Gargantua is a supermassive black hole, about 100 million solar masses, serving as a central anchor for the handful of planets in Christopher Nolan's Interstellar. Physicist Kip Thorne worked out the numbers before a frame was shot, so most of what's below traces back to actual general relativity instead of the usual movie-physics hand-waving.
Gargantua's spin is within one part in a hundred trillion of the theoretical maximum. That's the only way a planet could hold a stable orbit skimming the event horizon without being shredded. Light and heat come from the accretion disk, quietly dimmed down by the filmmakers from what would actually be a lethal X-ray furnace, on the theory that a habitable black hole system is a hard sell if it kills the cast.
Two of these worlds, Miller's and Mann's, orbit Gargantua itself. Background material for the film places the third planet, Edmunds', around a separate star called Pantagruel instead. Fitting choice of name: Gargantua and Pantagruel are the father-and-son giants from François Rabelais' 16th-century satirical novels. One more factoid while we're here: the wormhole itself is not "the Bulk." The Bulk is the five-dimensional space the wormhole (and later the tesseract) sits inside of, not a place with coordinates of its own, so it doesn't get a marker on this map.
A supermassive black hole weighing roughly 100 million Suns, spun up to within about one part in a hundred trillion of the theoretical limit on a black hole's spin. That precision isn't artistic license; it's what Kip Thorne calculated was required for a stable orbit as close to the horizon as the plot needs. Up close, the horizon would actually look warped and streaked with Doppler shift, filling something like 40% of the sky, and the accretion disk would be bright enough to cook everyone involved. The movie quietly turned that brightness down for the sake of the cast.
A small, unnamed neutron star also orbiting Gargantua, mentioned mostly in background material rather than dialogue. By Thorne's own numbers, any ship diving as deep into the well as Miller's planet would realistically need a gravity assist from something like this, or an intermediate-mass black hole, just to get back out again. The least glamorous object in the system and arguably the most load-bearing.
A shallow, planet-wide ocean orbiting so close to Gargantua that one hour here costs about seven years back on Earth. The crew's visit ran a little over three hours and still cost the people they left behind 23 years. Surface gravity runs around 130% of Earth's, and the "mountains" bearing down on the Ranger aren't terrain at all, just tides, whipped up by a black hole that is still terrifying even from this distance.
No solid ground anywhere, just an endless stack of frozen ammonia and water-ice clouds honeycombed with crevices deep enough to swallow a Ranger whole. Surface gravity sits around 80% of Earth's and the air runs near -108°F, cold enough that Dr. Mann's glowing survey data turned out to be, charitably, optimistic. He faked it to get rescued. It did not go well for him.
A spherical, traversable wormhole whose far mouth sits in orbit near Saturn, humanity's only door in or out of this system. Placed there about 48 years before the film's events by five-dimensional beings living in the Bulk, later revealed to be our own descendants reaching back to save the species from itself. They didn't put it here. We did. Try not to think too hard about the paradox.
A perfectly ordinary, well-behaved main-sequence star, which after Gargantua counts as a nice change of pace. Named, like Gargantua, after a giant from François Rabelais' 16th-century satirical novels (Gargantua's son, appropriately enough). It sits a considerable flight beyond Gargantua's own gravity, in a separate system the film only shows through the one planet that matters.
Rocky, breathable, and blessedly far from anything trying to kill you with relativity. Despite the family resemblance to Miller's and Mann's, this one isn't actually a Gargantua planet: background material places it in orbit around Pantagruel, a proper main-sequence star rather than a black hole's accretion disk. Dr. Edmunds' early "promising" signal, plus a fair amount of bias from Amelia Brand (she loved him), is what gets humanity's second act started here.