The European Southern Observatory (ESO) will announce an "unprecedented discovery" [eso.org] on Monday:
ESO will hold a press conference on 16 October 2017 at 16:00 CEST, at its Headquarters in Garching, Germany, to present groundbreaking observations of an astronomical phenomenon that has never been witnessed before.
[...] By registering for the conference, journalists agree to honour an embargo, details of which will be provided after registration, and not to publish or discuss any of the material presented before the start of the conference on 16 October 2017 at 16:00 CEST.
LEAK IT!