SIRIUS / STELLAR DOSSIER

Sirius B

8.61 light-years from Sol

Smaller than Earth, roughly as massive as Sol, and still glowing with stored heat.

Stellar view ↗

01
Artist’s impression of Sirius B
DA2 · white dwarf

A star compressed to a world.

Stellar conditions ↗

02
EFFECTIVE TEMPERATURE25,369 K

Small does not mean cool.

Sirius B25,369 K
Sol5,770 K
Shared scale 0–30,000 K · effective, not core temperature

Evolution ↗

03
CURRENT PHASE

The cooling remnant.

  1. NOWWhite dwarf
  2. ENERGYStored heat
  3. OUTLOOKGradual cooling
Core hydrogen fusion has ended. This is a cooling sequence, not a countdown.

Stellar family

04

Sirius A ↗

The larger main-sequence star responsible for most of Sirius’s visible light.

Photosphere & activity ↗

05
An imagined panorama of Sirius B’s hot hydrogen photosphere. Soft variations in the light are illustrative, not observed clouds, continents or a surface map. Color and exposure are compressed for visibility.Above the compact glow ↗ ARTIST’S IMPRESSION · 3 VIEWS

Diameter comparison ↗

06
0.8843 × Earth

Luminosity ↗

07
≈ 0.0245 × Sol

Total energy emitted · all wavelengths

Estimated from size and temperature
Sources ↗
SIRIUS B

Instrument detail

Artist’s impression of Sirius B

Artist’s impression · structure and color are illustrative.

What remains when the giant is gone.

A white dwarf is the exposed remnant left after a star sheds its outer layers. Sirius B no longer sustains core hydrogen fusion. It shines as stored heat escapes, gradually cooling. Its white glow is an afterlife of stellar evolution, not a smaller version of Sol’s present engine.

A tiny companion with enormous presence.

Sirius B is difficult to pick out beside the dazzling light of A. Yet its compact size conceals a star’s worth of matter. Hubble’s observations help disentangle the pair, turning an apparently insignificant speck into a laboratory for some of the most extreme conditions in ordinary stellar remnants.

Even the light carries the weight.

Light escaping Sirius B shifts toward longer wavelengths in its gravitational field. Researchers measured this effect by comparing its spectrum with A’s during the same Hubble orbit. Combining that shift with the known radius gave a mass near one Sun, independently agreeing with the mass measured from the binary’s motion.

Reading a star through its light.

A spectrum spreads starlight into wavelengths. In Sirius B, a hydrogen line provides a precise marker for measuring the gravitational shift. Careful calibration matters: comparing the two stars reduced systematic errors that affected earlier measurements. A tiny displacement in that line reveals something no imagined close-up can show directly.

STELLAR PROFILESIZE · TEMPERATURE · EVOLUTION

A star in perspective.

DIAMETER / EARTH0.88 ×

About 88% of Earth’s diameter.

Circles compare diameter, not mass or luminosity. Radius: 0.008098 solar radii (Bond et al., 2017). Earth comparison uses mean radii of 6,371 km and 695,700 km for Sol.

MASS / SOL
1.018 ×
WHAT THAT MEANS
Roughly a Sun’s mass in a body smaller than Earth.
EFFECTIVE TEMPERATURE

Small does not mean cool.

  • Sirius B≈ 25,369 K
  • Sol≈ 5,770 K

Shared scale: 0–30,000 K. Effective temperature describes total emitted energy per unit surface area; it is not the core temperature.

LIFE PHASE

The cooling remnant.

  1. NOWWhite dwarf
  2. ENERGYStored heat
  3. OUTLOOKGradual cooling

Core hydrogen fusion has ended. This is a cooling sequence, not a countdown.

Research · size and temperature ↗
ATMOSPHERE / SPECTRAL EVIDENCE

Hydrogen above a stellar remnant.

VISIBLE ATMOSPHERE
Hydrogen-dominated
INTERIOR MODEL
Carbon–oxygen core

Spectroscopy probes the outer gas; the core composition comes from white-dwarf models. These are different layers, not an atmospheric percentage chart.

Research · atmospheric spectrum ↗
LIFE & HUMAN SURVIVAL / THE STAR ITSELF
POSSIBILITY FOR LIFEIncompatible with known life

The intensely hot photosphere is incompatible with known life. Its small size does not make it an Earth-like environment.

WITHOUT PROTECTIONNot survivable

Extreme heat, radiation and gravity make this an unsurvivable destination without protection. There is no breathable atmosphere or walkable landscape.

NASA · stellar structure and evolution ↗

The cooling remnant.

  1. NOWWhite dwarf
  2. ENERGYStored heat
  3. OUTLOOKGradual cooling

Core hydrogen fusion has ended. This is a cooling sequence, not a countdown.

Research ↗

A white dwarf is the exposed remnant left after a star sheds its outer layers. Sirius B no longer sustains core hydrogen fusion. It shines as stored heat escapes, gradually cooling. Its white glow is an afterlife of stellar evolution, not a smaller version of Sol’s present engine.

How much energy leaves the star?

≈ 0.0245 × Sol

This compares total radiant power across all wavelengths, not just visible light or apparent brightness in our sky. The beams on the dashboard share a linear length scale.

The estimate combines this log’s diameter ratio (0.008098 × Sol) and effective temperature (25,369 K): luminosity scales with radius squared and temperature to the fourth power. It is derived from rounded values, not an independent luminosity measurement.

Radius: 0.008098 solar radii (Bond et al., 2017). Earth comparison uses mean radii of 6,371 km and 695,700 km for Sol.

Swinburne University · Stefan–Boltzmann law ↗

What remains when the giant is gone.

A white dwarf is the exposed remnant left after a star sheds its outer layers. Sirius B no longer sustains core hydrogen fusion. It shines as stored heat escapes, gradually cooling. Its white glow is an afterlife of stellar evolution, not a smaller version of Sol’s present engine.

A tiny companion with enormous presence.

Sirius B is difficult to pick out beside the dazzling light of A. Yet its compact size conceals a star’s worth of matter. Hubble’s observations help disentangle the pair, turning an apparently insignificant speck into a laboratory for some of the most extreme conditions in ordinary stellar remnants.

Even the light carries the weight.

Light escaping Sirius B shifts toward longer wavelengths in its gravitational field. Researchers measured this effect by comparing its spectrum with A’s during the same Hubble orbit. Combining that shift with the known radius gave a mass near one Sun, independently agreeing with the mass measured from the binary’s motion.

Reading a star through its light.

A spectrum spreads starlight into wavelengths. In Sirius B, a hydrogen line provides a precise marker for measuring the gravitational shift. Careful calibration matters: comparing the two stars reduced systematic errors that affected earlier measurements. A tiny displacement in that line reveals something no imagined close-up can show directly.

An imagined panorama of Sirius B’s hot hydrogen photosphere. Soft variations in the light are illustrative, not observed clouds, continents or a surface map. Color and exposure are compressed for visibility.

Above the compact glow

An imagined panorama of Sirius B’s hot hydrogen photosphere. Soft variations in the light are illustrative, not observed clouds, continents or a surface map. Color and exposure are compressed for visibility.

A hypothetical close view of the white dwarf’s curved luminous edge. The thin glow and subtle texture are artistic choices; the carbon–oxygen interior is hidden beneath the atmosphere.

The rim of a remnant

A hypothetical close view of the white dwarf’s curved luminous edge. The thin glow and subtle texture are artistic choices; the carbon–oxygen interior is hidden beneath the atmosphere.

An artistic view of Sirius B against space. The luminous disk and fine gaseous texture are illustrative; color and exposure are adjusted for visibility, not a resolved stellar photograph.

The star against space

An artistic view of Sirius B against space. The luminous disk and fine gaseous texture are illustrative; color and exposure are adjusted for visibility, not a resolved stellar photograph.

Stellar images are artistic interpretations, not resolved photographs of this star.