LIGO-Detection Paper2

Advanced LIGO has detected gravitational waves from the coalescence of two black holes, again. The new event, denoted GW151226, occurred on Dec 25th (US time).

What did we see?This event reveals another population of coalescing black holes. This time, the coalescing black holes were more similar in mass to black holes detected by other means (i.e., telescopes). Also, This coalesence of two smaller black holes

With two highly signifiant events, we can only begin to sketch the relative probabilities at which different binaries form…and only in the region we’re reporting on so far.

• Masses: GW151226 was smaller and probably had one member bigger than another.

Based on how far we can see sources like GW151226 versus GW150914, we can figure out how frequently the two objects occur. The lower mass object (GW151226) is most likely more frequent than the more massive one (GW150914). So, keeping in mind considerable uncertainty, the event rate is roughly consistent a population of more frequent binary mergers at lower mass, and somewhat fewer at higher mass.

• Spins: The new coalescing binary had at least one spinning black hole in it. But like before, the net effect of spin is small. And like before, we can’t tell if the binary is precessing or not.

• Fundamental physics: The coalescence is still consistent with GR, as demonstrated by comparison with models and several NR similations.

What does it mean? (for experts) Personally, I think the low net aligned spins of GW150914 and GW151226, combined with the low mass of GW151226, place serious constraints on isolated chemical eveolution. Globular cluster models too are harder to reconcile with the low (and uneven) mass of GW151226.

For more information, see the links below, and prior posts

• papers.ligo.org: a one-stop location for the latest results!

• The new event: a paper; the LIGO Open Science Center data; and a summary of the latest news.