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Three baby planets spotted around infant star

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Two independent teams of astronomers have discovered three baby planets forming around an infant star using a new technique.

Scientists' using the Atacama Large Millimetre Array (ALMA) telescope have been able to examine the protoplanetary disks circling young stars.

The telescope is based in the Atacama desert, in Chile, at an elevation of 5km.

The new technique analyses unusual patterns in how gas moves around the dusty disks that protoplanets are made of, and both teams used it to confirm that baby planets were forming around an infant star in the Milky Way.

In a pair of papers published in Astrophysical Journal Letters, the teams explain how they analysed the data captured by ALMA's array of 66 radio telescopes when they were pointed at the young star HD 163296.

HD 163296 is only 4 million years old, a newborn infant compared to our Sun's 4.6 billion years, and is located about 330 light-years from Earth towards the constellation Sagittarius.

Image: ALMA's radio telescope antennas at an elevation of 5km in the Atacama

The astronomers studied the distribution and motion of carbon monoxide gas throughout the disk, which emits a specific wavelength of light that ALMA is designed to detect.

Subtle changes in the wavelength of that light as it travelled through the gas allowed the scientists to figure out what was orbiting the star.

Analysing the mass and velocity of the gas in protoplanetary disks was the crucial ability allowed by ALMA's high-resolution data on the flow of carbon monoxide throughout the disks.

"The precision is mind boggling," said co-author Dr Til Birnstiel of the University Observatory of Munich.

In a system where gas rotates at about 5km per second, ALMA detected velocity changes as small as a few metres per second, said the scientists.

ALMA image of the protoplanetary disk surrounding the young star HD 163296 as seen in dust. Credit: ALMA (ESO/NAOJ/NRAO); A. Isella; B. Saxton (NRAO/AUI/NSF)
Image: ALMA image of the protoplanetary disk surrounding the young star HD 163296. Pic: ALMA

"Though thousands of exoplanets [planets orbiting stars outside of our solar system] have been discovered in the last few decades, detecting protoplanets is at the frontier of science," said Dr Christophe Pinte, lead author on one of the two papers.

The current techniques that astronomers use to find exoplanets don't work for protoplanets, which aren't massive enough to make the star wobble or to dim the light of the star when they pass between it and the telescope.

The images captured by ALMA of HD 163296 show concentric rings and gaps around the star, which scientists believe are the protoplanetary disks.

According to the astronomers, the gaps suggest that the protoplanets are absorbing the dust and gas within these rings into their own atmospheres.

A previous study of HD 163296 showed that the dust and gas gaps overlap, suggesting that at least two planets have formed there.

ALMA has uncovered convincing evidence that three young planets are in orbit around the infant star HD 163296. Using a novel planet-finding technique, astronomers have identified three discrete disturbances in the young star's gas-filled disc: the strongest evidence yet that newly formed planets are in orbit there. These are considered the first planets discovered with ALMA.This image shows part of the ALMA data set at one wavelength and reveals a clear 'kink' in the material, which indicates un
Image: The ALMA data set shows a 'kink' in the material, which indicates a planets. Pic: ALMA

Dr Richard Teague, an astronomer at the University of Michigan and principal author on one of the papers, said that the rings only provided circumstantial evidence of the baby planets however.

"Since other mechanisms can also produce ringed gaps in a protoplanetary disk, it is impossible to say conclusively that planets are there by merely looking at the overall structure of the disk," said Dr Teague.

The new technique "allows us to find very small deviations from the expected normal rotation in a disk," Dr Teague added.

This was caused by the protoplanets changing the density of the gas near their orbits which subsequently changes the pressure of the gas and its velocity.

"We compared the observations with computer models to show that the observed flows fit beautifully with predictions for the flow pattern around a newborn planet a few times the mass of Jupiter," said co-author Dr Daniel Price.

Both teams of astronomers will continue refining the method of analysis.

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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.

Original Article

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