Sun’s closest solo star may have company
Ars Technica said:From the phenomenal success of the Kepler mission and a proliferation of ground-based telescopes, we now know that planets are common in our galaxy. But the methods we've used to detect most of them are biased toward finding large planets that orbit close to their host stars. The farther a planet is, the less its gravity pulls at the star and the less light it blocks out when it passes between that star and Earth. Meanwhile, the focus has shifted to nearby stars, as astronomers have started building a catalog of targets for the next generation of telescopes.
These issues provide an intriguing backdrop for today's announcement that one of the closest stars to Earth has a super-Earth companion. Barnard's star is a red dwarf that is only six light years from our Solar System; only the three stars of the Centauri system are closer. But the new planet orbits far enough from Barnard's star that it had been missed by earlier attempts. The detailed follow-up that spotted it also hints at the possibility of a separate, more distant planet, and both could help inform our models of planet formation.
A new look
Barnard's star has been observed extensively over the years, partly because it's so close, partly because it's a prototypic example of a red dwarf star. These observations have included exoplanet searches, but nothing about the system stood out. But unless you observe a star regularly, there's a chance you won't happen to be looking at critical points in the planet's orbit.
That seemed to be the case when a team of researchers started checking archival data for Barnard's star images. Their analysis suggested there might be a signal of something orbiting with a 230 day period, but the data suffered from what the researchers term "very poor sampling." So they obtained time on some telescopes to do an extensive monitoring campaign in 2016 and 2017, including simultaneous observations with more than one instrument.
The team was looking for signs that Barnard's star was shifting back and forth due to the gravitational pull of a planet, a planet-hunting approach called the radial velocity method. This would create slight changes in the color of the light from Earth's perspective due to the Doppler effect. If a planet produced these changes, then they would appear regularly with each of the planet's orbits.
Analysis of Barnard's star suggested it rotated about every 140 days (this can also cause changes, as more or less active regions of the star rotate in and out of view). But a variety of analysis methods suggested that there was an additional signal at 233 days, with a false alarm probability of only one in 10-15. (There was one approach that suggested the signal wasn't real, but that analysis is known to produce false negative results.) The strength of the signal also increased as new observations were added, reinforcing indications that it's real.
...
