A student researching astronomy has taken notes:
• Dark matter doesn't emit or absorb light • Its presence is inferred from gravitational effects • Dark matter outweighs visible matter about 5 to 1 • Galaxies would fly apart without dark matter's gravity • Scientists still don't know what dark matter is made of
The student wants to explain why scientists believe dark matter exists.
Dark matter doesn't emit or absorb light, making it invisible.
Scientists believe dark matter exists because galaxies behave as if they contain far more mass than we can see—without this invisible matter's gravity, galaxies would fly apart.
Dark matter outweighs visible matter by approximately 5 to 1.
Scientists still don't know what dark matter is composed of.
Correct Answer: B
Choice B. Gravitational behavior and galaxies flying apart explain belief in dark matter.