Since their discovery in 2007, fewer than two dozen have been detected by the world's largest radio telescopes - and their origin remains unknown. Astronomers know almost nothing about them other than that they appear to occur in very remote galaxies billions of light years away.
In this Nov. 7, 2011 file photo, Facebook creator and CEO Mark Zuckerberg takes questions from the media at Harvard University in Cambridge, Mass. Harvard announced Tuesday, March 7, 2017, that Zuckerberg, who went to Harvard as an undergraduate in 2002 but left after his sophomore year to pursue his company, will be the commencement speaker at the school's May 25, 2017 graduation ceremony.
There are two kinds of people in the world - those who ignore food expiration dates and those who don't. You can slice off a piece of mold from that block of cheese, but that doesn't mean you should.