Sirius B

Sirius B is a white dwarf star and the faint companion to Sirius A, the brightest star in Earth's night sky (also known as the "Dog Star"), located in the constellation of Canis Major or the "Greater Dog". It is a white dwarf, a remnant of an intermediate-mass star that has exhausted its fuel, and is the closest example to Earth. It is the secondary component of the Sirius binary system, of which the 'A' component is the brightest star in the night sky. Sirius B, on the other hand, cannot be seen to the naked eye as its luminosity is only 2% that of the Sun. Sirius is the fifth-nearest star system to the Sun, 8.6 light-years distant. Like all white dwarfs, Sirius B is dense: while its size is comparable to that of Earth, its mass is equivalent to that of the Sun. It is the remains of a 5 M☉ star that existed until around 100 million years ago. Sirius B's current temperature is 25,000 K (24,700 °C; 44,500 °F), 2.5 times hotter than Sirius A and over four times hotter than the Sun. It no longer produces energy via nuclear fusion, and it will cool as its remaining heat escapes to space over time. Due to its proximity, Sirius B has been the target of many studies in the last decades in attempt to discover extrasolar planets. None of them have detected a planet around Sirius B, though some planetary architecture still cannot be ruled out by current observations.