For retail, it’s #BlackFriday. But for #NASA, it’s our 6th annual #BlackHoleFriday! Black holes have one basic rule: They are so incredibly dense that to escape their surface you’d have to travel faster than light. But light speed is the cosmic speed limit … so nothing can escape a black hole’s surface! Learn more on NASA.gov/blackholes or check out todays awesome Tumblr post! nasa.tumblr.com Credit: NASA #nasa #blackholes #colorful #universe #explore #exploration #space #science #collage