Ann-Marie Madigan

Kirk Long and Constanza Echiburú‑Trujillo Receive 2026 R. N. Thomas Award

Steven Burrows — Fri, 24 Apr 2026 15:07:32 +0000

Kirk Long and Constanza Echiburú‑Trujillo Receive 2026 R. N. Thomas Award Steven Burrows Fri, 04/24/2026 - 09:07

Constanza Echiburú‑Trujillo and nominee Drake Miller III.

JILA is pleased to announce that graduate students Kirk Long and Constanza Echiburú‑Trujillo are the recipients of the 2026 Richard Nelson Thomas Award, which recognizes outstanding experimental contributions by JILA graduate students. This year’s nominees also included Drake Miller III and Sajal Gupta, highlighting the strength and breadth of graduate research across the institute.

Long was recognized for his contributions at JILA prior to beginning a postdoctoral appointment in Germany. Although he was unable to attend the award presentation in person, his work and engagement during his time at JILA exemplify the standards of excellence and collaboration the Thomas Award is meant to recognize.

Echiburú‑Trujillo was honored for her accomplishments as a JILA graduate student and her contributions to the JILA research community. In addition to her academic work, she has been an active and supportive presence within her group and the broader institute.

The R. N. Thomas Award is presented annually in memory of Richard Nelson Thomas, whose dedication to experimental science and graduate education left a lasting impact at JILA. The award recognizes students whose work and service reflect those values and who contribute meaningfully to JILA’s collaborative research environment.

Kirk Long.

Graduate students Kirk Long and Constanza Echiburú‑Trujillo have been awarded the 2026 Richard Nelson Thomas Award, an honor rooted in JILA’s astronomy tradition that recognizes outstanding experimental contributions by graduate students. Drake Miller III and Sajal Gupta were also nominated, underscoring the depth of student research across the institute.

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JILA Graduate Student Tatsuya Akiba Awarded 2024 Richard Nelson Thomas Award

Steven Burrows — Fri, 26 Jul 2024 19:24:17 +0000

JILA Graduate Student Tatsuya Akiba Awarded 2024 Richard Nelson Thomas Award Steven Burrows Fri, 07/26/2024 - 13:24

Kenna Hughes-Castleberry / JILA Science Communicator

JILA graduate student Tatsuya Akiba (left) celebrates with advisor JILA Fellow and Astrophysical and Planetary Sciences Associate Professor Ann-Marie Madigan. Credit: Kenna Hughes-Castleberry/JILA

"Receiving an award named after R. N. Thomas, a notable astrophysicist and one of the founding members of JILA, means a lot to me," Akiba mentioned. "JILA has hosted and trained many successful astrophysicists in the past and present, so it is a great honor to be named the astrophysics graduate student of the year at such a prestigious institution."

This honor is bestowed annually to an outstanding APS graduate student at JILA and recognizes excellence in research and academic achievements.

“Tatsuya is an enthusiastic researcher, educator, and mentor,” said JILA Fellow and Associate Professor of Astrophysical & Planetary Sciences Ann-Marie Madigan, who advises Akiba. “He won the ��Ҵ�ý�ƽ�� Award for Excellence in Teaching in 2021. Last semester, he taught an undergraduate course on Python coding. He has served as a mentor for CU Prime, a graduate peer mentor, and the McNair programs, and he has advised several undergraduates.”

Akiba reciprocated Madigan's compliments by stating: "I couldn’t have done it without the help of Ann-Marie Madigan, who I’ve been lucky enough to work with for four years now. My research progress wouldn’t have been possible without an advisor who cares just as much as (probably even more than) me about the weird orbits of stars and planets - just look at the chalkboard in her office if you ever get the chance. In all seriousness, though, thank you to the award’s committee members, Ann-Marie, and the other members of the Madigan Group for all of your support!"

Akiba and Madigan study the gravitational dynamics of bodies in orbit around compact objects. Their current work delves into the dynamics of eccentric disks in various astrophysical contexts, including stars orbiting supermassive black holes and planetesimals around white dwarfs.

This award highlights Akiba's significant contributions to the field and underscores the innovative research being conducted at JILA. Congratulations to Tatsuya Akiba for this well-deserved recognition!

JILA graduate student Tatsuya Akiba, a Ph.D. candidate in the Astrophysical & Planetary Sciences department at the University of Colorado Boulder, has received the prestigious 2024 Richard Nelson Thomas Award. This honor is bestowed annually to an outstanding APS graduate student at JILA and recognizes excellence in research and academic achievements.

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Hungry, Hungry White Dwarfs: Solving the Puzzle of Stellar Metal Pollution

Steven Burrows — Fri, 03 May 2024 17:11:35 +0000

Hungry, Hungry White Dwarfs: Solving the Puzzle of Stellar Metal Pollution Steven Burrows Fri, 05/03/2024 - 11:11

Kenna Hughes-Castleberry / JILA Science Communicator

Planetesimal orbits around a white dwarf. Initially, every planetesimal has a circular, prograde orbit. The kick forms an eccentric debris disk which with prograde (blue) and retrograde orbits (orange). Image Credit: Steven Burrows / JILA

Despite their prevalence, the chemical makeup of these stellar remnants has been a conundrum for astronomers for years. The presence of heavy metal elements—like silicon, magnesium, and calcium—on the surface of many of these compact objects is a perplexing discovery that defies our expectations of stellar behavior.

“We know that if these heavy metals are present on the surface of the white dwarf, the white dwarf is dense enough that these heavy metals should very quickly sink toward the core,” explains JILA graduate student Tatsuya Akiba. “So, you shouldn't see any metals on the surface of a white dwarf unless the white dwarf is actively eating something.”

While white dwarfs can consume various nearby objects, such as comets or asteroids (known as planetesimals), the intricacies of this process have yet to be fully explored. However, this behavior could hold the key to unraveling the mystery of a white dwarf's metal composition, potentially leading to exciting revelations about white dwarf dynamics.

In results reported in a new paper in The Astrophysical Journal Letters, Akiba, along with JILA Fellow and University of Colorado Boulder Astrophysical and Planetary Sciences professor Ann-Marie Madigan and undergraduate student Selah McIntyre, believe they have found a reason why these stellar zombies eat their nearby planetesimals. Using computer simulations, the researchers simulated the white dwarf receiving a “natal kick” during its formation (which has been observed) caused by asymmetric mass loss, altering its motion and the dynamics of any surrounding material.

In 80% of their test runs, the researchers observed that, from the kick, the orbits of comets and asteroids within a range of 30 to 240 AU of the white dwarf (corresponding to the Sun–Neptune distance and beyond) became elongated and aligned. Furthermore, around 40% of subsequently eaten planetesimals come from counter-rotating (retrograde) orbits.

The researchers also extended their simulations to examine the white dwarf's dynamics after 100 million years. They found that the white dwarf’s nearby planetesimals still had elongated orbits and moved as one coherent unit, a result never seen before.

“This is something I think is unique about our theory: we can explain why the accretion events are so long-lasting,” states Madigan. “While other mechanisms may explain an original accretion event, our simulations with the kick show why it still happens hundreds of millions of years later.”
These results explain why the heavy metals are found on the surface of a white dwarf, as that white dwarf continuously consumes smaller objects in its path.

It’s All ��Ҵ�ý�ƽ�� Gravity

As Madigan’s research group at JILA focuses on gravitational dynamics, looking at the gravity surrounding white dwarfs seemed like a natural focus of study.

“Simulations help us understand the dynamics of different astrophysical objects,” Akiba says. “So, in this simulation, we throw a bunch of asteroids and comets around the white dwarf, which is significantly bigger, and see how the simulation evolves and which of these asteroids and comets the white dwarf eats.”

The researchers hope to take their simulations to greater scales in future projects, looking at how white dwarfs interact with larger planets.

As Akiba elaborates, “Other studies have suggested that asteroids and comets, the small bodies, might not be the only source of metal pollution on the white dwarf’s surface. So, the white dwarfs might eat something bigger, like a planet.”

Discovering More about Solar System Formation

These new findings further reveal more about the formation of white dwarfs, which is important in understanding how solar systems change over millions of years. They also help shed light on the origins and future evolution of our solar system, revealing more about the chemistry involved.

“The vast majority of planets in the universe will end up orbiting a white dwarf,” Madigan says. “It could be that 50% of these systems get eaten by their star, including our own solar system. Now, we have a mechanism to explain why this would happen.”

“Planetesimals can give us insight into other solar systems and planetary compositions beyond where we live in our solar region” McIntyre adds. “White dwarfs aren't just a lens into the past. They're also kind of a lens into the future.”

Dead stars known as white dwarfs, have a mass like the Sun while being similar in size to Earth. They are common in our galaxy, as 97% of stars are white dwarfs. As stars reach the end of their lives, their cores collapse into the dense ball of a white dwarf, making our galaxy seem like an ethereal graveyard.

Despite their prevalence, the chemical makeup of these stellar remnants has been a conundrum for astronomers for years. The presence of heavy metal elements—like silicon, magnesium, and calcium—on the surface of many of these compact objects is a perplexing discovery that defies our expectations of stellar behavior.

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A Look at She Has the Floor

Steven Burrows — Mon, 07 Nov 2022 18:34:38 +0000

A Look at She Has the Floor Steven Burrows Mon, 11/07/2022 - 11:34

Kenna Hughes-Castleberry / JILA Science Communicator

Poster for the "She has the Floor" event

Image Credit: Pretty Brainy

When it comes to inspiring young people to pursue a career within the sciences, you can't start too early. At least, that's what the JILA Excellence in Diversity and Inclusivity (JEDI) group believed when they collaborated with the Colorado non-profit organization Pretty Brainy to develop a speaker series. The series, designed for girls from ages 11 and up, featured the voices of several women JILAns, all focusing on their work and giving tools for success to this younger generation. Over the course of 8 weeks, women of all ages could virtually tune in to hear some of the brightest female minds from JILA discuss the importance of mentorship, perseverance, failure, and of course, some of the newest findings within physics.

In the first event, held on October 5th, JILA Fellow Ann-Marie Madigan spoke on her research within the field of astrophysics, and her day-to-day life as a scientist. "I'll go to work where I'll have a group meeting," Madigan said. "In there, we will discuss our latest results, we might read scientific papers, we might present to each other if we're going to give a talk. It's really good fun. This is a joy in my life, as I'm with really smart people." Madigan elaborated about how fulfilling this job was to her. "It's a really fun job and sometimes it doesn't feel like a job. Sometimes, I'm just walking around, reading, and talking to great people all day."

The next two talks were given by JILA graduate students. Ph.D. student Olivia Krohn, from JILA Fellow Heather Lewandowski's group, discussed her work on molecular collisions in cold, low-pressure environments. “I always knew I liked science and math,” Krohn said. She went on to emphasize the importance of finding what you love to learn about. Similarly, graduate student Rebecca Hirsch of JILA Fellow Mathias Weber's laboratory spoke on her research around cold, gaseous molecules in outer space, giving history on studying space molecules using the Hubble telescope, simulations, and other tools. Both of these talks, given by younger female scientists, inspired many of the young women in the audience, who gave significant positive feedback after each event.

The last two talks of the speaker series were given by JILA staff members: Chief Operating Officer (COO) Beth Kroger, and Science Communicator Kenna Castleberry. Kroger discussed the importance of perseverance for female scientists. “Each of you has already persevered,” Kroger explained. “It helps me to remember that it’s just a bad day, and it won’t always be this way.” In contrast, Castleberry focused on the importance of failing forward. "It's important to use your past mistakes as lessons to learn from, for your future successes," Castleberry explained. "We as female scientists take a lot on, and that can cause us to get overwhelmed and to focus more on our failures. It's important to take a step back and to say no if we have too much going on. No doesn't have to be a scary word."

A bonus talk was later added featuring Dr. Judith Olson from ColdQuanta, a Colorado quantum company.

From the feedback and impact the speaker series had on young women and their families, it was deemed to be a success. No doubt this is just the beginning of a collaboration between JILA JEDI and Pretty Brainy, as both work to inspire powerful young leaders within the scientific community.

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Gravitational ‘kick’ may explain the strange shape at the center of Andromeda

Steven Burrows — Tue, 02 Nov 2021 18:16:24 +0000

Gravitational ‘kick’ may explain the strange shape at the center of Andromeda Steven Burrows Tue, 11/02/2021 - 12:16

Daniel Strain / ��Ҵ�ý�ƽ�� Strategic Communications

Graphic showing stars orbiting supermassive black holes. Image credit: Steven Burrows / JILA

The research, published Oct. 29 in The Astrophysical Journal Letters, helps solve a decades-old mystery surrounding a strangely-shaped cluster of stars at the heart of the Andromeda Galaxy. It might also help researchers better understand the process of how galaxies grow by feeding on each other.

“When scientists first looked at Andromeda, they were expecting to see a supermassive black hole surrounded by a relatively symmetric cluster of stars,” said Ann-Marie Madigan, a fellow of JILA, a joint research institute between ��Ҵ�ý�ƽ�� and the National Institute of Standards and Technology (NIST). “Instead, they found this huge, elongated mass.”

Now, she and her colleagues think they have an explanation.

In the 1970s, scientists launched balloons high into Earth’s atmosphere to take a close look in ultraviolet light at Andromeda, the galaxy nearest to the Milky Way. The Hubble Space Telescope followed up on those initial observations in the 1990s and delivered a surprising finding: Like our own galaxy, Andromeda is shaped like a giant spiral. But the area rich in stars near that spiral’s center doesn’t look like it should––the orbits of these stars take on an odd, ovalish shape like someone stretched out a wad of Silly Putty.

And no one knew why, said Madigan, also an assistant professor of astrophysics. Scientists call the pattern an “eccentric nuclear disk.”

In the new study, the team used computer simulations to track what happens when two supermassive black holes go crashing together––Andromeda likely formed during a similar merger billions of years ago. Based on the team’s calculations, the force generated by such a merger could bend and pull the orbits of stars near a galactic center, creating that telltale elongated pattern.

“When galaxies merge, their supermassive black holes are going to come together and eventually become a single black hole,” said Tatsuya Akiba, lead author of the study and a graduate student in astrophysics. “We wanted to know: What are the consequences of that?”

Bending space and time

He added that the team’s findings help to reveal some of the forces that may be driving the diversity of the estimated two trillion galaxies in the universe today––some of which look a lot like the spiral-shaped Milky Way, while others look more like footballs or irregular blobs.

Mergers may play an important role in shaping these masses of stars: When galaxies collide, Akiba said, the black holes at the centers may begin to spin around each other, moving faster and faster until they eventually slam together. In the process, they release huge pulses of “gravitational waves,” or literal ripples in the fabric of space and time.

“Those gravitational waves will carry momentum away from the remaining black hole, and you get a recoil, like the recoil of a gun,” Akiba said.

He and Madigan wanted to know what such a recoil could do to the stars within 1 parsec, or roughly 19 trillion miles, of a galaxy’s center. Andromeda, which contains about twice the number of stars as the Milky Way, stretches 67,000 parsecs from end to end.

It gets pretty wild.

Galactic recoil

The duo used computers to build models of fake galactic centers containing hundreds of stars––then kicked the central black hole to simulate the recoil from gravitational waves.

Madigan explained the gravitational waves produced by this kind of disastrous collision won’t affect the stars in a galaxy directly. But the recoil will throw the remaining supermassive black hole back through space––at speeds that can reach millions of miles per hour, not bad for a body with a mass millions or billions of times greater than that of Earth’s sun.

“If you’re a supermassive black hole, and you start moving at thousands of kilometers per second, you can actually escape the galaxy you’re living in,” Madigan said.

When black holes don’t escape, however, the team discovered they may pull on the orbits of the stars right around them, causing those orbits to stretch out. The result winds up looking a lot like the shape scientists see at the center of Andromeda.

Madigan and Akiba said they want to grow their simulations so they can directly compare their computer results to that real-life galaxy core––which contains many times more stars. They noted their findings might also help scientists to understand the unusual happenings around other objects in the universe, such as planets orbiting mysterious bodies called neutron stars.

“This idea––if you’re in orbit around a central object and that object suddenly flies off––can be scaled down to examine lots of different systems,” Madigan said.

When two galaxies collide, the supermassive black holes at their cores release a devastating gravitational “kick,” similar to the recoil from a shotgun. New research led by ��Ҵ�ý�ƽ�� suggests that this kick may be so powerful it can knock millions of stars into wonky orbits. The research, published Oct. 29 in The Astrophysical Journal Letters, helps solve a decades-old mystery surrounding a strangely-shaped cluster of stars at the heart of the Andromeda Galaxy. It might also help researchers better understand the process of how galaxies grow by feeding on each other.

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Galaxy Quest: Stellar Bars and Dark Halos

Steven Burrows — Fri, 04 Jun 2021 18:59:05 +0000

Galaxy Quest: Stellar Bars and Dark Halos Steven Burrows Fri, 06/04/2021 - 12:59

Kenna Hughes-Castleberry / JILA Science Communicator

A model of isodensity contours for the surface density of the stellar disks for three galaxy models. Image credit: Steven Burrows / JILA

When it comes to galaxies in our universe, there is still much work to do. Part of this work is being done by JILA Fellow and Assistant Professor of Astrophysics, Ann-Marie Madigan, and postdoc Dr. Angela Collier. In a paper recently published in The Astrophysical Journal Collier and Madigan postulate that the evolution of a galaxy can be affected by dark matter interacting with the stars within the galaxy. Galaxies evolve over billions of years, changing shape, speed of rotation, and other factors. Studying what affects galaxy evolution is important in answering questions about the foundation of our universe, of how stars and planets are formed, and the origins of dark matter.

The Importance of Dark Matter Halos

The type of dark matter being studied by Collier and Madigan is in the form of a dark matter halo. All galaxies live within these massive, invisible dark matter halos. While these halos have never been observed directly, their presence has been inferred from their gravitational effects on a spiral galaxy’s rotation curve. These dark matter halos are important as they provide clues to the origins of dark matter, and how it interacts with other matter.

According to Collier: “We are looking at how dark matter affects the material we can observe. By studying the interaction between the dark halo and the stars, we can look at other galaxies and see how the stars are moving and, hopefully, make inferences about what the dark matter is doing in those systems.” Dark matter halos can also hint at galaxy formation. Madigan explained that “what Angela's work is showing is that dark matter evolves in response to baryonic material (this is the material we can observe--stars and gas for example). It sometimes forms really interesting and unexpected structures that are not at the center of the galaxy. So, it gives us new places to look for evidence of dark matter.” In studying the effects of these dark matter halos, Collier and Madigan found that a fraction of this dark matter spun in an opposite rotation to the stellar bar. Stellar bars are clusters of stars that travel in a group, as if they’re rigidly connected.These opposite rotations would make it easier to see and study the dark matter, answering many important questions.

Stellar Bars and Galaxy Evolution:

In their paper, Collier and Madigan postulated that dark matter halos must be coupled with stellar bars. Collier explained how a stellar bar functions: “Stellar bars are the drivers of galaxy evolution; they funnel angular momentum throughout the galaxy. The stellar bar rotates as a solid object and as it does that, it kind of hits the dark matter halo and slows down. In this way it can move angular momentum to the dark matter halo. But also, the stellar bar is this deep gravitational well that can trap dark matter which forms the dark matter bar. The strength of your dark bar can affect how much the [stellar] bar slows down over time.” Using numerical simulations, Collier and Madigan theorized that the dark matter halos and stellar bars interacted over billions of years to affect the formation of a galaxy’s structure and shape. This shift in shape could affect how the galaxy evolved over these billions of years. This galaxy evolution is what Collier plans to focus on in the next phase of her work as she studies galaxies that are closer to home. “The next steps will be trying to simulate a more representative model of our galaxy. One that looks more like the Milky Way and then makes a prediction of what we think the dark matter bar at our galactic center looks like and what the observables of that would be.”

Collier’s and Madigan’s work will be tested when new galactic surveys are completed using the soon-to-be-launched James Webb Space Telescope. The team also postulates that using their theory of coupling dark halos and stellar bars could help explain the exotic structures that make up observed galaxies. Collier is looking forward to continuing to study these dark halos and stellar bars. She has received a prestigious NSF postdoctoral fellowship to fund this research.

This research was possible due to funding from the NSF

When it comes to galaxies in our universe, there is still much work to do. Part of this work is being done by JILA Fellow and Assistant Professor of Astrophysics, Ann-Marie Madigan, and postdoc Dr. Angela Collier. In a paper recently published in The Astrophysical Journal, Collier and Madigan postulate that the evolution of a galaxy can be affected by dark matter interacting with the stars within the galaxy. Galaxies evolve over billions of years, changing shape, speed of rotation, and other factors. Studying what affects galaxy evolution is important in answering questions about the foundation of our universe, of how stars and planets are formed, and the origins of dark matter.

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Ann-Marie Madigan takes home prestigious award for research in dynamical astronomy

Steven Burrows — Tue, 25 May 2021 20:43:32 +0000

Ann-Marie Madigan takes home prestigious award for research in dynamical astronomy Steven Burrows Tue, 05/25/2021 - 14:43

Kenna Hughes-Castleberry / JILA Science Communicator

Photo of Anne-Marie Madigan

��Ҵ�ý�ƽ�� astrophysicist Ann-Marie Madigan has taken home a prestigious prize in recognition of her research exploring the dynamics of objects in space—from stars circling black holes to icy dwarf planets in the outer solar system.

This week, the American Astronomical Society (AAS) Division on Dynamical Astronomy (DDA) awarded Madigan its 2021 Vera Rubin Early Career Prize. The scientist, an assistant professor in the Department of Astrophysical and Planetary Sciences and a fellow at JILA, will present a lecture at the 53rd annual DDA meeting in spring 2022.

Read more of the full article here, courtesy of Dan Strain, ��Ҵ�ý�ƽ�� Science Writer

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Loren Matilsky and Heather Wernke win 2020 R. N. Thomas Award

Steven Burrows — Fri, 04 Dec 2020 22:01:03 +0000

Loren Matilsky and Heather Wernke win 2020 R. N. Thomas Award Steven Burrows Fri, 12/04/2020 - 15:01

Steven Burrows / JILA Science Communications Manager

Loran Matilsky and Heather Wernke

The Richard Nelson Thomas Award was established by the friends and family of R.N. "Dick" Thomas to provide an annual award to the year's most outstanding graduate student in astrophysics. Each year, the JILA astrophysical faculty nominates outstanding students and vote to determine the recipient of the award.

This year two graduate students have won the award:

Loren Matilsky

Loren is majoring in global-scale simulations studying highly nonlinear stellar and solar convection and dynamo processes, and has published three papers in The Astrophysical Journal this year and last. He published another paper on Rossby vortices in accretion disks in Monthly Notices of the Royal Astronomical Society (MNRAS), along with a number of conference proceedings. His work has revealed how strong wreaths of magnetism can be build within turbulent convection zones that go through complex cycling, and has tackled the subtleties of achieving differential rotations profiles that capture the spirit of helioseismic findings.

He works under Fellow Juri Toomre and Senior Research Associate Brad Hindman. In announcing the award to JILA, Toomre said, “Loren is highly motivated and very effective in such research in astrophysical fluid dynamics. He is also a decidedly graceful and friendly young colleague, and keenly involved in helping to consider diversity issues.

Loren will be defending his thesis in the spring or early summer.

Heather Wernke

Heather plans to defend her thesis in 2021 on the dynamics of stars in eccentric disks around massive black holes. Her research involves "observing" simulations of such systems with a view to comparing them directly to observations of local galactic nuclei. She has uncovered interesting results particularly with respect to the location of compact objects (i.e. stellar mass black holes, etc.) in these systems.

Fellow Ann-Marie Madigan said, "I am very happy to nominate Heather for this award. She is a wonderful teacher and is looking forward to continuing teaching physics and astronomy past graduation."

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The Collective Power of the Solar System's Dark, Icy Bodies

Steven Burrows — Tue, 07 Jul 2020 17:26:37 +0000

The Collective Power of the Solar System's Dark, Icy Bodies Steven Burrows Tue, 07/07/2020 - 11:26

Daniel Strain / ��Ҵ�ý�ƽ�� Strategic Communications

Scientists have long struggled to explain the existence of the solar system's "detached objects," which have orbits that tilt like seesaws and often cluster in one part of the night sky. Image credit: Steven Burrows / JILA

The outermost reaches of our solar system are a strange place-filled with dark and icy bodies with nicknames like Sedna, Biden and The Goblin, each of which span several hundred miles across.

Two new studies by researchers at the University of Colorado Boulder may help to solve one of the biggest mysteries about these far away worlds: why so many of them don't circle the sun the way they should.

The orbits of these planetary oddities, which scientists call "detached objects," tilt and buckle out of the plane of the solar system, among other unusual behaviors.

"This region of space, which is so much closer to us than stars in our galaxy and other things that we can observe just fine, is just so unknown to us," said JILA Fellow Ann-Marie Madigan, an assistant professor in the Department of Astrophysical and Planetary Sciences (APS) at ��Ҵ�ý�ƽ��.

Some researchers have suggested that something big could be to blame-like an undiscovered planet, dubbed "Planet 9," that scatters objects in its wake.

But Madigan and graduate student Alexander Zderic prefer to think smaller. Drawing on exhaustive computer simulations, the duo makes the case that these detached objects may have disrupted their own orbits-through tiny gravitational nudges that added up over millions of years.

The findings, Madigan said, provide a tantalizing hint to what may be going on in this mysterious region of space.

"We're the first team to be able to reproduce everything, all the weird orbital anomalies that scientists have seen over the years," said Madigan. "It's crazy to think that there's still so much we need to do."

The team published its results July 2 in The Astronomical Journal and last month in The Astronomical Journal Letters.

Power to the asteroids

The problem with studying the outer solar system, Madigan added, is that it's just so dark.

"Ordinarily, the only way to observe these objects is to have the sun's rays smack off their surface and come back to our telescopes on Earth," she said. "Because it's so difficult to learn anything about it, there was this assumption that it was empty."

She's one of a growing number of scientists who argue that this region of space is far from empty-but that doesn't make it any easier to understand.

Just look at the detached objects. While most bodies in the solar system tend to circle the sun in a flat disk, the orbits of these icy worlds can tilt like a seesaw. Many also tend to cluster in just one slice of the night sky, a bit similar to a compass that only points north.

Madigan and Zderic wanted to find out why. To do that, they turned to supercomputers to recreate, or model, the dynamics of the outer solar system in greater detail than ever before.

"We modeled something that may have once existed in the outer solar system and also added in the gravitational influence of the giant planets like Jupiter," said Zderic, also of APS.

In the process, they discovered something unusual: the icy objects in their simulations started off orbiting the sun like normal. But then, over time, they began to pull and push on each other.

As a result, their orbits grew wonkier until they started to resemble the real thing. What was most remarkable was that they did it all on their own-the asteroids and minor planets didn't need a big planet to throw them for a loop.

"Individually, all of the gravitational interactions between these small bodies are weak," Madigan said. "But if you have enough of them, that becomes important."

Earth times 20

Madigan and Zderic had seen hints of similar patterns in earlier research, but their latest results provide the most exhaustive evidence yet.

The findings also come with a big caveat. In order to make Madigan and Zderic's theory of "collective gravity" work, the outer solar system once needed to contain a huge amount of stuff.

"You needed objects that added up to something on the order of 20 Earth masses," Madigan said. "That's theoretically possible, but it's definitely going to be bumping up against people's beliefs."

One way or another, scientists should find out soon. A new telescope called the Vera C. Rubin Observatory is scheduled to come online in Chile in 2022 and will begin to shine a new light on this unknown stretch of space.

"A lot of the recent fascination with the outer solar system is related to technological advances," Zderic said. "You really need the newest generation of telescopes to observe these bodies."

This research was supported by NASA Solar System Workings and the David and Lucile Packard Foundation.

Within our solar system are icy planetary bodies that do not orbit the Sun. Astrophysicists want to understand why these orbital anomalies exist. Two recent studies by JILA Fellow Ann Marie Madigan's group suggest that these detached objects have steadily nudged themselves out of solar orbit over millions of years. Using supercomputers, the Madigan Group can test their theory of collective gravity.

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Black Holes Continue to Tear Stars Apart

Steven Burrows — Tue, 23 Jul 2019 18:34:44 +0000

Black Holes Continue to Tear Stars Apart Steven Burrows Tue, 07/23/2019 - 12:34

Catherine Klauss / JILA Science Communicator

While we've known for a while that black holes could rip stars apart, we don’t know why these events occur so frequently. Now, a model by JILA researchers explaining this discrepancy is shown to be promising after passing its first reality test. Image credit: Steven Burrows / JILA

As the original maps, calendar, and fortune tellers, stars have forever complemented our nightly imaginations with their consistent patterns. But like everything, they too come and go. Sometimes they fade with a peaceful final twinkle, but other times, they’re destroyed in violent calamity.

When a star ventures too close to a black hole, gravitational forces can stretch the once brilliant ball of light like taffy in what is called a tidal disruption event, or TDE. The stretch eventually rips the star apart, pulling some into the abyss and leaving merely debris to circle the drain.

At JILA, astrophysicists have been simulating TDEs in an effort to understand not only why these events occur, but how often. Recently, they made a simple-yet-promising model more realistic by including the effects of general relativity. And while the researchers expected general relativity to destroy all promise, they were happily surprised to find their model still stands.

TDEs were predicted decades ago as the inevitable outcome of a star that ventures too close to a black hole. But since the first, and subsequently many, detections, we’ve noticed their occurrence is much more frequent than first predicted. This discrepancy challenges our understanding of not only TDEs, but possibly even our universe.

Yet one simple solution, proposed by JILA Fellow Ann-Marie Madigan, is that TDEs occur more often than first predicted because eccentric nuclear disks are more common than first predicted.

Eccentric nuclear disk is a term that describes an entire group of stars closely orbiting a black hole in flat, elongated paths, like stellar race cars with a daredevil mindset. While once thought be exotic (the prevailing picture today is that most black holes host a ball of randomly orbiting stars), there is evidence suggesting they might be common. In 1995, researchers discovered that our nearest neighbor, the Andromeda Galaxy, hosts an eccentric nuclear disk at its center.

Vital to Madigan’s solution, however, is the idea that TDEs can occur in eccentric nuclear disks. And so, last year Madigan and her team modeled a basic eccentric nuclear disk. They found that TDEs do occur, and quite frequently.

But Heather Wernke, part of Madigan’s team and JILA graduate student in astrophysics, points out that this original simulation wasn’t realistic.

“You want to make sure understand the basic idea before you start adding in complications,” said Wernke. “Once you understand the basic physics, then you add things in to make it more realistic.”

And according to Wernke, one of the most striking deficiencies of the original model was a lack of general relativity.

“A black hole is general relativistic, so these stars will feel the effect of that general relativity anytime they get close.”

General relativity amends our original picture of gravity—the force which pulled Newton’s apple downward—as arising from the curvature of spacetime. Because black holes are so massive, their dominating force is gravity. Our researchers therefore expected general relativistic effects to significantly modify their TDE-predicting simulations.

And by modify, the researchers meant destroy. Wernke said that general relativistic effects usually round-out an orbit, or make it less eccentric. This rounding would suppress the orbital torques, which are the primary cause of TDEs.

“We thought that general relativistic precession would totally kill the TDE rate,” she said, “but it turns out it didn’t.”

In fact, after simulating the eccentric nuclear disks both with and without general relativity, Wernke found the orbits looked statistically the same. “It was very surprising.”

Wernke believes the TDEs still occur because the orbital torques work on timescales much too fast for general relativity to suppress.

And not only are Wernke’s simulated TDEs occurring too fast to be suppressed, they are occurring so often that their debris might entangle.

“You could have two TDEs occur close enough in time that their debris steams cross. We don’t know exactly what that would like, but it could be observationally really cool.”

Having passed the first test of realism, eccentric nuclear disks are still a strong candidate for the explanation of frequent TDEs. But Wernke said the next step is to make the eccentric nuclear disk simulations even more realistic, this time by varying the mass of the stars. “In the simulations that I’ve done, it’s all equal-mass stars… but other people in our group are adding in different mass populations.”

And as for Wernke, she is now focused on visualizing an eccentric nuclear disk. “What would it look like if we saw this in the sky? Knowing this will help us determine how common they are in the local universe.”

This research was published in The Astrophysical Journal on 23 July 2019.

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