TMC1A is a still
developing star in the constellation Taurus. Red are areas with many
dust particles. Green and blue are two types of carbon monoxide. The
absence of green / blue carbon monoxide in the inner part indicates that
dust particles in the young protoplanetary disk have grown from less
than a thousandth of a millimeter to a millimeter. (c) Jørgensen/Harsono/ESASky/ESAC [CC-BY-SA 3.0]
Artistic impression of a star with a protoplanetary disk and growing grains.
(c) Daria Dall'Olio [CC-BY-SA 3.0]
A European team of astronomers has discovered that dust particles around
a star already coagulate before the star is fully grown. Dust particle
growth is the first step in the formation of planets. The researchers
from the Netherlands, Sweden and Denmark publish their findings in
Nature Astronomy.
In recent years, astronomers have discovered numerous planetary systems
around other stars. Almost every star is likely to have at least one
planet orbiting it. Some of the major questions are centered around how
planetary systems form and how this process leads to the observed
diversity of planets in numbers and masses. The results of a European
research project suggest that planet formation starts very early in the
star formation process.
The researchers used the Atacama Large Millimeter Array for their
discovery. ALMA is a collection of 66 linked radio telescopes spread
over 16 kilometer in the Atacama desert in Chile. The researchers
pointed the telescope toward TMC1A, a still developing star in the
constellation Taurus (the Bull).
The astronomers saw a striking lack of carbon monoxide radiation in a
disc-shaped area near the star. They suspected that the radiation was
blocked by big dust particles. Using numerical models, they could
demonstrate that indeed the dust particles in the young protoplanetary
disk have probably grown from a thousandth of a millimeter to a
millimeter.
Lead researcher Daniel Harsono (Leiden University, the Netherlands)
explains why this is so surprising: "The results indicate that planets
already start forming while the star is still developing. The star is
only half to three-quarters of its final mass. This is new."
Per Bjerkeli (Chalmers University, Sweden) highlights the implication of
early grain growth: "It can be an explanation for the formation of
giant planets that are comparable to Jupiter and Saturn. Only early
protoplanetary discs contain sufficient mass to form giant planets."
Co-researcher Matthijs van der Wiel (ASTRON, Netherlands Institute for
Radio Astronomy) is pleased with the clear and unambiguous observations.
"This early particle growth could be an exception, of course. Maybe
this young disk is very special."
In the future, the researchers want to look for tell-tale signs of
planet formation around other protostars in similar manner. "Currently,
ALMA is the only observatory capable of resolving dust and gas emission
at scales where new planets are forming, matching the scales in our
Solar system. In the future, similarly high resolution observations will
be attained with the dishes of the Square Kilometre Array (SKA) to be
built in South Africa. Compared with ALMA’s millimeter wave detectors,
the SKA will be sensitive to wavelengths of 2 cm and above, and will
therefore help to localize centimeter-sized grains, the next step up in
the journey from tiny dust particles to planets," says Van der Wiel.
Reference:
"Evidence for the start of planet formation in a young circumstellar disk."
By: Daniel Harsono (1), Per Bjerkeli (2), Matthijs H.D. van der Wiel
(4), Jon P. Ramsey (3), Luke T. Maud (1), Lars E. Kristensen (3) &
Jes K. Jørgensen (3). 1. Leiden University, the Netherlands. 2. Chalmers
University of Technology, Sweden. 3. University of Copenhagen, Danmark.
4. ASTRON, Dwingeloo, the Netherlands. In: Nature Astronomy, 25 June
2018.
