The latest report from the European Southern Observatory (ESO):

Beautiful nebula, violent history:
clash of stars solves stellar mystery

When astronomers looked at a stellar pair at the heart of a stunning cloud of gas and dust, they were in for a surprise. Star pairs are typically very similar, like twins, but in HD 148937, one star appears younger and, unlike the other, is magnetic. New data from the European Southern Observatory (ESO) suggest there were originally three stars in the system, until two of them clashed and merged. This violent event created the surrounding cloud and forever altered the system’s fate.

“When doing background reading, I was struck by how special this system seemed,”

says Abigail Frost, an astronomer at ESO in Chile and lead author of the study published today in Science. The system, HD 148937, is located about 3800 light-years away from Earth in the direction of the Norma constellation. It is made up of two stars much more massive than the Sun and surrounded by a beautiful nebula, a cloud of gas and dust.

“A nebula surrounding two massive stars is a rarity, and it really made us feel like something cool had to have happened in this system. When looking at the data, the coolness only increased.”

[Frost say:]

“After a detailed analysis, we could determine that the more massive star appears much younger than its companion, which doesn’t make any sense since they should have formed at the same time!”

The age difference — one star appears to be at least 1.5 million years younger than the other — suggests something must have rejuvenated the more massive star.

Another piece of the puzzle is the nebula surrounding the stars, known as NGC 6164/6165. It is 7500 years old, hundreds of times younger than both stars. The nebula also shows very high amounts of nitrogen, carbon and oxygen. This is surprising as these elements are normally expected deep inside a star, not outside; it is as if some violent event had set them free.

To unravel the mystery, the team assembled nine years’ worth of data from the PIONIER and GRAVITY instruments, both on ESO’s Very Large Telescope Interferometer (VLTI), located in Chile’s Atacama Desert. They also used archival data from the FEROS instrument at ESO’s La Silla Observatory.

“We think this system had at least three stars originally; two of them had to be close together at one point in the orbit whilst another star was much more distant,”

explains Hugues Sana, a professor at KU Leuven in Belgium and the principal investigator of the observations.

“The two inner stars merged in a violent manner, creating a magnetic star and throwing out some material, which created the nebula. The more distant star formed a new orbit with the newly merged, now-magnetic star, creating the binary we see today at the centre of the nebula.”

[Co-author Laurent Mahy, currently a senior researcher at the Royal Observatory of Belgium, adds: ]

“The merger scenario was already in my head back in 2017 when I studied nebula observations obtained with the European Space Agency’s Herschel Space Telescope,”

“Finding an age discrepancy between the stars suggests that this scenario is the most plausible one and it was only possible to show it with the new ESO data.”

This scenario also explains why one of the stars in the system is magnetic and the other is not — another peculiar feature of HD 148937 spotted in the VLTI data.

At the same time, it helps solve a long-standing mystery in astronomy: how massive stars get their magnetic fields. While magnetic fields are a common feature of low-mass stars like our Sun, more massive stars cannot sustain magnetic fields in the same way. Yet some massive stars are indeed magnetic.

Astronomers had suspected for some time that massive stars could acquire magnetic fields when two stars merge. But this is the first time researchers find such direct evidence of this happening. In the case of HD 148937, the merger must have happened recently.

“Magnetism in massive stars isn’t expected to last very long compared to the lifetime of the star, so it seems we have observed this rare event very soon after it happened,”

Frost adds.

ESO’s Extremely Large Telescope (ELT), currently under construction in the Chilean Atacama Desert, will enable researchers to work out what happened in the system in more detail, and perhaps reveal even more surprises.

Links

• Research paper (preprint; for the final version of the embargoed paper, please check https://www.eurekalert.org/press/scipak/ or contact scipak@aaas.org while the embargo lasts)
• Photos of the VLT/VLTI
• Find out more about ESO’s Extremely Large Telescope on our dedicated website and press kit
• For journalists: subscribe to receive our releases under embargo in your language
• For scientists: got a story? Pitch your research

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An Infinity of Worlds:
Cosmic Inflation and the Beginning of the Universe

A new report from the European Southern Observatory (ESO):

Groundbreaking survey reveals secrets of planet birth
around dozens of stars

In a series of studies, a team of astronomers has shed new light on the fascinating and complex process of planet formation. The stunning images, captured using the European Southern Observatory’s Very Large Telescope (ESO’s VLT) in Chile, represent one of the largest ever surveys of planet-forming discs. The research brings together observations of more than 80 young stars that might have planets forming around them, providing astronomers with a wealth of data and unique insights into how planets arise in different regions of our galaxy.

“This is really a shift in our field of study,”

says Christian Ginski, a lecturer at the University of Galway, Ireland, and lead author of one of three new papers published today in Astronomy & Astrophysics.

“We’ve gone from the intense study of individual star systems to this huge overview of entire star-forming regions.”

To date more than 5000 planets have been discovered orbiting stars other than the Sun, often within systems markedly different from our own Solar System. To understand where and how this diversity arises, astronomers must observe the dust- and gas-rich discs that envelop young stars — the very cradles of planet formation. These are best found in huge gas clouds where the stars themselves are forming.

Much like mature planetary systems, the new images showcase the extraordinary diversity of planet-forming discs.

“Some of these discs show huge spiral arms, presumably driven by the intricate ballet of orbiting planets,”

says Ginski.

“Others show rings and large cavities carved out by forming planets, while yet others seem smooth and almost dormant among all this bustle of activity,”

adds Antonio Garufi, an astronomer at the Arcetri Astrophysical Observatory, Italian National Institute for Astrophysics (INAF), and lead author of one of the papers.

The team studied a total of 86 stars across three different star-forming regions of our galaxy: Taurus and Chamaeleon I, both around 600 light-years from Earth, and Orion, a gas-rich cloud about 1600 light-years from us that is known to be the birthplace of several stars more massive than the Sun. The observations were gathered by a large international team, comprising scientists from more than 10 countries.

The team was able to glean several key insights from the dataset. For example, in Orion they found that stars in groups of two or more were less likely to have large planet-forming discs. This is a significant result given that, unlike our Sun, most stars in our galaxy have companions. As well as this, the uneven appearance of the discs in this region suggests the possibility of massive planets embedded within them, which could be causing the discs to warp and become misaligned.

While planet-forming discs can extend for distances hundreds of times greater than the distance between Earth and the Sun, their location several hundreds of light-years from us makes them appear as tiny pinpricks in the night sky. To observe the discs, the team employed the sophisticated Spectro-Polarimetric High-contrast Exoplanet REsearch instrument (SPHERE) mounted on ESO’s VLT. SPHERE’s state-of-the-art extreme adaptive optics system corrects for the turbulent effects of Earth’s atmosphere, yielding crisp images of the discs. This meant the team were able to image discs around stars with masses as low as half the mass of the Sun, which are typically too faint for most other instruments available today. Additional data for the survey were obtained using the VLT’s X-shooter instrument, which allowed astronomers to determine how young and how massive the stars are. The Atacama Large Millimeter/submillimeter Array (ALMA), in which ESO is a partner, on the other hand, helped the team understand more about the amount of dust surrounding some of the stars.

As technology advances, the team hopes to delve even deeper into the heart of planet-forming systems. The large 39-metre mirror of ESO’s forthcoming Extremely Large Telescope (ELT), for example, will enable the team to study the innermost regions around young stars, where rocky planets like our own might be forming.

For now, these spectacular images provide researchers with a treasure trove of data to help unpick the mysteries of planet formation.

“It is almost poetic that the processes that mark the start of the journey towards forming planets and ultimately life in our own Solar System should be so beautiful,”

concludes Per-Gunnar Valegård, a doctoral student at the University of Amsterdam, the Netherlands, who led the Orion study. Valegård, who is also a part-time teacher at the International School Hilversum in the Netherlands, hopes the images will inspire his pupils to become scientists in the future.

Links

• Research paper
• Photos of the VLT
• Find out more about ESO’s Extremely Large Telescope on our dedicated website and press kit
• For journalists: subscribe to receive our releases under embargo in your language
• For scientists: got a story? Pitch your research

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An Infinity of Worlds:
Cosmic Inflation and the Beginning of the Universe

Another report from the European Southern Observatory (ESO):

Astronomers reveal a new link
between water and planet formation

Researchers have found water vapour in the disc around a young star exactly where planets may be forming. Water is a key ingredient for life on Earth, and is also thought to play a significant role in planet formation. Yet, until now, we had never been able to map how water is distributed in a stable, cool disc — the type of disc that offers the most favourable conditions for planets to form around stars. The new findings were made possible thanks to the Atacama Large Millimeter/submillimeter Array (ALMA), in which the European Southern Observatory (ESO) is a partner.

“I had never imagined that we could capture an image of oceans of water vapour in the same region where a planet is likely forming,”

says Stefano Facchini, an astronomer at the University of Milan, Italy, who led the study published today in Nature Astronomy. The observations reveal at least three times as much water as in all of Earth’s oceans in the inner disc of the young Sun-like star HL Tauri, located 450 light-years away from Earth in the constellation Taurus.

“It is truly remarkable that we can not only detect but also capture detailed images and spatially resolve water vapour at a distance of 450 light-years from us ,”

adds co-author Leonardo Testi, an astronomer at the University of Bologna, Italy. The ‘spatially resolved’ observations with ALMA allow astronomers to determine the distribution of water in different regions of the disc.

“Taking part in such an important discovery in the iconic HL Tauri disc was beyond what I had ever expected for my first research experience in astronomy,”

adds Mathieu Vander Donckt from the University of Liège, Belgium, who was a master’s student when he participated in the research.

A significant amount of water was found in the region where a known gap in the HL Tauri disc exists. Ring-shaped gaps are carved out in gas- and dust-rich discs by orbiting young planet-like bodies as they gather up material and grow.

Our recent images reveal a substantial quantity of water vapour at a range of distances from the star that include a gap where a planet could potentially be forming at the present time,”

says Facchini. This suggests that this water vapour could affect the chemical composition of planets forming in those regions.

Observing water with a ground-based telescope is no mean feat as the abundant water vapour in Earth’s atmosphere degrades the astronomical signals. ALMA, operated by ESO together with its international partners, is an array of telescopes in the Chilean Atacama Desert at about 5000 metres elevation that was built in a high and dry environment specifically to minimise this degradation, providing exceptional observing conditions.

“To date, ALMA is the only facility able to spatially resolve water in a cool planet-forming disc,”

says co-author Wouter Vlemmings, a professor at the Chalmers University of Technology in Sweden [1].

“It is truly exciting to directly witness, in a picture, water molecules being released from icy dust particles,”

says Elizabeth Humphreys, an astronomer at ESO who also participated in the study. The dust grains that make up a disc are the seeds of planet formation, colliding and clumping into ever larger bodies orbiting the star. Astronomers believe that where it is cold enough for water to freeze onto dust particles, things stick together more efficiently — an ideal spot for planet formation.

“Our results show how the presence of water may influence the development of a planetary system, just like it did some 4.5 billion years ago in our own Solar System,”

Facchini adds.

With upgrades happening at ALMA and ESO’s Extremely Large Telescope (ELT) coming online within the decade, planet formation and the role water plays in it will become clearer than ever.  In particular METIS, the Mid-infrared ELT Imager and Spectrograph, will give astronomers unrivalled views of the inner regions of planet-forming discs, where planets like Earth form.

Notes

[1] The new observations used the Band 5 and Band 7 receivers on ALMA. Bands 5 and 7 were European developments, at Chalmers/NOVA (Netherlands Research School for Astronomy) and IRAM (Institut de radioastronomie millimétrique), respectively, with involvement of ESO. Band 5 expanded ALMA into a new frequency range specifically for detecting and imaging water in the local Universe. In this study, the team observed three spectral lines of water across the two receiver frequency ranges to map gas at different temperatures within the disc.

Links

• Research paper (pre-print version, with provisional title)
• Photos of ALMA
• Find out more about ESO’s Extremely Large Telescope on our dedicated website and press kit
• For journalists: subscribe to receive our releases under embargo in your language
• For scientists: got a story? Pitch your research

=== Amazon Ads ===

Celestron – NexStar 130SLT Computerized Telescope –
Compact and Portable –
Newtonian Reflector Optical Design –
SkyAlign Technology –
Computerized Hand Control –
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For the Love of Mars:
A Human History of the Red Planet