ISO establishes that half of all young stars have protoplanetary discs
23 October 1998
Most young stars are surrounded by discs of dust and gas which in a fewmillion years will probably condense to form planets. This is one of theresults presented today during the international ISO meeting being held inParis this week, "The Universe as seen by ISO"."Thanks to the European Space Agency's ISO space telescope astronomers can finally establish the relationship between the age of the star and the presence of the disc," said US astronomer Eric Becklin, chairman of this morning's session.
The first of these discs were found in 1984, circling the stars Beta Pictoris and Vega. They're both stars entering the adult stage but still quite young - they're only a few hundred million years old. In comparison, the Sun is about five thousand million years old. The radius of their discs is well over the distance between our Sun and Jupiter. Now, ISO astronomers have made more observations of these stars with greater sensitivity and resolution, and have also been searching for more discs to study just how common is this phenomenon.
Their results come from two separate large teams of researchers in Europe and the United States, led respectively by Harm Habing (Leiden University, The Netherlands) and Eric Becklin (University of California at Los Angeles, US). According to them, it is now clear that about 50% of all stars born some million years ago do have discs, but that they start to lose them when they age. Thus, when the stars are about 400 million years old, the discs begin to disappear, because the material in them has collapsed in larger planet-like bodies. ISO data show that only 20% of old stars (hundreds of million years) do have discs.
But, how many of these 'disked-stars' do have planets now? "Probably most of them, but that cannot be yet established," Becklin answers.
For the moment at least, "ISO has clearly given us a most valuable new insight in this exciting field of research. It's breaking the ground for projects that will go in search for planets, even Earth-like planets, in the far future," Habing said.
Another ISO result in this field was presented by Carsten Dominik (Leiden University, The Netherlands), who has found for the first time a disc surrounding a star in which a planet had been already detected. The star is called Rho Cancri, and is being orbited at a very close distance by a planet about the size of Jupiter.
ISO has also produced new valuable data about the origin of these rings and the minerals composing them.