Question

read the text. a black hole is an area in space that is so compact and stuffed with matter that its gravity is extremely strong. since black holes have such a powerful gravitational pull, they suck in material—including light—at very high speeds. black holes dont reflect any light, so they are completely invisible. if we cant see them, how do we know they exist? as black holes rapidly pull in surrounding material, the material is heated and emits x - rays that radiate into space. in this way, black holes have profound effects on the matter surrounding them. by studying these effects, astronomers are thus able to detect the presence of black holes. match causes with their effects. black holes are compactly stuffed with matter. black holes are invisible. scientists can infer the locations of black holes. cause effect black holes have very strong gravity. black holes reflect no light. material pulled in by black holes emits radiation.

Explanation:

1. The fact that black holes are compactly stuffed with matter leads to them having very strong gravity as stated in the text "A black hole is an area in space that is so compact and stuffed with matter that its gravity is extremely strong."
2. Since black holes reflect no light, they are invisible according to "Black holes don't reflect any light, so they are completely invisible."
3. When material is pulled in by black holes and emits radiation (X - rays), scientists can infer the locations of black holes as "As black holes rapidly pull in surrounding material, the material is heated and emits X - rays that radiate into space. In this way...astronomers are thus able to detect the presence of black holes."

Answer:

Cause: Black holes are compactly stuffed with matter. Effect: Black holes have very strong gravity.
Cause: Black holes reflect no light. Effect: Black holes are invisible.
Cause: Material pulled in by black holes emits radiation. Effect: Scientists can infer the locations of black holes.