Wednesday, 9 November 2011

Black hole noms: planetary treats for the galactic monster

I didn't write the title, and had to check the dictionary on what a nom is (and was surprised that it was actually a word), but I wrote a brief article for The Conversation

It summarizes a paper by Kastytis Zubovas of the University of Leicester on the continual burps of energy from the black hole at the centre of the Milky Way. You can read the original paper here

Sgr A* flares: tidal disruption of asteroids and planets?

Kastytis Zubovas, Sergei Nayakshin, Sera Markoff
It is theoretically expected that a supermassive black hole (SMBH) in the centre of a typical nearby galaxy disrupts a Solar-type star every ~ 10^5 years, resulting in a bright flare lasting for months. Sgr A*, the resident SMBH of the Milky Way, produces (by comparison) tiny flares that last only hours but occur daily. Here we explore the possibility that these flares could be produced by disruption of smaller bodies - asteroids. We show that asteroids passing within an AU of Sgr A* could be split into smaller fragments which then vaporise by bodily friction with the tenuous quiescent gas accretion flow onto Sgr A*. The ensuing shocks and plasma instabilities may create a transient population of very hot electrons invoked in several currently popular models for Sgr A* flares, thus producing the required spectra. We estimate that asteroids larger than ~ 10 km in size are needed to power the observed flares, with the maximum possible luminosity of the order 10^39 erg s^-1. Assuming that the asteroid population per parent star in the central parsec of the Milky Way is not too dissimilar from that around stars in the Solar neighbourhood, we estimate the asteroid disruption rates, and the distribution of the expected luminosities, finding a reasonable agreement with the observations. We also note that planets may be tidally disrupted by Sgr A* as well, also very infrequently. We speculate that one such disruption may explain the putative increase in Sgr A* luminosity ~ 300 yr ago.
Basically, what he is saying is the energy is released as small objects, planets and asteroids, as ripped apart on their final death plunge into the black hole.

This is not a new idea, as I remember people suggesting that such flares could be due to comets etc being ripped apart, but he has a little twist on the story that some of these objects are effectively recycled from objects that were smashed in the frenetic orbits close to the black hole.

Anyway, you can read my article here - questions and comments below :)


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