SMBHB stands for Super Massive Black Hole Binary. If the results get confirmed, this shows that we have observed inactive SMBHBs for the first time ever! SMBHs can be 10^7 times more massive than our own Sun. The Sun is one million times more massive than the Earth. The mass of Earth is about 10^24 kg, by the way.
SMBHBs can be used as excellent natural labs for testing many aspects of gravitational and high-energy physics. As you might know already or might just guess from the term “black hole”, a black hole cannot be seen by our usual optical telescopes (not even by other common types of telescopes in other ranges of frequencies of electromagnetic waves such as radio-telescopes and x-ray telescopes). A black hole is such a massive object that even light cannot scape from its gravitational field. That’s also why you can not see a black hole, simply because neither light nor other electromagnetic waves can scape from the gravitational field of a black hole and reach your eyes. The only way to observe black holes is studying their gravitational field effect on the motion of nearby stars. An even better way to study and observe these inconspicuous giants is listening to them! (check out this note to see how) They are pretty loud!
To check out more details about this first serious candidate of SMBHB at the galaxy SDSS J120136.02+300305.5, see the original article, published today at The Astrophysical Journal: F. K. Liu et al. 2014 ApJ 786 103!