But if it's the core you want to talk about it's also hot due to radioactive decay. Hotter than the mantle. And not just the outer core but the inner core as well.
5 Facts About the Earth's Inner CoreThe temperature of the inner core is estimated to be between 3,000 and 5,000 Kelvins (4,940 to 8,540 degrees Fahrenheit). The high temperature comes from three main sources. There is residual heat left from the Earth's formation, and heat is generated by gravitational forces from the sun and moon as they tug and pull on the inner core. Finally, the radioactive decay of elements deep within the Earth also produces heat.
Please join me in a moment of angst.
Thank you. Resume your normal lives.