One can infer a bit about the masses of the black hole and neutron star already. The chirp mass would be something near ~ 1.96 solar masses. That's a particular combination of the two object masses, so if the NS were 1.4 solar masses that would mean the black hole is ~ 3.8 solar masses.

The localization of this event is somewhat large and it is over a billion light years away. However, the mass of this merger might allow for the neutron star to be torn apart and produce detectable light.

Yes, absolutely! He's retired now, but he was the senior faculty of the group at Syracuse when I was a PhD student.

Congratulations!

So CE/ET, LISA, and PTAs will be sensitive to different types of sources (or in different parts of their evolution), but CE/ET will be an order of magnitude (or more) more sensitive than current LIGO/Virgo.

How does this related to say LISA or pulsar timing? Both of these use arm lengths much longer than ground-based observatories. However, their ability to measure displacements is actually *much* worse. LISA's design will be sensitive to 10^-4 -> 10^-1 H, while Pulsar timing focusing on ~ 10^-8 Hz.

In many ways a CE facility is endgame for gravitational-wave astronomy on the ground. There is the potential for upgrading the detectors within the facilities, but there would likely not be an effort for an even larger observatory on the ground.

You can't build much longer than 40km (say 400 km) on the earth due to civil engineering problems (we need actually arms not following earth curvature) and issues with designing and controlling a cavity. The returns would not be as high as you'd hope even if you could solve the engineering issues.

Ground based detectors because they are fixed in place, use resonant cavities for their arms to store the laser light. This increases the "effective" arm length by orders of magnitude (or conversely allows them to measure very small displacements because they average the measurement of many photons)

If you could ignore all other considerations, longer arms are better because the gravitational wave causes a larger displacement, however, in practice you can't ignore how you actually measure this displacement itself.

Great question with a lot to unpack. The short answer is that what matters is the combination of measurement method/technology + arm length. CE is the sweet spot for what you can build on the Earth and will have strictly better sensitivity than current ground based detectors at all frequencies.

Then what do we call the sum of everything else?