Cosmic Scale
Sirius B
White dwarf · 8.6 light-years
How big is Sirius B?
Sirius B is about 11,690 km across.
See Sirius B in 3D, at true scale
Sirius B is the burnt-out core of a star that was once more massive than Sirius itself. It has about the mass of the Sun packed into a body the size of Earth, and it no longer produces energy — it is simply cooling, and will keep cooling for billions of years.
At a glance
| Diameter | 11,690 km |
|---|---|
| Mass | 2.03 × 10³⁰ kg |
| Diameter compared with Earth | 0.917 × Earth |
| Size | Slightly smaller than Earth |
| Surface | About 25,000 °C |
| Found | 1862 |
Good to know
- Its existence was predicted in 1844 from a wobble in Sirius's motion, 18 years before anyone saw it.
- One teaspoon of it would weigh about five tonnes.
- It is 10,000 times fainter than Sirius A, which is why it is so hard to see beside it.
- Next smaller: Mars · 6,779 km
- Next larger: TRAPPIST-1e · 11,720 km