Sirius B

Sirius B is a white dwarf star. It is the quiet companion to Sirius A, the brightest star we can see at night. Sirius A is also called the "Dog Star". Both stars are in the constellation of Canis Major, which means the "Greater Dog".

Sirius B is a very heavy star. It is about the size of Earth but holds as much weight as the Sun. Long ago, Sirius B was a star about five times bigger than the Sun. Now, it has used up all its nuclear fuel and cannot make energy through nuclear fusion.

Even though Sirius B is part of the closest star system to Earth, we cannot see it without a telescope. This is because it is much dimmer than Sirius A. The whole system is about 8.6 light-years away from us. It is the fifth-nearest star system to the Sun. Scientists have looked closely at Sirius B but have not found any extrasolar planets around it.

Background

Main article: White dwarf

White dwarfs are what is left of stars like our Sun after they run out of fuel. These stars start by joining small atoms to make bigger ones. This gives off energy and keeps the star shining. But after a long time, the star runs out of fuel. It grows big and cool, then shrinks to a very small, dense core.

White dwarfs stop making energy, but they still give off heat and cool down slowly. They are extremely dense — a small piece could weigh as much as a large truck! Sirius B, the companion to the brightest star we see at night, is one of these interesting white dwarfs.

Discovery and observations

The discovery of Sirius B began in 1844 when the German astronomer Friedrich Wilhelm Bessel noticed that Sirius A, the brightest star in our night sky, moved strangely. This suggested it had an unseen companion. In 1862, the American astronomer Alvan Graham Clark first saw Sirius B while testing a large telescope for Dearborn Observatory.

In 1915, astronomer Walter Sydney Adams studied the light from Sirius B and found it to be a white dwarf, a type of small, dense star. Because Sirius A is much brighter, studying Sirius B has always been hard. But using special telescopes that see ultraviolet light, scientists have learned more about this interesting star.

Characteristics

Sirius B is a white dwarf. This means it is a small, dense remnant of a star that has run out of fuel. It is very heavy for its size, weighing almost twice as much as the average white dwarf. Even though it is heavy, it is also very small, about the size of Earth.

Sirius B used to be a bright star that burned its fuel quickly because it was more massive than Sirius A, the brightest star we see in the night sky. Over time, it expanded greatly and then shrank down to its current tiny size. Today, it is made mostly of carbon and oxygen, with a thin layer of hydrogen on the outside.

Search for planets

Scientists look for planets around Sirius B by watching how the star moves and taking pictures. So far, no planets have been found. But there might be a small planet that is too faint to see yet. Other white dwarf stars, like PSR B1620−26 b, have had planets found around them.