Planet formation may be more commonplace
Young stars with no visible disc of dust and gas, long dismissed as ever likely to develop planets, may still be breeding them - it's just that their planet-forming dust is hard to see, according to two American astronomers.
Assistant Professor David Weintraub and astronomer Jeff Bary of
Vanderbilt University in Nashville, USA, argue in a recent issue of
The Astrophysical Journal that many of these stars - known as T Tauri and generally less than 10 million years old - may still be forming planets.
Normally, T Tauri stars less than 3 million years old are surrounded by a thick disc of dust and gas, known as a protoplanetary disc because it is a breeding ground for planet formation. But most older T Tauri stars show no sign of a disc and, because they are not old enough for planets to form, astronomers have long assumed that these stars had lost their discs before planets could form.
The two astronomers have challenged this assumption by successfully finding hydrogen around a T Tauri star known as DoAr21, a star for which no evidence of a planetary disc had ever been detected.
"We found evidence for hydrogen molecules where no hydrogen molecules were thought to exist," said Weintraub. Hydrogen strongly indicates the presence of a protoplanetary disc.
The researchers looked for evidence of hydrogen by searching for any infrared light it might be giving off, and discovered a faint signal. Although the signal only accounted for enough hydrogen to make a planetary body the size of Earth's Moon, they believe most of the hydrogen present was not radiating in the infrared, and therefore went undetected.
Dr Warrick Lawson, an astrophysicist at the Australian Defence Force Academy in Canberra said the discovery meant that astronomers would be able to get a much better handle on how many planetary systems there are in our galactic neighbourhood.
"There are thousands of T Tauri stars out there - we can now go back to the supposedly discless ones and look for gas which was previously assumed to no longer be there," he told ABC Science Online.
"Why this is interesting is that the planet-forming theorists want longer time scales [for planet formation]. If it is shown that the gas reservoirs are around for a lot longer, that means the lifetime of the disc is longer than previously thought, and that means planets might still be forming."
Weintraub and Bary hope to strengthen their theory by surveying 50 more 'naked' T Tauri stars at the massive Gemini South telescope in Chile's Andean mountains in the next few months to see how many produce the same molecular hydrogen emissions.