SPACE
NASA’s Webb reveals new features in heart of Milky Way
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THE NIRCAM (NEAR-INFRARED CAMERA) INSTRUMENT ON NASA’S JAMES WEBB SPACE TELESCOPE’S REVEALS A PORTION OF THE MILKY WAY’S DENSE CORE IN A NEW LIGHT. AN ESTIMATED 500,000 STARS SHINE IN THIS IMAGE OF THE SAGITTARIUS C (SGR C) REGION, ALONG WITH SOME AS-YET UNIDENTIFIED FEATURES. A LARGE REGION OF IONIZED HYDROGEN, SHOWN IN CYAN, CONTAINS INTRIGUING NEEDLE-LIKE STRUCTURES THAT LACK ANY UNIFORM ORIENTATION.
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CREDIT: NASA, ESA, CSA, STSCI, AND S. CROWE (UNIVERSITY OF VIRGINIA).
The latest image from NASA’s James Webb Space Telescope shows a portion of the dense center of our galaxy in unprecedented detail, including never-before-seen features astronomers have yet to explain. The star-forming region, named Sagittarius C (Sgr C), is about 300 light-years from the Milky Way’s central supermassive black hole, Sagittarius A*.
“There’s never been any infrared data on this region with the level of resolution and sensitivity we get with Webb, so we are seeing lots of features here for the first time,” said the observation team’s principal investigator Samuel Crowe, an undergraduate student at the University of Virginia in Charlottesville. “Webb reveals an incredible amount of detail, allowing us to study star formation in this sort of environment in a way that wasn’t possible previously.”
“The galactic center is the most extreme environment in our Milky Way galaxy, where current theories of star formation can be put to their most rigorous test,” added professor Jonathan Tan, one of Crowe’s advisors at the University of Virginia.
Protostars
Amid the estimated 500,000 stars in the image is a cluster of protostars – stars that are still forming and gaining mass – producing outflows that glow like a bonfire in the midst of an infrared-dark cloud. At the heart of this young cluster is a previously known, massive protostar over 30 times the mass of our Sun. The cloud the protostars are emerging from is so dense that the light from stars behind it cannot reach Webb, making it appear less crowded when in fact it is one of the most densely packed areas of the image. Smaller infrared-dark clouds dot the image, looking like holes in the starfield. That’s where future stars are forming.
Webb’s NIRCam (Near-Infrared Camera) instrument also captured large-scale emission from ionized hydrogen surrounding the lower side of the dark cloud, shown cyan-colored in the image. Typically, Crowe says, this is the result of energetic photons being emitted by young massive stars, but the vast extent of the region shown by Webb is something of a surprise that bears further investigation. Another feature of the region that Crowe plans to examine further is the needle-like structures in the ionized hydrogen, which appear oriented chaotically in many directions.
“The galactic center is a crowded, tumultuous place. There are turbulent, magnetized gas clouds that are forming stars, which then impact the surrounding gas with their outflowing winds, jets, and radiation,” said Rubén Fedriani, a co-investigator of the project at the Instituto Astrofísica de Andalucía in Spain. “Webb has provided us with a ton of data on this extreme environment, and we are just starting to dig into it.”
Around 25,000 light-years from Earth, the galactic center is close enough to study individual stars with the Webb telescope, allowing astronomers to gather unprecedented information on how stars form, and how this process may depend on the cosmic environment, especially compared to other regions of the galaxy. For example, are more massive stars formed in the center of the Milky Way, as opposed to the edges of its spiral arms?
“The image from Webb is stunning, and the science we will get from it is even better,” Crowe said. “Massive stars are factories that produce heavy elements in their nuclear cores, so understanding them better is like learning the origin story of much of the universe.”
Approximate outlines help to define the features in the Sagittarius C (Sgr C) region. Astronomers are studying data from NASA’s James Webb Space Telescope to understand the relationship between these features, as well as other influences in the chaotic galaxy center.
CREDIT
NASA, ESA, CSA, STScI, Samuel Crowe (UVA)
The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.
“Triple star” discovery could revolutionise understanding of stellar evolution
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IMAGE CAPTION: ARTIST’S IMPRESSION COMPOSED OF A STAR WITH A DISC AROUND IT (A BE “VAMPIRE” STAR; FOREGROUND) AND ITS COMPANION STAR THAT HAS BEEN STRIPPED OF ITS OUTER PARTS (BACKGROUND).
view moreCREDIT: PIC CREDIT: ESO/L. CALÇADA
A ground-breaking new discovery by University of Leeds scientists could transform the way astronomers understand some of the biggest and most common stars in the Universe.
Research by PhD student Jonathan Dodd and Professor René Oudmaijer, from the University’s School of Physics and Astronomy, points to intriguing new evidence that massive Be stars – until now mainly thought to exist in double stars – could in fact be “triples”.
The remarkable discovery could revolutionise our understanding of the objects – a subset of B stars - which are considered an important “test bed” for developing theories on how stars evolve more generally.
These Be stars are surrounded by a characteristic disc made of gas – similar to the rings of Saturn in our own Solar System. And although Be stars have been known for about 150 years – having first been identified by renowned Italian astronomer Angelo Secchi in 1866 - until now, no one has known how they were formed.
Consensus among astronomers so far has said the discs are formed by the rapid rotation of the Be stars, and that itself can be caused by the stars interacting with another star in a binary system.
Triple systems
Mr Dodd, corresponding author of the research, said: “The best point of reference for that is if you've watched Star Wars, there are planets where they have two Suns.”
But now, by analysing data from the European Space Agency’s Gaia satellite, the scientists say they have found evidence these stars actually exist in triple systems – with three bodies interacting instead of just two.
Mr Dodd added: “We observed the way the stars move across the night sky, over longer periods like 10 years, and shorter periods of around six months. If a star moves in a straight line, we know there’s just one star, but if there is more than one, we will see a slight wobble or, in the best case, a spiral.
“We applied this across the two groups of stars that we are looking at – the B stars and the Be stars – and what we found, confusingly, is that at first it looks like the Be stars have a lower rate of companions than the B stars. This is interesting because we’d expect them to have a higher rate.”
However, Principal Investigator Prof Oudmaijer said: “The fact that we do not see them might be because they are now too faint to be detected.”
Mass transfer
The researchers then looked at a different set of data, looking for companion stars that are further away, and found that at these larger separations the rate of companion stars is very similar between the B and Be stars.
From this, they were able to infer that in many cases a third star is coming into play, forcing the companion closer to the Be star – close enough that mass can be transferred from one to the other and form the characteristic Be star disc. This could also explain why we do not see these companions anymore; they have become too small and faint to be detected after the “vampire” Be star has sucked in so much of their mass.
The discovery could have huge impacts on other areas of astronomy – including our understanding of black holes, neutron stars and gravitational wave sources.
Prof Oudmaijer said: “There's a revolution going on in physics at the moment around gravitational waves. We have only been observing these gravitational waves for a few years now, and these have been found to be due to merging black holes.
“We know that these enigmatic objects – black holes and neutron stars – exist, but we don't know much about the stars that would become them. Our findings provide a clue to understanding these gravitational wave sources.”
He added: “Over the last decade or so, astronomers have found that binarity is an incredibly important element in stellar evolution. We are now moving more towards the idea it is even more complex than that and that triple stars need to be considered.”
“Indeed,” Oudmaijer said, “triples have become the new binaries”.
The team behind the discovery includes PhD student Mr Dodd and Prof Oudmaijer from Leeds, along with University of Leeds PhD student Isaac Radley and two former Leeds academics Dr Miguel Vioque of the ALMA Observatory in Chile and Dr Abigail Frost at the European Southern Observatory in Chile. The team received funding from the Science and Technology Facilities Council (STFC).
The paper - “Gaia uncovers difference in B and Be star binarity at small scales: evidence for mass transfer causing the Be phenomenon” – will be published on 21 November at 00.01 Universal Time Coordinated (UTC), in the journal Monthly Notices of the Royal Astronomical Society.
Artist’s impression of a vampire star (left) stealing material from its victim: New research using data from ESO’s Very Large Telescope has revealed that the hottest and brightest stars, which are known as O stars, are often found in close pairs. Many of such binaries will at some point transfer mass from one star to another, a kind of stellar vampirism depicted in this artist’s impression.
CREDIT
Pic credit: ESO/M. Kornmesser/S.E. de Mink
Artist’s Animation [VIDEO] |
JOURNAL
Monthly Notices of the Royal Astronomical Society
METHOD OF RESEARCH
Observational study
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Gaia uncovers difference in B and Be star binarity at small scales: evidence for mass transfer causing the Be phenomenon
ARTICLE PUBLICATION DATE
21-Nov-2023
Physicists answer question of Supergalactic Plane’s absent spiral galaxies
IMAGE:
ARTIST CONCEPT OF THE MILKY WAY.
view moreCREDIT: NASA/JPL-CALTECH.
Astrophysicists say they have found an answer to why spiral galaxies like our own Milky Way are largely missing from a part of our Local Universe called the Supergalactic Plane.
The Supergalactic Plane is an enormous, flattened structure extending nearly a billion light years across in which our own Milky Way galaxy is embedded.
While the Plane is teeming with bright elliptical galaxies, bright disk galaxies with spiral arms are conspicuously scarce.
Now an international team of researchers, co-led by Durham University, UK, and the University of Helsinki, Finland, say different distributions of elliptical and disk galaxies arise naturally due to the contrasting environments found inside and outside the Plane.
In the dense galaxy clusters found on the Supergalactic Plane, galaxies experience frequent interactions and mergers with other galaxies. This transforms spiral galaxies into elliptical galaxies – smooth galaxies with no apparent internal structure or spiral arms – and leads to the growth of supermassive black holes.
By contrast, away from the Plane, galaxies can evolve in relative isolation, which helps them preserve their spiral structure.
The findings are published in the journal Nature Astronomy.
The Milky Way is part of the Supergalactic Plane, which contains several massive galaxy clusters and thousands of individual galaxies. The vast majority of galaxies found here are elliptical galaxies.
The research team used the SIBELIUS (Simulations Beyond the Local Universe) supercomputer simulation, which follows the evolution of the Universe over 13.8 billion years from the early Universe to the present day.
While most cosmological simulations consider random patches of the Universe, which cannot be directly compared to observations, SIBELIUS aims to precisely reproduce the observed structures, including the Supergalactic Plane. The final simulation is remarkably consistent with observations of our Universe through telescopes.
Research co-author Professor Carlos Frenk, Ogden Professor of Fundamental Physics, in the Institute for Computational Cosmology, Durham University, said: “The distribution of galaxies in the Supergalactic Plane is indeed remarkable.
“It is rare but not a complete anomaly: our simulation reveals the intimate details of the formation of galaxies such as the transformation of spirals into ellipticals through galaxy mergers.
“Further, the simulation shows that our standard model of the Universe, based on the idea that most of its mass is cold dark matter, can reproduce the most remarkable structures in the Universe, including the spectacular structure of which the Milky Way is part.”
The peculiar separation of spiral and elliptical galaxies in the Local Universe, which has been known about since the 1960s, features prominently in a recent list of "cosmic anomalies" compiled by renowned cosmologist and 2019 Nobel laureate Professor Jim Peebles.
Research lead author Dr Till Sawala, a postdoctoral researcher at Durham University and at the University of Helsinki, said: “By chance, I was invited to a symposium in honour of Jim Peebles last December at Durham, where he presented the problem in his lecture.
“And I realised that we had already completed a simulation that might contain the answer. Our research shows that the known mechanisms of galaxy evolution also work in this unique cosmic environment.”
The supercomputer simulations were performed on the Cosmology Machine (COSMA 8) supercomputer, hosted by the Institute for Computational Cosmology at Durham University on behalf of the UK’s DiRAC High-Performance Computing facility and on CSC’s Mahti supercomputer in Finland.
The research was funded by the European Research Council, the Academy of Finland and the UK Science and Technology Facilities Council.
ENDS
This image, showing an elliptical galaxy (left) and a spiral galaxy (right) includes near-infrared light from the James Webb Space Telescope, and ultraviolet and visible light from the Hubble Space Telescope.
CREDIT
NASA, ESA, CSA, Rogier Windhorst (ASU), William Keel (University of Alabama), Stuart Wyithe (University of Melbourne), JWST PEARLS Team, Alyssa Pagan (STScI).
Distribution of the brightest galaxies in the Local Universe, observed in the 2MASS survey (left panel) and reproduced in the SIBELIUS simulation (right panel). Both panels show projections in supergalactic coordinates, out to approximately 100 Megaparsec (Mpc). The nearly vertical empty stripe represents the region of the sky hidden behind our own Milky Way galaxy. The simulation accurately reproduces the structures seen in the Local Universe.
CREDIT
Dr Till Sawala
JOURNAL
Nature Astronomy
METHOD OF RESEARCH
Computational simulation/modeling
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Distinct distributions of elliptical and disk galaxies across the Local Supercluster as a ΛCDM prediction
ARTICLE PUBLICATION DATE
20-Nov-2023
University of Helsinki researchers solve cosmic conundrum
Why is the vast supergalactic plane teeming with only one type of galaxies? This old cosmic puzzle may now have been solved.
Peer-Reviewed PublicationIMAGE:
IN THE SUPERGALACTIC PLANE, WHICH LIES ON THE EQUATOR OF THE PICTURE, GALAXIES EXPERIENCE FREQUENT INTERACTIONS AND MERGERS, LEADING TO THE FORMATION OF MASSIVE ELLIPTICAL GALAXIES. BY CONTRAST, GALAXIES AWAY FROM THE PLANE EVOLVE IN RELATIVE ISOLATION, ALLOWING THEM TO PRESERVE THEIR DISK-LIKE STRUCTURE.
view moreCREDIT: TILL SAWALA
University of Helsinki researchers solve cosmic conundrum
Why is the vast supergalactic plane teeming with only one type of galaxies? This old cosmic puzzle may now have been solved.
Our own Milky Way galaxy is part of a much larger formation, the local Supercluster structure, which contains several massive galaxy clusters and thousands of individual galaxies. Due to its pancake-like shape, which measures almost a billion light years across, it is also referred to as the Supergalactic Plane.
Most galaxies in the universe fall into one of two categories: firstly, elliptical galaxies, made mostly of old stars and containing typically extremely massive central black holes, and secondly actively star-forming disk galaxies, with a spiral-like structure similar to the Milky Way’s. Both types of galaxies are also found in the Local Supercluster, but while the Supergalactic Plane is teeming with bright ellipticals, bright disk galaxies are conspicuously absent.
A cosmic anomaly challenges the standard model of cosmology
This peculiar segregation of galaxies in the Local Universe, which has been known since the 1960s, features prominently in a recent list of "cosmic anomalies" compiled by renowned cosmologist and 2019 Nobel laureate Jim Peebles.
Now an international team led by University of Helsinki astrophysicists Till Sawala and Peter Johansson appear to have found an explanation. In an article published in Nature Astronomy, they show how the different distributions of elliptical and disk galaxies arise naturally due to the different environments found inside and outside of the Supergalactic Plane.
“In the dense galaxy clusters that are found on the Supergalactic Plane, galaxies experience frequent interactions and mergers, which leads to the formation of ellipticals and the growth of supermassive black holes. By contrast, away from the plane, galaxies can evolve in relative isolation, which helps them preserve their spiral structure”, says Till Sawala.
In their work, the team made use of the SIBELIUS (Simulations Beyond The Local Universe) simulation, that follows the evolution of the universe over 13.8 billion years, from the early universe to the present. It was run on supercomputers in England and on CSC’s Mahti supercomputer in Finland.
While most similar simulations consider random patches of the universe which cannot be directly compared to observations, the SIBELIUS simulation aims to precisely reproduce the observed structures, including the Local Supercluster. The final simulation result is remarkably consistent with the observations.
“By chance, I was invited to a symposium in honour of Jim Peebles last December, where he presented the problem in his lecture. And I realised that we had already completed a simulation that might contain the answer”, comments Till Sawala. “Our research shows that the known mechanisms of galaxy evolution also work in this unique cosmic environment”.
Next to the physics department, the University of Helsinki’s Kumpula campus hosts a large statue showing the distribution of galaxies in the Local Supercluster. It was inaugurated 20 years ago by the British cosmologist Carlos Frenk, who is one of the co-authors of this new study. “The distribution of galaxies in the Local Supercluster is indeed remarkable”, says Frenk of the new results. “But it is not an anomaly: our result shows that our standard model of dark matter can produce the most remarkable structures in the universe”.
Original publication:
Till Sawala, Carlos Frenk, Jens Jasche, Peter H. Johansson, Guilhem Lavaux, Distinct distributions of elliptical and disk galaxies across the Local Supercluster as a ΛCDM prediction, Nature Astronomy, 20 Nov 2023.
More information:
University Researcher Till Sawala (in English and in German)
University of Helsinki
+358 44 0418 000
till.sawala@helsinki.fi
Professor Peter Johansson (in Finnish and Swedish)
University of Helsinki
+358 50 318 3930
peter.johansson@helsinki.fi
Media (download high-resolution here): https://drive.google.com/file/d/1k8H4lQ3NO2-bbeRxrmyEdmIGCKt6Nv3E/view?usp=sharing
JOURNAL
Nature Astronomy
METHOD OF RESEARCH
Computational simulation/modeling
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Distinct distributions of elliptical and disk galaxies across the Local Supercluster as a ΛCDM prediction
ARTICLE PUBLICATION DATE
20-Nov-2023
Remarkably detailed view of “teenage galaxies” from just 2 to 3 billion years after the Big Bang revealed by JWST
Studying “teenage galaxies” from the ancient universe can teach scientists about how these massive systems of stars mature and evolve
Peer-Reviewed PublicationIMAGE:
JWST TELESCOPE IMAGE OF A GALAXY CLUSTER KNOWN AS "EL GORDO," WHICH IS AN EXAMPLE OF A "COSMIC TEENAGER."
view moreCREDIT: CREDIT: NASA/ESA/CSA.
Pasadena, CA—Galaxies that formed just 2 to 3 billion years after the Big Bang are unusually hot and glow with light from surprising elements, like nickel, according to new work led by Carnegie’s Gwen Rudie and Northwestern University’s Allison Strom. Studying “teenage galaxies” from the ancient universe can teach scientists about how these massive systems of stars mature and evolve.
Their findings, published in The Astrophysical Journal Letters, are part of the CECILIA (Chemical Evolution Constrained using Ionized Lines in Interstellar Aurorae) survey, developed by Rudie and Strom—a former Carnegie postdoc. Last July, they pointed JWST at 33 specially selected ancient galaxies whose light traveled more than 10 billion years to reach us and stared with the new telescope for more than a day, providing the most detailed view of these early galaxies yet captured.
In the universe’s youth, many galaxies, including the 33 chosen for this study, experienced a period of intense star formation. Today, some galaxies, such as our own Milky Way, still form new stars, albeit not as rapidly. Other galaxies have stopped forming stars altogether. This new work can help astronomers understand the reasons behind these different trajectories.
“We’re trying to understand how galaxies grew and changed over the 14 billion years of cosmic history,” said first author Allison Strom. “Using the JWST, our program targets teenage galaxies when they were going through a messy time of growth spurts and change. Teenagers often have experiences that determine their trajectories into adulthood. For galaxies, it’s the same.”
The CECILIA team studied the spectra from these distant galaxies, separating their light into its component wavelengths, just as a prism spreads sunlight into the colors of the rainbow. Looking at the light in this way helps astronomers measure the temperature and chemical composition of cosmic sources.
“We averaged together the spectra from all 33 galaxies to create the deepest spectrum of a distant galaxy ever seen—which it would take 600 hours of telescope time to replicate,” Rudie explained. “This enabled us to create an atlas, of sorts, that will inform future JWST observations of very distant objects.”
Using the spectra, the researchers were able to identify eight distinct elements: Hydrogen, helium, nitrogen, oxygen, silicon, sulfur, argon and nickel.
“These elements existing in these galaxies is not a surprise, but our ability to measure their light is unprecedented and shows the power of JWST,” said Rudie.
All elements that are heavier than hydrogen and helium form inside stars. When stars explode in violent events like supernovae, they spew these elements out into the cosmic surroundings, where they are incorporated into the next stellar generation. So, by revealing the presence of certain elements in these early galaxies, astronomers can learn about how star formation changes over the course of their evolution.
The CECILIA team were surprised by the presence of nickel, which is particularly difficult to observe.
“Never in my wildest dreams did I imagine we would see nickel,” Strom said. “Even in nearby galaxies, people don’t observe this. There has to be enough of an element present in a galaxy and the right conditions to observe it. No one ever talks about observing nickel. Elements have to be glowing in gas in order for us to see them. So, in order for us to see nickel, there may be something unique about the stars within the galaxies.”
"JWST is still a very new observatory," added co-author Ryan Trainor of Franklin & Marshall College. "Astronomers around the world are still trying to figure out the best ways to analyze the data we receive from the telescope."
Another surprise: The teenage galaxies were extremely hot. By examining the spectra, physicists can calculate a galaxy’s temperature. While the hottest pockets with galaxies can reach over 9,700 degrees Celsius or 17,492 degrees Fahrenheit, the teenage galaxies clock in at higher than 13,350 degrees Celsius or 24,062 degrees Fahrenheit.
“We expected these early galaxies to have very, very different chemistry from our own Milky Way and the galaxies that surround us today,” Rudie said. “But we were still surprised by what JWST revealed.”
The project was named in honor of Cecilia Payne-Gaposchkin, who did pioneering work on the chemistry of our Sun nearly 100 years ago. Her findings upended the scientific community’s understanding of the Sun’s composition, and she faced unfair criticism for years before her breakthrough work was finally recognized.
“Naming our JWST survey after Cecilia Payne was intended to pay homage to her pioneering studies of the chemical makeup of stars. Allison and I recognize that our own work revealing the chemistry of these very early galaxies is built upon her legacy.” Rudie said.
CECILIA was the first of six initial JWST projects led by Carnegie and Carnegie-affiliated astronomers selected to make observations using the incredible space telescope. Earlier this year, another four Carnegie-led initiatives were chosen for the second cycle of JWST time allocations.
__________________
This work was supported by NASA, the Pittsburgh Foundation and the Research Corporation for Scientific Advancement. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute and from the W.M. Keck Observatory.
The Carnegie Institution for Science (carnegiescience.edu) is a private, nonprofit organization headquartered in Washington, D.C., with three research divisions on both coasts. Since its founding in 1902, the Carnegie Institution has been a pioneering force in basic scientific research. Carnegie scientists are leaders in the life and environmental sciences, Earth and planetary science, and astronomy and astrophysics.
JOURNAL
The Astrophysical Journal Letters
METHOD OF RESEARCH
Observational study
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
CECILIA: The Faint Emission Line Spectrum of z ∼ 2–3 Star-forming Galaxies
ARTICLE PUBLICATION DATE
20-Nov-2023
‘Teenage galaxies’ are unusually hot, glowing with unexpected elements
JWST unexpectedly reveals nickel and oxygen, which are typically difficult to observe
IMAGE:
LIGHT FROM 23 DISTANT GALAXIES, IDENTIFIED WITH RED RECTANGLES IN THE HUBBLE SPACE TELESCOPE IMAGE AT THE TOP, WERE COMBINED TO CAPTURE INCREDIBLY FAINT EMISSION FROM EIGHT DIFFERENT ELEMENTS, WHICH ARE LABELLED IN THE JWST SPECTRUM AT THE BOTTOM.ALTHOUGH SCIENTISTS REGULARLY FIND THESE ELEMENTS ON EARTH, ASTRONOMERS RARELY, IF EVER, OBSERVE MANY OF THEM IN DISTANT GALAXIES.
view moreCREDIT: AARON M. GELLER, NORTHWESTERN, CIERA + IT-RCDS
Similar to human teenagers, teenage galaxies are awkward, experience growth spurts and enjoy heavy metal — nickel, that is.
A Northwestern University-led team of astrophysicists has just analyzed the first results from the CECILIA (Chemical Evolution Constrained using Ionized Lines in Interstellar Aurorae) Survey, a program that uses NASA’s James Webb Space Telescope (JWST) to study the chemistry of distant galaxies.
According to the early results, so-called “teenage galaxies” — which formed two-to-three billion years after the Big Bang — are unusually hot and contain unexpected elements, like nickel, which are notoriously difficult to observe.
The research will be published on Monday (Nov. 20) in The Astrophysical Journal Letters. It marks the first in a series of forthcoming studies from the CECILIA Survey.
“We’re trying to understand how galaxies grew and changed over the 14 billion years of cosmic history,” said Northwestern’s Allison Strom, who led the study. “Using the JWST, our program targets teenage galaxies when they were going through a messy time of growth spurts and change. Teenagers often have experiences that determine their trajectories into adulthood. For galaxies, it’s the same.”
One of the principal investigators of the CECILIA Survey, Strom is an assistant professor of physics and astronomy at Northwestern’s Weinberg College of Arts and Sciences and a member of Northwestern’s Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA). Strom co-leads the CECILIA Survey with Gwen Rudie, a staff scientist at Carnegie Observatories.
‘Chemical DNA’ gives insight into galaxy formation
Named after Cecilia Payne-Gaposchkin, one of the first women to earn a Ph.D. in astronomy, the CECILIA Survey observes spectra (or the amount of light across different wavelengths) from distant galaxies. Strom likens a galaxy’s spectra to its “chemical DNA.” By examining this DNA during a galaxy’s “teenage” years, researchers can better understand how it grew and how it will evolve into a more mature galaxy.
For example, astrophysicists still don’t understand why some galaxies appear “red and dead” while others, like our Milky Way, are still forming stars. A galaxy’s spectrum can reveal its key elements, such as oxygen and sulfur, which provide a window into what a galaxy was previously doing and what it might do in the future.
“These teenage years are really important because that’s when the most growth happens,” Strom said. “By studying this, we can begin exploring the physics that caused the Milky Way to look like the Milky Way — and why it might look different from its neighboring galaxies.”
In the new study, Strom and her collaborators used the JWST to observe 33 distant teenaged galaxies for a continuous 30 hours this past summer. Then, they combined spectra from 23 of those galaxies to construct a composite picture.
“This washes out the details of individual galaxies but gives us a better sense of an average galaxy. It also allows us to see fainter features,” Strom said. “It’s significantly deeper and more detailed than any spectrum we could collect with ground-based telescopes of galaxies from this time period in the universe’s history.”
Spectra surprises
The ultra-deep spectrum revealed eight distinct elements: Hydrogen, helium, nitrogen, oxygen, silicon, sulfur, argon and nickel. All elements that are heavier than hydrogen and helium form inside stars. So, the presence of certain elements provides information about star formation throughout a galaxy’s evolution.
While Strom expected to see lighter elements, she was particularly surprised by the presence of nickel. Heavier than iron, nickel is rare and incredibly difficult to observe.
“Never in my wildest dreams did I imagine we would see nickel,” Strom said. “Even in nearby galaxies, people don’t observe this. There has to be enough of an element present in a galaxy and the right conditions to observe it. No one ever talks about observing nickel. Elements have to be glowing in gas in order for us to see them. So, in order for us to see nickel, there may be something unique about the stars within the galaxies.”
Another surprise: The teenage galaxies were extremely hot. By examining the spectra, physicists can calculate a galaxy’s temperature. While the hottest pockets with galaxies can reach over 9,700 degrees Celsius (17,492 degrees Fahrenheit), the teenage galaxies clock in at higher than 13,350 degrees Celsius (24,062 degrees Fahrenheit).
“This is just additional evidence of how different galaxies likely were when they were younger,” Strom said. “Ultimately, the fact that we see a higher characteristic temperature is just another manifestation of their different chemical DNA because the temperature and chemistry of gas in galaxies are intrinsically linked.”
The study, “CECILIA: Faint emission line spectrum of z~2-3 star-forming galaxies,” was supported by NASA, the Pittsburgh Foundation and the Research Corporation for Scientific Advancement. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute and from the W.M. Keck Observatory.
JOURNAL
The Astrophysical Journal Letters
METHOD OF RESEARCH
Experimental study
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
CECILIA: Faint emission line spectrum of z~2-3 star-forming galaxies
ARTICLE PUBLICATION DATE
20-Nov-2023
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