By using the Atacama Large Millimeter/submillimeter Array (ALMA), Japanese astronomers have spotted strong evidence of a massive planet-forming disk around a young star known as HD 142527.
HD 142527 lies in the constellation Lupus at a distance of about 457 light-years from Earth.
The astronomers have used ALMA to detect the submillimeter emission from the dust ring around this baby star. The emission has a non-uniform distribution and the northern side is 30 times brighter than the faint southern side, according to the team.
Recent near-infrared observations with the NAOJ Subaru Telescope revealed that protoplanetary disks have structures that are far more complex than astronomers expected. Spiral or gap structures are thought to be associated with hidden planets in the disk.
However, it is impossible to measure the amount of dust and gas in the densest part of the disk by near-infrared observations. Since near-infrared light is easily absorbed or scattered by a large amount of dust, it isn’t suitable for observing the innermost part of the dense region of the disk. Then, the key to the solution will be millimeter and submillimeter wave.
The new image of HD 142527, which was taken with ALMA, shows that cosmic dust is circling around the star in a form of asymmetric ring.
By measuring the density of dust in the densest part of the ring, the astronomers found that it is highly possible that Jupiter-like giant gaseous exoplanets or Earth-like rocky planets are now being formed in that region. This region is far from the central star, about 5 times larger than the distance between the Sun and the Neptune.
“We are very surprised at the brightness of the northern side,” said Dr Misato Fukagawa of Osaka University, who is the lead author of the paper appearing in the Publications of the Astronomical Society of Japan (full paper in .pdf / arXiv.org version).
“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 material is accumulated in this position. 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 calculating the amount of material based on the submillimeter emission strength, the temperature of the material is an important parameter. The scientists estimated the temperature in the dense region from the observations of isotopomers of carbon monoxide and reached two possibilities – formation of gaseous giant planet or rocky planet.
If the abundance of dust and gas is comparable to that in typical environment in the Universe, 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. 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. 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 exoplanets are being formed in the dense part of the disk around HD142527.
The astronomers plan 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.
Fukagawa M et al. 2013. Local Enhancement of Surface Density in the Protoplanetary Ring Surrounding HD 142527. Publ. Astron. Soc. Japan 65, L14