Selections from 2018: X-Rays from Alpha Centauri


Editor’s note: In these last two weeks of 2018, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded papers published in AAS journals this year. The usual posting schedule will resume in January.

Alpha Centauri Beyond the Crossroads

Published January 2018

Main takeaway:

A scientist from University of Colorado Boulder, Tom Ayres, has compiled observations from the Chandra X-ray Observatory tracking the X-ray emission from the two stars of the Alpha Centauri binary system. Alpha Centauri is the closest star system to us, at just 4.37 light-years away.

Why it’s interesting:

Alpha Centauri A and B are both Sun-like dwarf stars with coronae very similar to our Sun’s. By studying the X-ray activity of these stars, we can learn more about how stars like the Sun bombard their environments with harsh radiation. This is useful both from the perspective of protecting our own interests — since this so-called space weather can affect astronauts, satellites, our power grid, etc. — and from the perspective of learning about potential habitability around our nearby stellar neighbors.

On Alpha Centauri’s recent crossroads:

X-ray light curves

X-ray light curves of Alpha Centauri A (blue), Alpha Centauri B (red), and the Sun (gray) for 1995–2018. [Ayres 2018]

The latest Chandra observations are cool because we can distinctly see the stellar activity cycles in both Alpha Centauri A and B, in much the same way that our own Sun has an 11-year cycle. For Alpha Centauri B, the cycle is about 8 years; for Alpha Centauri A, it appears to be closer to 19 years. In 2016, the system reached what Ayres describes as a crossroads: not only did Alpha Centauri A hit a maximum in activity and Alpha Centauri B hit a minimum, but around the same time, we also witnessed the crossing of the apparent trajectories of the two stars on the sky.


T. R. Ayres 2018 Res. Notes AAS 2 17. doi:10.3847/2515-5172/aaa88f