Category Archives: Astronomy

ESO: Five exoplanets found locked in a rhythmic dance

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

Puzzling six-exoplanet system with rhythmic movement
challenges theories of how planets form

This artist’s impression shows the view from the planet in the TOI-178 system found orbiting furthest from the star. New research by Adrien Leleu and his colleagues with several telescopes, including ESO’s Very Large Telescope, has revealed that the system boasts six exoplanets and that all but the one closest to the star are locked in a rare rhythm as they move in their orbits.  But while the orbital motion in this system is in harmony, the physical properties of the planets are more disorderly, with significant variations in density from planet to planet. This contrast challenges astronomers’ understanding of how planets form and evolve. This artist’s impression is based on the known physical parameters for the planets and the star seen, and uses a vast database of objects in the Universe.Credits: ESO

Using a combination of telescopes, including the Very Large Telescope of the European Southern Observatory (ESO’s VLT), astronomers have revealed a system consisting of six exoplanets, five of which are locked in a rare rhythm around their central star. The researchers believe the system could provide important clues about how planets, including those in the Solar System, form and evolve.

The first time the team observed TOI-178, a star some 200 light-years away in the constellation of Sculptor, they thought they had spotted two planets going around it in the same orbit. However, a closer look revealed something entirely different.

“Through further observations we realised that there were not two planets orbiting the star at roughly the same distance from it, but rather multiple planets in a very special configuration,”

says Adrien Leleu from the Université de Genève and the University of Bern, Switzerland, who led a new study of the system published today in Astronomy & Astrophysics.

The new research has revealed that the system boasts six exoplanets and that all but the one closest to the star are locked in a rhythmic dance as they move in their orbits. In other words, they are in resonance. This means that there are patterns that repeat themselves as the planets go around the star, with some planets aligning every few orbits. A similar resonance is observed in the orbits of three of Jupiter’s moons: Io, Europa and Ganymede. Io, the closest of the three to Jupiter, completes four full orbits around Jupiter for every orbit that Ganymede, the furthest away, makes, and two full orbits for every orbit Europa makes.

The five outer exoplanets of the TOI-178 system follow a much more complex chain of resonance, one of the longest yet discovered in a system of planets. While the three Jupiter moons are in a 4:2:1 resonance, the five outer planets in the TOI-178 system follow a 18:9:6:4:3 chain: while the second planet from the star (the first in the resonance chain) completes 18 orbits, the third planet from the star (second in the chain) completes 9 orbits, and so on. In fact, the scientists initially only found five planets in the system, but by following this resonant rhythm they calculated where in its orbit an additional planet would be when they next had a window to observe the system.

More than just an orbital curiosity, this dance of resonant planets provides clues about the system’s past.

“The orbits in this system are very well ordered, which tells us that this system has evolved quite gently since its birth,”

explains co-author Yann Alibert from the University of Bern. If the system had been significantly disturbed earlier in its life, for example by a giant impact, this fragile configuration of orbits would not have survived.

Disorder in the rhythmic system

But even if the arrangement of the orbits is neat and well-ordered, the densities of the planets

“are much more disorderly,” says Nathan Hara from the Université de Genève, Switzerland, who was also involved in the study. “It appears there is a planet as dense as the Earth right next to a very fluffy planet with half the density of Neptune, followed by a planet with the density of Neptune. It is not what we are used to.”

In our Solar System, for example, the planets are neatly arranged, with the rocky, denser planets closer to the central star and the fluffy, low-density gas planets farther out.

“This contrast between the rhythmic harmony of the orbital motion and the disorderly densities certainly challenges our understanding of the formation and evolution of planetary systems,”

says Leleu.

Combining techniques

To investigate the system’s unusual architecture, the team used data from the European Space Agency’s CHEOPS satellite, alongside the ground-based ESPRESSO instrument on ESO’s VLT and the NGTS and SPECULOOS, both sited at ESO’s Paranal Observatory in Chile. Since exoplanets are extremely tricky to spot directly with telescopes, astronomers must instead rely on other techniques to detect them. The main methods used are imaging transits — observing the light emitted by the central star, which dims as an exoplanet passes in front of it when observed from the Earth — and radial velocities — observing the star’s light spectrum for small signs of wobbles which happen as the exoplanets move in their orbits. The team used both methods to observe the system: CHEOPS, NGTS and SPECULOOS for transits and ESPRESSO for radial velocities.

By combining the two techniques, astronomers were able to gather key information about the system and its planets, which orbit their central star much closer and much faster than the Earth orbits the Sun. The fastest (the innermost planet) completes an orbit in just a couple of days, while the slowest takes about ten times longer. The six planets have sizes ranging from about one to about three times the size of Earth, while their masses are 1.5 to 30 times the mass of Earth. Some of the planets are rocky, but larger than Earth — these planets are known as Super-Earths. Others are gas planets, like the outer planets in our Solar System, but they are much smaller — these are nicknamed Mini-Neptunes.

Although none of the six exoplanets found lies in the star’s habitable zone, the researchers suggest that, by continuing the resonance chain, they might find additional planets that could exist in or very close to this zone. ESO’s Extremely Large Telescope (ELT), which is set to begin operating this decade, will be able to directly image rocky exoplanets in a star’s habitable zone and even characterise their atmospheres, presenting an opportunity to get to know systems like TOI-178 in even greater detail.

More information

This research was presented in the paper “Six transiting planets and a chain of Laplace resonances in TOI-178” to appear in Astronomy & Astrophysics (doi: 10.1051/0004-6361/202039767).

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ESO: Galaxy dying after collision leads to rapid loss of mass for new stars

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

ALMA captures distant colliding galaxy dying out
as it loses the ability to form stars

This artist’s impression of ID2299 shows the galaxy, the product of a galactic collision, and some of its gas being ejected by a “tidal tail” as a result of the merger. New observations made with ALMA, in which ESO is a partner, have captured the earliest stages of this ejection, before the gas reached the very large scales depicted in this artist’s impression.

Galaxies begin to “die” when they stop forming stars, but until now astronomers had never clearly glimpsed the start of this process in a far-away galaxy. Using the Atacama Large Millimeter/submillimeter Array (ALMA), in which the European Southern Observatory (ESO) is a partner, astronomers have seen a galaxy ejecting nearly half of its star-forming gas. This ejection is happening at a startling rate, equivalent to 10 000 Suns-worth of gas a year — the galaxy is rapidly losing its fuel to make new stars. The team believes that this spectacular event was triggered by a collision with another galaxy, which could lead astronomers to rethink how galaxies stop bringing new stars to life.

“This is the first time we have observed a typical massive star-forming galaxy in the distant Universe about to ‘die’ because of a massive cold gas ejection,”

says Annagrazia Puglisi, lead researcher on the new study, from the Durham University, UK, and the Saclay Nuclear Research Centre (CEA-Saclay), France. The galaxy, ID2299, is distant enough that its light takes some 9 billion years to reach us; we see it when the Universe was just 4.5 billion years old.

The gas ejection is happening at a rate equivalent to 10 000 Suns per year, and is removing an astonishing 46% of the total cold gas from ID2299. Because the galaxy is also forming stars very rapidly, hundreds of times faster than our Milky Way, the remaining gas will be quickly consumed, shutting down ID2299 in just a few tens of million years.

The event responsible for the spectacular gas loss, the team believes, is a collision between two galaxies, which eventually merged to form ID2299. The elusive clue that pointed the scientists towards this scenario was the association of the ejected gas with a “tidal tail”. Tidal tails are elongated streams of stars and gas extending into interstellar space that result when two galaxies merge, and they are usually too faint to see in distant galaxies. However, the team managed to observe the relatively bright feature just as it was launching into space, and were able to identify it as a tidal tail.

This panoramic view of the Chajnantor plateau, spanning about 180 degrees from north (on the left) to south (on the right) shows the antennas of the Atacama Large Millimeter/submillimeter Array (ALMA) ranged across the unearthly landscape. … Credits: ESO/ALMA

Most astronomers believe that winds caused by star formation and the activity of black holes at the centres of massive galaxies are responsible for launching star-forming material into space, thus ending galaxies’ ability to make new stars. However, the new study published today in Nature Astronomy suggests that galactic mergers can also be responsible for ejecting star-forming fuel into space.

“Our study suggests that gas ejections can be produced by mergers and that winds and tidal tails can appear very similar,”

says study co-author Emanuele Daddi of CEA-Saclay. Because of this, some of the teams that previously identified winds from distant galaxies could in fact have been observing tidal tails ejecting gas from them. “This might lead us to revise our understanding of how galaxies ‘die’,” Daddi adds.

Puglisi agrees about the significance of the team’s finding, saying:

“I was thrilled to discover such an exceptional galaxy! I was eager to learn more about this weird object because I was convinced that there was some important lesson to be learned about how distant galaxies evolve.”

This surprising discovery was made by chance, while the team were inspecting a survey of galaxies made with ALMA, designed to study the properties of cold gas in more than 100 far-away galaxies. ID2299 had been observed by ALMA for only a few minutes, but the powerful observatory, located in northern Chile, allowed the team to collect enough data to detect the galaxy and its ejection tail.

“ALMA has shed new light on the mechanisms that can halt the formation of stars in distant galaxies. Witnessing such a massive disruption event adds an important piece to the complex puzzle of galaxy evolution,”

says Chiara Circosta, a researcher at the University College London, UK, who also contributed to the research.

In the future, the team could use ALMA to make higher-resolution and deeper observations of this galaxy, enabling them to better understand the dynamics of the ejected gas. Observations with the future ESO’s Extremely Large Telescope could allow the team to explore the connections between the stars and gas in ID2299, shedding new light on how galaxies evolve.

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Videos: Night sky highlights for January 2021

** What’s Up: January 2021 – Skywatching Tips from NASA JPL

What are some skywatching highlights in January 2021? Mark Earth’s closest approach to the Sun for the year, called perihelion, at the start of the month, then spot a couple of elusive planets: Uranus on Jan. 20th and Mercury throughout the second half of the month. Additional information about topics covered in this episode of What’s Up, along with still images from the video, and the video transcript, are available at https://solarsystem.nasa.gov/whats-up….

** What’s in the Night Sky January 2021 #WITNS | Quadrantid Meteor Shower | MercuryAlyn Wallace

00:00 Intro
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** Tonight’s Sky: JanuarySpace Telescope Science Institute

In January, the northern hemisphere features beautiful views of Capella, a pair of giant yellow stars; Aldebaran, a red giant star; and two star clusters—the Hyades and the Pleiades. Keep watching for the awe-inspiring space-based views of the Crab Nebula, the remains of a star that exploded as a supernova.

**  What to see in the night sky, January 2021BBC Sky at Night Magazine

A new year means a new stargazing calendar! Pete Lawrence and Paul Abel reveal what’s in the night sky throughout January 2021. Head out and see what you can spot tonight.

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Videos: Night sky highlights for December 2020

Update: What’s Up: December 2020 Skywatching Tips from NASA – JPL

What are some skywatching highlights in December 2020? Catch the year’s best meteor shower, the Geminids, in the middle of the month. Then witness an extremely close pairing of Jupiter and Saturn that won’t be repeated for decades. And mark the shortest day of the year on the northern winter solstice. Additional information about topics covered in this episode of What’s Up, along with still images from the video, and the video transcript, are available at https://solarsystem.nasa.gov/whats-up….

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** Tonight’s Sky: DecemberSpace Telescope Science Institute

Step outside on a cold December night when the stars shine bright to find the Big Dipper, Cassiopeia, and Cepheus. They will help you locate a binary star system, a fan-shaped open star cluster, and a variable star. Stay tuned for space-based views of a ragged spiral galaxy, an open star cluster, and an edge-on galaxy.

** What to see in the night sky, December 2020BBC Sky at Night Magazine

What can you see in the night sky tonight? Astronomers Pete Lawrence and Paul Abel talk us through the best sights to see in the night sky throughout December 2020, including how to see the Great Conjunction of Jupiter and Saturn (03:30) and the Geminid meteor shower (08:48).

** What’s in the Night Sky December 2020 #WITNS | Great Conjunction | Solar Eclipse | Geminid Meteors – Alyn Wallace

** The Night Sky & A Telescope – The Night Sky Sights – December 2020Richard J. Bartlett

This month, Jupiter and Saturn are at their closest for 400 years, while Mars still shines in the evening hours. The Geminid meteor shower reaches its maximum on the 13th, and we’ll take a closer look at the Pleiades star cluster.

** More night sky advice:

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Videos: Night sky highlights for November 2020

** What’s Up: November 2020 Skywatching Tips from NASA – NASA JPL

What are some skywatching highlights in November 2020? Cool autumn evenings are a great time to look for the Pleiades star cluster. You’ll also have a couple of great opportunities to observe the Moon with Jupiter and Saturn. Plus, check out the phenomenon known as Earthshine. Additional information about topics covered in this episode of What’s Up, along with still images from the video, and the video transcript, are available at https://solarsystem.nasa.gov/whats-up…

** Tonight’s Sky: NovemberSpace Telescope Science Institute

In November, hunt for the fainter constellations of fall, including Pisces, Aries, and Triangulum. They will guide you to find several galaxies and a pair of white stars. Stay tuned for space-based views of spiral galaxy M74 and the Triangulum Galaxy, which are shown in visible, infrared, and ultraviolet light.

** What to see in the night sky: November 2020BBC Sky at Night Magazine

What can you see in the night sky tonight? Astronomers Pete Lawrence and Paul Abel guide us through November 2020’s night-sky highlights.

** What’s in the Night Sky November 2020 #WITNS | Leonids Meteor Shower | Lunar EclipseAlyn Wallace

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