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Planet-forming disc imaged in sharpest detail ever

Charles Black, Founder and CEO of Sen
Nov 9, 2014, 16:55 UTC

Sen—A planet-forming disc around a young star has been imaged in great detail for the first time. Scientists will be able to study the image to obtain a better understanding of how solar systems are formed.

The image, taken by the Atacama Large Millimeter/submillimeter Array (ALMA), a ground based telescope array in Chile, shows the protoplanetary disc surrounding the young star HL Tauri, located about 450 light years away.

Although we have a growing understanding and knowledge about planets found around other stars, known as exoplanets, very little is known about the process by which such planets form. The new image, the sharpest picture taken to date of an early solar system forming, provides greater insight into the process.

The image shows rings of dust left over after the birth of the star, and importantly shows gaps in the rings—evidence that the particles of dust have begun clumping together to form celestial bodies. 

HL Tauri is not more than one million years old, and the fact that planets appear to be forming so soon after the star's birth may suggest planet formation happens more quickly than astronomers previously thought.

“When we first saw this image we were astounded at the spectacular level of detail. HL Tauri is no more than a million years old, yet already its disc appears to be full of forming planets. This one image alone will revolutionise theories of planet formation,” said Catherine Vlahakis, ALMA Deputy Program Scientist and Lead Program Scientist for the ALMA Long Baseline Campaign.

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This shows the protoplanetary disc surrounding the young star HL Tauri. The observations reveal substructures within the disc and show the possible positions of planets forming in the dark patches within the system. Image credit: ALMA (ESO/NAOJ/NRAO)

Stars are born when clouds of gas and dust eventually collapse due to the effects of gravitation, a process which creats a dense hot core that ignites to become a new star. The leftover gas and dust which is not consumed in creating the star then forms a protoplanetary disc. The gas and dust particles gradually clump together to form planets and rocky bodies such as asteroids and comets orbiting the star.

Looked at in visible light, HL Tauri appears shrouded by a dusty haze. ALMA looks at longer wavelengths and is able to pierce through this haze with such precision that it can see the detail of the structured protoplanetary disc and the gaps in the rings, evidence that asteroids, comets and planets are likely forming. The structures are seen in the image with a resolution of 5 Astronomical Units—five times the distance between the Sun and Earth (750 million km).

"These features are almost certainly the result of young planet-like bodies that are being formed in the disc. This is surprising since such young stars are not expected to have large planetary bodies capable of producing the structures we see in this image," explained Stuartt Corder, ALMA Deputy Director, in a press statement.

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This image compares the size of our Solar System with HL Tauri and its surrounding protoplanetary disc. Although the star is much smaller than the Sun, the disc around HL Tauri stretches out to almost three times as far from the star as Neptune is from the Sun. Image credit: ALMA (ESO/NAOJ/NRAO)

Between 25-30 of ALMA's 66 antennas were used for the observations that produced the image over several days. Whilst the image shows more detail than has ever previously been shown of a protoplanetary disk, sharper images could be taken in the future.

Catherine Vlahakis told Sen: "The ALMA antennas are periodically placed into different configurations, with the antennas either further apart or closer together. The configuration, or layout, of the array therefore changes regularly. In the future, a configuration that produces a slightly higher resolution—allowing slightly sharper images—may be possible.

"Another way to achieve sharper images is to make observations at higher frequencies. As part of the ALMA Science Verification process, we are making images of HL Tau at 233 GHz (the current image) and at 345 GHz."

ALMA, located in the Atacama desert in Chile, is an internationally funded and operated telescope array. The array is based at an altitude of 5,000 metres (16,000 feet). Click here to read Sen's feature on ALMA.