Bizarre star trio may form glowing ring

A bizarre star trio

Katrina Exter: Shuster West 2 is a puzzle, first of all because it’s a nebula, which is basically too bright.

EarthSky caught up with astronomer Katrina Exter of the Space Telescope Science Institute at a 2008 meeting of astronomers, where she spoke about the planetary nebula Shuster West 2. It’s a glowing ring of ionized gases over 4,000 light years away – thought to be the remnant of a hot, dying star. But, so far, the original star hasn’t been viewed directly.

Katrina Exter: We took observations of the point in the middle, which should be that star and found out that it wasn’t, but that it was instead a binary star system, two stars gravitationally bound together.

In other words, two stars orbiting each other in the center of the nebula – neither of which are the star that’s causing the nebula to glow.

Katrina Exter: And so they’re neither old enough, nor hot enough to have created, and then heat up the nebula.

But what these two stars are is very slow. Exter talked about their unusually slow spin.

Katrina Exter: It’s a hint that there has been some sort of dynamical interaction with a third body, with a third star which has basically stirred up the two to make them rotate slowly.

That third star might be what was missing – the star lighting up Shuster West 2. That would make this a triple star system inside the glowing ring of gas.

Dr. Exter added more about how study of the triple system inside Shuster West 2 advances understanding about the evolution of binary stars.

Katrina Exter: This is because in order to know what the past evolution of a multiple star system was, as well as what it’s future could be, you need at a minimum to know what the current configuration of the stars are – size, mass, age, separation among other parameters. Multiple systems are extremely hard to model because the way they can dynamically interact with each other can completely change their evolution; but you can’t very easily know what this past dynamical interaction was, as a whole range of possible past dynamical interactions can result in the same current configuration (position of the stars with respect to each other.

Our thanks to:
Katrina Exter
Space Telescope Science Institute
Baltimore, MD

September 5, 2008

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