On Jan. 11 at the 241st meeting of the American Astronomical Society in Seattle, a team led by scientists at the University of Washington and the Center for Computational Astrophysics will unveil results using the Panchromatic Hubble Andromeda Treasury Triangulum Extended Region — or PHATTER — survey. The endeavor is giving astrophysicists their first in-depth look at the distinct populations of stars that make up the Triangulum galaxy.

Researchers discovered that this satellite galaxy, a close companion of the much larger Andromeda galaxy, has two drastically different structures depending on the age of the stars.

“The youngest stars and the oldest stars in the Triangulum galaxy — which we can separate out using multiple wavelength filters on the Hubble Space Telescope — are organized very differently,” said Adam Smercina, a postdoctoral researcher at the UW. “This is surprising. For a lot of galaxies, like the Milky Way and Andromeda, the stars are distributed roughly consistently, regardless of their age. That is not the case with Triangulum.”

At about 61,000 light years across, Triangulum is the third-largest galaxy in our local group, after Andromeda and our own Milky Way. In lower-resolution images it has a “flocculent” structure — with many small spiral arms radiating out from a well-defined center.

For the PHATTER survey, the Hubble Space Telescope obtained hundreds of high-resolution images of different sections of the Triangulum galaxy in 108 orbits over the course of more than a year. The team tiled these smaller-section images together to create a comprehensive, high-resolution dataset for Triangulum that for the first time showed the galaxy’s individual stars over a large region in its center.

Thanks to Hubble’s array of filters, researchers could also separate those stars by age. The distribution of younger, massive stars — those less than 1 billion years in age — were roughly in line with the “flocculent” pattern, for which the Triangulum is so renowned. But its older, redder stars are distributed in a very different pattern: two spiral arms radiating out from a rectangular bar at the galaxy’s center.

“This was a largely unknown and hidden feature of the Triangulum galaxy that was very difficult to see without this kind of detailed survey,” said Smercina.

Old stars make up the majority of Triangulum’s mass, but are dimmer than their younger counterparts, according to Smercina. That could explain why the “flocculent” pattern prevails in low-resolution images of the galaxy.

The survey team also does not know why young and old stars have such divergent distributions in Triangulum. Satellite galaxies in general are an eclectic bunch, and many questions remain about their formation and evolution. Satellite galaxies come in many different shapes and can be molded by interactions with their parent galaxies. The Milky Way’s largest satellite galaxy, the Large Magellanic Cloud, for example, is similar in size and mass to Triangulum, but has an irregular and globular shape due to its proximity to our own galaxy.

The PHATTER survey’s on-going analysis should shed light on how these types of galaxies form and interact with their larger neighbors. The team plans to follow up on these initial findings by tracing the history of star formation in Triangulum, comparing different sections of the galaxy.

“A major goal of the PHATTER survey was to generate the kind of detailed, high-resolution data on this prominent satellite galaxy that will allow us to examine its structure in depth, trace its history of star formation and compare what we see to theories of galaxy formation and evolution,” said Smercina. “We’re already finding surprises.”

Other team members include Julianne Dalcanton, director of the Center for Computational Astrophysics in New York, a UW professor of astronomy and principal investigator of the PHATTER project; UW research associate professor of astronomy Benjamin Williams; UW doctoral student Meredith Durbin; and Margaret Lazzarini, a postdoctoral researcher at Caltech.

It can be hard to remember, or for some to even imagine, what life was like before most of us carried around a dynamic mapping platform in our back pocket. Being able to quickly map out the most efficient route by car, bike, or foot has become second nature. What if the same principle of having an easily accessible and easy-to-use tool could be applied to mapping energy infrastructure?

The Geospatial Energy Mapper (GEM) is a comprehensive, interactive online mapping tool that can help identify areas across the country that are suitable for wind, solar and more. First publicly launched in 2013 as the Energy Zones Mapping Tool (EZMT), GEM has been redesigned, rebranded and reengineered. GEM is hosted by the U.S. Department of Energy’s (DOE) Argonne National Laboratory with funding from the DOE’s Office of Electricity.

“In GEM we applied lessons learned from almost 10 years hosting the EZMT, including making it easier to learn and use, updating the software architecture, and choosing a name fitting its current scope of uses,” said Jim Kuiper, principal geospatial engineer and GEM technical coordinator.

GEM offers an extensive catalog of mapping data. This includes energy resources and infrastructure, and other information that might influence energy infrastructure siting decisions. With over 190 different mapping layers — including demographics, boundaries and utilities — users can locate areas for clean power generation, electric vehicle charging stations and more.

One of the new features is mapping themes, which allow the map to be rapidly set up for a particular focus, like solar, wind or electric vehicles. This new feature helps users quickly load multiple layers related to a particular technology or resource without having to manually browse the mapping catalog and add individual layers to the map.

With GEMs modeling capabilities, users can generate a customized suitability map or “heat map.” This map shows which geographical areas in the United States are favorable for the development of certain energy resources and infrastructures. GEM includes preconfigured models for over 40 types of energy infrastructure. Land-based wind turbines or utility-scale photovoltaic solar are two examples. This provides a convenient starting point that users can then easily customize.

“Choosing where to build utility-scale renewable energy development is a tremendously important decision with effects that reverberate beyond the generation of electricity,” said Michael Levin, a GEM user and Ph.D. student studying renewable energy landscapes at Columbia University. ?”GEM not only makes energy suitability maps public but allows for the user to customize the model used to produce such a map.”

GEM has nearly 100 modeling criteria to choose from. Population density, proximity to nearest substation, slope, wildfire risk and low-income household percentage are just a few examples. Nine types of energy resources can be analyzed for clean energy resource development. They include biomass, coal (with carbon capture and sequestration), geothermal, natural gas, nuclear, solar, storage, water and wind.

GEM is expected to have a diverse community of users much like the EZMT. The tool has been used by planners and regulators at all levels of government. For instance, Kentucky’s Office of Energy Policy used the EZMT for prototyping their Solar Site Suitability on Reclaimed Mine Lands tool. Other users include private industry, public service commissions and regional transmission organizations. Finally, national laboratories, educational institutions, energy and natural resource non-profit organizations, and private individuals have all been EZMT users.

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Materials provided by DOE/Argonne National Laboratory. Original written by Marguerite Huber. Note: Content may be edited for style and length.

The two stars are so close that it takes them less than one Earth day to revolve around each other. In other words, each star’s “year” lasts just 20.5 hours.

The newly discovered system, named LP 413-53AB, is composed of a pair of ultracool dwarfs, a class of very low-mass stars that are so cool that they emit their light primarily in the infrared, making them completely invisible to the human eye. They are nonetheless one of the most common types of stars in the universe.

Previously, astronomers had only detected three short-period ultracool dwarf binary systems, all of which are relatively young — up to 40 million years old. LP 413-53AB is estimated to be billions of years old — similar age to our sun — but has an orbital period that is at least three times shorter than the all ultracool dwarf binaries discovered so far.

“It’s exciting to discover such an extreme system,” said Chih-Chun “Dino” Hsu, a Northwestern astrophysicist who led the study. “In principle, we knew these systems should exist, but no such systems had been identified yet.”

Hsu will present this research during a press briefing at the 241st Meeting of the American Astronomical Society in Seattle. “Discovery of the shortest-period ultracool dwarf binary” will take place at 2:15 p.m. PST on Tuesday, Jan. 10, as part of a session on “Stars and Their Activity.”

Hsu is a postdoctoral researcher in 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). He began this study while a Ph.D. student at UC San Diego, where he was advised by Professor Adam Burgasser.

The team first discovered the strange binary system while exploring archival data. Hsu developed an algorithm that can model a star based on its spectral data. By analyzing the spectrum of light emitted from a star, astrophysicists can determine the star’s chemical composition, temperature, gravity and rotation. This analysis also shows the star’s motion as it moves toward and away from the observer, known as radial velocity.

When examining the spectral data of LP 413-53AB, Hsu noticed something strange. Early observations caught the system when the stars were roughly aligned and their spectral lines overlapped, leading Hsu to believe it was just one star. But as the stars moved in their orbit, the spectral lines shifted in opposite directions, splitting into pairs in later spectral data. Hsu realized there were actually two stars locked into an incredibly tight binary.

Using powerful telescopes at the W.M. Keck Observatory, Hsu decided to observe the phenomenon for himself. On March 13, 2022, the team turned the telescopes toward the constellation Taurus, where the binary system is located, and observed it for two hours. Then, they followed up with more observations in July, October and December.

“When we were making this measurement, we could see things changing over a couple of minutes of observation,” Burgasser said. “Most binaries we follow have orbit periods of years. So, you get a measurement every few months. Then, after a while, you can piece together the puzzle. With this system, we could see the spectral lines moving apart in real time. It’s amazing to see something happen in the universe on a human time scale.”

The observations confirmed what Hsu’s model predicted. The distance between the two stars is about 1% of the distance between the Earth and the sun. “This is remarkable, because when they were young, something like 1 million years old, these stars would have been on top of each other,” said Burgasser.

The team speculates that the stars either migrated toward each other as they evolved, or they could have come together after the ejection of a third — now lost — stellar member. More observations are needed to test these ideas.

Hsu also said that by studying similar star systems researchers can learn more about potentially habitable planets beyond Earth. Ultracool dwarfs are much fainter and dimmer than the sun, so any worlds with liquid water on their surfaces — a crucial ingredient to form and sustain life — would need to be much closer to the star. However, for LP 413-53AB, the habitable zone distance happens to be the same as the stellar orbit, making it impossible to form habitable planets in this system.

“These ultracool dwarfs are neighbors of our sun,” Hsu said. “To identify potentially habitable hosts, it’s helpful to start with our nearby neighbors. But if close binaries are common among ultracool dwarfs, there may be few habitable worlds to be found.”

To fully explore these scenarios, Hsu, Burgasser and their collaborators hope to pinpoint more ultracool dwarf binary systems to create a full data sample. New observational data could help strengthen theoretical models for binary-star formation and evolution. Until now, however, finding ultracool binary stars has remained a rare feat.

“These systems are rare,” said Chris Theissen, study co-author and a Chancellor’s Postdoctoral Fellow at UC San Diego. “But we don’t know whether they are rare because they rarely exist or because we just don’t find them. That’s an open-ended question. Now we have one data point that we can start building on. This data had been sitting in the archive for a long time. Dino’s tool will enable us to look for more binaries like this.”

As Tzanidakis will report on Jan. 10 at the 241st meeting of the American Astronomical Society in Seattle, follow-up analyses indicated that Gaia17bpp itself wasn’t changing. Instead, the star is likely part of a rare type of binary system, and its apparent brightening was the end a years-long eclipse by an unusual stellar companion.

“We believe that this star is part of an exceptionally rare type of binary system, between a large, puffy older star — Gaia17bpp — and a small companion star that is surrounded by an expansive disk of dusty material,” said Tzanidakis, a UW doctoral student in astronomy. “Based on our analysis, these two stars orbit each other over an exceptionally long period of time — as much as 1,000 years. So, catching this bright star being eclipsed by its dusty companion is a once-in-a-lifetime opportunity.”

Since the Gaia spacecraft’s observations about the star only went back to 2014, Tzanidakis and Davenport, a UW research assistant professor of astronomy and associate director of the DiRAC Institute, had to do a little detective work to reach this conclusion. First, they stitched together Gaia’s observations of the star with observations by other missions stretching back to 2010 — including Pan-STARRS1, WISE/NEOWISE and the Zwicky Transient Facility.

Those observations, coupled with the Gaia data, showed that Gaia17bpp dimmed by about 4.5 orders of magnitude — or roughly 45,000 times. The star remained dim over the course of nearly seven years, from 2012 to 2019. The sudden brightening that the Gaia survey had uncovered was the end of that seven-year dim.

No other stars near Gaia17bpp showed similar dimming behavior. Through the DASCH program, a digital catalog of more than a century’s worth of astro-photographic plates at Harvard, Tzanidakis and Davenport analyzed observations of the star stretching back to the 1950s.

“Over 66 years of observational history, we found no other signs of significant dimming in this star,” said Tzanidakis.

The two believe that Gaia17bpp is part of a rare type of binary star system, with a stellar companion that is — quite simply — dusty.

“Based on the data currently available, this star appears to have a slow-moving companion that is surrounded by a large disk of material,” said Tzanidakis. “If that material were in the solar system, it would extend from the sun to Earth’s orbit, or farther.”

A handful of other similar, “dusty” systems have been identified over the years, most notably Epsilon Aurigae, a star in the constellation Auriga that is eclipsed for two out of every 27 years by a relatively large, dim companion. The system that Tzanidakis and Davenport discovered is unique among these few dusty binaries in the length of the eclipse — at nearly seven years, it is by far the longest. Unlike the Epsilon Aurigae binary, Gaia17bpp and its companion are also so far apart that it would be centuries or more before an astute observer on Earth witnesses another such eclipse.

For Epsilon Aurigae and similar systems, the identity of the dusty companion is a matter of debate. Some preliminary data indicate that Gaia17bpp’s companion could be a small, massive white dwarf star. The source of its debris disk is also a mystery.

“This was a serendipitous discovery,” said Tzanidakis. “If we had been a few years off, we would’ve missed it. It also indicates that these types of binaries might be much more common. If so, we need to come up with theories about how this type of pairing even arose. It’s definitely an oddity, but it might be much more common than anyone has appreciated.”

Additional team members on this study are Eric Bellm, a UW research assistant professor of astronomy, and David Wang, a UW graduate student in astronomy.

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Materials provided by University of Washington. Original written by James Urton. Note: Content may be edited for style and length.