Astronomers once thought the dusty clouds that spawn planets all look pretty much the same: disc-shaped formations. The dust, which circles young stars, eventually clumps up to form new worlds.

But researchers say they’re increasingly learning that these “protoplanetary discs,” as they’re called, come in a dazzling variety of shapes.

Astronomers inspecting a protoplanetary disc around a star named HD142527, for example, have reported finding that part of the disc actually consists of two banana-shaped arcs facing each other.


HD142527's protoplanetary disk. A mask hides the central star to reduce glare. Visible are two banana-shaped arcs, above and below the blackened circle, and a more extended arc to the lower right. The vertical line represents a distance of 200 AU, about five times the Sun-Pluto distance. The image was captured in near-infrared light with a wavelength of 1.65 microns. (Courtesy Subaru Telescope)

This adds more variety to a plethora of protoplanetary disk shapes—from donuts to spirals—that astronomers are finding as they study the birthing grounds of planets around other stars.

Two Japanese research teams studied HD142527 using instruments at the Subaru telescope facility on Mauna Kea, Hawaii. Their findings appeared in the Jan. 10 June 20 issues of the Astrophysical Journal.

Misato Fukagawa of Nagoya University in Japan and colleagues studied the disc out to a distance comparable to Neptune’s orbit in our Solar system. Using a different instrument, Hideaki Fujiwara of the University of Tokyo and colleagues studied the surroundings out to three times that distance.

The first team reported finding what they called a “banana split” shape of two arcs facing each other in the inner zone.

The second team described a compact disk extending out from the star as far as twice the distance from the Sun to Pluto. They also reported an extended disk echoing the banana-split shape seen by the first team, and reaching out further than four times the Sun-Pluto distance.

Before these findings, recent observations of protoplanetary disks around at least two other stars had been changing astronomers’ view of planetary birthplaces, the researchers said.

For instance, a donut-shaped disc is believed to surround an orbiting pair of stars in a multiple-star system GG Tauri, in the direction of the constellation Taurus, about 450 light-years from Earth. A light-year is the distance light travels in a year.


An image of the disk around the binary star pair GG Tauri A-B obtained using instruments on the Gemini North 8-meter telescope on Mauna Kea, Hawaii in 2001. (Courtesy National Optical Astronomy Observatory)

And a spiral-shaped protoplanetary disc surrounds the young star AB Aurigae, about the same distance away in the direction of the constellation Auriga.


Images released in 2004 of protoplanetary disk surrounding the star AB Aurigae shows gas and dust swirling in a complex spiral pattern, astronomers say. (Courtesy Subaru Telescope)

The Japanese teams scrutinized HD142527 using instruments on Subaru that could pick up two different parts of the infrared light spectrum. Infrared is a type of light lower in energy than visible light.

The most likely explanation for the “banana-split” shape is the presence of another object orbiting the star, a much dimmer companion star or possibly a planet, the researchers said.

The extended arc, they added, is most likely due to the gravitational tug of a passing star sometime in the last thousand years. Because most stars seem to be born in groups, many features of the newly charted disk may be common, they added.

The new images are among the first examples of successful direct imaging of a protoplanetary disk from an Earth-based telescope, the researchers claimed. The star is about 650 light-years from Earth in the approximate direction of the constellation Lupus.

Turbulence in our planet’s atmosphere makes clear images of its faint protoplanetary disk extremely hard to get, the astronomers added. The successful observations relied on the size, stability and location of the telescope, they said, along with devices designed to counteract the distortion due to air movements in our atmosphere and glare from the starlight.

Protoplanetary disks are accumulations of gas and dust that surround young stars. As a star is born and grows, the disk forms out of the the same material as the star.

Over time, astronomers believe the dust accumulates into larger objects, which eventually create protoplanets. These collide to form planets. Recently astronomers have surveyed stars that are about a million years old to understand the dusty environments in which planets form. Infrared observations are particularly powerful tools to understand the discs, revealing information about their structure, temperature and density, according to scientists.

Attached Thumbnails