Radius of Sirius B
| Value | 5,634,000 m |
| Status | Measured: ± 32,000 m (0.0057 relative) |
| Source | Bond et al. (2017), 0.008098 ± 0.000046 R⊙, photometry and gravitational redshift |
| Categories | Astronomicalstellar |
| Planck length | 3.4858361e+41 lP |
| femtometer | 5.6340000e+21 fm |
| picometer | 5.6340000e+18 pm |
| bohr radius | 1.0646717e+17 a0 |
| angstrom | 5.6340000e+16 Å |
| nanometer | 5.6340000e+15 nm |
| micrometer | 5,634,000,000,000 μm |
| thou | 221,811,020,000 thou |
| point | 15,970,394,000 pt |
| millimeter | 5,634,000,000 mm |
| pica | 1,330,866,100 pc |
| centimeter | 563,400,000 cm |
| inch | 221,811,020 in |
| decimeter | 56,340,000 dm |
| hand | 55,452,756 hh |
| link | 28,006,442 li |
| foot | 18,484,252 ft |
| US survey foot | 18,484,215 ftUS |
| yard | 6,161,417.3 yd |
| meter | 5,634,000 m |
| fathom | 3,080,708.7 ftm |
| rod | 1,120,257.7 rd |
| chain | 280,064.42 ch |
| cable length | 30,421.166 cb |
| furlong | 28,006.442 fur |
| kilometer | 5,634 km |
| mile | 3,500.8053 mi |
| nautical mile | 3,042.1166 nmi |
| league | 1,166.9351 lea |
| megameter | 5.634 Mm |
| Earth radius | 0.88431957 REarth |
| light-second | 0.018793001 ls |
| lunar distance | 0.014656646 LD |
| solar radius | 0.0080983182 Rsun |
| light-minute | 0.00031321669 lmin |
| astronomical unit | 0.000037660964 AU |
| light-year | 5.9551427e-10 ly |
| parsec | 1.8258551e-10 pc |
| kiloparsec | 1.8258551e-13 kpc |
| megaparsec | 1.8258551e-16 Mpc |
| gigaparsec | 1.8258551e-19 Gpc |
Learning zone
Sirius B's radius is smaller than Earth's own 6371 km, and against its solar mass the arithmetic turns brutal: mean density around 2.5 tonnes per cubic centimetre, surface gravity near 400 000 g, and an escape velocity — plug this radius and its mass into the escape-velocity solver — of about 6900 km/s, over two per cent of the speed of light. Matter in this state is degenerate: nuclei swimming in a quantum sea of electrons whose refusal to share states, not heat, supplies the pressure. A white dwarf is nuclear-dense physics at one remove — the same compression continued past the Chandrasekhar limit produces a neutron star, effectively a single nucleus kilometres wide.
The radius is measured two independent ways that agree: photometry with the temperature, and the gravitational redshift of its spectral lines — light climbing out of that gravity well arrives measurably reddened, 80.65 km/s in velocity units by Hubble's measurement, a general-relativistic effect first sought in Sirius B by Adams in 1925 as an early test of Einstein.