A neutron star is not as hot as the star it is formed from. While the core of a massive star can reach temperatures of millions of degrees, a neutron star is much cooler, typically in the range of hundreds of thousands to a few million degrees Celsius. However, it's important to note that the term "hot" can have different meanings in different contexts.
When a massive star exhausts its nuclear fuel and undergoes a supernova explosion, the core collapses under gravity, resulting in the formation of a neutron star. During this collapse, the gravitational potential energy is converted into kinetic energy, causing the core to heat up significantly. The temperatures in the core can be extremely high immediately after the collapse, but they rapidly cool down as the newly formed neutron star evolves.
The cooling process of a neutron star is complex and not fully understood. It involves various mechanisms such as neutrino emission, which carries away energy, and the cooling of the surface through radiation. Over time, a neutron star cools down and reaches a more stable temperature.
So, while a neutron star is still extremely hot compared to everyday objects, it is not as hot as the star it originated from during its main sequence or other stages of stellar evolution.