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NASA’s Hubble Provides Bird’s-Eye View of Andromeda Galaxy’s Ecosystem
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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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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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Hubble’s Galaxies
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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
- Hubble Space Telescope
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Reshaping Our Cosmic View: Hubble Science Highlights
Our Galaxy’s central black hole puts on a fireworks show
Nature, Published online: 27 February 2025; doi:10.1038/d41586-025-00578-2
The James Webb Space Telescope uncovered repeated flares from the supermassive object called Sagittarius A*.Glacial isostatic adjustment reveals Mars’s interior viscosity structure
Nature, Published online: 26 February 2025; doi:10.1038/s41586-024-08565-9
Emplacement of the north polar cap of Mars is investigated by combining viscoelastic deformation calculations and observations, showing that it formed over the last 1.7–12.0 Myr atop a stiff lithosphere and high-viscosity mantle (1022 Pa s), and that glacial isostatic adjustment could be further constrained.Meet the ice-hunting robots headed for the Moon right now
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Two US probes launched today, one laden with a drill and a hopper looking for lunar water.NASA: New Study on Why Mars is Red Supports Potentially Habitable Past
4 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)A new international study partially funded by NASA on how Mars got its iconic red color adds to evidence that Mars had a cool but wet and potentially habitable climate in its ancient past.
Mosaic of the Valles Marineris hemisphere of Mars projected into point perspective, a view similar to that which one would see from a spacecraft. The distance is 2500 kilometers from the surface of the planet, with the scale being .6km/pixel. The mosaic is composed of 102 Viking Orbiter images of Mars. The center of the scene (lat -8, long 78) shows the entire Valles Marineris canyon system, over 2000 kilometers long and up to 8 kilometers deep, extending form Noctis Labyrinthus, the arcuate system of graben to the west, to the chaotic terrain to the east. Many huge ancient river channels begin from the chaotic terrain from north-central canyons and run north. The three Tharsis volcanoes (dark red spots), each about 25 kilometers high, are visible to the west. South of Valles Marineris is very ancient terrain covered by many impact craters.NASA
The current atmosphere of Mars is too cold and thin to support liquid water, an essential ingredient for life, on its surface for lengthy periods. However, various NASA and international missions have found evidence that water was abundant on the Martian surface billions of years ago during a more clement era, such as features that resemble dried-up rivers and lakes, and minerals that only form in the presence of liquid water.
Adding to this evidence, results from a study published February 25 in the journal Nature Communications suggest that the water-rich iron mineral ferrihydrite may be the main culprit behind Mars’ reddish dust. Martian dust is known to be a hodgepodge of different minerals, including iron oxides, and this new study suggests one of those iron oxides, ferrihydrite, is the reason for the planet’s color.
The finding offers a tantalizing clue to Mars’ wetter and potentially more habitable past because ferrihydrite forms in the presence of cool water, and at lower temperatures than other previously considered minerals, like hematite. This suggests that Mars may have had an environment capable of sustaining liquid water before it transitioned from a wet to a dry environment billions of years ago.
“The fundamental question of why Mars is red has been considered for hundreds if not for thousands of years,” said lead author Adam Valantinas, a postdoctoral fellow at Brown University, Providence, Rhode Island, who started the work as a Ph.D. student at the University of Bern, Switzerland. “From our analysis, we believe ferrihydrite is everywhere in the dust and also probably in the rock formations, as well. We’re not the first to consider ferrihydrite as the reason for why Mars is red, but we can now better test this using observational data and novel laboratory methods to essentially make a Martian dust in the lab.”
Laboratory sample showing simulated Martian dust. The ochre color is characteristic of iron-rich ferrihydrite, a mineral that provides crucial insights into ancient water activity and environmental conditions on Mars. The fine-powder mixture consists of ferrihydrite and ground basalt with particles less than one micrometer in size (1/100th diameter of a human hair) (Sample scale: 1 inch across).Adam Valantinas
“These new findings point to a potentially habitable past for Mars and highlight the value of coordinated research between NASA and its international partners when exploring fundamental questions about our solar system and the future of space exploration,” said Geronimo Villanueva, the Associate Director for Strategic Science of the Solar System Exploration Division at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and co-author of this study.
The researchers analyzed data from multiple Mars missions, combining orbital observations from instruments on NASA’s Mars Reconnaissance Orbiter, ESA’s (the European Space Agency) Mars Express and Trace Gas Orbiter with ground-level measurements from NASA rovers like Curiosity, Pathfinder, and Opportunity. Instruments on the orbiters and rovers provided detailed spectral data of the planet’s dusty surface. These findings were then compared to laboratory experiments, where the team tested how light interacts with ferrihydrite particles and other minerals under simulated Martian conditions.
“What we want to understand is the ancient Martian climate, the chemical processes on Mars — not only ancient — but also present,” said Valantinas. “Then there’s the habitability question: Was there ever life? To understand that, you need to understand the conditions that were present during the time of this mineral’s formation. What we know from this study is the evidence points to ferrihydrite forming and for that to happen there must have been conditions where oxygen from air or other sources and water can react with iron. Those conditions were very different from today’s dry, cold environment. As Martian winds spread this dust everywhere, it created the planet’s iconic red appearance.”
Whether the team’s proposed formation model is correct could be definitively tested after samples from Mars are delivered to Earth for analysis.
“The study really is a door-opening opportunity,” said Jack Mustard of Brown University, a senior author on the study. “It gives us a better chance to apply principles of mineral formation and conditions to tap back in time. What’s even more important though is the return of the samples from Mars that are being collected right now by the Perseverance rover. When we get those back, we can actually check and see if this is right.”
Part of the spectral measurements were performed at NASA’s Reflectance Experiment Laboratory (RELAB) at Brown University. RELAB is supported by NASA’s Planetary Science Enabling Facilities program, part of the Planetary Science Division of NASA’s Science Mission Directorate at NASA Headquarters in Washington.
NASA Goddard Space Flight Center, Greenbelt, Maryland
Share Details Last Updated Feb 24, 2025 EditorWilliam SteigerwaldContactLonnie Shekhtmanlonnie.shekhtman@nasa.govLocationNASA Goddard Space Flight Center Related Terms Explore More 2 min read NASA Prepares Gateway Lunar Space Station for Journey to MoonAssembly is underway for Gateway's Power and Propulsion Element, the module that will power the…
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Chance of giant asteroid hitting Earth in 2032 falls to 0.0017%
Asteroid 2024 YR4 had reached a 3.1% likelihood of impact but further data has rendered it negligible
It was a discovery that led to panic-inducing headlines: a giant asteroid found to be hurtling towards Earth that, while unlikely to wipe out life, could do some serious damage.
But now the world can breathe a sigh of relief. After the odds of a future collision rose earlier this year, the likelihood of an impact is now so low as to be negligible.
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Hubble Captures a Cosmic Cloudscape
The universe is a dusty place, as this NASA/ESA Hubble Space Telescope image featuring swirling clouds of gas and dust near the Tarantula Nebula reveals. Located in the Large Magellanic Cloud about 160,000 light-years away in the constellations Dorado and Mensa, the Tarantula Nebula is the most productive star-forming region in the nearby universe, home to the most massive stars known.
The nebula’s colorful gas clouds hold wispy tendrils and dark clumps of dust. This dust is different from ordinary household dust, which may include bits of soil, skin cells, hair, and even plastic. Cosmic dust is often comprised of carbon or of molecules called silicates, which contain silicon and oxygen. The data in this image was part of an observing program that aims to characterize the properties of cosmic dust in the Large Magellanic Cloud and other nearby galaxies.
Dust plays several important roles in the universe. Even though individual dust grains are incredibly tiny, far smaller than the width of a single human hair, dust grains in disks around young stars clump together to form larger grains and eventually planets. Dust also helps cool clouds of gas so that they can condense into new stars. Dust even plays a role in making new molecules in interstellar space, providing a venue for individual atoms to find each other and bond together in the vastness of space.
Asteroid 2024 YR4 will now almost certainly miss Earth in 2032
Asteroid 2024 YR4 now unlikely to hit Earth — but scientists are ready for future threats
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Ultra-low-noise Infrared Detectors for Exoplanet Imaging
5 min read
Ultra-low-noise Infrared Detectors for Exoplanet Imaging A linear-mode avalanche photodiode array in the test dewar. The detector is the dark square in the center. Michael Bottom, University of Hawai’i
One of the ultimate goals in astrophysics is the discovery of Earth-like planets that are capable of hosting life. While thousands of planets have been discovered around other stars, the vast majority of these detections have been made via indirect methods, that is, by detecting the effect of the planet on the star’s light, rather than detecting the planet’s light directly. For example, when a planet passes in front of its host star, the brightness of the star decreases slightly.
However, indirect methods do not allow for characterization of the planet itself, including its temperature, pressure, gravity, and atmospheric composition. Planetary atmospheres may include “biosignature” gases like oxygen, water vapor, carbon dioxide, etc., which are known to be key ingredients needed to support life as we know it. As such, direct imaging of a planet and characterization of its atmosphere are key to understanding its potential habitability.
But the technical challenges involved in imaging Earth-like extrasolar planets are extreme. First such planets are detected only by observing light they reflect from their parent star, and so they typically appear fainter than the stars they orbit by factors of about 10 billion. Furthermore, at the cosmic distances involved, the planets appear right next to the stars. A popular expression is that exoplanet imaging is like trying to detect a firefly three feet from a searchlight from a distance of 300 miles.
Tremendous effort has gone into developing starlight suppression technologies to block the bright glare of the star, but detecting the light of the planet is challenging in its own right, as planets are incredibly faint. One way to quantify the faintness of planetary light is to understand the photon flux rate. A photon is an indivisible particle of light, that is, the minimum detectable amount of light. On a sunny day, approximately 10 thousand trillion photons enter your eye every second. The rate of photons entering your eye from an Earth-like exoplanet around a nearby star would be around 10 to 100 per year. Telescopes with large mirrors can help collect as much of this light as possible, but ultra-sensitive detectors are also needed, particularly for infrared light, where the biosignature gases have their strongest effects. Unfortunately, state-of-the-art infrared detectors are far too noisy to detect the low level of light emitted from exoplanets.
With support from NASA’s Astrophysics Division and industrial partners, researchers at the University of Hawai’i are developing a promising detector technology to meet these stringent sensitivity requirements. These detectors, known as avalanche photodiode arrays, are constructed out of the same semiconductor material as conventional infrared sensors. However, these new sensors employ an extra “avalanche” layer that takes the signal from a single photon and multiplies it, much like an avalanche can start with a single snowball and quickly grow it to the size of a boulder. This signal amplification occurs before any noise from the detector is introduced, so the effective noise is proportionally reduced. However, at high avalanche levels, photodiodes start to behave badly, with noise exponentially increasing, which negates any benefits of the signal amplification. Late University of Hawai’i faculty member Donald Hall, who was a key figure in driving technology for infrared astronomy, realized the potential use of avalanche photodiodes for ultra-low-noise infrared astronomy with some modifications to the material properties.
University of Hawai’i team members with cryogenic dewar used to test the sensors. From left to right, Angelu Ramos, Michael Bottom, Shane Jacobson, Charles-Antoine Claveau. Michael Bottom, University of Hawai’i
The most recent sensors benefit from a new design including a graded semiconductor bandgap that allows for excellent noise performance at moderate amplification, a mesa pixel geometry to reduce electronic crosstalk, and a read-out integrated circuit to allow for short readout times. “It was actually challenging figuring out just how sensitive these detectors are,” said Michael Bottom, associate professor at the University of Hawai’i and lead of development effort. “Our ‘light-tight’ test chamber, which was designed to evaluate the infrared sensors on the James Webb Space Telescope, was supposed to be completely dark. But when we put these avalanche photodiodes in the chamber, we started seeing light leaks at the level of a photon an hour, which you would never be able to detect using the previous generation of sensors.”
The new designs have a format of one megapixel, more than ten times larger than the previous iteration of sensors, and circuitry that allows for tracking and subtracting any electronic drifts. Additionally, the pixel size and control electronics are such that these new sensors could be drop-in replacements for the most common infrared sensors used on the ground, which would give new capabilities to existing instruments.
Image of the Palomar-2 globular cluster located in the constellation of Auriga, taken with the linear-mode avalanche photodiode arrays, taken from the first on-sky testing of the sensors using the University of Hawai’i’s 2.2 meter telescope. Michael Bottom, University of Hawai’i
Last year, the team took the first on-sky images from the detectors, using the University of Hawai’i’s 2.2-meter telescope. “It was impressive to see the avalanche process on sky. When we turned up the gain, we could see more stars appear,” said Guillaume Huber, a graduate student working on the project. “The on-sky demonstration was important to prove the detectors could perform well in an operational environment,” added Michael Bottom.
According to the research team, while the current sensors are a major step forward, the megapixel format is still too small for many science applications, particularly those involving spectroscopy. Further tasks include improving detector uniformity and decreasing persistence. The next generation of sensors will be four times larger, meeting the size requirements for the Habitable Worlds Observatory, NASA’s next envisioned flagship mission, with the goals of imaging and characterizing Earth-like exoplanets.
Project Lead: Dr. Michael Bottom, University of Hawai’i
Sponsoring Organization: NASA Strategic Astrophysics Technology (SAT) Program
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