Stars like the sun eventually run out of hydrogen fuel and puff-up into red giants at the end of their lives — a precursor to a suicidal shedding of gas, decimating any nearby planets, eventually leaving a tiny white dwarf remnant. But a nearby star, located around 100 light-years away, has been spotted in the brief stage before the red giant phase of its death throes — and it has a dusty disk usually exclusive to young stars.
Kappa Coronae Borealis (κ CrB) is a little more massive than our sun, weighing-in at 1.5 solar masses. It has been steadily burning through its supply of hydrogen for 2.5 billion years, but now it has entered its “retirement years” as a subgiant. κ CrB is known to have one massive planet (around two Jupiter masses) in orbit with evidence of a second world. But most interesting is the presence of a dusty ring of debris surrounding the star, and the European Herschel space observatory is the first telescope to see such a ring surrounding such an old star.
“This is the first ‘retired’ star that we have found with a debris disc and one or more planets,” said Amy Bonsor of the Institute de Planétologie et d’Astrophysique de Grenoble, and lead author of the study published in the journal Monthly Notices of the Royal Astronomical Society.
Herschel’s sensitivity to far-infrared wavelengths has allowed Bonsor’s team an incredible view of κ CrB disk (pictured top). The bright emission from the disk appears to show a region of debris from asteroid and/or comet collisions. It is thought that the solar system possessed a similar region during the sun’s early evolution, but the debris was swept away during the sun’s formative years.
“The disc has survived (κ CrB’s) entire lifetime without being destroyed. That’s very different to our own solar system, where most of the debris was cleared away in a phase called the Late Heavy Bombardment era, around 600 million years after the sun formed,” added Bonsor.
Not only is the disk interesting in regards to κ CrB’s evolution, it may be being actively shaped by planets in orbit around the star. Using Herschel data, the astronomers think there are three possible configurations of the planetary system, one of which suggests the second exoplanet may even be a brown dwarf.
“It is a mysterious and intriguing system: is there a planet or even two planets sculpting one wide disc, or does the star have a brown dwarf companion that has split the disc in two?”
This may be the first subgiant star to be observed with a dusty disk, but it won’t be the last.
Image credit: ESA/Bonsor et al (2013)