The Star Earendel (WHL0137-LS)!

The video introduces Earendel, the most distant known star, surpassing Icarus. Discovered by the Hubble Space Telescope through gravitational lensing, Earendel is located in the constellation of Satosa. It is a hot blue star with a mass between 50 and 100 times that of the sun and is approximately 28 billion light years away. The James Webb Observatory has revealed that Earendel may be part of a binary or trinary star system. The star has a surface temperature of at least 20,000 Kelvin.

What astronomical tool was used to discover the star?

What is the significance of the star's surface temperature mentioned in the text?