Finding Out Where Binary Black Holes Form

Most people are now very aware of at least the words gravitational waves. A considerable number know that they were discovered because of two black holes spiralling into each other, no other event could be as massively (very literally) catastrophic as to produce such waves. The common wisdom would probably end when asked how big a black hole is. The confused faces that result from the question stem from the misleading idea that you can never escape a black hole’s gravitational pull. Of course we’re all getting pulled by black holes right now, every piece of mass in the universe attracts every other. If the Sun was to suddenly turn into a black hole with the same mass, the Earth’s orbit wouldn’t change. All the Earth knows is that there is a big mass resulting in a gravitational pull forcing it to go in a circle; the size (as in volume) of the object, whether it is a star or a black hole, is quite irrelevant.

As you get closer to the black hole the stronger the gravitational force, until even an escape velocity of the speed of light could not allow you to launch away from the object. At this point you have reached the Schwarzschild radius and most people would call this the size of the black hole. Now the binary black holes of the scale to produce gravitational waves can either come from an absolutely colossal binary star system or by the interactions of stellar clusters. The exact formation of binary black holes is of key significance if we wish to use their gravitational waves to learn something about the cosmos. The mass ratio between the two black holes, their spin as well as their orbit wobbling as they approach each other givefact us hints as to their formation. What we need is to see a distinctive pattern in the gravitational waves so we can associate this pattern with a particular formation path when other data is unavailable.

This paper has examined the luminous active galactic nuclei as a possible location for finding coupled black holes and therefore making a connection between their formation and the surroundings. An advantage of looking in these locations is that the large quantity of gas in the galactic nuclei in essence acts as friction to rapidly slow down the black holes and cause their impact on a shorter time scale. The statistics show that a correlation between the spacial coordinates of binary black holes and luminous galactic nuclei could be confirmed or denied within a few years of the LIGO observation. The mathematical methods are not unique to galactic nuclei either and so could easily be redeployed in order to examine other possible fosterers of black holes.

Paper links: Gravitational-wave localization alone can probe origin of stellar-mass black hole mergers


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