Category Archives: Astronomy

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
00:39 Skillshare
01:30 Northern Hemisphere Night Sky
07:39 Southern Hemisphere Night Sky
12:19 Quadrantids Meteor Shower
15:20 #WITNS Winners

** 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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ESO: Telescopes observe final moments of a star eaten by a black hole

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

Death by Spaghettification:
ESO Telescopes Record Last Moments of Star Devoured by a Black Hole

This illustration depicts a star (in the foreground) experiencing spaghettification as it’s sucked in by a supermassive black hole (in the background) during a ‘tidal disruption event’. In a new study, done with the help of ESO’s Very Large Telescope and ESO’s New Technology Telescope, a team of astronomers found that when a black hole devours a star, it can launch a powerful blast of material outwards.Credits ESO

Using telescopes from the European Southern Observatory (ESO) and other organisations around the world, astronomers have spotted a rare blast of light from a star being ripped apart by a supermassive black hole. The phenomenon, known as a tidal disruption event, is the closest such flare recorded to date at just over 215 million light-years from Earth, and has been studied in unprecedented detail. The research is published today in Monthly Notices of the Royal Astronomical Society.

“The idea of a black hole ‘sucking in’ a nearby star sounds like science fiction. But this is exactly what happens in a tidal disruption event,”

says Matt Nicholl, a lecturer and Royal Astronomical Society research fellow at the University of Birmingham, UK, and the lead author of the new study. But these tidal disruption events, where a star experiences what’s known as spaghettification as it’s sucked in by a black hole, are rare and not always easy to study. The team of researchers pointed ESO’s Very Large Telescope (VLT) and ESO’s New Technology Telescope (NTT) at a new flash of light that occurred last year close to a supermassive black hole, to investigate in detail what happens when a star is devoured by such a monster.

Astronomers know what should happen in theory.

“When an unlucky star wanders too close to a supermassive black hole in the centre of a galaxy, the extreme gravitational pull of the black hole shreds the star into thin streams of material,”

explains study author Thomas Wevers, an ESO Fellow in Santiago, Chile, who was at the Institute of Astronomy, University of Cambridge, UK, when he conducted the work. As some of the thin strands of stellar material fall into the black hole during this spaghettification process, a bright flare of energy is released, which astronomers can detect.

Although powerful and bright, up to now astronomers have had trouble investigating this burst of light, which is often obscured by a curtain of dust and debris. Only now have astronomers been able to shed light on the origin of this curtain.

“We found that, when a black hole devours a star, it can launch a powerful blast of material outwards that obstructs our view,” 

explains Samantha Oates, also at the University of Birmingham. This happens because the energy released as the black hole eats up stellar material propels the star’s debris outwards.

The discovery was possible because the tidal disruption event the team studied, AT2019qiz, was found just a short time after the star was ripped apart.

“Because we caught it early, we could actually see the curtain of dust and debris being drawn up as the black hole launched a powerful outflow of material with velocities up to 10 000 km/s,” says Kate Alexander, NASA Einstein Fellow at Northwestern University in the US. “This unique ‘peek behind the curtain’ provided the first opportunity to pinpoint the origin of the obscuring material and follow in real time how it engulfs the black hole.”

The team carried out observations of AT2019qiz, located in a spiral galaxy in the constellation of Eridanus, over a 6-month period as the flare grew in luminosity and then faded away.

“Several sky surveys discovered emission from the new tidal disruption event very quickly after the star was ripped apart,” says Wevers. “We immediately pointed a suite of ground-based and space telescopes in that direction to see how the light was produced.”

Multiple observations of the event were taken over the following months with facilities that included X-shooter and EFOSC2, powerful instruments on ESO’s VLT and ESO’s NTT, which are situated in Chile. The prompt and extensive observations in ultraviolet, optical, X-ray and radio light revealed, for the first time, a direct connection between the material flowing out from the star and the bright flare emitted as it is devoured by the black hole.

“The observations showed that the star had roughly the same mass as our own Sun, and that it lost about half of that to the monster black hole, which is over a million times more massive,”

says Nicholl, who is also a visiting researcher at the University of Edinburgh.

The research helps us better understand supermassive black holes and how matter behaves in the extreme gravity environments around them. The team say AT2019qiz could even act as a ‘Rosetta stone’ for interpreting future observations of tidal disruption events. ESO’s Extremely Large Telescope (ELT), planned to start operating this decade, will enable researchers to detect increasingly fainter and faster evolving tidal disruption events, to solve further mysteries of black hole physics.

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