LIGO and its recent measurement of gravitational waves

[Eise]

It is written,(e.g. here), that the detected waves originated from a merger of two black holes, originally having masses of 29 and 36 sun-masses 1.3 billion years ago.

 

I can imagine that the form of the signal shows what kind of event it was. But where I have difficulty is understanding how they know this moment and these masses. Would two lighter black holes closer by not give the same signal? If one compares this with all the difficulties one has to gauge the cosmic distance ladder, it is quite astonishing.

 

Can somebody explain how they know this?

[Strange]

The rate at which the objects orbit and merge is dependent, very precisely, on their mass. By comparing simulations of a range of different size black hole mergers they can determine the mass of the two black holes. The characteristics of the "ringdown" phase after merger are dependent on the final mass. From all this, the amount of energy radiated is know. By comparing this with the received amplitude, it is possible to calculate the distance.

[pavelcherepan]

Scientists working on a project have calculated a wide range of templates for different phenomena that can cause major gravitational waves and each of those has very specific characteristics in terms of final wave form. So when the signal was received the team was pretty confident pretty much straight away that it was black hole merger.

[Eise]

Scientists working on a project have calculated a wide range of templates for different phenomena that can cause major gravitational waves and each of those has very specific characteristics in terms of final wave form. So when the signal was received the team was pretty confident pretty much straight away that it was black hole merger.

 

I understand that. But why do these characteristics inform us also of the distance and/or the masses of the black holes?

The rate at which the objects orbit and merge is dependent, very precisely, on their mass. By comparing simulations of a range of different size black hole mergers they can determine the mass of the two black holes. The characteristics of the "ringdown" phase after merger are dependent on the final mass. From all this, the amount of energy radiated is know. By comparing this with the received amplitude, it is possible to calculate the distance.

 

Oh, sorry, missed your answer. That answers my question. Thanks.

Edited February 19, 2016 by Eise

[pavelcherepan]

It's on the page 3 of the paper published:

 

http://journals.aps.org/prl/pdf/10.1103/PhysRevLett.116.061102

[Eise]

It's on the page 3 of the paper published:

 

http://journals.aps.org/prl/pdf/10.1103/PhysRevLett.116.061102

 

Great! Thanks for the link.

 

Fascinating to read that of a total of 65 sun masses, 3 sun masses were transformed to the energy of these gravitational waves.