If you're wondering why aliens haven't visited yet, don't blame those transmissions of Jersey Shore warning intelligent life away from planet Earth—blame super-supernovas like SN2007bi, according to dailygalaxy.
Late last year, scientists recorded the largest space explosion ever: a super giant star—200 times bigger than the sun—completely destroyed by runaway thermonuclear reactions triggered by gamma-ray-driven antimatter production. The resulting blast, which was visible for months, gave off a nuclear fission glow visible from galaxies away—and would have killed off any alien life in that area.
Most astronomers today believe that one of the possible reasons we've yet to detect intelligent life in the universe is due to the deadly effects of local supernova explosions that wipe out all life in a given region of a galaxy.
And since according to dailygalaxy—
While there is, on average, only one supernova per galaxy per century, there is something on the order of 100 billion galaxies in the observable Universe. Taking 10 billion years for the age of the Universe (it's actually 13.7 billion, but stars didn't form for the first few hundred million), Dr. Richard Mushotzky of the NASA Goddard Space Flight Center, derived a figure of 1 billion supernovae per year, or 30 supernovae per second in the observable Universe!
—it could be quite some time before E.T.s drop by, assuming any have survived out there.