Another important astronomical breakthrough has been made using a major southern hemisphere radio telescope array, in this latest case the Atacama Large Millimetre/Submillimetre Array (ALMA), located in Chile. The publishing of the new breakthrough (in the Astrophysical Journal Letters) came shortly after the announcement of the discovery of gigantic radiowave-emitting ‘bubbles’ in the centre of our galaxy by researchers using South Africa’s MeerKAT radio telescope array.

Again, an international team of scientists was involved, led by UK Leeds University PhD researcher Alice Booth. They were studying the protoplanetary disc of gas and dust around a young star designated HD 163296 (it is in a protoplanetary disc that new planets form), which formed during the last six-million years. It lies 330 light years from earth.

ALMA detected a very faint signal, which revealed that the disc contained a rare form of carbon monoxide, called an isotopologue. This has the chemical formula 13C17O (normal carbon monoxide has the chemical formula CO), and has more mass that normal CO. As a result, the team was able to measure the mass of the disc with unprecedented accuracy.

“Our new observations showed there was between two and six times more mass hiding in the disc than previous observations could measure,” reported Booth. “This is an important finding in terms of the birth of planetary systems in discs – if they contain more gas, then they have more building material to form more massive planets.”

Recent observations of protoplanetary discs had puzzled astronomers because they did not appear to possess enough gas and dust to create the observed planets (known as exoplanets, because they are outside our solar system). “The disc-exoplanet mass discrepancy raises serious questions about how and when planets were formed,” explained Leeds University researcher and team member Dr John Ilee. “However, if other discs are hiding similar amounts of mass as HD 163296, then we may just have underestimated their masses until now.

“We can measure disc masses by looking at how much light is given off by molecules like CO,” he elucidated. “If the discs are sufficiently dense, then they can block the light given off by more common forms of CO – and that could result in scientists underestimating the mass of the gas present. This study has used a technique to observe the much rarer 13C17O molecule – and that’s allowed us to peer deep inside the disc and find a previously hidden reservoir of gas.”

“We suspect that ALMA will allow us to observe this rare form of CO in many other discs,” pointed out Booth. “By doing that, we can more accurately measure their mass, and determine whether scientists have been underestimating how much matter they contain.

“Our work shows the amazing contribution that ALMA is making to our understanding of the universe,” she highlighted. “It is helping build a more accurate picture of the physics leading to the formation of new planets. This, of course. then helps us understand how the solar system and Earth came to be.”

ALMA is an international project, composed of 66 dishes located high in the Atacama Desert. The ALMA partner institutions are the European Southern Observatory, the US National Science Foundation (NSF), Japan’s National Institute of Natural Sciences (NINS) and the Republic of Chile. Also involved, through the NSF, are Canada’s National Research Council and Taiwan’s National Science Council. In addition, the (South) Korea Astronomy and Space Science Institute and Taiwan’s Academia Sinica participaten through NINS.