ALMA Discovers Trio of Infant Planets
Planets in the making
The young star HD 163296 in the constellation of Sagittarius
Surroundings of the young star HD 163296
ALMA Discovers Trio of Infant Planets
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ESOcast 164 Light: ALMA Discovers Trio of Infant Planets (4K UHD)
Zooming in on the young star HD 163296
Two independent teams of astronomers have
used ALMA to uncover convincing evidence that three young planets are
in orbit around the infant star HD 163296. Using a novel planet-finding
technique, the astronomers identified three disturbances in the
gas-filled disc around the young star: the strongest evidence yet that
newly formed planets are in orbit there. These are considered the first
planets to be discovered with ALMA.
The Atacama Large Millimeter/submillimeter Array (ALMA) has transformed our understanding of protoplanetary discs
— the gas- and dust-filled planet factories that encircle young stars.
The rings and gaps in these discs provide intriguing circumstantial
evidence for the presence of protoplanets [1]. Other phenomena, however, could also account for these tantalising features.
But now, using a novel planet-hunting technique that identifies
unusual patterns in the flow of gas within a planet-forming disc around a
young star, two teams of astronomers have each confirmed distinct,
telltale hallmarks of newly formed planets orbiting an infant star [2].
“Measuring the flow of gas within a protoplanetary disc gives us
much more certainty that planets are present around a young star,” said Christophe Pinte of Monash University in Australia and Institut de Planétologie et d'Astrophysique de Grenoble (Université de Grenoble-Alpes/CNRS) in France, and lead author on one of the two papers. “This technique offers a promising new direction to understand how planetary systems form.”
To make their respective discoveries, each team analysed ALMA observations of HD 163296, a young star about 330 light-years from Earth in the constellation of Sagittarius (The Archer) [3]. This star is about twice the mass of the Sun but is just four million years old — just a thousandth of the age of the Sun.
“We looked at the localised, small-scale motion of gas in the
star’s protoplanetary disc. This entirely new approach could uncover
some of the youngest planets in our galaxy, all thanks to the
high-resolution images from ALMA,” said Richard Teague, an astronomer at the University of Michigan and principal author on the other paper.
Rather than focusing on the dust within the disc, which was clearly imaged in earlier ALMA observations,
the astronomers instead studied carbon monoxide (CO) gas spread
throughout the disc. Molecules of CO emit a very distinctive
millimetre-wavelength light that ALMA can observe in great detail.
Subtle changes in the wavelength of this light due to the Doppler effect reveal the motions of the gas in the disc.
The team led by Teague identified two planets located approximately
12 billion and 21 billion kilometres from the star. The other team, led
by Pinte, identified a planet at about 39 billion kilometres from the
star [4].
The two teams used variations on the same technique, which looks for
anomalies in the flow of gas — as evidenced by the shifting wavelengths
of the CO emission — that indicate the gas is interacting with a massive
object [5].
The technique used by Teague, which derived averaged variations in
the flow of the gas as small as a few percent, revealed the impact of
multiple planets on the gas motions nearer to the star. The technique
used by Pinte, which more directly measured the flow of the gas, is
better suited to studying the outer portion of the disc. It allowed the
authors to more accurately locate the third planet, but is restricted to
larger deviations of the flow, greater than about 10%.
In both cases, the researchers identified areas where the flow of the
gas did not match its surroundings — a bit like eddies around a rock in
a river. By carefully analysing this motion, they could clearly see the
influence of planetary bodies similar in mass to Jupiter.
This new technique allows astronomers to more precisely estimate
protoplanetary masses and is less likely to produce false positives. “We are now bringing ALMA front and centre into the realm of planet detection,” said coauthor Ted Bergin of the University of Michigan.
Both teams will continue refining this method and will apply it to
other discs, where they hope to better understand how atmospheres are
formed and which elements and molecules are delivered to a planet at its
birth.
Notes
Notes
[1] Although thousands of exoplanets have been discovered in the last
two decades, detecting protoplanets remains at the cutting edge of
science and there have been no unambiguous detections before now. The
techniques currently used for finding exoplanets in fully formed
planetary systems — such as measuring the wobble of a star or the
dimming of starlight due to a transiting planet — do not lend themselves
to detecting protoplanets.
[2] The motion of gas around a star in
the absence of planets has a very simple, predictable pattern
(Keplerian rotation) that is nearly impossible to alter both coherently
and locally, so that only the presence of a relatively massive object
can create such disturbances.
[3] ALMA’s stunning images of HD 163296 and other similar systems
have revealed intriguing patterns of concentric rings and gaps within
protoplanetary discs. These gaps may be evidence that protoplanets are
ploughing the dust and gas away from their orbits, incorporating some of
it into their own atmospheres. A previous study
of this particular star’s disc shows that the gaps in the dust and gas
overlap, suggesting that at least two planets have formed there.
These initial observations, however, merely provided circumstantial
evidence and could not be used to accurately estimate the masses of the
planets.
[5] This technique is similar to the
one that led to the discovery of the planet Neptune in the nineteenth
century. In that case anomalies in the motion of the planet Uranus were
traced to the gravitational effect of an unknown body, which was
subsequently discovered visually in 1846 and found to be the eighth
planet in the Solar System.
More Information
This research was presented in two papers to appear in the same edition of the Astrophysical Journal Letters.
The first is entitled “Kinematic evidence for an embedded protoplanet
in a circumstellar disc”, by C. Pinte et al. and the second “A Kinematic
Detection of Two Unseen Jupiter Mass Embedded Protoplanets”, by R.
Teague et al.
The Pinte team is composed of: C. Pinte (Monash University, Clayton,
Victoria, Australia; Univ. Grenoble Alpes, CNRS, IPAG, Grenoble,
France), D. J. Price (Monash University, Clayton, Victoria, Australia),
F. Ménard (Univ. Grenoble Alpes, CNRS, IPAG, Grenoble, France), G.
Duchêne (University of California, Berkeley California, USA; Univ.
Grenoble Alpes, CNRS, IPAG, Grenoble, France), W.R.F. Dent (Joint ALMA
Observatory, Santiago, Chile), T. Hill (Joint ALMA Observatory,
Santiago, Chile), I. de Gregorio-Monsalvo (Joint ALMA Observatory,
Santiago, Chile), A. Hales (Joint ALMA Observatory, Santiago, Chile;
National Radio Astronomy Observatory, Charlottesville, Virginia, USA)
and D. Mentiplay (Monash University, Clayton, Victoria, Australia).
The Teague team is composed of: Richard D. Teague (University of
Michigan, Ann Arbor, Michigan, USA), Jaehan Bae (Department of
Terrestrial Magnetism, Carnegie Institution for Science, Washington, DC,
USA), Edwin A. Bergin (University of Michigan, Ann Arbor, Michigan,
USA), Tilman Birnstiel (University Observatory,
Ludwig-Maximilians-Universität München, Munich, Germany) and Daniel
Foreman- Mackey (Center for Computational Astrophysics, Flatiron
Institute, New York, USA).
The Atacama Large Millimeter/submillimeter Array (ALMA), an
international astronomy facility, is a partnership of ESO, the U.S.
National Science Foundation (NSF) and the National Institutes of Natural
Sciences (NINS) of Japan in cooperation with the Republic of Chile.
ALMA is funded by ESO on behalf of its Member States, by NSF in
cooperation with the National Research Council of Canada (NRC) and the
National Science Council of Taiwan (NSC) and by NINS in cooperation with
the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space
Science Institute (KASI). ALMA construction and operations are led by
ESO on behalf of its Member States; by the National Radio Astronomy
Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on
behalf of North America; and by the National Astronomical Observatory of
Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO)
provides the unified leadership and management of the construction,
commissioning and operation of ALMA. ESO is the foremost
intergovernmental astronomy organisation in Europe and the world’s most
productive ground-based astronomical observatory by far. It has 15
Member States: Austria, Belgium, the Czech Republic, Denmark, France,
Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain,
Sweden, Switzerland and the United Kingdom, along with the host state of
Chile and with Australia as a strategic partner. ESO carries out an
ambitious programme focused on the design, construction and operation of
powerful ground-based observing facilities enabling astronomers to make
important scientific discoveries. ESO also plays a leading role in
promoting and organising cooperation in astronomical research. ESO
operates three unique world-class observing sites in Chile: La Silla,
Paranal and Chajnantor. At Paranal, ESO operates the Very Large
Telescope and its world-leading Very Large Telescope Interferometer as
well as two survey telescopes, VISTA working in the infrared and the
visible-light VLT Survey Telescope. ESO is also a major partner in two
facilities on Chajnantor, APEX and ALMA, the largest astronomical
project in existence. And on Cerro Armazones, close to Paranal, ESO is
building the 39-metre Extremely Large Telescope, the ELT, which will
become “the world’s biggest eye on the sky”.
Links
- Research paper Pinte et al. in Astrophysical Journal Letters
- Research paper Teague et al. in Astrophysical Journal Letters
- Photos of ALMA
Contacts
Christophe Pinte
Monash University
Clayton, Victoria, Australia
Tel: +61 4 90 30 24 18
Email: christophe.pinte@univ-grenoble-alpes.fr
Richard Teague
University of Michigan
Ann Arbor, Michigan, USA
Tel: +1 734 764 3440
Email: rteague@umich.edu
Calum Turner
ESO Assistant Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6670
Email: calum.turner@eso.org
Source: ESO/News
