Atacama Large Millimetre/submillimetre Array (ALMA) antennas

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13-Dec-2018: ALMA finds protoplanetary disks depicting planet formation

Astronomers have obtained stunning, high-resolution images of 20 nearby protoplanetary disks, depicting the birth of planets, using Chile's Atacama Large Millimeter/submillimeter Array (ALMA).

The observations are part of a major ALMA initiative known as the Disk Substructures at High Angular Resolution Project, or DSHARP campaign.

According to the researchers, the most compelling interpretation of these observations is that large planets, likely similar in size and composition to Neptune or Saturn, form quickly, much faster than current theory would allow. It may also help explain how smaller rocky planets manage to survive in the chaos of young systems.

The goal of this months-long observing campaign was to search for structural commonalities and differences in protoplanetary disks. ALMA's remarkably sharp vision has revealed previously unseen structures and unexpectedly complex pattern.

Leading models for planet formation hold that planets are born by the gradual accumulation of dust and gas inside a protoplanetary disk, a process that takes many millions of years to unfold. This suggests that its impact on protoplanetary disks would be most prevalent in older, more mature systems.

But ALMA's early observations of young protoplanetary disks, some only about one million years old, reveal surprisingly well-defined structures, including prominent rings and gaps, which appear to be the hallmarks of planets. It was important to find out whether these were anomalies or if those signatures were common in disks.

The DSHARP campaign was designed to do precisely that by studying the relatively small-scale distribution of dust particles around 20 nearby protoplanetary disks. These dust particles naturally glow in millimeter-wavelength light, enabling ALMA to precisely map the density distribution of small, solid particles around young stars.

13-Jun-2018: ALMA discovers trio of infant planets around newborn star

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. Other phenomena, however, could also account for these tantalizing 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.

Measuring the flow of gas within a protoplanetary disc gives us much more certainty that planets are present around a young star. 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). 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.

The localised, small-scale motion of gas in the star’s protoplanetary disc was observed. This entirely new approach could uncover some of the youngest planets in our galaxy.

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.

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.

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.

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.

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13-Dec-2018: ALMA finds protoplanetary disks depicting planet formation

Astronomers have obtained stunning, high-resolution images of 20 nearby protoplanetary disks, depicting the birth of planets, using Chile's Atacama Large Millimeter/submillimeter Array (ALMA).

The observations are part of a major ALMA initiative known as the Disk Substructures at High Angular Resolution Project, or DSHARP campaign.

According to the researchers, the most compelling interpretation of these observations is that large planets, likely similar in size and composition to Neptune or Saturn, form quickly, much faster than current theory would allow. It may also help explain how smaller rocky planets manage to survive in the chaos of young systems.

The goal of this months-long observing campaign was to search for structural commonalities and differences in protoplanetary disks. ALMA's remarkably sharp vision has revealed previously unseen structures and unexpectedly complex pattern.

Leading models for planet formation hold that planets are born by the gradual accumulation of dust and gas inside a protoplanetary disk, a process that takes many millions of years to unfold. This suggests that its impact on protoplanetary disks would be most prevalent in older, more mature systems.

But ALMA's early observations of young protoplanetary disks, some only about one million years old, reveal surprisingly well-defined structures, including prominent rings and gaps, which appear to be the hallmarks of planets. It was important to find out whether these were anomalies or if those signatures were common in disks.

The DSHARP campaign was designed to do precisely that by studying the relatively small-scale distribution of dust particles around 20 nearby protoplanetary disks. These dust particles naturally glow in millimeter-wavelength light, enabling ALMA to precisely map the density distribution of small, solid particles around young stars.

13-Jun-2018: ALMA discovers trio of infant planets around newborn star

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. Other phenomena, however, could also account for these tantalizing 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.

Measuring the flow of gas within a protoplanetary disc gives us much more certainty that planets are present around a young star. 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). 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.

The localised, small-scale motion of gas in the star’s protoplanetary disc was observed. This entirely new approach could uncover some of the youngest planets in our galaxy.

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.

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.

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.

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.

2017

21-Jan-2017: Scientists discover sunspot with centre twice the size of Earth.

A dark, contorted centre of a sunspot nearly twice the diameter of the Earth, along with other invisible details of our Sun, has been discovered by scientists.

Astronomers have harnessed ALMA’s capabilities to image the millimetre-wavelength light emitted by the Sun’s chromosphere(region that lies just above the photosphere, which forms the visible surface of the Sun).

Researchers including those from European Southern Observatory (ESO), produced the images as a demonstration of ALMA’s ability to study solar activity at longer wavelengths of light than are typically available to solar observatories on Earth.

Astronomers have studied the Sun and probed its dynamic surface and energetic atmosphere in many ways through the centuries.

To achieve a fuller understanding, astronomers need to study it across the entire electromagnetic spectrum, including the millimetre and submillimetre portion that ALMA can observe. Since the Sun is many billions of times brighter than the faint objects ALMA typically observes, the ALMA antennas were specially designed to allow them to image the Sun in exquisite detail using the technique of radio interferometry - and avoid damage from the intense heat of the focused sunlight.

The team observed an enormous sunspot at wavelengths of 1.25 millimeters and three millimetres using two of ALMA's receiver bands. The images reveal differences in temperature between parts of the Sun's chromosphere.

Understanding the heating and dynamics of the chromosphere are key areas of research that will be addressed in the future using ALMA.

Sunspots are transient features that occur in regions where the Sun's magnetic field is extremely concentrated and powerful. They are lower in temperature than the surrounding regions, which is why they appear relatively dark.

The difference in appearance between the two images is due to the different wavelengths of emitted light being observed.

Observations at shorter wavelengths are able to probe deeper into the Sun, meaning the 1.25 millimetre images show a layer of the chromosphere that is deeper, and therefore closer to the photosphere, than those made at a wavelength of three millimetres.