I think the the answer is satellite, I could be wrong
<h2>
Answer: dark matter</h2>
It is believed that the Milky Way has 90% dark matter and only 10% ordinary matter (known matter). Because, like gravity, <u>dark matter can not be observed directly</u>, however its existence is inferred through the movement of the stars and the cosmic dust within the galaxy.
It is important to note that dark matter composition is unknown and corresponds to 80% of the matter in the universe. It does not emit or interact with any type of electromagnetic radiation, but it interacts with the known matter through gravity.
The answer should be Methane
I'd suppose that the universe is largest, considering that it contains earth-moon system, the solar system, AND hundreds of thousands of galaxies
Endothermic: ice melting into water, and an instant ice pack turning cold
Exothermic: fireworks exploding, and gasoline burning