Question

what is a neutron star?

Answer 1

A neutron star is the collapsed core of a large star which before collapse had a total of between 10 and 29 solar masses. Neutron stars are the smallest and densest stars known to exist. 

Answer 2

Hope it will help you,

Neutron stars

Neutron star are the tiniest, densest stars known and pack the mass of the whole Sun into an area smaller than London. They are so compact that a mere pinhead of matter has more than twice the mass of the largest supertanker on Earth. All neutron stars spin round at a furious rate, some rotating as fast as 700 times a second. We know this because neutron star send out beams of radiation that sweep round the sky as they spin, making them appear to flash on and off they sweep across Earth. Neutron stars that flash like this are called Pulsars.

Important

1.A neutron star's gravity is so great than an object dropped from 1 m (3ft) above its surface would acclerate to 7 million kph (4 million mph) by the time it landed.

2. At 15-25 km (9-15 miles) wide, neutron stars are about as big as a city.

3. The material that makes up a neutron stars is to dense that a single teaspoonful brought to Earth would weigh more than the entire world population.