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By European Space Agency
The European Space Agency is releasing the first catalogue of astronomical data from the Euclid space telescope, including three new enormous image mosaics with zoom-ins. Follow the reveal live on Wednesday 19 March at 11:00 BST / 12:00 CET.
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By NASA
Explore Hubble Hubble Home Overview About Hubble The History of Hubble Hubble Timeline Why Have a Telescope in Space? Hubble by the Numbers At the Museum FAQs Impact & Benefits Hubble’s Impact & Benefits Science Impacts Cultural Impact Technology Benefits Impact on Human Spaceflight Astro Community Impacts Science Hubble Science Science Themes Science Highlights Science Behind Discoveries Hubble’s Partners in Science Universe Uncovered Explore the Night Sky Observatory Hubble Observatory Hubble Design Mission Operations Missions to Hubble Hubble vs Webb Team Hubble Team Career Aspirations Hubble Astronauts News Hubble News Hubble News Archive Social Media Media Resources Multimedia Multimedia Images Videos Sonifications Podcasts e-Books Online Activities Lithographs Fact Sheets Posters Hubble on the NASA App Glossary More 35th Anniversary Online Activities 5 Min Read NASA’s Hubble Provides Bird’s-Eye View of Andromeda Galaxy’s Ecosystem
A view of the distribution of known satellite galaxies orbiting the large Andromeda galaxy (M31), located 2.5 million light-years away. Credits:
NASA, ESA, Alessandro Savino (UC Berkeley), Joseph DePasquale (STScI), Akira Fujii DSS2 Located 2.5 million light-years away, the majestic Andromeda galaxy appears to the naked eye as a faint, spindle-shaped object roughly the angular size of the full Moon. What backyard observers don’t see is a swarm of nearly three dozen small satellite galaxies circling the Andromeda galaxy, like bees around a hive.
These satellite galaxies represent a rambunctious galactic “ecosystem” that NASA’s Hubble Space Telescope is studying in unprecedented detail. This ambitious Hubble Treasury Program used observations from more than a whopping 1,000 Hubble orbits. Hubble’s optical stability, clarity, and efficiency made this ambitious survey possible. This work included building a precise 3D mapping of all the dwarf galaxies buzzing around Andromeda and reconstructing how efficiently they formed new stars over the nearly 14 billion years of the universe’s lifetime.
This is a wide-angle view of the distribution of known satellite galaxies orbiting the large Andromeda galaxy (M31), located 2.5 million light-years away. The Hubble Space Telescope was used to study the entire population of 36 mini-galaxies circled in yellow. Andromeda is the bright spindle-shaped object at image center. All the dwarf galaxies seem to be confined to a plane, all orbiting in the same direction. The wide view is from ground-based photography. Hubble’s optical stability, clarity, and efficiency made this ambitious survey possible. Hubble close up snapshots of four dwarf galaxies are on image right. The most prominent dwarf galaxy is M32 (NGC 221), a compact ellipsoidal galaxy that might be the remnant core of a larger galaxy that collided with Andromeda a few billion years ago. NASA, ESA, Alessandro Savino (UC Berkeley), Joseph DePasquale (STScI), Akira Fujii DSS2 In the study published in The Astrophysical Journal, Hubble reveals a markedly different ecosystem from the smaller number of satellite galaxies that circle our Milky Way. This offers forensic clues as to how our Milky Way galaxy and Andromeda have evolved differently over billions of years. Our Milky Way has been relatively placid. But it looks like Andromeda has had a more dynamic history, which was probably affected by a major merger with another big galaxy a few billion years ago. This encounter, and the fact that Andromeda is as much as twice as massive as our Milky Way, could explain its plentiful and diverse dwarf galaxy population.
Surveying the Milky Way’s entire satellite system in such a comprehensive way is very challenging because we are embedded inside our galaxy. Nor can it be accomplished for other large galaxies because they are too far away to study the small satellite galaxies in much detail. The nearest galaxy of comparable mass to the Milky Way beyond Andromeda is M81, at nearly 12 million light-years.
This bird’s-eye view of Andromeda’s satellite system allows us to decipher what drives the evolution of these small galaxies. “We see that the duration for which the satellites can continue forming new stars really depends on how massive they are and on how close they are to the Andromeda galaxy,” said lead author Alessandro Savino of the University of California at Berkeley. “It is a clear indication of how small-galaxy growth is disturbed by the influence of a massive galaxy like Andromeda.”
“Everything scattered in the Andromeda system is very asymmetric and perturbed. It does appear that something significant happened not too long ago,” said principal investigator Daniel Weisz of the University of California at Berkeley. “There’s always a tendency to use what we understand in our own galaxy to extrapolate more generally to the other galaxies in the universe. There’s always been concerns about whether what we are learning in the Milky Way applies more broadly to other galaxies. Or is there more diversity among external galaxies? Do they have similar properties? Our work has shown that low-mass galaxies in other ecosystems have followed different evolutionary paths than what we know from the Milky Way satellite galaxies.”
For example, half of the Andromeda satellite galaxies all seem to be confined to a plane, all orbiting in the same direction. “That’s weird. It was actually a total surprise to find the satellites in that configuration and we still don’t fully understand why they appear that way,” said Weisz.
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This animation begins with a view of the neighboring Andromeda galaxy. We zoom through a scattering of foreground stars and enter the inky blackness of intergalactic space. We cross 2.5 million light-years to reach the Andromeda system, consisting of 36 dwarf satellite galaxies orbiting the giant spindle-shaped Andromeda galaxy at image center. An ambitious survey by the Hubble Space Telescope was made to plot the galaxy locations in three-dimensional space. In this video we circle around a model of the Andromeda system based on real Hubble observational data. NASA, ESA, Christian Nieves (STScI), Alessandro Savino (UC Berkeley); Acknowledgment: Joseph DePasquale (STScI), Frank Summers (STScI), Robert Gendler The brightest companion galaxy to Andromeda is Messier 32 (M32). This is a compact ellipsoidal galaxy that might just be the remnant core of a larger galaxy that collided with Andromeda a few billion years ago. After being gravitationally stripped of gas and some stars, it continued along its orbit. Galaxy M32 contains older stars, but there is evidence it had a flurry of star formation a few billion years ago. In addition to M32, there seems to be a unique population of dwarf galaxies in Andromeda not seen in the Milky Way. They formed most of their stars very early on, but then they didn’t stop. They kept forming stars out of a reservoir of gas at a very low rate for a much longer time.
“Star formation really continued to much later times, which is not at all what you would expect for these dwarf galaxies,” continued Savino. “This doesn’t appear in computer simulations. No one knows what to make of that so far.”
“We do find that there is a lot of diversity that needs to be explained in the Andromeda satellite system,” added Weisz. “The way things come together matters a lot in understanding this galaxy’s history.”
Hubble is providing the first set of imaging where astronomers measure the motions of the dwarf galaxies. In another five years Hubble or NASA’s James Webb Space Telescope will be able to get the second set of observations, allowing astronomers to do a dynamical reconstruction for all 36 of the dwarf galaxies, which will help astronomers to rewind the motions of the entire Andromeda ecosystem billions of years into the past.
The Hubble Space Telescope has been operating for over three decades and continues to make ground-breaking discoveries that shape our fundamental understanding of the universe. Hubble is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope and mission operations. Lockheed Martin Space, based in Denver, also supports mission operations at Goddard. The Space Telescope Science Institute in Baltimore, which is operated by the Association of Universities for Research in Astronomy, conducts Hubble science operations for NASA.
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NASA’s Hubble Traces Hidden History of Andromeda Galaxy
Hubble’s High-Definition Panoramic View of the Andromeda Galaxy
Explore the Night Sky: Messier 31
Hubble’s Galaxies
Facebook logo @NASAHubble @NASAHubble Instagram logo @NASAHubble Media Contact:
Claire Andreoli (claire.andreoli@nasa.gov)
NASA’s Goddard Space Flight Center, Greenbelt, Maryland
Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
Science Contact:
Alessandro Savino
University of California, Berkeley, California
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Last Updated Feb 27, 2025 Editor Andrea Gianopoulos Location NASA Goddard Space Flight Center Related Terms
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Since its 1990 launch, the Hubble Space Telescope has changed our fundamental understanding of the universe.
Galaxy Details and Mergers
Reshaping Our Cosmic View: Hubble Science Highlights
Hubble’s Night Sky Challenge
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By NASA
An image of a coastal marshland combines aerial and satellite views in a technique similar to hyperspectral imaging. Combining data from multiple sources gives scientists information that can support environmental management.John Moisan When it comes to making real-time decisions about unfamiliar data – say, choosing a path to hike up a mountain you’ve never scaled before – existing artificial intelligence and machine learning tech doesn’t come close to measuring up to human skill. That’s why NASA scientist John Moisan is developing an AI “eye.”
Oceanographer John MoisanNASA Moisan, an oceanographer at NASA’s Wallops Flight Facility near Chincoteague, Virginia, said AI will direct his A-Eye, a movable sensor. After analyzing images his AI would not just find known patterns in new data, but also steer the sensor to observe and discover new features or biological processes.
“A truly intelligent machine needs to be able to recognize when it is faced with something truly new and worthy of further observation,” Moisan said. “Most AI applications are mapping applications trained with familiar data to recognize patterns in new data. How do you teach a machine to recognize something it doesn’t understand, stop and say ‘What was that? Let’s take a closer look.’ That’s discovery.”
Finding and identifying new patterns in complex data is still the domain of human scientists, and how humans see plays a large part, said Goddard AI expert James MacKinnon. Scientists analyze large data sets by looking at visualizations that can help bring out relationships between different variables within the data.
Infrared images like this one from a marsh area on the Maryland/Virginia Eastern Shore coastal barrier and back bay regions reveal clues to scientists about plant health, photosynthesis, and other conditions that affect vegetation and ecosystems.John Moisan It’s another story to train a computer to look at large data streams in real time to see those connections, MacKinnon said. Especially when looking for correlations and inter-relationships in the data that the computer hasn’t been trained to identify.
Moisan intends first to set his A-Eye on interpreting images from Earth’s complex aquatic and coastal regions. He expects to reach that goal this year, training the AI using observations from prior flights over the Delmarva Peninsula. Follow-up funding would help him complete the optical pointing goal.
“How do you pick out things that matter in a scan?” Moisan asked. “I want to be able to quickly point the A-Eye at something swept up in the scan, so that from a remote area we can get whatever we need to understand the environmental scene.”
Moisan’s on-board AI would scan the collected data in real-time to search for significant features, then steer an optical sensor to collect more detailed data in infrared and other frequencies.
Thinking machines may be set to play a larger role in future exploration of our universe. Sophisticated computers taught to recognize chemical signatures that could indicate life processes, or landscape features like lava flows or craters, might offer to increase the value of science data returned from lunar or deep-space exploration.
Today’s state-of-the-art AI is not quite ready to make mission-critical decisions, MacKinnon said.
“You need some way to take a perception of a scene and turn that into a decision and that’s really hard,” he said. “The scary thing, to a scientist, is to throw away data that could be valuable. An AI might prioritize what data to send first or have an algorithm that can call attention to anomalies, but at the end of the day, it’s going to be a scientist looking at that data that results in discoveries.”
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Last Updated Feb 10, 2025 Related Terms
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By NASA
The ring of light surrounding the center of the galaxy NGC 6505, captured by ESA’s Euclid telescope, is an example of an Einstein ring. NGC 6505 is acting as a gravitational lens, bending light from a galaxy far behind it. ESA/Euclid/Euclid Consortium/NASA, image processing by J.-C. Cuillandre, G. Anselmi, T. Li; CC BY-SA 3.0 IGO or ESA Standard Licence Euclid, an ESA (European Space Agency) mission with NASA contributions, has made a surprising discovery in our cosmic backyard: a phenomenon called an Einstein ring.
An Einstein ring is light from a distant galaxy bending to form a ring that appears aligned with a foreground object. The name honors Albert Einstein, whose general theory of relativity predicts that light will bend and brighten around objects in space.
In this way, particularly massive objects like galaxies and galaxy clusters serve as cosmic magnifying glasses, bringing even more distant objects into view. Scientists call this gravitational lensing.
Euclid Archive Scientist Bruno Altieri noticed a hint of an Einstein ring among images from the spacecraft’s early testing phase in September 2023.
“Even from that first observation, I could see it, but after Euclid made more observations of the area, we could see a perfect Einstein ring,” Altieri said. “For me, with a lifelong interest in gravitational lensing, that was amazing.”
The ring appears to encircle the center of a well-studied elliptical galaxy called NGC 6505, which is around 590 million light-years from Earth in the constellation Draco. That may sound far, but on the scale of the entire universe, NGC 6505 is close by. Thanks to Euclid’s high-resolution instruments, this is the first time that the ring of light surrounding the galaxy has been detected.
Light from a much more distant bright galaxy, some 4.42 billion light-years away, creates the ring in the image. Gravity distorted this light as it traveled toward us. This faraway galaxy hasn’t been observed before and doesn’t yet have a name.
“An Einstein ring is an example of strong gravitational lensing,” explained Conor O’Riordan, of the Max Planck Institute for Astrophysics, Germany, and lead author of the first scientific paper analyzing the ring. “All strong lenses are special, because they’re so rare, and they’re incredibly useful scientifically. This one is particularly special, because it’s so close to Earth and the alignment makes it very beautiful.”
Einstein rings are a rich laboratory for scientists to explore many mysteries of the universe. For example, an invisible form of matter called dark matter contributes to the bending of light into a ring, so this is an indirect way to study dark matter. Einstein rings are also relevant to the expansion of the universe because the space between us and these galaxies — both in the foreground and the background — is stretching. Scientists can also learn about the background galaxy itself.
“I find it very intriguing that this ring was observed within a well-known galaxy, which was first discovered in 1884,” said Valeria Pettorino, ESA Euclid project scientist. “The galaxy has been known to astronomers for a very long time. And yet this ring was never observed before. This demonstrates how powerful Euclid is, finding new things even in places we thought we knew well. This discovery is very encouraging for the future of the Euclid mission and demonstrates its fantastic capabilities.”
A close-up view of the center of the NGC 6505 galaxy, with the bright Einstein ring aligned with it, captured by ESA’s Euclid space telescope.ESA/Euclid/Euclid Consortium/NASA, image processing by J.-C. Cuillandre, G. Anselmi, T. Li; CC BY-SA 3.0 IGO or ESA Standard Licence By exploring how the universe has expanded and formed over its cosmic history, Euclid will reveal more about the role of gravity and the nature of dark energy and dark matter. Dark energy is the mysterious force that appears to be causing the universe’s expansion. The space telescope will map more than a third of the sky, observing billions of galaxies out to 10 billion light-years. It is expected to find around 100,000 strong gravitational lenses.
“Euclid is going to revolutionize the field with all this data we’ve never had before,” added O’Riordan.
Although finding this Einstein ring is an achievement, Euclid must look for a different, less visually obvious type of gravitational lensing called “weak lensing” to help fulfil its quest of understanding dark energy. In weak lensing, background galaxies appear only mildly stretched or displaced. To detect this effect, scientists will need to analyze billions of galaxies.
Euclid launched from Cape Canaveral, Florida, July 1, 2023, and began its detailed survey of the sky Feb. 14, 2024. The mission is gradually creating the most extensive 3D map of the universe yet. The Einstein ring find so early in its mission indicates Euclid is on course to uncover many more secrets of the universe.
More About Euclid
Euclid is a European mission, built and operated by ESA, with contributions from NASA. The Euclid Consortium — consisting of more than 2,000 scientists from 300 institutes in 15 European countries, the United States, Canada, and Japan — is responsible for providing the scientific instruments and scientific data analysis. ESA selected Thales Alenia Space as prime contractor for the construction of the satellite and its service module, with Airbus Defence and Space chosen to develop the payload module, including the telescope. Euclid is a medium-class mission in ESA’s Cosmic Vision Programme.
Three NASA-supported science teams contribute to the Euclid mission. In addition to designing and fabricating the sensor-chip electronics for Euclid’s Near Infrared Spectrometer and Photometer (NISP) instrument, NASA’s Jet Propulsion Laboratory led the procurement and delivery of the NISP detectors as well. Those detectors, along with the sensor chip electronics, were tested at NASA’s Detector Characterization Lab at Goddard Space Flight Center in Greenbelt, Maryland. The Euclid NASA Science Center at IPAC (ENSCI), at Caltech in Pasadena, California, will archive the science data and support U.S.-based science investigations. JPL is a division of Caltech.
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Elizabeth Landau
Headquarters, Washington
202-358-0845
elandau@nasa.gov
Calla Cofield
Jet Propulsion Laboratory, Pasadena, Calif.
626-808-2469
calla.e.cofield@jpl.nasa.gov
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By European Space Agency
Euclid, the European Space Agency’s dark Universe detective, has made an astonishing discovery – right in our cosmic backyard.
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