Dark matter is an invisible and undetectable form of matter that is thought to make up about 27% of the universe's mass-energy content. Its existence is inferred from its gravitational effects on visible matter, but its true nature remains unknown.
Dark energy is a mysterious force that appears to be causing the universe's expansion to accelerate. It makes up approximately 68% of the universe's mass-energy content.
The cosmic microwave background radiation (CMB) is the afterglow of the Big Bang and provides crucial information about the early universe.
The Pioneer 10 and 11 spacecraft experienced an unexpected deceleration as they moved away from the Sun. This phenomenon, known as the Pioneer Anomaly, has yet to be fully explained, although it may be due to the uneven radiation of heat from the spacecraft.
Fast Radio Bursts are brief and intense bursts of radio waves from distant galaxies. Their origins are still a subject of debate, and while some have been attributed to neutron stars or black holes, the true source of many FRBs remains unknown.
High-energy particles called cosmic rays bombard Earth from space. Their origins, especially the ultra-high-energy cosmic rays, are not well understood. Some may come from supernovae, while others may have more exotic sources like gamma-ray bursts.
There is a large region of space in the direction of the Centaurus and Hydra constellations that seems to be pulling our Milky Way galaxy and thousands of other galaxies toward it.
Given the vast number of stars and planets in the observable universe, it's puzzling that we have not yet detected any clear signs of extraterrestrial life.