The earth's center is made of an element we have never seen before. This is because every large ball of matter (planets, moons, suns) has this element hidden deep in its center. This element is magnetic to all matter in the universe. The element creates gravity. If we were to extract this material, it would pull all objects to it. Yhe Earth's core is this matter. Black holes are the results of this material at its rawest state. As more more matter is collected, a planet is formed.