Very cool, this works uses a lot of observational data from different telescopes. The LBT [1] is, depending on how you measure, the largest optical telescope in the world (two 8 meter mirrors on the same mount versus 10.4 m GCT [2]).<p>But one of the things that the articles mentions that I think is really cool and may not be familiar to many people, what with LIGO and gravitational waves in the news:<p>> LIGO is not able to detect gravitational waves from supermassive black hole pairs. Instead, pulsar timing arrays such as the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) are currently performing this search. In the future, the Laser Interferometer Space Antenna (LISA) project could also search for these gravitational waves.<p>I've visited the GBT [3,4] several times for observing and have heard some presentations on the NANOGrav [5] project. It's very cool. The signal properties of pulsars can be measured so accurately, that they can be used to accurately constrain very low frequency gravitational waves, ie nanohertz frequencies (hence the clever acronym), for binary supermassive blackholes with wide separations. This complements the high frequency gravitational waves detected by LIGO of merging compact objects, in the 10-100 Hz range. If I'm remembering correctly, you don't measure any particular pair of supermassive black holes, but measure the field from all such systems (at the Earth). Measurements have not been sensitive enough yet to detect this field, but as they dig to higher sensitivity, they are able to place constraints on cosmological models that predict how common binary supermassive blackholes are (we really don't have a good idea) and what the distribution of masses and separations are.<p>[1] <a href="https://en.wikipedia.org/wiki/Large_Binocular_Telescope" rel="nofollow">https://en.wikipedia.org/wiki/Large_Binocular_Telescope</a>
[2] <a href="https://en.wikipedia.org/wiki/Gran_Telescopio_Canarias" rel="nofollow">https://en.wikipedia.org/wiki/Gran_Telescopio_Canarias</a>
[3] <a href="http://greenbankobservatory.org/" rel="nofollow">http://greenbankobservatory.org/</a>
[4] <a href="https://en.wikipedia.org/wiki/Green_Bank_Telescope" rel="nofollow">https://en.wikipedia.org/wiki/Green_Bank_Telescope</a>
[5] <a href="http://nanograv.org/" rel="nofollow">http://nanograv.org/</a>