According to the passage, what is
Reading
Read the text and answer the multiple-choice question by selecting the correct response. Only one is correct.
Passage
Neutron stars are among the densest objects in the universe, formed when massive stars exhaust their nuclear fuel and collapse under gravity. The resulting core is so compressed that protons and electrons merge to form neutrons. A typical neutron star packs roughly 1.4 times the mass of our Sun into a sphere only about 20 kilometres in diameter. Their surfaces can reach temperatures exceeding one million degrees Celsius, and they rotate at extraordinary speeds, some completing hundreds of revolutions per second.
According to the passage, what is the approximate diameter of a typical neutron star?