When studying gravitational wave sources, we just consider BNS, NSBH, and BBH systems since their inspiraling and collisions can produce detectable graviational waves. Also according to the paper "The population of merging compact binaries inferred using gravitational waves through GWTC-3" the minimum mass for the components of the events observed is set as a prior condition of above 1 solar mass, that is, I am guessing we don't take into consideration the EM radiation of these bodies, so how do we know that the GWs produced and recorded by the detectors of LIGO/VIRGO are purely from NS and BH binaries? Can't massive stars (still undergoing fusion, that is, stars that haven't reached the end of their lifecycles) in inspiraling binaries produce GWs significant enough to be captured by the detectors and falsely be read as signals from NS and BH binaries? Or is this taken into account when a False Alarm Rate, FAR of <0.25 per year is taken (as taken in paper)?


1 Answer 1


Although any binary pair of bodies will produce gravitational radiation, our current technology is only able to detect very powerful source of GW radiation.

When a pair of black holes are in their final gravitational spiral, the power is enormous, of the order of $10^{50}$ watts. Far more power than the entire observable universe produces in EM radiation. Even so, they are only just detectable by gravitational wave detectors.

These extreme amount of power are possible because the two black holes can orbit each other extremely closely. Their orbital speeds approach the speed of light. Two normal stars could not orbit so closely. They would collide with each other and merge while they were moving much more slowly. They could never reach velocities at which relativity becomes significant. While they do emit gravitational radiation, the level of radiation is much much lower. Well below our ability to detect it.

There is no significant inspiral of two regular stars. The amount of gravitational radiation given off is not significant to their orbits. So there are no inspiralling binaries of regular stars due to the emission of gravitational radiation, and if two stars are on a collision course, the amount of gravitational radiation given off is not enough for our detectors.

False alarms are caused by seismic strains, thermal noise, and other similar sources of error.

  • 2
    $\begingroup$ This answer could be further improved by giving a sense of the scale difference between the orbital radius of a typical LIGO merger and the size of a typical star. $\endgroup$
    – TimRias
    Jan 12 at 23:47

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