AAS: Planets, planets everywhere
It’s almost as startling as 60-year-old women giving birth. Astronomers think they have spotted two stars that are well into middle age and shockingly may still be forming planets around themselves.
Most of the time, planets are born soon after their parent star is. Think of our sun, which in its infancy 4.5 billion years ago also saw planets forming right away, condensing out of the cocoon of dust and gas that swirled around it. You don’t see any newborn planets popping into existence in our solar system today.
But that may be exactly what’s happening at two puzzling stars, says Carl Melis, a graduate student at the University of California, Los Angeles. Despite being well advanced in age, both appear to be surrounded by a dust disk that could be forming planets now. It could, in fact, be a second wave of planetary formation for these stars; the first coming soon after they were born, possibly hundreds of millions of years ago, and the second happening now.
The two stars are odd. One, called BP Piscium in the constellation Pisces (right), 
was thought to be a young star because of the dusty disk that surrounds it. But studies of its chemical composition and other factors revealed that it is in fact quite old – maybe not to menopause yet, but definitely pushing the limit. The second star, called TYC 4144 392 2 in the constellation Ursa Major, has a dust disk and itself orbits a separate star, which does not have such a disk.
So how did these two old stars end up with dust disks around them? Melis thinks they may have, in the recent past, each swallowed another companion object – something a bit too small to be called a proper star – and, in the digestive process, belched out a giant wave of dust. That dust settled into orbit around the star.
Sara Seager, an expert on extrasolar planets at MIT, says Melis’ idea is plausible. There’s no getting around the fact that these two stars have dust disks, she says. The question now is, how exactly did they get there, and are planets in fact actually forming within them?