@melizeche @Rainmaker1973 @ProfBrianCox Amazing question. There are perhaps 3 neat ways to think about it:
@melizeche @Rainmaker1973 @ProfBrianCox 1. All the properties of a black hole scale with its mass: Big black holes are *identical* to small ones except scaled up. They are not like other objects where you could count the number of atoms or LEGO bricks they are made of
@melizeche @Rainmaker1973 @ProfBrianCox If you were to see a picture of a black hole without a scale bar, it'd be impossible to tell how big it is. The luminosity during merger is one of their universal properties, the same no matter how you scale the system
@melizeche @Rainmaker1973 @ProfBrianCox 2. Luminosity is energy emitted divided by time over which it is emitted. The energy scales linearly with the mass (think E = mc²), twice the mass, twice the energy. The time is set by the orbital period. This *also* scales linearly with the total mass (think Kepler's law).
@melizeche @Rainmaker1973 @ProfBrianCox Therefore, when you divide the energy by the time, the mass cancels out! If you're interested in the details, it's the total mass of the binary that cancels. The ratio of masses does effect the answer
@melizeche @Rainmaker1973 @ProfBrianCox 3. Black holes are just made of warped spacetime. Therefore, you'd expect their properties, like this luminosity to be set by the properties of spacetime. This is the case. The luminosity depends upon Newton's gravitational constant G and the speed of light (and gravity) c
@melizeche @Rainmaker1973 @ProfBrianCox There's a particular combination of these constants called the Planck power (en.wikipedia.org/wiki/Planck_un…) which is kind of a universal luminosity scale, it's c^5/G. The luminosity of a merging binary black hole system is 0.1% of this. This is the most luminous event we know of!
