Professor of Mathematics
Paata Ivanisvili
Department of Mathematics, University of California, Irvine
Candidate 21: a Sun-like star with a doubtful wobble
Why this estimate. The orbit comes from Gaia’s less reliable alternative orbit solutions, which most published studies leave out, and it fails the published quality cuts: the fit is degenerate, the orbit is only about eight times its uncertainty, and the parallax is too uncertain. No measurements along the line of sight confirm it.
How to read the pictures. The orbit figure has three panels. On the left is the small ellipse that Gaia’s orbit traces on the sky, measured in thousandths of an arcsecond, with grey orbits that fit the data about equally well. In the middle is the mass the unseen companion would need for each possible mass of the visible star; the shaded band is the likely range, the red line marks the star’s estimated mass, and the dotted and dashed lines mark 3 and 1.4 solar masses, roughly where black holes begin and where a typical neutron star lies. On the right, the star (red) sits among other stars in Gaia’s diagram of colour against brightness. The finder chart shows a patch of sky two arcminutes across, about a fifteenth of the Moon’s width, with north up and east to the left; the star sits between the two yellow ticks, and the white bar is 30 arcseconds long. On the light curve the vertical axis is magnitude, a brightness scale on which larger numbers mean fainter stars, and it is drawn so that down means fainter. Here the orange band marks the years in which Gaia measured the orbit, not a change in brightness. Each survey uses slightly different filters, so each is compared with its own normal level.
What Gaia found. This is a Sun-like star, about 5,600 K, some 1,100 parsecs away in Hercules. One of Gaia’s alternative orbit-fitting methods found a 753-day wobble that, for a star of about one solar mass, implies a companion of about 1.8 solar masses (1.6 to 2.3) giving off no visible light. If the orbit were real, the companion would be a neutron star or a heavy white dwarf.
Why the estimate is low. Gaia’s alternative orbit solutions are less reliable than its main ones and are left out of most published studies, and this one fails the published quality cuts. There are no measurements of the star’s speed along the line of sight.
No record of a dark companion for this star could be found.
- Star
- Gaia DR3 1334956997595864960, a Sun-like star
- Location
- RA 259.76536°, Dec +34.27371° (J2000), in Hercules
- Distance
- about 1,100 parsecs (3,600 light-years)
- Brightness
- Gaia G = 15.6
- Probability
- This candidate is unconfirmed. The percentage under the title is an estimate of the chance that it is a real, previously unrecorded case of the kind described. The estimate has not been checked by outside experts. See the introduction to all fifty-eight candidates.
- Caveat
- The orbit is a less reliable kind of Gaia solution and fails the published quality cuts, and no measurements along the line of sight confirm it.
