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Sirius B
Details
Sirius B is the white dwarf companion of Sirius A, the brightest star in the night sky. Hubble measurements show it packs about the Sun’s mass into a body smaller than Earth, with gravity so strong that a person would weigh tens of millions of pounds on its surface.
Sirius B matters because it turns the idea of a white dwarf into something concrete. It is not a small ordinary star. It is the compressed remnant of a once more normal star, now stripped down to a state where the familiar rules of stellar life no longer apply. As the companion to Sirius A, it also sits in one of the best-known stellar systems in the sky, which makes that strange state easier to grasp.
What makes Sirius B physically striking is how much mass it retains in such a compact body. It packs roughly the Sun's mass into an object smaller than Earth, which means its matter is held up not by ordinary thermal pressure but by electron degeneracy. That is the key intuition. Sirius B is what happens when a star stops being a normal star but does not collapse all the way into something even more extreme. It is dense, hot, compact, and still deeply legible as a stage of stellar evolution.
That is why Sirius B matters on this scale. It shows that the end of a star's life is not always an explosion or a black hole. Sometimes it is a white dwarf: a brilliant, compact remnant that preserves the mass of a star in a radically altered form. Sirius B is important because it makes stellar death look less like disappearance and more like transformation.
4,185km
Visual creditscaleofspace.org / CC BY-NC 4.0
Key facts
- Category
- Stellar remnants
- Object class
- White dwarf
- Mass
- ~1.02 solar masses
- Host
- Sirius system
- Scale fact
- 11,268 kmdiameter
- Estimated age
- ~228 million years
- Composition
- Electron-degenerate carbon-oxygen matter
- Temperature
- ~25,000 K surface
Scale context
Where Sirius B sits on the full axis
Shared physical scale
7,324km
Together, these objects make the size change around Sirius B easy to compare at a glance.
Between the smallest and the largest, perspective is everything.
About
Scale of Space is a scroll-based journey through the universe, placing objects on a single logarithmic scale so you can compare size across an unbroken range.
Guides turn parts of that scale into curated essays, while focused views let you explore the same range through specific groups of objects.