The gravitational redshift of Sirius B

S. R.G. Joyce, M. A. Barstow, J. B. Holberg, H. E. Bond, S. L. Casewell, M. R. Burleigh

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15 Scopus citations


Einstein's general theory of relativity predicts that the light from stars will be gravitationally shifted to longer wavelengths.We previously used this effect to measure the mass of the white dwarf Sirius B from the wavelength shift observed in its Hα line based on spectroscopic data from the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST), but found that the results did not agree with the dynamical mass determined from the visual-binary orbit. We have devised a new observing strategy using STIS, where the shift is measured relative to the Hα line of Sirius A rather than comparing it to a laboratory based rest wavelength. Sirius A was observed during the same orbit with HST. This strategy circumvents the systematic uncertainties which have affected previous attempts to measure Sirius B. We measure a gravitational redshift of 80.65 ± 0.77 km s-1. From the measured gravitational redshift and the known radius, we find a mass of 1.017 ± 0.025 M which is in agreement with the dynamical mass and the predictions of a C/O white dwarf mass-radius relation with a precision of 2.5 per cent.

Original languageEnglish (US)
Pages (from-to)2361-2370
Number of pages10
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
StatePublished - Dec 1 2018

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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