Magnetars, and example of cool science
A magnetar forms when a massive star that's spinning fast and has a strong magnetic field collapses, exploding in a supernova and eventually settling into a spinning neutron star. Unlike neutron stars, magnetars have ridiculously strong magnetic fields (caused by the dynamo mechanism). To give an idea of how powerful the magnetic field is, it's 1,000,000,000,000 times stronger than the earth's magnetic field, and 10,000,000,000 times stronger than a neodymium magnet. These fields are so strong that they have an energy density over 10,000 times as great as lead, and at 1000 km would actually be lethal, tearing flesh apart because of water's dipole moment.
We know they exist because the super-strong fields have weird effects on photons, and some rare phenomenon are best explained through this mechanism (there are less than 20 found so far).
This is an example of really cool science, and it fills me with a sense of wonder and awe that such magnificent and bizarre phenomenon actually exist in our universe.