I suppose it's probably not what the theoretical physicists are into (they probably like anomalies I can't really appreciate), but I'm into the exoplanets and other star systems. It's hard to choose a favorite, it could probably change all the time, but for now I'm going to say it's
this one.
Let me tell you how I feel about these things.
I was born at an interesting time for this subject. You see, I spent all my childhood without knowing about exoplanets. I'd already been alive for several years when the first one was discovered, and of course scientific discoveries both take time to ramp up and to become common public knowledge. So, I was taught a certain view about astronomy as a kid. The view was that the solar systems were very,
very boring. It was often assumed that other solar systems existed, but they were imagined to exist within a strict set of parameters. They were, unsurprisingly, imagined to stick very closely to the structure of our own solar system. The boundaries for what kinds of planets could form was also given only a little freedom outside of what sort of planets existed in our solar system. As a child, I found this disappointingly monotonous, and so inferior to my imagination.
I only vaguely started to be aware that exoplanets existed and that they might be pretty strange in my teen years, but of course the real glut of information on other planetary systems did not begin until Kepler was launched, and then everything changed. Mind you, right from the very beginning, things were strange. The first confirmed exoplanet orbited a pulsar, and that was a good harbinger for how many assumptions were going to be blown out of the water. In less then 10 years Kepler has discovered over 2000 exoplanets which have been a parade of curiosities. Planets around all classes of stars, and super giants, pulsars, binary systems, maybe even black holes. A large portion of the planet's we've found are of a kind unprescribed when I was a child, hot jupiters and neptunes, or sometimes called Cthonic planets; large gas planets that orbit their stars nearly as or even nearer than Mercury, causing their thick gaseous atmospheres to constantly blaze off of the core. But there are lots of interesting one-offs. An almost entirely water planet that probably has a core of extremely hot ice. An almost entirely carbon planet with core of non-crystaline diamond and surface that may have dunes of graphite. One of my favorites is a very hot, silicon rich planet that may actually have a weather system analogous to earth's except its made of pure silicon or silicon compounds. That is, it may have silicon vapor clouds, and rain molten glass, which turns into solid glass on the ground like snow or ice. I could keep listing them, but I have to stop myself somewhere.
The stars themselves get pretty crazy, too. There's a star with a diameter wider than that of our entire solar system. There are stars closely orbiting the super massive black hole at the center of our galaxy, some orbiting at speeds around 3% the speed of light.
The funny thing is, I'm very pessimistic about space exploration. I do not think humans will ever see any of these places up close. I think this solar system is the only place we'll ever live. And yet, I still love learning about these things, knowing they are out there, and trying to imagine their implications. And it feels so good compared to the boring universe I was told existed when I was a child.