Space

Magnetars. I want to throw an asteroid or something at one and watch it get ripped apart on a subatomic level purely by magnetism.

Honestly earth.

Here is so much undiscovered that could help us understand space a lot better.

Lagrange Points (L4 and L5 specifically). Here's a bit of space with a gravitational effect keeping you inside, but not due to mass inside it. It's due to the relation of two other masses. Mind-boggling.

Venus. It's got this mega-dense atmosphere. Why? It's an anomaly when you compare it to the other similarly-sized planets in our solar system. The gas giants having thick atmospheres makes sense, but Venus? Actually, I just had a thought. The Sun's mass generally pulls gas toward it. Gas that is in between the Sun and Mercury gets pulled into the Sun. Gas between Mercury and Venus gets pulled into the Sun too, since the closeness of the Sun makes its gravitational effect very influential compared to Mercury's. Gas between Venus and the Earth, however, is far away enough from the Sun that it will stabilize around a Venus-sized planet. This explains the discrepancy between Mercury's and Venus's atmospheres. Not sure about the Venus/Earth discrepancy, but perhaps Mars's light atmosphere is due to its lower mass.

Callisto. Why is it so dark? Why is the ice (the light splotches on the surface) like polka dots, rather than either an ocean or more diffuse?

I find neutron stars fascinating. The remnant of a star that was almost big enough to form a black hole but not quite. The gravity pulls all the matter left after a supernova into a bizarre form of matter. The protons and electrons are smushed together making basically the whole thing neutrons. They’re packed together so densely, a teaspoon would weigh as much as a mountain. A star much bigger than the sun suddenly condensed into like 20km.

Plus, some form pulsars spinning so fast that it seems impossible. The record is over 1,000 rotations per second. Some form magnetars, the strongest magnets in the universe. There might be an even more exotic form of matter — “strange matter” made of strange quarks — in their core.

I am going to mention the rogue planets, since no one else has mentioned them here yet. Those unlucky celestial bodies ejected by their home star, destined to fly through the universe alone, dark and cold, forever.

Black Holes are infinitely fascinating!

They’re ’a thing’ we knew nothing about until Einstein wrote a paper, and even though his own math showed their existence, he doubted that they could be real.

Turns out that they are, and that they form the structure of the entire universe.

That’s my object.

My favorite thing is Quantum Field Theory! You know the field of magnetism, you played with it as a kid when you got your hands on two magnets the first time.

Turns out every particle in the standard model has its own field, and an excitation of that field manifests as that type of particle.

David Tong explains it masterfully: https://youtu.be/zNVQfWC_evg

As does HOTU: https://youtu.be/UYW1lKNVI90

EDIT: Both links above are 1+ hours each, and done in layperson terms. No degree needed, just a desire to learn something fascinating.

The idea behind the heliosphere and all its related parts are really interesting. Something about a giant space bubble/teardrop flying through the galaxy that blows my mind. Learning about termination shock and the sink basin example really gave off this weird sense of cosmic grandeur that can be somewhat replicated on earth. As above so below kinda thing.

Super Earths, because we know so little about them. They are the most common planet type (based on census from Kepler and TESS), but our solar system doesn’t have one, so we have no idea what they are like. Models and simulations give a few possible compositions, resembling mini-Neptunes, or water worlds with thick oceans, or more like Earth. Maybe all are possible. Earth-like rocky super-earths may be more geologically active than Earth, due to stronger convection and thinner crust. If they orbit a K-type dwarf, they could be candidates for super-habitable planets, with conditions even better for life than Earth.

Przybylski's Star. A star that, based on its spectrum appears to have several elements in it that really shouldn't be there.

The S-IVB-506.

This was the third stage of the launch vehicle for Apollo 11. After entering Earth orbit, the S-IVB rocket was responsible for the translunar injection burn. Once the burn was complete, the command module, LEM, astronauts and the spent rocket were then coasting to the moon. The astronauts would detach the CSM, pitch up, translate in, extract the LEM, then thrust with RCS to get clear of the S-IVB. At this point, the rocket is still on a coarse to the moon.

Many of them orbit between the Earth and moon to this day. One is speculated to orbit between the Earth and Sun. Many impacted the lunar surface, including the one from Apollo 13.

The S-IVB-506 rocket was the one that carried Apollo 11 to the moon. It’s a piece of human history, floating silently in a heliocentric orbit above us.

Honestly, our moon.

I firmly believe that our moon gives us the solar system in short order.

Fuel in the form of Helium-3 (if we can figure that out). Plenty of building material. Much lower gravity well that will allow larger payloads into it's orbit and larger ships to be constructed. As well as that lower gravity well meaning better fuel efficiency in launching just about any trajectory to anywhere else in the solar system.

Once we have the Moon, we're 90% of the way to a solar system spanning species. Mars is cool, but not useful in any real sense other than bragging rights.

That oamua thing that zipped through the solar system a few years back.

That irregularly light reflecting thing that didn’t quite follow the trajectory it was supposed to that just flew through the solar system a few years back on its way to somewhere else and we never got a chance to look closely at it to see what the fuck it even was

Hypothetical, but Black Hole Stars (one of my favourite Kurzgesagt videos).

"Normally that would be the end – today’s stars go supernova, a black hole forms and things calm down. But in this case, the star survives its own death."

"An impossibly dangerous balance has been created – millions of solar masses pushing in, the angry radiation of a force fed black hole pushing out."

I'm hoping that some of the new long wavelength teleescopes like JWST might have a chance of seeing one of these beasts.

This going to sound basic but I find the vacuum part of space to be the most interesting from an engineering POV.

We are all use to having an atmosphere we can convex heat out to but as there is no atmosphere where do you send your excess heat to?

My two biggest are probably Sol and voids. I wish I could directly observe the phase transition as you approach the star's core, understand it's corona patterns and behavior, observe deeper to predict CMEs, etc it's just so close and present in our daily lives and still very mysterious. For the voids I'm not sure maybe because it's defined by its boundary more than its contents, but they are pretty common and some are huge and it's just difficult to study something that is defined by its lack of something.

M87

What would one even look like?

Like a reddish glowing Jupiter.

Recent paper theorizes that dark matter could be evidence of entanglement with another universe.

I'm fascinated by the ice moons of the gas giants, which is why I am so excited for missions like Juice, Europa Clipper, and Dragonfly.

Black Hole and Neutron Star are my favorite celestial body.

Quasars

The great attractor. It's the biggest object we known of, but actually know almost nothing about. and it's in a spot that's hard to see through, our galaxy's center. Almost everything we see in the sky is heading towards that point, hence the name.

Rogue black holes are terrifying