Hello Guy! At a distance of 1000 light years, am I correct to assume that the orbit of the inner star in this triple object system falls within the diffraction disk of the inner star and thus its motion would be visibly imperceptible to us? No mention was made of the orbital period of the outer star, but does anyone know the orbital period of that star? Jon H.

Jon:

Thanks for the question. I'll try to answer it.

Let's discuss each of the objects separately -- The black hole at the center, the inner orbiting star, and the outer orbiting star.

When you ask about the airy disk of the "inner star," I assume you are referring to the "inner orbiting star" since the black hole at the center (which emits no light) does not create an airy disk.

If that is the case, then an observer on Earth would see this inner orbiting star (along with its airy disk) oscillate back and forth with a period of 40 days. The instrumentation at the observatory is apparently sensitive enough to measure that oscillating motion.

Regarding the outer orbiting star, I was not able to find the its orbital period.

BTW - The HR 6819 triple system is in the constellation Telescopium, so it is not viewable from the northern hemisphere. However, the two orbiting stars in HR 6819 can be viewed from the southern hemisphere on a dark, clear night without binoculars or a telescope.

Hope this helps.

Thanks,

Guy Pirro

Well... Thanks Guy...!!!!
Frank

Welcome to Astromart Frank!

Guy Pirro