The Cosmic Snooker Match

It’s not every day astronomers get to see a game of cosmic snooker. A joint team of astrophysicists based here at Warwick and Sheffield Universities, as part of a consortium of astronomy departments, have discovered a peculiar double-star system which resembles something of a real life space based snooker match.

The focus of the team was on the NN Serpentis binary star system, located approximately 1,700 light years away. The system consists of two stars: a red dwarf and a white dwarf, which orbit each other in an incredibly tight orbit.

Earth sits in the same plane as NN Serpentis, so astronomers were able to observe the larger red dwarf eclipse the white dwarf every three hours and seven minutes. Using these frequent “eclipses”, the team was able to spot a pattern of small yet significant irregularities in the orbit of stars. From these observations of gravitational effects, the team concluded that there must be perhaps one, but more probably two, gas giants (i.e. “Jupiters”) in the midst. The more massive gas giant is about 6 times the mass of Jupiter and orbits the binary star every 15.5 years, whilst the other orbits every 7.75 years and is about 1.6 times the mass of Jupiter.
Prof. Tom Marsh, of the Astronomy & Astrophysics group based here at Warwick, stated:

> …the two gas giants have different masses, but they may actually be roughly the same size as each other, and in fact will also be roughly the same size as the red dwarf star they orbit…

> …if they follow the patterns we see in our own star system of gas giants with dominant yellow or blue colours, then it’s hard to escape the image of this system as being like a giant snooker frame with a red ball, two coloured balls, and a dwarf white cue ball.

This discovery represents a greater understanding of the formation and evolution of planetary systems around binary star systems. The team concluded that if the planetary system around NN Serpentis was born at the same time as their parent stars then they would’ve had to survived the period when the primary star bloated itself into a red giant.

This bloating effect would have caused the primary’s companion to be pulled into the very tight orbit that is observed today. This would have resulted in very unstable and chaotic planetary orbits.

However, the team went on to theorise that the planets may have formed as a result from any “cast off” material after the bloating, which is a common phenomenon among post-AGB binary stars. In particular the tiny separation of the present binary poses no problem for stable orbits of second-generation planets even at significantly shorter distances than the inner planet that the team detected.

Either way, NN Serpentis would have seen a vast shock to the orbits of both the stars and their constituent planets.


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