Washington | Scientists have captured new images of a young star, located about 450 light-years away from Earth, which show the very earliest stages in the formation of planets.
The scientists used the Karl G Jansky Very Large Array (VLA) to see unprecedented detail of the inner portion of a dusty disk surrounding the star. The star and its disk were studied in 2014 with the Atacama Large Millimetre/submillimetre Array (ALMA), which produced what astronomers then called the best image ever of planet formation in progress. The ALMA image showed gaps in the disk, caused by planet-like bodies sweeping out the dust along their orbits.
The star, called HL Tau, is only about a million years old – very young by stellar standards. The ALMA image showed details of the system in the outer portions of the disk, but in the inner portions of the disk, nearest to the young star, the thicker dust is opaque to the short radio wavelengths received by ALMA. To study this region, astronomers turned to the VLA, which receives longer wavelengths. The new VLA images showed a distinct clump of dust in the inner region of the disk.
The clump contains roughly three to eight times the mass of the Earth, researchers said. We believe this clump of dust represents the earliest stage in the formation of protoplanets, and this is the first time we’ve seen that stage, said Thomas Henning, of the Max Planck Institute for Astronomy (MPIA) in Germany.
This is an important discovery, because we have not yet been able to observe most stages in the process of planet formation, said Carlos Carrasco-Gonzalez from the Institute of Radio Astronomy and Astrophysics (IRyA) of the National Autonomous University of Mexico (UNAM). The VLA data indicates that the inner region of the disk contains grains as large as one centimetre in diameter. This region is presumably where Earth-like planets would form, as clumps of dust grow by pulling in material from their surroundings, scientists say.
Eventually, the clumps would gather enough mass to form solid bodies that would continue to grow into planets. The VLA observations, made in 2014 and 2015, received radio waves with a wavelength of 7 millimetres. The earlier ALMA observations of HL Tau were made at a wavelength of 1 millimetre.
The VLA images showed a similar level of detail as the ALMA images. These VLA observations are the most sensitive and show the most detail of any yet made of HL Tau’s disk at these longer wavelengths, said Claire Chandler, of the National Radio Astronomy Observatory (NRAO) in US. The VLA’s ability to produce such high-quality images in this region is very important to advancing our understanding of these initial stages of planet formation, Chandler said.
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