What is the scariest thing on the universe?

1. Black Holes: These are regions of space where gravity is so strong that nothing, not even light, can escape them. If an object gets too close to a black hole, it can be sucked in and stretched into a long thin shape in a process known as spaghettification.

2. Gamma Ray Bursts: These are the most powerful explosions known in the universe, and they release more energy in a few seconds than our Sun will release in its entire lifetime. If a gamma ray burst occurred close enough to Earth, it could potentially cause a mass extinction event.

3. Vacuum Decay: This is a hypothetical event where a quantum field such as the Higgs field could transition to a lower energy state, creating a bubble of true vacuum that expands at the speed of light and destroys everything in its path. However, the likelihood of vacuum decay occurring is extremely low.

4. Heat Death of the Universe: This is a proposed end scenario for the universe, in which the universe has cooled as it expands and all thermodynamic free energy is minimal, leading to a state of no thermodynamic free energy and hence no possibility of heat exchange or work. This would mean the universe would come to a state of uniform temperature and maximum entropy where no more processes can occur.

5. Rogue Planets: These are planets that do not orbit any star and drift through space alone. If a rogue planet were to pass through our solar system, it could potentially throw off the orbits of the planets, leading to catastrophic consequences.

6. Alien Life: While the discovery of extraterrestrial life would be exciting for many, it could also be scary, especially if the aliens were significantly more technologically advanced than us and had hostile intentions.

7. Thermo nuclear explosion here on Earth

Remember, though, that many of these phenomena are extremely unlikely to affect us on Earth, and we continue to learn more about the universe every day. The universe is full of mysteries, and while some can be considered scary, they also make the universe a fascinating place to study.