How we know Sagittarius A* is a supermassive black hole

≈4.3 million Suns

Stars reveal a giant black hole at our galaxy’s center

More than 100 stars have been tracked orbiting something invisible at the center of the Milky Way. Their motion shows that about 4.3 million Suns’ worth of mass is packed into an extremely small region, providing strong evidence for a supermassive black hole.

A global treaty sharply reduced chemicals that damaged the ozone layer

Scientists discovered that CFC refrigerants could damage the ozone layer, which helps block harmful ultraviolet radiation from the Sun. In 1987, countries adopted the Montreal Protocol to sharply reduce their use around the world.

Goodness is not simply a god’s command

In Plato’s dialogue *Euthyphro*, Socrates asks whether something is good because a god wills it, or whether a god wills it because it is good. The dilemma treats goodness as independent of divine command: even gods must answer to what is good.

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How we know Sagittarius A* is a supermassive black hole

Stars reveal a giant black hole at our galaxy’s center

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