Super-Jupiter Found Orbiting Kappa Andromedae

An international team of astronomers using infrared data from the Subaru Telescope in Hawaii has discovered a super-Jupiter around the star Kappa Andromedae.

This false-color near-infrared image shows the planet Kappa Andromedae b (NOAJ / Subaru / J. Carson / College of Charleston)

Kappa Andromedae is a B-type massive star located in the constellation Andromeda about 170 light years away. It has a mass 2.5 times that of the Sun and now holds the record for the most massive star known to host a directly imaged planet or lightweight brown dwarf companion.

The planet, named Kappa Andromedae b, has a mass at least 13 times that of Jupiter, and orbits its star at a projected distance of 55 times Earth’s average distance from the Sun and about 1.8 times as far as Neptune. It has a temperature of about 2,600 degrees Fahrenheit (1,400 Celsius) and would appear bright red if seen up close by the human eye.

“Our team identified a faint object located very close to Kappa Andromedae in January that looks much like other young, massive directly imaged planets but does not look like a star. It’s likely a directly imaged planet,” said Dr Thayne Currie of the University of Toronto, co-author of a paper reporting the discovery in the Astrophysical Journal Letters (arXiv.org version).

“According to conventional models of planetary formation, Kappa Andromedae b falls just shy of being able to generate energy by fusion, at which point it would be considered a brown dwarf rather than a planet,” added Dr Michael McElwain, a member of the discovery team at NASA’s Goddard Space Flight Center in Greenbelt. “But this isn’t definitive, and other considerations could nudge the object across the line into brown dwarf territory.”

“This planetary system is very different from our own,” Dr Currie said. “The star is much more massive than our Sun and Kappa Andromedae b is at least 10 times more massive than any planet in the solar system. And, Kappa Andromedae b is located further from the star than any of the solar system planets are from the Sun. Because it is generally much harder to form massive planets at large distances from the parent star, Kappa Andromedae b could really be a challenge for our theories about how planets form.”

“Kappa Andromedae b, the previously imaged planets around HR 8799 and Beta Pictoris, and the most massive planets discovered by non-imaging techniques likely all represent a class of object that formed in much the same way as lower-mass exoplanets,” said lead author Dr Joseph Carson of the College of Charleston and the Max Planck Institute for Astronomy in Heidelberg, Germany.

This is an artist’s impression of the planet Kappa Andromedae b (NASA’s Goddard Space Flight Center / S. Wiessinger)

The discovery of Kappa Andromedae b also allows astronomers to explore another theoretical limit. Astronomers have argued that large stars likely produce large planets, but experts predict that this stellar scaling can only extend so far, perhaps to stars with just a few times the sun’s mass. The more massive a young star is, the brighter and hotter it becomes, resulting in powerful radiation that could disrupt the formation of planets within a circumstellar disk of gas and dust.

“This object demonstrates that stars as large as Kappa Andromedae, with 2.5 times the Sun’s mass, remain fully capable of producing planets,” Dr Carson concluded.

_______

Bibliographic information: Carson J. 2012. Direct Imaging Discovery of a `Super-Jupiter’ Around the late B-Type Star Kappa And. Accepted for publication in Astrophysical Journal Letters; arXiv: 1211.3744