Huge exoplanet puzzles astronomers

Very dense object orbits its parent star in just four days and six hours

Astronomers have sighted a very dense planet-sized object that orbits its parent star in just four days and six hours.

The object, COROT-exo-3b, fits into the category of a failed star known as a brown dwarf, but the team that made the discovery has not ruled out the possibility that it is a planet. Brown dwarfs are failed stars.
They burn lithium but are not massive enough to generate the
thermonuclear fusion of hydrogen and helium that powers real stars.
Planets do none of that.

"It
has puzzled us; we're not sure where to draw the boundary between
planets and brown dwarfs," said Hans Deeg, an astronomer at the
Instituto de Astrofisica de Canarias in the Canary Islands, Spain.

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If astronomers confirm the object as a planet, it would weigh in as the most massive and densest planet found so far. A full study will be detailed in the journal Astronomy and Astrophysics.

"COROT-exo-3b
might turn out to be a rare object found by sheer luck", said Francois
Bouchy, an astronomer at the Institut d'Astrophysique in Paris. "But it
might just be a member of a new-found family of very massive planets
that encircle stars more massive than our sun. We're now beginning to
think that the more massive the star, the more massive the planet."