy merger. Such event increases the possibility of formation of black-hole binaries, perturbed stellar orbits and a spatially-concentrated population of A giant stars.

Figure: Tidal disruption of a star. Credit: NASA/Goddard Space Flight Center/Swift

▪ French, Arcavi & Zabludoff (ApJL) - Tidal drisuption events prefer unusual host galaxies. (arXiv)

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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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