Exoplanet Excursions: May 2015

Jon pays a visit to the vast rings spinning around the brown dwarf J1407b.

There’s an intriguing star in the constellation of Centaurus, about 90 per cent the mass of the Sun. It glows at a magnitude of +12.3, so it is visible to a telescope from southern latitudes.

Image Credit: 
Mark Garlick
Credit: Illustration by Mark Garlick

This fascinating star has the name of (get ready) 1SWASP J140747.93-394542.6, a name with all the hallmarks of a complicated moment halfway through the Shipping Forecast. Thankfully it’s usually abbreviated to a more manageable J1407.

There’s something highly perplexing about this star when seen by the SuperWASP observatories. Its light is dimmed and brightened in the most astonishingly variable and complex fashion. At times, 95 per cent of its light ebbs away before once again returning, emulating the tides of Earth’s oceans with stellar light. What could be creating light fluctuations of such enormity?

The cause of this phenomena goes by the mercifully short name of J1407b, a foreboding companion brown dwarf surrounded by a singularly spectacular ring system, the discovery of which left astronomers slack-jawed with stupefaction. Fanning out for 145 million km and 200 times the size of Saturn’s magnificent rings, you have no choice but to marvel at this system while feverishly speculating about its formation.

Settling my new ship, the Perihelion, upon the ring system’s outer edge gives an awesome view of a seemingly infinite banded horizon. You feel like a microbe perched on the edge of Status Quo’s Piledriver vinyl album. Endless, beautifully circular grooves appear together like compressed isobars on a weather map.

There are several gaps at intervals within the rings, similar to concentric Cassini divisions, cleared paths occupied by exomoons orbiting their parent brown dwarf. The view from the surface of these moons must be utterly breathtaking, with the sky dominated by the arcs of the rings and the smouldering, rusty glow of the brown dwarf hanging steadfastly above them.

The sight of this exo-ring system could easily be one of the 700 Wonders of the Universe. If the rings swapped places with Saturn’s and were observed from Earth, they would span the width of about 20 apparent full Moons across our sky. Perhaps in the past there was a cataclysmic clash of planetary bodies of sufficient force to completely reduce the objects into proverbial smithereens. It seems that the wreckage settled down after a period and the gravity of the brown dwarf was enough to sustain a magnificent ring system spanning the best part of an astronomical unit.

Surveying the scene, I wonder if we’re witnessing a period of planet and moon formation around the brown dwarf – quite a privilege if so. Or does the gravity of J1407b coupled with the manner of the initial clash mean that fragments of the rings and the moons are moving towards the brown dwarf and being absorbed by it, a fate similar to Phobos around Mars? If that’s the case, I imagine a cosmic domino effect where eventually every fragment of the ring system becomes absorbed. Perhaps when a sufficient amount of fragments have been digested, J1407b might take on enough extra mass to reboot and upgrade from a brown dwarf to a proper star. Nothing like an exoplanet excursion to set the imagination in motion.

Jon Culshaw is a comedian, impressionist and guest on The Sky at Night
This column appeared in the May 2015 issue of BBC Sky at Night Magazine
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