Black holes and neutron stars

In short: A black hole is a region where gravity is so strong that not even light can escape. Neutron stars are extremely dense remnants of exploded stars.

In more detail: The boundary beyond which there is no return is called the event horizon. Black holes form when very massive stars collapse at the end of their lives.

In detail

• Neutron star: A teaspoon of matter would weigh billions of tonnes. Rotating neutron stars emit pulses (pulsars).
• Types of black holes: Stellar holes (a few solar masses) and supermassive holes in galaxy centres (millions to billions of solar masses).
• Observation: They are seen indirectly through hot gas falling in, through X-rays and, since 2015, through gravitational waves. In 2019 the first image of an event horizon was achieved.
• No danger: A black hole does not suck in everything; from afar it acts like any other mass.
• Formation: See sterne-und-sternentwicklung.