̽��ֱ�� of Cambridge - milky way

Farewell, Gaia: spacecraft operations come to an end

sc604 — Thu, 27 Mar 2025 10:27:38 +0000

On 27 March 2025, Gaia’s control team at ESA’s European Space Operations Centre switched off the spacecraft’s subsystems and sent it into a ‘retirement orbit’ around the Sun.

Though the spacecraft’s operations are now over, the scientific exploitation of Gaia’s data has just begun.

Launched in 2013, Gaia has transformed our understanding of the cosmos by mapping the positions, distances, motions, and properties of nearly two billion stars and other celestial objects. It has provided the largest, most precise multi-dimensional map of our galaxy ever created, revealing its structure and evolution in unprecedented detail.

̽��ֱ��mission uncovered evidence of past galactic mergers, identified new star clusters, contributed to the discovery of exoplanets and black holes, mapped millions of quasars and galaxies, and tracked hundreds of thousands of asteroids and comets. ̽��ֱ��mission has also enabled the creation of the best visualisation of how our galaxy might look to an outside observer.

“ ̽��ֱ��data from the Gaia satellite has and is transforming our understanding of the Milky Way, how it formed, how it has evolved and how it will evolve,” said Dr Nicholas Walton from Cambridge’s Institute of Astronomy, lead of the Gaia UK project team. “Gaia has been in continuous operation for over 10 years, faultless, without interruption, reflecting the quality of the engineering, with significant elements of Gaia designed and built in the UK. But now it is time for its retirement. Gaia has finished its observations of the night sky. But the analysis of the Gaia mission data continues. Later in 2026 sees the next Gaia Data Release 4, to further underpin new discovery unravelling the beauty and mystery of the cosmos.”

Gaia far exceeded its planned lifetime of five years, and its fuel reserves are dwindling. ̽��ֱ��Gaia team considered how best to dispose of the spacecraft in line with ESA’s efforts to responsibly dispose of its missions.

They wanted to find a way to prevent Gaia from drifting back towards its former home near the scientifically valuable second Lagrange point (L2) of the Sun-Earth system and minimise any potential interference with other missions in the region.

“Switching off a spacecraft at the end of its mission sounds like a simple enough job,” said Gaia Spacecraft Operator Tiago Nogueira. “But spacecraft really don’t want to be switched off.

“We had to design a decommissioning strategy that involved systematically picking apart and disabling the layers of redundancy that have safeguarded Gaia for so long, because we don’t want it to reactivate in the future and begin transmitting again if its solar panels find sunlight.”

On 27 March, the Gaia control team ran through this series of passivation activities. One final use of Gaia’s thrusters moved the spacecraft away from L2 and into a stable retirement orbit around the Sun that will minimise the chance that it comes within 10 million kilometres of Earth for at least the next century.

̽��ֱ��team then deactivated and switched off the spacecraft’s instruments and subsystems one by one, before deliberately corrupting its onboard software. ̽��ֱ��communication subsystem and the central computer were the last to be deactivated.

Gaia’s final transmission to ESOC mission control marked the conclusion of an intentional and carefully orchestrated farewell to a spacecraft that has tirelessly mapped the sky for over a decade.

Though Gaia itself has now gone silent, its contributions to astronomy will continue to shape research for decades. Its vast and expanding data archive remains a treasure trove for scientists, refining knowledge of galactic archaeology, stellar evolution, exoplanets and much more.

“No other mission has had such an impact over such a broad range of astrophysics. It continues to be the source of over 2,000 peer-reviewed papers per year, more than any other space mission,” said Gaia UK team member Dr Dafydd Wyn Evans, also from the Institute of Astronomy. “It is sad that its observing days are over, but work is continuing in Cambridge, and across Europe, to process and calibrate the final data so that Gaia will still be making its impact felt for many years in the future.”

A workhorse of galactic exploration, Gaia has charted the maps that future explorers will rely on to make new discoveries. ̽��ֱ��star trackers on ESA’s Euclid spacecraft use Gaia data to precisely orient the spacecraft. ESA’s upcoming Plato mission will explore exoplanets around stars characterised by Gaia and may follow up on new exoplanetary systems discovered by Gaia.

̽��ֱ��Gaia control team also used the spacecraft’s final weeks to run through a series of technology tests. ̽��ֱ��team tested Gaia’s micro propulsion system under different challenging conditions to examine how it had aged over more than ten years in the harsh environment of space. ̽��ֱ��results may benefit the development of future ESA missions relying on similar propulsion systems, such as the LISA mission.

̽��ֱ��Gaia spacecraft holds a deep emotional significance for those who worked on it. As part of its decommissioning, the names of around 1500 team members who contributed to its mission were used to overwrite some of the back-up software stored in Gaia’s onboard memory.

Personal farewell messages were also written into the spacecraft’s memory, ensuring that Gaia will forever carry a piece of its team with it as it drifts through space.

As Gaia Mission Manager Uwe Lammers put it: “We will never forget Gaia, and Gaia will never forget us.”

̽��ֱ��Cambridge Gaia DPAC team is responsible for the analysis and generation of the Gaia photometric and spectro-photometric data products, and it also generated the Gaia photometric science alert stream for the duration of the satellite's in-flight operations.

Adapted from a media release by the European Space Agency.

̽��ֱ��European Space Agency’s Gaia spacecraft has been powered down, after more than a decade spent gathering data that are now being used to unravel the secrets of our home galaxy.

ESA/Gaia/DPAC, Stefan Payne-Wardenaar

Artist's impression of the Milky Way

̽��ֱ��text in this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

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Last starlight for ground-breaking Gaia

Anonymous — Wed, 15 Jan 2025 09:22:32 +0000

Launched on 19 December 2013, Gaia’s fuel tank is now approaching empty – it uses about a dozen grams of cold gas per day to keep it spinning with pinpoint precision. But this is far from the end of the mission. Technology tests are scheduled for the weeks ahead before Gaia is moved to its ‘retirement’ orbit, and two massive data releases are tabled for around 2026 and the end of this decade, respectively.

“Today marks the end of science observations and we are celebrating this incredible mission that has exceeded all our expectations, lasting for almost twice its originally foreseen lifetime,” said ESA Director of Science Carole Mundell.

“ ̽��ֱ��treasure trove of data collected by Gaia has given us unique insights into the origin and evolution of our Milky Way galaxy, and has also transformed astrophysics and Solar System science in ways that we are yet to fully appreciate. Gaia built on unique European excellence in astrometry and will leave a long-lasting legacy for future generations.”

“Today marks the last day of science data collection from Gaia, these observations to form part of the final data release,” said Dr Nicholas Walton from Cambridge’s Institute of Astronomy, lead of the UK Gaia Project team and ESA Gaia Science Team member. “Our Gaia team in the UK is now working hard on the incredibly complex data analysis for the upcoming Gaia data releases. These will enable a wealth of new discovery, adding to the science from one of the world’s most productive science discovery machines.”

Gaia delivers best Milky Way map

Gaia has been charting the positions, distances, movements, brightness changes, composition and numerous other characteristics of stars by monitoring them with its three instruments many times throughout the mission.

This has enabled Gaia to deliver on its primary goal of building the largest, most precise map of the Milky Way, showing us our home galaxy like no other mission has done before.

Gaia’s repeated measurements of stellar distances, motions and characteristics are key to performing ‘galactic archeology’ on our Milky Way, revealing missing links in our galaxy’s complex history to help us learn more about our origins. From detecting ‘ghosts’ of other galaxies and multiple streams of ancient stars that merged with the Milky Way in its early history, to finding evidence for an ongoing collision with the Sagittarius dwarf galaxy today, Gaia is rewriting the Milky Way’s history and making predictions about its future.

Warning! More ground-breaking science ahead

̽��ֱ��Gaia scientific and engineering teams are already working on the preparations for Gaia Data Release 4 (DR4), expected in 2026.

“This is the Gaia release the community has been waiting for, and it’s exciting to think this only covers half of the collected data,” said Antonella Vallenari, Deputy Chair of DPAC based at the Istituto Nazionale di Astrofisica (INAF), Astronomical Observatory of Padua, Italy. “Even though the mission has now stopped collecting data, it will be business as usual for us for many years to come as we make these incredible datasets ready for use.”

“Over the next months we will continue to downlink every last drop of data from Gaia, and at the same time the processing teams will ramp up their preparations for the fifth and final major data release at the end of this decade, covering the full 10.5 years of mission data,” said Rocio Guerra, Gaia Science Operations Team Leader based at ESA’s European Space Astronomy Centre (ESAC) near Madrid in Spain.

Gaia’s retirement plan

While today marks the end of science observations, a short period of technology testing now begins. ̽��ֱ��tests have the potential to further improve the Gaia calibrations, learn more about the behaviour of certain technology after ten years in space, and even aid the design of future space missions.

After several weeks of testing, Gaia will leave its current orbit around Lagrange point 2, 1.5 million km from the Earth in the direction away from the Sun, to be put into its final heliocentric orbit, far away from Earth’s sphere of influence. ̽��ֱ��spacecraft will be passivated on 27 March 2025, to avoid any harm or interference with other spacecraft.

Wave farewell to Gaia

During the technology tests Gaia’s orientation will be changed, meaning it will temporarily become several magnitudes brighter, making observations through small telescopes a lot easier (it won’t be visible to the naked eye). A guide to locating Gaia has been set up here, and amateur astronomers are invited to share their observations.

“Gaia will treat us with this final gift as we bid farewell, shining among the stars ahead of its well-earned retirement,” said Uwe Lammers, Gaia Mission Manager.

“It’s a moment to celebrate this transformative mission and thank all of the teams for more than a decade of hard work operating Gaia, planning its observations, and ensuring its precious data are returned smoothly to Earth.”

Adapted from a European Space Agency press release.

̽��ֱ��European Space Agency’s Milky Way-mapper Gaia has completed the sky-scanning phase of its mission, racking up more than three trillion observations of about two billion stars and other objects over the last decade to revolutionise the view of our home galaxy and cosmic neighbourhood.

ESA/Gaia/DPAC, Stefan Payne-Wardenaar

This is a new artist’s impression of our galaxy, the Milky Way, based on data from ESA’s Gaia space telescope.

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Latest Gaia data release reveals rare lenses, cluster cores and unforeseen science

sc604 — Tue, 10 Oct 2023 12:47:51 +0000

Gaia is mapping our galaxy and beyond in multi-dimensional detail, completing the most accurate stellar census ever. ̽��ֱ��mission is painting a detailed picture of our place in the Universe, enabling us to better understand the diverse objects within it.

̽��ֱ��mission’s latest data release provides new and improved insights into the space around us. ̽��ֱ��release also brings findings that go far beyond what Gaia was initially designed to discover and digs deep into our cosmic history.

“This focused product data release will open up new insights across astronomy, from the precise orbits of asteroids in our Solar System, to quasar discovery in the distant cosmos,” said Dr Nicholas Walton from Cambridge’s Institute of Astronomy, lead of the UK Gaia Project team and ESA Gaia Science Team member. “It demonstrates the breadth of science enabled by Gaia, and the role of Cambridge and UK Gaia teams in the creation of these data products. This release represents but a small taste of the riches to be revealed with the publication of the next full release, Gaia DR4.”

So – what’s new from Gaia?

Half a million new stars: Gaia's observing mode extended to unlock cluster cores

Gaia’s third data release (DR3) contained data on over 1.8 billion stars, building a pretty complete view of the Milky Way and beyond. However, there remained gaps in our mapping. Gaia had not yet fully explored areas of sky that were especially densely packed with stars, leaving these comparatively unexplored – and overlooking stars shining less brightly than their many neighbours.

Globular clusters are a key example of this. These clusters are some of the oldest objects in the Universe, making them especially valuable to scientists looking at our cosmic past. Unfortunately, their bright cores, chock-full of stars, can overwhelm telescopes attempting to get a clear view. As such, they remain missing pieces in our maps of the Universe.

To patch the gaps in our maps, Gaia selected Omega Centauri, the largest globular cluster that can be seen from Earth. Rather than just focusing on individual stars, as it typically would, Gaia enabled a special mode to truly map a wider patch of sky surrounding the cluster’s core every time the cluster came into view.

“In Omega Centauri, we discovered over half a million new stars Gaia hadn't seen before – from just one cluster!” says lead author Katja Weingrill of the Leibniz-Institute for Astrophysics Potsdam (AIP), Germany, and a member of the Gaia collaboration.

“Through a new use of one of Gaia’s specialised engineering modes, we have been able to generate an imaging catalogue of some of the densest stellar fields in our galaxy,” said Dr Dafydd Wyn Evans, lead of the Gaia photometric development team. “This is enabling us to provide a more complete view of all components of the Milky Way, including the cores of Globular Clusters, some of the oldest structures in our Galaxy.”

This finding not only meets but actually exceeds Gaia’s planned potential. ̽��ֱ��team used an observing mode designed to ensure that all of Gaia’s instruments are running smoothly.

“ ̽��ֱ��Gaia Sky Mapper images required the development of a new processing pipeline to measure the accurate brightness of the hundreds of thousands faint stars not seen by Gaia before,” said Dr Francesca De Angeli, lead of Gaia’s Photometric Data Processing Centre in Cambridge. “This rich data probes regions of the sky previously unseen by Gaia, and fills in important gaps in earlier data releases.”

̽��ֱ��new stars revealed in Omega Centauri mark one of the most crowded regions explored by Gaia so far.

Gaia is currently exploring eight more regions in this way, with the results to be included in Gaia Data Release 4. These data will help astronomers to truly understand what is happening within these cosmic building blocks, a crucial step for scientists aiming to confirm the age of our galaxy, locate its centre, figure out whether it has gone through any past collisions, verify how stars change through their lifetimes, constrain our models of galactic evolution, and ultimately infer the possible age of the Universe itself.

Looking for lenses: Gaia the accidental cosmologist

While Gaia was not designed for cosmology, its new findings peer deep into the distant Universe, hunting for elusive and exciting objects that hold clues to some of humanity’s biggest questions about the cosmos: gravitational lenses.

Gravitational lensing occurs when the image of a faraway object becomes warped by a disturbing mass – a star or galaxy, for instance – sitting between us and the object. This intermediate mass acts as a giant magnifying glass, or lens, that can amplify the brightness of light and cast multiple images of the faraway source onto the sky. These rare configurations hold immense scientific value, revealing clues about the earliest days of the Universe.

̽��ֱ��team identified the candidates from an extensive list of possible quasars (including those from Gaia DR3). Five of the possible lenses are potential Einstein crosses, rare lensed systems with four different image components shaped like a cross. (See 12 such configurations discovered by Gaia in 2021.)

Finding lensed quasars is challenging. A lensed system’s constituent images can clump together on the sky in misleading ways, and most are very far away, making them faint and tricky to spot.

Extending Gaia’s value into cosmology brings synergy with ESA’s Euclid mission, recently launched on its quest to explore the dark Universe. While both focus on different parts of the cosmos – Euclid on mapping billions of galaxies, Gaia on mapping billions of stars – the lensed quasars discovered by Gaia can be used to guide future exploration with Euclid.

Asteroids, stacked starlight and pulsating stars

Other papers published today offer further insight into the space around us, and the diverse and sometimes mysterious objects within it.

One reveals more about 156,823 of the asteroids identified as part of Gaia DR3. ̽��ֱ��new dataset pinpoints the positions of these rocky bodies over nearly double the previous timespan, making most of their orbits – based on Gaia observations alone – 20 times more precise. In the future, Gaia DR4 will complete the set and include comets, planetary satellites and double the number of asteroids, improving our knowledge of the small bodies in nearby space.

Another paper maps the disc of the Milky Way by tracing weak signals seen in starlight, faint imprints of the gas and dust that floats between the stars. ̽��ֱ��Gaia team stacked six million spectra to study these signals, forming a dataset of weak features that have never been measured in such a large sample. ̽��ֱ��dataset will hopefully allow scientists to narrow down the source of these signals, which the team suspects to be a complex organic molecule. Knowing more about where this signal comes from helps us to study the physical and chemical processes active throughout our galaxy, and to understand more about the material lying between stars.

Finally, a paper characterises the dynamics of 10,000 pulsating and binary red giant stars in by far the largest such database available to date. These stars were part of a catalogue of two million variable star candidates released in Gaia DR3, and are key when calculating cosmic distances, confirming stellar characteristics, and clarifying how stars evolve throughout the cosmos. ̽��ֱ��new release provides a better understanding of how these stars change over time.

“This data release further demonstrates Gaia’s broad and fundamental value – even on topics it wasn’t initially designed to address,” said Timo Prusti, Project Scientist for Gaia at ESA.

̽��ֱ��next steps

Gaia’s previous Data Release, Gaia DR3, came on 13 June 2022. It was the most detailed survey of the Milky Way to date, and a treasure trove of data on strange ‘starquakes’, asymmetrically moving stars, stellar DNA and more. Gaia DR3 contained new and improved details for almost two billion stars in the Milky Way, and included the largest catalogues of binary stars, thousands of Solar System objects, and – more distantly and outside of our galaxy – millions of galaxies and quasars.

̽��ֱ��mission’s next Data Release, Gaia DR4, is expected not before the end of 2025. It will build upon both Gaia DR3 and this interim focused product release to further improve our understanding of the multi-dimensional Milky Way. It will refine our knowledge of stars’ colours, positions, and movements; resolve variable and multiple star systems; identify and characterise quasars and galaxies; list exoplanet candidates; and more.

Adapted from an ESA press release.

̽��ֱ��European Space Agency’s Gaia mission has released a goldmine of knowledge about our galaxy and beyond. Among other findings, the star surveyor has surpassed its planned potential to reveal half a million new and faint stars in a massive cluster, identified over 380 possible cosmic lenses, and pinpointed the positions of more than 150,000 asteroids within the Solar System.

This release represents but a small taste of the riches to be revealed with the publication of the next full release, Gaia DR4

Nicholas Walton

ESA/Gaia/DPAC

Gaia view of Omega Centauri

̽��ֱ��text in this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

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Dark energy could be measured by studying the galaxy next door

sc604 — Mon, 14 Aug 2023 14:31:03 +0000

̽��ֱ��researchers, from the ̽��ֱ�� of Cambridge, found that it may be possible to detect and measure dark energy by studying Andromeda, our galactic next-door neighbour that is on a slow-motion collision course with the Milky Way.

Since it was first identified in the late 1990s, scientists have used very distant galaxies to study dark energy but have yet to directly detect it. However, the Cambridge researchers found that by studying how Andromeda and the Milky Way are moving toward each other given their collective mass, they could place an upper limit on the value of the cosmological constant, which is the simplest model of dark energy. ̽��ֱ��upper limit they found is five times higher than the value of the cosmological constant that can be detected from the early universe.

Although the technique is still early in its development, the researchers say that it could be possible to detect dark energy by studying our own cosmic neighbourhood. ̽��ֱ��results are reported in ̽��ֱ��Astrophysical Journal Letters.

Everything we can see in our world and in the skies – from tiny insects to massive galaxies – makes up just five percent of the observable universe. ̽��ֱ��rest is dark: scientists believe that about 27% of the universe is made of dark matter, which holds objects together, while 68% is dark energy, which pushes objects apart.

“Dark energy is a general name for a family of models you could add to Einstein’s theory of gravity,” said first author Dr David Benisty from the Department of Applied Mathematics and Theoretical Physics. “ ̽��ֱ��simplest version of this is known as the cosmological constant: a constant energy density that pushes galaxies away from each other.”

̽��ֱ��cosmological constant was temporarily added by Einstein to his theory of general relativity. From the 1930s to the 1990s, the cosmological constant was set at zero, until it was discovered that an unknown force – dark energy – was causing the expansion of the universe to accelerate. There are at least two big problems with dark energy, however: we don’t know exactly what it is, and we haven’t directly detected it.

Since it was first identified, astronomers have developed a variety of methods to detect dark energy, most of which involve studying objects from the early universe and measuring how quickly they are moving away from us. Unpacking the effects of dark energy from billions of years ago is not easy: since it is a weak force between galaxies, dark energy is easily overcome by the much stronger forces inside galaxies.

However, there is one region of the universe that is surprisingly sensitive to dark energy, and it’s in our own cosmic backyard. ̽��ֱ��Andromeda galaxy is the closest to our own Milky Way, and the two galaxies are on a collision course. As they draw closer, the two galaxies will start to orbit each other – very slowly. A single orbit will take 20 billion years. However, due to the massive gravitational forces, well before a single orbit is complete, about five billion years from now, the two galaxies will start merging and falling into each other.

“Andromeda is the only galaxy that isn’t running away from us, so by studying its mass and movement, we may be able to make some determinations about the cosmological constant and dark energy,” said Benisty, who is also a Research Associate at Queens’ College.

Using a series of simulations based on the best available estimates of the mass of both galaxies, Benisty and his co-authors – Professor Anne Davis from DAMTP and Professor Wyn Evans from the Institute of Astronomy – found that dark energy is affecting how Andromeda and the Milky Way are orbiting each other.

“Dark energy affects every pair of galaxies: gravity wants to pull galaxies together, while dark energy pushes them apart,” said Benisty. “In our model, if we change the value of the cosmological constant, we can see how that changes the orbit of the two galaxies. Based on their mass, we can place an upper bound on the cosmological constant, which is about five times higher than we can measure from the rest of the universe.”

̽��ֱ��researchers say that while the technique could prove immensely valuable, it is not yet a direct detection of dark energy. Data from the James Webb Telescope (JWST) will provide far more accurate measurements of Andromeda’s mass and motion, which could help reduce the upper bounds of the cosmological constant.

In addition, by studying other pairs of galaxies, it could be possible to further refine the technique and determine how dark energy affects our universe. “Dark energy is one of the biggest puzzles in cosmology,” said Benisty. “It could be that its effects vary over distance and time, but we hope this technique could help unravel the mystery.”

Reference:
David Benisty, Anne-Christine Davis, and N. Wyn Evans. ‘Constraining Dark Energy from the Local Group Dynamics.’ ̽��ֱ��Astrophysical Journal Letters (2023). DOI: 10.3847/2041-8213/ace90b

Researchers have found a new way to measure dark energy – the mysterious force that makes up more than two-thirds of the universe and is responsible for its accelerating expansion – in our own cosmic backyard.

Andromeda is the only galaxy that isn’t running away from us, so by studying its mass and movement, we may be able to make some determinations about dark energy

David Benisty

NASA; ESA; Z. Levay and R. van der Marel, STScI; T. Hallas; and A. Mellinger

Artist's impression of the predicted collision between the Milky Way and Andromeda

̽��ֱ��text in this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

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Largest chemical map of the Milky Way unveiled

sc604 — Mon, 13 Jun 2022 07:59:38 +0000

̽��ֱ��European Space Agency’s (ESA) Gaia mission has released a new treasure trove of data about our home galaxy, including stellar DNA, asymmetric motions, strange ‘starquakes’, and other fascinating insights.

Gaia: scientists take a step closer to revealing origins of our galaxy

sc604 — Thu, 03 Dec 2020 12:09:57 +0000

̽��ֱ��measurements of stellar positions, movement, brightness and colours are in the third early data release from the European Space Agency’s Gaia space observatory, and are now publicly available. Initial findings include the first optical measurement of the acceleration of the Solar system.

Launched in 2013, Gaia operates in an orbit around the so-called Lagrange 2 (L2) point, located 1.5 million kilometres behind the Earth in the direction away from the Sun. At L2 the gravitational forces between the Earth and Sun are balanced, so the spacecraft stays in stable position, allowing long-term essentially unobstructed views of the sky.

̽��ֱ��primary objective of Gaia is to measure stellar distances using the parallax method. In this case astronomers use the observatory to continuously scan the sky, measuring the apparent change in the positions of stars over time, resulting from the Earth’s movement around the Sun.

Knowing that tiny shift in the positions of stars allows their distances to be calculated. On Earth this is made more difficult by the blurring of the Earth’s atmosphere, but in space the measurements are only limited by the optics of the telescope.

Two previous releases included the positions of 1.6 billion stars. Today’s release brings the total to just under 2 billion stars, whose positions are significantly more accurate than in the earlier data. Gaia also tracks the changing brightness and the positions of the stars over time across the line of sight (their so-called proper motion), and by splitting their light into spectra, measures how fast they are moving towards or away from the Sun and assesses their chemical composition.

̽��ֱ��new data include exceptionally accurate measurements of the 300,000 stars within the closest 326 light years to the Sun. ̽��ֱ��researchers use these data to predict how the star background will change in the next 1.6 million years. They also confirm that the Solar system is accelerating in its orbit around the Galaxy.

This acceleration is gentle, and is what would be expected from a system in a circular orbit. Over a year the Sun accelerates towards the centre of the Galaxy by 7 mm per second, compared with its speed along its orbit of about 230 kilometres a second.

Gaia data additionally deconstruct the two largest companion galaxies to the Milky Way, the Small and Large Magellanic Clouds, allowing researchers to see their different stellar populations. A dramatic visualisation shows these subsets, and the bridge of stars between the two systems.

Dr Floor van Leeuwen of Cambridge’s Institute of Astronomy said: “Gaia is measuring the distances of hundreds of millions of objects that are many thousands of light years away, at an accuracy equivalent to measuring the thickness of hair at a distance of more than 2000 kilometres. These data are one of the backbones of astrophysics, allowing us to forensically analyse our stellar neighbourhood, and tackle crucial questions about the origin and future of our Galaxy.”

Gaia will continue gathering data until at least 2022, with a possible mission extension until 2025. ̽��ֱ��final data releases are expected to yield stellar positions 1.9 times as accurate as those released so far, and proper motions more than 7 times more accurate, in a catalogue of more than two billion objects.

“ ̽��ֱ��mysteries of the Milky Way and our Solar System have captured the imagination of generations of scientists and astronomers across the world – all eager to learn more about the origins of the Universe,” said Science Minister Amanda Solloway. “Through this remarkable government-backed mission, UK scientists have taken us a giant leap closer to advancing our knowledge of how our Solar System began by painting the most detailed picture yet that could help to redefine astronomy as we know it.”

Adapted from a Royal Astronomical Society press release.

An international team of astronomers, led by the ̽��ֱ�� of Cambridge, announced the most detailed ever catalogue of the stars in a huge swathe of our Milky Way galaxy.

Gaia is measuring the distances of hundreds of millions of objects that are many thousands of light years away, at an accuracy equivalent to measuring the thickness of hair at a distance of more than 2000 kilometres

Floor van Leeuwen

ESA/Gaia/DPAC; Acknowledgement: A. Moitinho.

̽��ֱ��colour of the sky from Gaia’s Early Data Release 3

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

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A bridge of stars connects two dwarf galaxies

ps748 — Wed, 08 Feb 2017 12:36:40 +0000

For the past 15 years, scientists have been eagerly anticipating the data from Gaia. ̽��ֱ��first portion of information from the satellite was released three months ago and is freely accessible to everyone. This dataset of unprecedented quality is a catalogue of the positions and brightness of a billion stars in our Milky Way galaxy and its environs.

What Gaia has sent to Earth is unique. ̽��ֱ��satellite’s angular resolution is similar to that of the Hubble Space Telescope, but given its greater field of view, it can cover the entire sky rather than a small portion of it. In fact, Gaia uses the largest number of pixels to take digital images of the sky for any space-borne instrument. Better still, the Observatory has not just one telescope but two, sharing the one metre wide focal plane.

Unlike typical telescopes, Gaia does not just point and stare: it constantly spins around its axis, sweeping the entire sky in less than a month. Therefore, it not only measures the instantaneous properties of the stars, but also tracks their changes over time. This provides a perfect opportunity for finding a variety of objects, for example stars that pulsate or explode - even if this is not what the satellite was primarily designed for.

̽��ֱ��Cambridge team concentrated on the area around the Magellanic Clouds and used the Gaia data to pick out pulsating stars of a particular type: the so-called RR Lyrae, very old and chemically un-evolved. As these stars have been around since the earliest days of the Clouds’ existence, they offer an insight into the pair’s history. Studying the Large and Small Magellanic Clouds (LMC and SMC respectively) has always been difficult as they sprawl out over a large area. But with Gaia’s all-sky view, this has become a much easier task.

Around the Milky Way, the clouds are the brightest, and largest, examples of dwarf satellite galaxies. Known to humanity since the dawn of history (and to Europeans since their first voyages to the Southern hemisphere) the Magellanic Clouds have remained an enigma to date. Even though the clouds have been a constant fixture of the heavens, astronomers have only recently had the chance to study them in any detail.

̽��ֱ��Magellanic Clouds can be seen just above the horizon and below the arc of the Milky Way - D Erkal

Whether the clouds fit the conventional theory of galaxy formation or not depends critically on their mass and the time of their first approach to the Milky Way. ̽��ֱ��researchers at Cambridge’s Institute of Astronomy found clues that could help answer both of these questions.

Firstly, the RR Lyrae stars detected by Gaia were used to trace the extent of the Large Magellanic Cloud. ̽��ֱ��LMC was found to possess a fuzzy low-luminosity ‘halo’ stretching as far as 20 degrees from its centre. ̽��ֱ��LMC would only be able to hold on to the stars at such large distances if it was substantially bigger than previously thought, totalling perhaps as much as a tenth of the mass of the entire Milky Way.

An accurate timing of the clouds’ arrival to the galaxy is impossible without knowledge of their orbits. Unfortunately, satellite orbits are difficult to measure: at large distances, the object’s motion in the sky is so minute that it is simply unobservable over a human lifespan. In the absence of an orbit, Dr Vasily Belokurov and colleagues found the next best thing: a stellar stream.

Streams of stars form when a satellite - a dwarf galaxy or a star cluster - starts to feel the tidal force of the body around which it orbits. ̽��ֱ��tides stretch the satellite in two directions: towards and away from the host. As a result, on the periphery of the satellite, two openings form: small regions where the gravitational pull of the satellite is balanced by the pull of the host. Satellite stars that enter these regions find it easy to leave the satellite altogether and start orbiting the host. Slowly, star after star abandons the satellite, leaving a luminous trace on the sky, and thus revealing the satellite’s orbit.

“Stellar streams around the Clouds were predicted but never observed,” explains Dr Belokurov. “Having marked the locations of the Gaia RR Lyrae on the sky, we were surprised to see a narrow bridge-like structure connecting the two clouds. We believe that at least in part this ‘bridge’ is composed of stars stripped from the Small Cloud by the Large. ̽��ֱ��rest may actually be the LMC stars pulled from it by the Milky Way.”

̽��ֱ��researchers believe the RR Lyrae bridge will help to clarify the history of the interaction between the clouds and our galaxy.

"We have compared the shape and the exact position of the Gaia stellar bridge to the computer simulations of the Magellanic Clouds as they approach the Milky Way”, explains Dr Denis Erkal, a co-author of the study. "Many of the stars in the bridge appear to have been removed from the SMC in the most recent interaction, some 200 million years ago, when the dwarf galaxies passed relatively close by each other. “We believe that as a result of that fly-by, not only the stars but also hydrogen gas was removed from the SMC. By measuring the offset between the RR Lyrae and hydrogen bridges, we can put constraints on the density of the gaseous Galactic corona.”

Composed of ionised gas at very low density, the hot Galactic corona is notoriously difficult to study. Nevertheless, it has been the subject of intense scrutiny because scientists believe it may contain most of the missing baryonic - or ordinary - matter. Astronomers are trying to estimate where this missing matter (the atoms and ions that make up stars, planets, dust and gas) is. It’s thought that most, or even all, of these missing baryons are in the corona. By measuring the coronal density at large distances they hope to solve this conundrum.

During the previous encounter between the Small and Large Magellanic Cloud, both stars and gas were ripped out of the Small Cloud, forming a tidal stream. Initially, the gas and stars were moving at the same speed. However, as the Clouds approached our Galaxy, the Milky Way’s corona exerted a drag force on both of them. ̽��ֱ��stars, being relatively small and dense, punched through the corona with no change in their speed. However, the more tenuous neutral hydrogen gas slowed down substantially in the corona. By comparing the current location of the stars and the gas, taking into account the density of the gas and how long the Clouds have spent in the corona, the team estimated the density of the corona. Dr. Erkal concludes, “Our estimate showed that the corona could make up a significant fraction of the missing baryons, in agreement with previous independent techniques. With the missing baryon problem seemingly alleviated, the current model of galaxy formation is holding up well to the increased scrutiny possible with Gaia.”

Reference
Vasily Belokurov et al. “Clouds, Streams and Bridges. Redrawing the blueprint of the Magellanic System with Gaia DR1”. Monthly Notices of the Royal Astronomical Society; 8th Feb. 2017; DOI:10.1093/mnras/stw3357

̽��ֱ��Magellanic Clouds, the two largest satellite galaxies of the Milky Way, appear to be connected by a bridge stretching across 43,000 light years, according to an international team of astronomers led by researchers from the ̽��ֱ�� of Cambridge. ̽��ֱ��discovery is reported in the journal Monthly Notices of the Royal Astronomical Society (MNRAS) and is based on the Galactic stellar census being conducted by the European Space Observatory, Gaia.

We believe that at least in part this 'bridge' is composed of stars stripped from the Small Cloud by the Large

Vasily Belokurov

V Belokurov, D Erkal, A Mellinger

Pale white veils and the narrow bridge between the clouds represent the distribution of the RR Lyrae stars

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One year and 272 billion measurements later, Gaia team celebrates first anniversary of observations

sjr81 — Tue, 25 Aug 2015 16:06:41 +0000

̽��ֱ��Gaia satellite, which orbits the sun at a distance of 1.5million km from the earth, was launched by the European Space Agency in December 2013 with the aim of observing a billion stars and revolutionising our understanding of the Milky Way.

̽��ֱ��unique mission is reliant on the work of Cambridge researchers who collect the vast quantities of data transmitted by Gaia to a data processing centre at the university, overseen by a team at the Institute of Astronomy.

Since the start of its observations in August 2014, Gaia has recorded 272 billion positional (or astrometric) measurements and 54.4 billion brightness (or photometric) data points.

Gaia surveys stars and many other astronomical objects as it spins, observing circular swathes of the sky. By repeatedly measuring the positions of the stars with extraordinary accuracy, Gaia can tease out their distances and motions throughout the Milky Way galaxy.

Dr Francesca de Angeli, lead scientist at the Cambridge data centre, said: “ ̽��ֱ��huge Gaia photometric data flow is being processed successfully into scientific information at our processing centre and has already led to many exciting discoveries.”

̽��ֱ��Gaia team have spent a busy year processing and analysing data, with the aim of developing enormous public catalogues of the positions, distances, motions and other properties of more than a billion stars. Because of the immense volumes of data and their complex nature, this requires a huge effort from expert scientists and software developers distributed across Europe, combined in Gaia’s Data Processing and Analysis Consortium (DPAC).

“ ̽��ֱ��past twelve months have been very intense, but we are getting to grips with the data, and are looking forward to the next four years of operations,” said Timo Prusti, Gaia project scientist at ESA.

“We are just a year away from Gaia's first scheduled data release, an intermediate catalogue planned for the summer of 2016. With the first year of data in our hands, we are now halfway to this milestone, and we’re able to present a few preliminary snapshots to show that the spacecraft is working well and that the data processing is on the right track.”

As Gaia has been conducting its repeated scans of the sky to measure the motions of stars, it has also been able to detect whether any of them have changed their brightness, and in doing so, has started to discover some very interesting astronomical objects.

Gaia has detected hundreds of transient sources so far, with a supernova being the very first on August 30, 2014. These detections are routinely shared with the community at large as soon as they are spotted in the form of ‘Science Alerts’, enabling rapid follow-up observations to be made using ground-based telescopes in order to determine their nature.

One transient source was seen undergoing a sudden and dramatic outburst that increased its brightness by a factor of five. It turned out that Gaia had discovered a so-called ‘cataclysmic variable’, a system of two stars in which one, a hot white dwarf, is devouring mass from a normal stellar companion, leading to outbursts of light as the material is swallowed. ̽��ֱ��system also turned out to be an eclipsing binary, in which the relatively larger normal star passes directly in front of the smaller, but brighter white dwarf, periodically obscuring the latter from view as seen from Earth.

Unusually, both stars in this system seem to have plenty of helium and little hydrogen. Gaia’s discovery data and follow-up observations may help astronomers to understand how the two stars lost their hydrogen.

Gaia has also discovered a multitude of stars whose brightness undergoes more regular changes over time. Many of these discoveries were made between July and August 2014, as Gaia performed many subsequent observations of a few patches of the sky.

Closer to home, Gaia has detected a wealth of asteroids, the small rocky bodies that populate our solar system, mainly between the orbits of Mars and Jupiter. Because they are relatively nearby and orbiting the Sun, asteroids appear to move against the stars in astronomical images, appearing in one snapshot of a given field, but not in images of the same field taken at later times.

Gaia scientists have developed special software to look for these ‘outliers’, matching them with the orbits of known asteroids in order to remove them from the data being used to study stars. But in turn, this information will be used to characterise known asteroids and to discover thousands of new ones.

Gerry Gilmore, Professor of Experimental Philosophy, and the Gaia UK Principal Investigator, said: “ ̽��ֱ��early science from Gaia is already supporting major education activity involving UK school children and amateur astronomers across Europe and has established the huge discovery potential of Gaia’s data.

"We are entering a new era of big-data astrophysics, with a revolution in our knowledge of what we see in the sky. We are moving beyond just seeing to knowing about the galaxy in which we live.”

A space mission to create the largest, most-accurate, three-dimensional map of the Milky Way is celebrating its first completed year of observations.

We are moving beyond just seeing to knowing about the galaxy in which we live.

Gerry Gilmore

Gaia's mission: solving the celestial puzzle

Credit: Marisa Grove/Institute of Astronomy

Artist’s impression of Gaia14aae

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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