Paper Review: Astrophysical Black Holes

This paper was not so much as a paper but more a trailer for a book of the same name. Produced by Pedro R. Capelo, the contents were the introductory chapter of the book which explained how black holes were first discovered and measured. It moves on to talk about the types of black hole and the difficulties in observing them. Finally it discusses how supermassive black holes correlate to its host galaxy.

Originally black holes were described by using 3 characteristics; mass, angular momentum and electric charge. It is now believed that any electric charge is immediately cancelled out by the surrounding plasma so this reduces the characteristics to 2, known as the Kerr metric. Capelo mentions the ISCO (Innermost Stable Circular Orbit) which is the closest a particle can orbit the black hole without falling into it. The ISCO of a black hole controls how much matter it can accrete in a given time.

Capelo discusses the different types of black hole; primordial, stellar mass, intermediate and supermassive. Primordial and intermediate black holes have not yet been detected as they have a low luminosity. Little is known about the mass function of stellar mass black holes as not many sources have been found. This means most of the knowledge we have comes from studying supermassive black holes.

Part of studying supermassive black holes involves looking at how the black hole became supermassive. One of the possible ways is through black hole merging. Below is a plot used by Capelo that shows how various features of a galaxy change as 2 black holes merge:

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The first panel shows the separation of the black holes, the second shows accretion rate of the black holes, the third shows SFR (Star formation rate) of the host galaxy and the final panel shows the specific angular momentum of the gas around the black holes.

Capelo points out the link between the dips in the separation of the 2 black holes and the peaks in the SFR, proving that the properties of the host galaxy are correlated with the properties of the supermassive black hole. The author explains that they go into more detail in the rest of the book as well as discussing some of the ways black holes could be first formed.

~ Will