planet formation
January 18, 2014

ALMA Telescope Used To Find Giant Planetary System Forming Around Young Star

[ Watch the Video: ALMA Makes A Starry Cosmic Discovery ]

redOrbit Staff & Wire Reports - Your Universe Online

A team of Japanese astronomers has located evidence of a giant planetary system forming around a young star named HD142527, and their discovery could change existing theories on how planets form and provide new insights into the formation of a vast array of different planetary systems.

Using the Atacama Large Millimeter/submillimeter Array (ALMA) telescope, scientists from Osaka University and Ibaraki University located HD142527 in the constellation Lupus, the National Astronomical Observatory of Japan (NAOJ) explained in a statement Friday. Those observations, the researchers said, showed that the star is being encircled by an asymmetric ring of cosmic dust, which is the component material of planets.

“By measuring the density of dust in the densest part of the ring, the astronomers found that it is highly possible that planets are now being formed in that region,” the NAOJ said. “This region is far from the central star, about 5 times larger than the distance between the Sun and the Neptune.”

“This is the first firm evidence of planet formation found so far from the central star in a protoplanetary disk,” the observatory added. “The research team plans further observations of HD142527 with ALMA for closer investigation, as well as other protoplanetary disks to have a comprehensive understanding of the planet formation in general.”

To date more than 1,000 extrasolar planets have been discovered, and while a diverse group of these worlds have been located, the actual process by which they form is not yet fully understood. In fact, the researchers call the search for planet-forming regions around young stars one of the top priorities for modern astronomers.

The study authors originally discovered HD142527 and a disk surrounding it using the Subaru Telescope. They located a gap inside that disk and a peculiar shape to the outer disk, and detected a submillimeter emission from the dust ring using ALMA. They described the emission as having a non-uniform distribution, with the southern side being 30 times fainter than the far brighter northern side.

“We are very surprised at the brightness of the northern side,” explained lead researcher Misato Fukagawa of the Osaka University Department of Earth and Space Science’s Infrared Astronomy Group. “The brightest part in submillimeter wave is located far from the central star, and the distance is comparable to five times the distance between the Sun and the Neptune.”

“I have never seen such a bright knot in such a distant position. This strong submillimeter emission can be interpreted as an indication that large amount of materials is accumulated in this position,” Fukagawa, who is also an assistant professor at the university, added. “When a sufficient amount of material is accumulated, planets or comets can be formed here. To investigate this possibility, we measured the amount of material.”

In order to calculate the amount of material based on the submillimeter emission strength, the astronomers had to estimate the temperature using observations of carbon monoxide isotopomers. Using this information, they determined that either a gaseous giant planet or a rocky planet was being formed.

“If the abundance of dust and gas is comparable to that in typical environment in the universe (the mass ratio of dust and gas is 1 to 100), the dense region is massive enough to attract large amount of gas due to the self-gravity and form giant gaseous planets several times more massive than Jupiter,” the NAOJ said. “Although this is similar to the formation process of stars in cosmic clouds, it was the first time that the possibility of such a planet formation process was directly suggested by observations of protoplanetary disks.”

“The other possibility is the formation of ‘dust trap’ in which the abundance of dust is exceptionally higher than the other part of the disk,” the observatory added. “If the dust trap is formed in the disk, earth-like rocky planets, small bodies such as comets, or cores of gaseous planets may be formed. In both cases, it is highly possible that planets are being formed in the dense part of the disk around HD142527.”

The basic tenants of the two planetary formation processes had been theoretically predicted over three decades ago, and experts assumed that planet formation in our solar system started with the collision and coalescence of massive amounts of dust. Under these conditions, the concentrated dust would grow and form into multiple propoplanets, and those planetary cores would then ultimately evolve into actual worlds.

“Some of the cores capture massive atmosphere to form gaseous giant. It was thought that both of the processes occurred close to the central star… but the new ALMA results undermine this conventional assumption,” the observatory said. “The next step will be a precise measurement of the amount of gas to identify which process is involved. The team will continue detailed observations using ALMA with improved capability.”

Fukagawa added that “HD142527 is [a] peculiar object, as far as our limited knowledge goes. However, other asymmetrical protoplanetary disks have been discovered since the early ALMA science operation started. Our final goal is to reveal the major physical process which controls the formation of planets. To achieve this goal, it is important to obtain a comprehensive view of the planet formation through observations of many protoplanetary disks. We hope to be part of this great venture.”