June 4, 2020

Astro-Challenge:When will T Pyxidis Finally Pop?

Earlier this year, the astronomical community was wowed by the eruption of the star U Scorpii. As reported last year in this space, U Sco is a recurrent nova, a flare star that undergoes outburst at irregular intervals. Less than 10 recurrent novae have been identified. The initial action was caught by two Florida based amateurs, and demonstrates that hands on, observational astronomy is still alive and well even in the modern age of astronomical automation. This week, as the waning gibbous moon slides out of the evening sky, I’d like to turn your attention to another of these rare beasts; T Pyxidis. Located in the constellation Pyxis, the Mariner’s Compass, this is one of those unimaginative southern hemisphere constellations thrust upon us in the 18th century. Visually unremarkable, it contains a handful of deep sky objects and clears the horizon sufficiently in the spring evenings for observers in the southern United States to perform routine observations. T Pyxidis itself is a binary system consisting of a white dwarf cannibalizing a sun-like star. When enough in falling matter accumulates, T Pyx flares up from its normal barely detectable magnitude +15.5 to +7.0, almost naked eye visibility. This has happened at roughly 20 year intervals in the years 1890, 1902, 1920, 1944, 1966…and then T Pyx fell silent. We are currently 44 years and counting for an outburst, and this is definitely a star worth continuous scrutiny. The light curve is that of a slow nova, rapidly brightening over a couple of nights, fluctuating at its peak brightness for about a month, and then fading out over proceeding months. T Pyx is a prime candidate for a galactic Type Ia supernova, and at a distance of 3260 light years, could put on quite a show. Of course, said final act could occur tonight, or 10 million years from now; but this current lull makes you think; there has to be a lot of material accreting up there! Its coordinates are;

R.A: 09h 04m 41.5s

Dec: -32 22m 47.5s

And for an uber-cool finder chart that Sky & Telescope produced a few years back, follow this link… (hint: for use in the field, take the chart and  invert the colors in Paint or Photoshop!)

Good luck, and with a little patience, YOU could be the next amateur to catch T Pyx in the act!

The Astro-term for this week is Chandrasekhar Limit. This is the mass limit of a body in which electron degeneracy pressure can push outward against gravitational collapse. First calculated by Indian astrophysicist Subrahmanyan Chandrasekhar in 1930, this mass is usually given as 1.44 solar masses. Below this limit, a white dwarf and an accompanying planetary nebula will occur; above this mass limit, a core collapse supernova will occur, leaving behind a pulsar or a black hole. T Pyxidis has to be very near its very own Chandrasekhar Limit, with the amount of in-falling mass it is accumulating… will it pop in our lifetime?