So what actually happens when a sungrazer comet decides to cool off with a plunge into the sun? The answer might be vaguely unsatisfying. Because what happens is generally what happens to a comet that doesn't hit the sun: It disintegrates into nothingness, as its icy, gravel nucleus proves no match for the sun's heat.
You might be surprised to hear that, because when a sungrazer makes the news, it's usually accompanied by screaming headlines going on about "comets hitting the sun," followed by a breathless recounting of "fiery explosions." While this is what you might think you see from videos of the occurrences, don't make too many assumptions.
What you're looking at are coronal mass ejections -- huge explosions of gas and magnetic energy that disrupt the solar wind (see: punch line to joke) [source: Hathaway]. And yes, we do occasionally see them emanating from the sun after comets make their way into the sun's pull. But there's no proof that the comet actually is causing the explosion; coronal mass ejections are seen often and it's hard to say that comets are causing them [source: Plait]. It's also important to note that comets have blasted into the sun with no resulting coronal mass ejections.
Which brings us to the important point that every comet is different. It's hard to say what will happen each time one approaches the sun. In 2013, the comet Ison was one example of unpredictability: While its nucleus appeared to break apart from the heat, at least some part of it seems to have survived the trip [source: Plait].
But don't feel totally let down about a comet's display. No, we might not see unusual explosions in the sky, but a comet that approaches the sun always leaves the possibility for a great show. That's because when the comet gets to the point where it's closest to the sun (known as perihelion), its solid state will sublimate and turn straight into a gaseous state. When that happens, the comet can brighten considerably, making a vivid sight in the sky [source: Rincon].