Crystallization, Convection, and a Magnetic White Dwarf Mystery

A white dwarf shines brightly at the center of this Hubble Space Telescope image. Credit: NASA, ESA, P. McGill (Univ. of California, Santa Cruz and University of Cambridge), K. Sahu (STScI), J. Depasquale (STScI); CC BY 4.0

Most stars in the Milky Way will evolve into white dwarfs: ultra-hot, crystallized stellar cores, some of which have magnetic fields millions of times stronger than Earth’s. Could the crystallization of white dwarf interiors explain why some of these stars have such strong magnetic fields?

When a super-hot white dwarf illuminates the diffuse shells of gas that surround it, we see a glowing planetary nebula. The central white dwarf is visible in this image of the Ring Nebula. Credit: NASA, ESA and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration

Magnetic Mystery

Roughly 5–6 billion years from now, the Sun will cease all nuclear fusion in its core and cast off the outer layers of its atmosphere. Left behind will be a blazingly hot, Earth-sized core of carbon and oxygen wreathed in a colorful and ephemeral planetary nebula. This carbon–oxygen core — a white dwarf — will slowly cool over trillions of years and fade from view. Such is the fate of more than 95% of the stars in our galaxy.

Some white dwarfs have extremely strong magnetic fields, and the origin of these fields isn’t yet clear. Though the magnetic fields in question are a million times stronger than Earth’s, they might form in similar ways, as new research from José Rafael Fuentes (University of Colorado Boulder) and collaborators shows.

The composition flux, τ, as a function of time for a 0.9-solar-mass white dwarf. Convection of the white dwarf’s liquid layer is only efficient while the composition flux is large. Credit: Fuentes et al. 2024

Creating Crystal Interiors

Many magnetic fields in the universe, including Earth’s, form in liquids that have three properties: they’re electrically conductive, they rotate, and they convect — rising and falling like the globs of wax in a lava lamp. As white dwarfs begin to cool, a process begins by which their liquid interiors may achieve all three criteria necessary to generate a magnetic field.

When first formed, white dwarfs are filled with a hot quantum liquid of carbon and oxygen. As they cool, their centers crystallize into a solid, with a layer of quantum liquid surrounding the crystal core. Crystallization changes the composition of the interior, as oxygen tends to be pulled into the crystal core and carbon tends to remain in the liquid. The difference in chemical makeup causes the electrically conductive, rotating fluid to convect — setting the stage for magnetic-field creation.

To probe whether crystallization could help create the million-Gauss magnetic fields seen in some white dwarfs, Fuentes and collaborators modeled the interiors of white dwarfs as they crystallize. The team used the Modules for Experiments in Stellar Astrophysics (MESA) stellar evolution model to show that during a brief, 10-million-year period, strong convection could generate magnetic fields of 1–100 million Gauss.

Comparison of the magnetic field strengths obtained though modeling (blue line) with the observed magnetic fields of white dwarfs (symbols). The filled symbols show white dwarfs that are expected to be crystallizing, given their ages, while the open symbols show white dwarfs that are likely not yet crystallizing. Adapted from Fuentes et al. 2024

Short Phase, Lasting Consequences

While the period of strong convection that creates magnetic fields is short lived, the magnetic field is likely to be long lasting; it takes a long time for magnetic fields to dissipate in a white dwarf, especially once it crystallizes completely.

The models used by Fuentes and coauthors reproduce some observed properties of white-dwarf magnetic fields, such as the lack of a dependence of the field strength on the rotation rate. However, the models also predict that magnetic fields should be stronger for more massive white dwarfs, which observations don’t support. Extending the modeling forward in time may reveal how the magnetic fields evolve and diffuse as the star cools, helping to make sense of these magnetic crystalline stars.

By Kerry Hensley

Source: American Astronomical Society/AAS-Nova

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Citation

“A Short Intense Dynamo at the Onset of Crystallization in White Dwarfs,” J. R. Fuentes et al 2024 ApJL 964 L15.
doi:10.3847/2041-8213/ad3100

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Never-Before-Seen Way to Annihilate a Star

Astronomers studying a powerful gamma-ray burst (GRB) with the International Gemini Observatory, operated by NSF’s NOIRLab, may have observed a never-before-seen way to destroy a star. Unlike most GRBs, which are caused by exploding massive stars or the chance mergers of neutron stars, astronomers have concluded that this GRB came instead from the collision of stars or stellar remnants in the jam-packed environment surrounding a supermassive black hole at the core of an ancient galaxy. Credit: International Gemini Observatory/NOIRLab/NSF/AURA/M. Garlick/M. Zamani. download: Large JPEG

This artist's impression illustrates how astronomers studying a powerful gamma-ray burst (GRB) with the Gemini South telescope, operated by NSF’s NOIRLab, may have detected a never-before-seen way to destroy a star. Unlike most GRBs, which are caused by exploding massive stars or the chance mergers of neutron stars, astronomers have concluded that this GRB came instead from the collision of stars or stellar remnants in the jam-packed environment surrounding a supermassive black hole at the core of an ancient galaxy. Credit:International Gemini Observatory/NOIRLab/NSF/AURA, M. Garlick, M. Zamani, K. O Chul, ESO/L. Calçada, NASA's Goddard Space Flight Center/CI Lab, N. Bartmann. Music: Stellardrone - Airglow.   Load Video

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International Gemini Observatory traces gamma-ray burst to nucleus of ancient galaxy, suggesting stars can undergo demolition-derby-like collisions

Astronomers studying a powerful gamma-ray burst (GRB) with the Gemini South telescope, operated by NSF’s NOIRLab, may have observed a never-before-seen way to destroy a star. Unlike most GRBs, which are caused by exploding massive stars or the chance mergers of neutron stars, astronomers have concluded that this GRB came instead from the collision of stars or stellar remnants in the jam-packed environment surrounding a supermassive black hole at the core of an ancient galaxy.

Most stars in the Universe die in predictable ways, depending on their mass. Relatively low-mass stars like our Sun slough off their outer layers in old age and eventually fade to become white dwarf stars. More massive stars burn brighter and die sooner in cataclysmic supernova explosions, creating ultradense objects like neutron stars and black holes. If two such stellar remnants form a binary system, they also can eventually collide. New research, however, points to a long-hypothesized, but never-before-seen, fourth option.

While searching for the origins of a long-duration gamma-ray burst (GRB), astronomers using the Gemini South telescope in Chile, part of the International Gemini Observatory operated by NSF’s NOIRLab, and other telescopes [1], have uncovered evidence of a demolition-derby-like collision of stars or stellar remnants in the chaotic and densely packed region near an ancient galaxy’s supermassive black hole.

“These new results show that stars can meet their demise in some of the densest regions of the Universe where they can be driven to collide,” said Andrew Levan, an astronomer with Radboud University in The Netherlands and lead author of a paper appearing in the journal Nature Astronomy. “This is exciting for understanding how stars die and for answering other questions, such as what unexpected sources might create gravitational waves that we could detect on Earth.”

Ancient galaxies are long past their star-forming prime and would have few, if any, remaining giant stars, the principal source of long GRBs. Their cores, however, are teeming with stars and a menagerie of ultra-dense stellar remnants, such as white dwarf stars, neutron stars, and black holes.  Astronomers have long suspected that in the turbulent beehive of activity surrounding a supermassive black hole, it would only be a matter of time until two stellar objects collide to produce a GRB. Evidence for that type of merger, however, has been elusive.

The first hints that such an event had occurred were seen on 19 October 2019 when NASA’s Neil Gehrels Swift Observatory detected a bright flash of gamma rays that lasted for a little more than one minute. Any GRB lasting more than two seconds is considered “long.” Such bursts typically come from the supernova death of stars at least 10 times the mass of our Sun — but not always.

The researchers then used Gemini South to make long-term observations of the GRB’s fading afterglow to learn more about its origins. The observations allowed the astronomers to pinpoint the location of the GRB to a region less than 100 light-years from the nucleus of an ancient galaxy, which placed it very near the galaxy’s supermassive black hole. The researchers also found no evidence of a corresponding supernova, which would leave its imprint on the light studied by Gemini South.

“Our follow-up observation told us that rather than being a massive star collapsing, the burst was most likely caused by the merger of two compact objects,” said Levan. “By pinpointing its location to the center of a previously identified ancient galaxy, we had the first tantalizing evidence of a new pathway to ‘kill’ a star.”

In normal galactic environments, the production of long GRBs from colliding stellar remnants such as neutron stars and black holes is thought to be vanishingly rare. The cores of ancient galaxies, however, are anything but normal and there may be a million or more stars crammed into a region just a few light-years across. Such extreme population density may be great enough that occasional stellar collisions can occur, especially under the titanic gravitational influence of a supermassive black hole, which would perturb the motions of stars and send them careening in random directions. Eventually, these wayward stars would intersect and merge, triggering a titanic explosion that could be observed from vast cosmic distances.

It is possible that such events occur routinely in similarly crowded regions across the Universe but have gone unnoticed until this point. A possible reason for their obscurity is that galactic centers are brimming with dust and gas, which could obscure both the initial flash of the GRB and the resulting afterglow. This particular GRB, identified as GRB 191019A, may be a rare exception, allowing astronomers to detect the burst and study its after effects.

The researchers would like to discover more of these events. Their hope is to match a GRB detection with a corresponding gravitational-wave detection, which would reveal more about their true nature and confirm their origins, even in the murkiest of environments. The Vera C. Rubin Observatory, when it comes online in 2025, will be invaluable in this kind of research.

“Studying gamma-ray bursts like these is a great example of how the field is really advanced by many facilities working together, from the detection of the GRB, to the discoveries of afterglows and distances with telescopes like Gemini, through to detailed dissection of events with observations across the electromagnetic spectrum,” said Levan.

“These observations add to Gemini’s rich heritage developing our understanding of stellar evolution,” says Martin Still, NSF’s program director for the International Gemini Observatory. “The time sensitive observations are a testament to Gemini’s nimble operations and sensitivity to distant, dynamic events across the Universe.”

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More Information

Reference: Levan, A. J., Malesani, D. B., Gompertz, B. P., et al. (2023) “A long-duration gamma-ray burst of dynamical origin from the nucleus of an ancient galaxy.” Nature Astronomy. DOI: 10.1038/s41550-023-01998-8

[1] Additional observations were made with the Nordic Optical Telescope and the NASA/ESA Hubble Space Telescope.

NSF’s NOIRLab, the US center for ground-based optical-infrared astronomy, operates the International Gemini Observatory (a facility of NSF, NRC–Canada, ANID–Chile, MCTIC–Brazil, MINCyT–Argentina, and KASI–Republic of Korea), Kitt Peak National Observatory (KPNO), Cerro Tololo Inter-American Observatory (CTIO), the Community Science and Data Center (CSDC), and Vera C. Rubin Observatory (operated in cooperation with the Department of Energy’s SLAC National Accelerator Laboratory). It is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with NSF and is headquartered in Tucson, Arizona. The astronomical community is honored to have the opportunity to conduct astronomical research on Iolkam Du’ag (Kitt Peak) in Arizona, on Maunakea in Hawai‘i, and on Cerro Tololo and Cerro Pachón in Chile. We recognize and acknowledge the very significant cultural role and reverence that these sites have to the Tohono O’odham Nation, to the Native Hawaiian community, and to the local communities in Chile, respectively.

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Links

• Research paper
• Photos of Gemini South
• Videos of Gemini South

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Contacts:

Andrew Levan
Radboud University
Email: a.levan@astro.ru.nl

Charles Blue
Public Information Officer
NSF’s NOIRLab
Tel: +1 202 236 6324
Email: charles.blue@noirlab.edu

Source: Gemini Observatory

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For The First Time Hubble Directly Measures The Mass of a Lone White Dwarf

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LAWD 37

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Hubble Measures Deflection of Starlight by a Foreground Object

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Hubble Uses Microlensing To Measure the Mass of a White Dwarf

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Hubble Uses Microlensing To Measure the Mass of a White Dwarf (Annotated)

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Hubble Uses Microlensing To Measure the Mass of a White Dwarf (Clean)

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Videos

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Gravitational Lensing: White Dwarf Passes In Front of Distant Background Star 

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Pan of LAWD 37

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Astronomers using the NASA/ESA Hubble Space Telescope have for the first time directly measured the mass of a single, isolated white dwarf star – the surviving core of a burned-out sunlike star.

Researchers found that the white dwarf is 56 percent of the mass of our Sun. This agrees with earlier theoretical predictions of its mass and corroborates current theories of how white dwarfs evolve as the end product of a typical star’s evolution. The unique observation yields insights into theories of the structure and composition of white dwarfs.

Until now, previous white dwarf mass measurements have been gleaned from observing white dwarfs in binary star systems. By watching the motion of two co-orbiting stars, straightforward Newtonian physics can be used to measure their masses. However, these measurements can be uncertain if the dwarf’s companion star is in a long-period orbit of hundreds or thousands of years. Orbital motion can be measured by telescopes only over a brief slice of the dwarf’s orbital motion.

For this companion-less white dwarf, researchers had to employ a trick of nature, called gravitational microlensing. The light from a background star was slightly deflected by the gravitational warping of space by the foreground dwarf star. As the white dwarf passed in front of the background star, microlensing caused the star to appear temporarily offset from its actual position on the sky.

The results are reported in the journal Monthly Notices of the Royal Astronomical Society. The lead author is Peter McGill, formerly of the University of Cambridge in the United Kingdom and now based at the University of California, Santa Cruz.

McGill used Hubble to precisely measure how light from a distant star bent around the white dwarf, known as LAWD 37, causing the background star to temporarily change its apparent position in the sky.

Kailash Sahu of the Space Telescope Science Institute in Baltimore, Maryland, USA, the principal Hubble investigator on this latest observation, first used microlensing in 2017 to measure the mass of another white dwarf, Stein 2051 B. But that dwarf is in a widely separated binary system. “Our latest observation provides a new benchmark because LAWD 37 is all by itself,” Sahu said.

The collapsed remains of a star that burned out 1 billion years ago, LAWD 37 has been extensively studied because it is only 15 light-years away in the constellation Musca. “Because this white dwarf is relatively close to us, we’ve got lots of data on it — we’ve got information about its spectrum of light, but the missing piece of the puzzle has been a measurement of its mass,” said McGill.

The team zeroed-in on the white dwarf thanks to ESA’s Gaia mission, which makes extraordinarily precise measurements of nearly two billion star positions. Multiple Gaia observations can be used to track a star’s motion. Based on these data, astronomers were able to predict that LAWD 37 would briefly pass in front of a background star in November 2019.

Once this was known, Hubble was used to precisely measure over several years how the background star’s apparent position in the sky was temporarily deflected during the white dwarf’s passage.

“These events are rare, and the effects are tiny,” said McGill. “For instance, the size of our measured offset is like measuring the length of a car on the Moon as seen from Earth.”

Since the light from the background star was so faint, the main challenge for astronomers was extracting its image from the glare of the white dwarf, which is 400 times brighter than the background star. Only Hubble can make these kinds of high-contrast observations in visible light.

"Even when you’ve identified such a one-in-a-million event, it’s still extremely difficult to make these measurements,” said Leigh Smith of the University of Cambridge. “The glare from the white dwarf can cause streaks in unpredictable directions, meaning we had to analyse each of Hubble’s observations extremely carefully, and their limitations, to model the event and estimate the mass of LAWD 37."

“The precision of LAWD 37’s mass measurement allows us to test the mass-radius relationship for white dwarfs,” said McGill. “This means testing the theory of degenerate matter (a gas so super-compressed under gravity that it behaves more like solid matter) under the extreme conditions inside this dead star,” he added.

event predictions with Gaia data. In addition to Hubble, these alignments can now be detected with the NASA/ESA/CSA James Webb Space Telescope. Because Webb works at infrared wavelengths, the blue glow of a foreground white dwarf looks dimmer in infrared light, and the background star looks brighter.

Based on Gaia’s predictive powers, Sahu is observing another white dwarf, LAWD 66, with Webb. The first observation was made in 2022. More observations will be taken as the deflection peaks in 2024 and then subsides.

“Gaia has really changed the game — it’s exciting to be able to use Gaia data to predict when events will happen, and then observe them happening,” said McGill. “We want to continue measuring the gravitational microlensing effect and obtain mass measurements for many more types of stars.”

In his 1915 general theory of relativity, Einstein predicted that when a massive compact object passes in front of a background star, the light from the star would bend around the foreground object because of the warping of space by its gravitational field.

Exactly a century before this latest Hubble observation, in 1919, two British-organised expeditions to the southern hemisphere first detected this lensing effect during a solar eclipse on 19 May. It was hailed as the first experimental proof of general relativity — that gravity warps space. However, Einstein was pessimistic that the effect could ever be detected for stars outside our Solar System because of the precision required. “Our measurement is 625 times smaller than the effect measured at the 1919 solar eclipse,” said McGill.

Source: ESA/Hubble/News

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More Information

The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

The international team of astronomers in this study consists of Peter McGill (University of Cambridge, UK; University of California Santa Cruz, USA), Jay Anderson (Space Telescope Science Institute, USA), Stefano Casertano (Space Telescope Science Institute, USA), Kailash C. Sahu (Space Telescope Science Institute, USA), Pierre Bergeron (University of Montreal, Canada), Simon Blouin (University of Victoria, Canada), Patrick Dufour (University of Montreal, Canada), Leigh C. Smith (University of Cambridge, UK), N. Wyn Evans (University of Cambridge, UK), Vasily Belokurov (University of Cambridge, UK), Richard L. Smart (INAF – Astrophysical Observatory of Torino, Italy), Andrea Bellini (Space Telescope Science Institute, USA), Annalisa Calamida (Space Telescope Science Institute, USA), Martin Dominik (University of St Andrews, UK), Noé Kains (Space Telescope Science Institute, USA), Jonas Klüter (Louisiana State University, USA), Martin Bo Nielsen (University of Birmingham, UK; Aarhus University, Denmark; New York University Abu Dhabi, United Arab Emirates), and Joachim Wambsganss (Heidelberg University, Germany)

Image credit: NASA, ESA, A. Feild

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Links

• Images of Hubble 
• ESA/Hubble Word Bank: Gravitational Lensing
• ESA’s Gaia mission
• Release on STScI website
• Science paper

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Contacts:

Peter McGill
University of California, Santa Cruz, California
University of Cambridge, Cambridge, United Kingdom
Email: pemcgill@ucsc.edu 

Kailash Sahu
Space Telescope Science Institute, Baltimore, Maryland
Email: sahu@stsci.edu

Bethany Downer
ESA/Hubble Chief Science Communications Officer
Email: Bethany.Downer@esahubble.org

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Peculiar white dwarf mergers

This artist’s impression shows how one White Dwarf star is disrupted during the merger with a second White Dwarf
Image: Marcelo Miller Bertolami

This diagram shows the evolution of four merger products with different masses, resulting from the merger of two white dwarfs. Interestingly, the mass of the star (measured by the gravitational force on its surface, y-axis) is directly correlated to its effective temperature. Thin lines indicate the fast evolution at the beginning, while thick lines show the slower evolution during the helium core burning stage and after. Purple and green circles (with error bars) indicate the locations of the observed peculiar hot, blue, light-but-dense stars, which can all be explained by the same model. © MPA

Two types of hot, blue and dense stars that show peculiar characteristics in their composition and vibrations have posed a challenge to astrophysicists for more than a decade. A team of scientists from MPA and La Plata in Argentina, has now been able to explain both types as a product of very similar merger events. In particular, the scientists think that the peculiar hot and blue stars are formed by the merger of two white dwarfs.

The majority of stars in the Universe have atmospheres composed principally by hydrogen and, in smaller amounts, by helium. Most of the hot, blue, light-but-dense stars, however, generally do not show their helium. The gravity on their surface is sufficiently high so that the slightly heavier helium sinks below the hydrogen. Many of these stars pulsate, or vibrate like music instruments – but instead of producing sound, they produce peculiar light patterns. These light patterns allow us to study their internal structure and to understand the origin of their vibrations.

Two types of hot, blue and dense stars, however, constitute a challenge for scientists: Only three stars are known of the first type and they have presented a puzzle to astronomers since the discovery of the first one, back in 2011. The atmospheres of these stars is a mixture of helium and hydrogen, while we expect this kind of stars to have only hydrogen on their surfaces. In addition, these helium-rich stars are vibrating, very differently from “normal” hot blue stars with atmospheres made of hydrogen. Several possible explanations of why these helium-rich blue stars are pulsating, their internal composition, and their history have been published since 2011 – none of them completely addressing all of these questions. Astronomers of the Universities of Tübingen and Potsdam have recently reported the discovery of another type of peculiar hot blue stars. These stars are covered by carbon and oxygen, a very exotic feature that is even more complicated to explain than the presence of helium in these stars.

While these two classes of hot and blue stars look very different, a group of scientists from MPA and La Plata in Argentina, has been able to explain the weird compositions in both and the vibrations in the helium-rich ones as a product of very similar merger events of two white dwarfs.

A merger event happens when two stars orbiting very closely are attracted by gravitational forces, finally fusing with each other to form a single star. Sometimes such a double star system consists of white dwarfs, small ancient stars, which are the final state of life of stars like our Sun. They are denser than the majority of the stars in the Universe, with a mass of around half the mass of the Sun compressed into a volume similar to the one of Earth. The majority of white dwarfs have a core of carbon and oxygen, surrounded by a mantle of helium, and an outer envelope of hydrogen.

In a merger of two white dwarfs, the less massive star will be disrupted and its material poured on top of the more massive companion. Therefore, if the less massive star is made principally of carbon and oxygen, carbon and oxygen should be observed in the product star after the merger. White dwarfs with carbon-oxygen cores usually have around 0.6 the mass of the Sun, or a bit more. Some of them, however, can be less than the half the mass of our Sun. Interestingly, a merger of such a low-mass carbon-oxygen white dwarf with a slightly more massive one can produce hot, blue, light-but-dense stars.

When the merger product has a low mass (around half of the Sun’s mass), the high gravity on the surface of the star will cause carbon and oxygen to sink, hiding below an atmosphere composed of hydrogen and helium. Still lurking close to the surface, however, the carbon and oxygen can trigger pulsations that look very similar to those of the helium-rich stars that have puzzled astronomers for more than a decade. The astrophysicists have also argued that, for slightly more massive merger products (around 0.8 the mass of the Sun) winds in the atmosphere might stop the sinking process of carbon and oxygen, making the stars look like the recently discovered ones.

Thus, the existence of both types of peculiar hot, blue, light-but-dense stars, including the vibrations presented by the helium-rich ones, can be explained as products of a similar merger history.

Author:

Tiara Battich
Postdoc
tel: 2198
tiara@mpa-garching.mpg.de

Original publication

1. M. M. Miller Bertolami, T. Battich, A. H. Córsico, L. G. Althaus, F. C. Wachlin

An evolutionary channel for CO-rich and pulsating He-rich subdwarfs Monthly Notices of the Royal Astronomical Society: Letters, Volume 511, Issue 1, March 2022, Pages L60–L65

DOI

Source:Max Planck Institute for Astrophysics

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NASA’s Webb Captures Dying Star’s Final ‘Performance’ in Fine Detail

Southern Ring Nebula (NIRCam and MIRI Images Side by Side)
Credits: Image: NASA, ESA, CSA, STScI
Release images

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Some stars save the best for last.

The dimmer star at the center of this scene has been sending out rings of gas and dust for thousands of years in all directions, and NASA’s James Webb Space Telescope has revealed for the first time that this star is cloaked in dust.

Two cameras aboard Webb captured the latest image of this planetary nebula, cataloged as NGC 3132, and known informally as the Southern Ring Nebula. It is approximately 2,500 light-years away.

Webb will allow astronomers to dig into many more specifics about planetary nebulae like this one – clouds of gas and dust expelled by dying stars. Understanding which molecules are present, and where they lie throughout the shells of gas and dust will help researchers refine their knowledge of these objects.

This observation shows the Southern Ring Nebula almost face-on, but if we could rotate it to view it edge-on, its three-dimensional shape would more clearly look like two bowls placed together at the bottom, opening away from one another with a large hole at the center.

Two stars, which are locked in a tight orbit, shape the local landscape. Webb's infrared images feature new details in this complex system. The stars – and their layers of light – are prominent in the image from Webb’s Near-Infrared Camera (NIRCam) on the left, while the image from Webb’s Mid-Infrared Instrument (MIRI) on the right shows for the first time that the second star is surrounded by dust. The brighter star is in an earlier stage of its stellar evolution and will probably eject its own planetary nebula in the future.

In the meantime, the brighter star influences the nebula’s appearance. As the pair continues to orbit one another, they “stir the pot” of gas and dust, causing asymmetrical patterns.

Each shell represents an episode where the fainter star lost some of its mass. The widest shells of gas toward the outer areas of the image were ejected earlier. Those closest to the star are the most recent. Tracing these ejections allows researchers to look into the history of the system.

Observations taken with NIRCam also reveal extremely fine rays of light around the planetary nebula. Starlight from the central stars streams out where there are holes in the gas and dust – like sunlight through gaps in a cloud.

Since planetary nebulae exist for tens of thousands of years, observing the nebula is like watching a movie in exceptionally slow motion. Each shell the star puffed off gives researchers the ability to precisely measure the gas and dust that are present within it.

As the star ejects shells of material, dust and molecules form within them – changing the landscape even as the star continues to expel material. This dust will eventually enrich the areas around it, expanding into what’s known as the interstellar medium. And since it’s very long-lived, the dust may end up traveling through space for billions of years and become incorporated into a new star or planet.

In thousands of years, these delicate layers of gas and dust will dissipate into surrounding space.

The James Webb Space Telescope is the world's premier space science observatory. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe 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.

NASA Headquarters oversees the mission for the agency’s Science Mission Directorate. NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages Webb for the agency and oversees work on the mission performed by the Space Telescope Science Institute, Northrop Grumman, and other mission partners. In addition to Goddard, several NASA centers contributed to the project, including the agency’s Johnson Space Center in Houston, Jet Propulsion Laboratory in Southern California, Marshall Space Flight Center in Huntsville, Alabama, Ames Research Center in California’s Silicon Valley, and others.

NIRCam was built by a team at the University of Arizona and Lockheed Martin’s Advanced Technology Center.

MIRI was contributed by ESA and NASA, with the instrument designed and built by a consortium of nationally funded European Institutes (The MIRI European Consortium) in partnership with JPL and the University of Arizona.

For a full array of Webb’s first images and spectra, including downloadable files, please visit: https://webbtelescope.org/news/first-images

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Credits:

Release: NASA, ESA, CSA, STScI

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Contact Us: Direct inquiries to the News Team.

Source: NASA's James Webb Space Telescope/Releases

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Dead Star Caught Ripping Up Planetary System

Material Accreting onto the White Dwarf G238-44

This illustration shows a white dwarf star siphoning off debris from shattered objects in a planetary system. The Hubble Space Telescope detects the spectral signature of the vaporized debris that revealed a combination of rocky-metallic and icy material, the ingredients of planets. The findings help describe the violent nature of evolved planetary systems and the composition of its disintegrating bodies. Credits: Illustration: NASA, ESA, Joseph Olmsted (STScI)

Layout of the White Dwarf System G238-44

This illustrated diagram of the planetary system G238-44 traces its destruction. The tiny white dwarf star is at the center of the action. A very faint accretion disk is made up of the pieces of shattered bodies falling onto the white dwarf. The remaining asteroids and planetary bodies make up a reservoir of material surrounding the star. Larger gas giant planets may still exist in the system. Much farther out is a belt of icy bodies such as comets, which also ultimately feed the dead star. Credits: Illustration: NASA, ESA, Joseph Olmsted (STScI)

Release Images

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A star's death throes have so violently disrupted its planetary system that the dead star left behind, called a white dwarf, is siphoning off debris from both the system's inner and outer reaches. This is the first time astronomers have observed a white dwarf star that is consuming both rocky-metallic and icy material, the ingredients of planets.

Archival data from NASA's Hubble Space Telescope and other NASA observatories were essential in diagnosing this case of cosmic cannibalism. The findings help describe the violent nature of evolved planetary systems and can tell astronomers about the makeup of newly forming systems.

The findings are based on analyzing material captured by the atmosphere of the nearby white dwarf star G238-44. A white dwarf is what remains of a star like our Sun after it sheds its outer layers and stops burning fuel though nuclear fusion. "We have never seen both of these kinds of objects accreting onto a white dwarf at the same time," said Ted Johnson, the lead researcher and recent University of California, Los Angeles (UCLA) bachelor's graduate. "By studying these white dwarfs, we hope to gain a better understanding of planetary systems that are still intact."

The findings are also intriguing because small icy objects are credited for crashing into and "irrigating" dry, rocky planets in our solar system. Billions of years ago comets and asteroids are thought to have delivered water to Earth, sparking the conditions necessary for life as we know it. The makeup of the bodies detected raining onto the white dwarf implies that icy reservoirs might be common among planetary systems, said Johnson.

"Life as we know it requires a rocky planet covered with a variety of elements like carbon, nitrogen, and oxygen," said Benjamin Zuckerman, UCLA professor and co-author. "The abundances of the elements we see on this white dwarf appear to require both a rocky and a volatile-rich parent body – the first example we've found among studies of hundreds of white dwarfs."

Demolition Derby

Theories of planetary system evolution describe the transition between a red giant star and white dwarf phases as a chaotic process. The star quickly loses its outer layers and its planets' orbits dramatically change. Small objects, like asteroids and dwarf planets, can venture too close to giant planets and be sent plummeting toward the star. This study confirms the true scale of this violent chaotic phase, showing that within 100 million years after the beginning of its white dwarf phase, the star is able to simultaneously capture and consume material from its asteroid belt and Kuiper belt-like regions.

The estimated total mass eventually gobbled up by the white dwarf in this study may be no more than the mass of an asteroid or small moon. While the presence of at least two objects that the white dwarf is consuming is not directly measured, it's likely one is metal-rich like an asteroid and another is an icy body similar to what's found at the fringe of our solar system in the Kuiper belt.

Though astronomers have cataloged over 5,000 exoplanets, the only planet where we have some direct knowledge of its interior makeup is Earth. The white dwarf cannibalism provides a unique opportunity to take planets apart and see what they were made of when they first formed around the star.

The team measured the presence of nitrogen, oxygen, magnesium, silicon and iron, among other elements. The detection of iron in a very high abundance is evidence for metallic cores of terrestrial planets, like Earth, Venus, Mars and Mercury. Unexpectedly high nitrogen abundances led them to conclude the presence of icy bodies. "The best fit for our data was a nearly two-to-one mix of Mercury-like material and comet-like material, which is made up of ice and dust," Johnson said. "Iron metal and nitrogen ice each suggest wildly different conditions of planetary formation. There is no known solar system object with so much of both."

Death of a Planetary System

When a star like our Sun expands into a bloated red giant late in its life, it will shed mass by puffing off its outer layers. One consequence of this can be the gravitational scattering of small objects like asteroids, comets and moons by any remaining large planets. Like pinballs in an arcade game, the surviving objects can be thrown into highly eccentric orbits.

"After the red giant phase, the white dwarf star that remains is compact – no larger than Earth. The wayward planets end up getting very close to the star and experience powerful tidal forces that tear them apart, creating a gaseous and dusty disk that eventually falls onto the white dwarf's surface," Johnson explained. The researchers are looking at the ultimate scenario for the Sun's evolution, 5 billion years from now. Earth might be completely vaporized along with the inner planets. But the orbits of many of the asteroids in the main asteroid belt will be gravitationally perturbed by Jupiter and will eventually fall onto the white dwarf that the remnant Sun will become. For over two years, the research group at UCLA, the University of California, San Diego and the Kiel University in Germany, has worked to unravel this mystery by analyzing the elements detected on the white dwarf star cataloged as G238-44. Their analysis includes data from NASA's retired Far Ultraviolet Spectroscopic Explorer (FUSE), the Keck Observatory's High Resolution Echelle Spectrometer (HIRES) in Hawaii, and the Hubble Space Telescope's Cosmic Origins Spectrograph (COS) and Space Telescope Imaging Spectrograph (STIS). The team's results were presented at an American Astronomical Society (AAS) press conference on Wednesday, June 15, 2022.

The Hubble Space Telescope 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. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C.

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Space Telescope Science Institute, Baltimore, Maryland

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Space Telescope Science Institute, Baltimore, Maryland

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University of California, Los Angeles, Los Angeles, California

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Contact Us: Direct inquiries to the News Team.

Related Links and Documents: NASA's Hubble Portal

Source: HubbleSite/News

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Two Stellar Evolution Roads Diverged at a Certain Mass…

A Hubble image of the globular cluster NGC 6397, which hosts numerous white dwarfs. The white dwarfs are incredibly faint and can be seen in a zoomed-in version of the right quadrant of the image. Credit: NASA, ESA, and H. Richer (University of British Columbia)

Just by knowing the mass of a star, can we predict if it will end its life in fire (a supernova) or ice (a white dwarf that eventually fades into a cool black dwarf)? A team led by astronomers at the University of British Columbia tries to answer that question by observing white dwarfs in order to find exactly where that dividing line is between a death of fire and ice.

Hubble Space Telescope image of the Crab Nebula, the remnant of a supernova that took place in the year 1054 AD. Credit: NASA, ESA, J. Hester and A. Loll

…But Which Road Leads to a White Dwarf?

When a star runs out of fuel, it can either eject its outer layers in an explosion so violent that it outputs more energy than the Sun will in its 10 billion years of life, or the star may simply expand and settle down into a stable star called a white dwarf about the size of our moon. What determines which route the star takes is its mass: lower masses die a death of ice, higher masses of fire. Though we believe the dividing line is somewhere around 8 solar masses, this number doesn’t always agree with what we observe.

T

he color–magnitude diagram of the Milky Way globular cluster 47 Tucanae. The x-axis shows the color, the left y-axis shows the apparent magnitude at 47 Tucanae’s distance, and the right y-axis shifts the cluster to the distance of the Large Magellanic Cloud. This diagram shows that even at the distance of the Large Magellanic Cloud, these massive WDs are detectable. Credit: Richer et al. 2022

In Two Words I Can Sum Up Everything I’ve Learned About Stars: They Evolve

If all stars greater than 8 solar masses end their lives in the fire of a supernova, we would see a lot more supernova explosions (specifically, Type II supernovae) than we actually do. This dearth of Type II supernovae could indicate that the maximum mass of a star that can end its life as a white dwarf is actually closer to 12 solar masses rather than 8. Constraining this mass limit of stars that can become white dwarfs could inform the formation rate of compact objects as well as the metal content of galaxies. The more massive a star is, the more massive its white dwarf remnant is. Therefore, by hunting for massive white dwarfs, we can effectively hunt for massive progenitor stars that weren’t heavy enough to end in a supernova. A team led by Harvey Richer at the University of British Columbia has looked deep into young open star clusters outside our own galaxy to try to identify massive white dwarfs.

Previous searches for massive white dwarfs in young Milky Way open clusters only found white dwarfs up to 1.1 solar masses, which come from stars no larger than 6.2 solar masses. To probe whether even more massive stars can become white dwarfs, Richer and coauthors searched young clusters in the Large Magellanic Clouds. The team looked at four Magellanic Cloud clusters in which stars of 5.7 to 10.2 solar masses were just about to enter the asymptotic giant phase (a late evolutionary stage in an intermediate–mass star’s life at which point the star has exhausted its main fuel source), which would mean the white dwarfs in these clusters must have come from stars more massive than that. They also chose these specific clusters because of their distance; the Magellanic Clouds are far enough away that there would be new clusters to search, but not so distant that Gaia parallaxes are unreliable and there is confusion with field white dwarfs.

Distributions of the various populations of stars in two of the clusters. The white dwarfs in the leftmost panel are the five potential white dwarf candidates. Credit: Richer et al. 2022

The Universe Is Lovely, Dark, and Deep, But We Need More Data To Put This Mystery To Sleep

The team found five potential candidates in the oldest of the four clusters they studied by looking at the ages and populations of the clusters. These stars represent the first extragalactic single white dwarfs ever discovered. This study demonstrated that it is possible to detect white dwarfs in nearby galaxies with only moderate exposure times with Hubble. However, to study them spectroscopically and determine their masses and ages, the team needs more resolution, which will come with future 30+ meter telescopes. Confirmation of these heavy white dwarfs may finally lead us to the point where the roads of stellar evolution diverged.

Citation

“When Do Stars Go Boom?” Harvey B. Richer et al 2022 ApJL 931 L20. doi:10.3847/2041-8213/ac6585

By Haley Wahl

Source: American Astronomical Society - AAS Nova

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Astronomers discover a new type of star covered in helium burning ashes

Artist's impression of a rare kind of stellar merger event between two white dwarf stars.
Credit: Nicole Reindl
Licence type:Attribution (CC BY 4.0)

A team of German astronomers, led by Professor Klaus Werner of the University of Tübingen, have discovered a strange new type of star covered in the by-product of helium burning. It is possible that the stars might have been formed by a rare stellar merger event. The fascinating results are published in Monthly Notices of the Royal Astronomical Society.

While normal stars have surfaces composed of hydrogen and helium, the stars discovered by Werner and his colleagues have their surfaces covered with carbon and oxygen, the ashes of helium burning – an exotic composition for a star. The situation becomes more puzzling as the new stars have temperatures and radii that indicate they are still burning helium in their cores – a property typically seen in more evolved stars than those observed by Werner and his team in this study.

Published alongside the work of Professor Werner and his team, a second paper from a group of astronomers from the University of La Plata and the Max Planck Institute for Astrophysics offers a possible explanation for their formation. “We believe the stars discovered by our German colleagues might have formed in a very rare kind of stellar merger event between two white dwarf stars”, says Dr Miller Bertolami of the Institute for Astrophysics of La Plata, lead author of the second paper. White dwarfs are the remnants of larger stars that have exhausted their nuclear fuel, and are typically very small and dense.

Stellar mergers are known to happen between white dwarfs in close binary systems due to the shrinking of the orbit caused by the emission of gravitational waves. “Usually, white dwarf mergers do not lead to the formation of stars enriched in carbon and oxygen”, explains Miller Bertolami, “but we believe that, for binary systems formed with very specific masses, a carbon- and oxygen-rich white dwarf might be disrupted and end up on top of a helium-rich one, leading to the formation of these stars”.

Yet no current stellar evolutionary models can fully explain the newly discovered stars. The team need refined models in order to assess whether these mergers can actually happen. These models could not only help the team to better understand these stars, but could also provide a deeper insight into the late evolution of binary systems and how their stars exchange mass as they evolve. Until astronomers develop more refined models for the evolution of binary stars, the origin of the helium covered stars will be up for debate.
p style="text-align: justify;">“Normally we expect stars with these surface compositions to have already finished burning helium in their cores, and to be on their way to becoming white dwarfs. These new stars are a severe challenge to our understanding of stellar evolution.” explains Professor Werner.

by Gurjeet Kahlon

 Source: Royal Astronomical Society (RAS)/News

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Media contacts

Gurjeet Kahlon
Royal Astronomical Society
Mob: +44 (0)7802 877 700
press@ras.ac.uk Dr Robert Massey
Royal Astronomical Society
Mob: +44 (0)7802 877 699
press@ras.ac.uk

Science Contacts

Professor Klaus Werner
Institute for Astronomy and Astrophysics, Kepler Center for Astro and Particle Physics, Eberhard Karls University, Germany
werner@astro.uni-tuebingen.de 

Dr Miller Bertolami
Institute for Astrophysics of La Plata, CONICET-National University of La Plata, Argentina
mmiller@fcaglp.unlp.edu.ar

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Further Information

The research appears in “Discovery of hot subdwarfs covered with helium-burning ash”, K. Werner, N. Reindl, S. Geier and M. Pritzkuleit and “An evolutionary channel for CO-rich and pulsating He-rich subdwarfs” M. M. Miller Bertolami T.Battich, A. H. Córsico, L. G. Althaus, F. C. Wachlin, both published in Monthly Notices of the Royal Astronomical Society, in press. The papers can be found at https://academic.oup.com/mnrasl/article-lookup/doi/10.1093/mnrasl/slac0… andhttps://academic.oup.com/mnrasl/advance-article-abstract/doi/10.1093/mn…, respectively.

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Notes for Editors

The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organises scientific meetings, publishes international research and review journals, recognises outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 4,000 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.

The RAS accepts papers for its journals based on the principle of peer review, in which fellow experts on the editorial boards accept the paper as worth considering. The Society issues press releases based on a similar principle, but the organisations and scientists concerned have overall responsibility for their content.

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Hubble fortuitously discovers a new galaxy in the cosmic neighbourhood

PR Image heic1903a

The accidentally discovered galaxy Bedin I

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Bedin 1 in NGC 6752

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Globular cluster NGC 6752

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Wide-field view of NGC 6752 (ground-based view)

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Videos 

PR Video heic1903a

Zooming in on NGC 6752 and Bedin 1

PR Video heic1903b

Flight to Bedin 1

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Astronomers using the NASA/ESA Hubble Space Telescope to study some of the oldest and faintest stars in the globular cluster NGC 6752 have made an unexpected finding. They discovered a dwarf galaxy in our cosmic backyard, only 30 million light-years away. The finding is reported in the journal Monthly Notices of the Royal Astronomical Society: Letters.

An international team of astronomers recently used the NASA/ESA Hubble Space Telescope to study white dwarf stars within the globular cluster NGC 6752. The aim of their observations was to use these stars to measure the age of the globular cluster, but in the process they made an unexpected discovery.

In the outer fringes of the area observed with Hubble’s Advanced Camera for Surveys a compact collection of stars was visible. After a careful analysis of their brightnesses and temperatures, the astronomers concluded that these stars did not belong to the cluster — which is part of the Milky Way — but rather they are millions of light-years more distant.

Our newly discovered cosmic neighbour, nicknamed Bedin 1 by the astronomers, is a modestly sized, elongated galaxy. It measures only around 3000 light-years at its greatest extent — a fraction of the size of the Milky Way. Not only is it tiny, but it is also incredibly faint. These properties led astronomers to classify it as a dwarf spheroidal galaxy.

Dwarf spheroidal galaxies are defined by their small size, low-luminosity, lack of dust and old stellar populations [1]. 36 galaxies of this type are already known to exist in the Local Group of Galaxies, 22 of which are satellite galaxies of the Milky Way.

While dwarf spheroidal galaxies are not uncommon, Bedin 1 has some notable features. Not only is it one of just a few dwarf spheroidals that have a well established distance but it is also extremely isolated. It lies about 30 million light-years from the Milky Way and 2 million light-years from the nearest plausible large galaxy host, NGC 6744. This makes it possibly the most isolated small dwarf galaxy discovered to date.

From the properties of its stars, astronomers were able to infer that the galaxy is around 13 billion years old — nearly as old as the Universe itself. Because of its isolation — which resulted in hardly any interaction with other galaxies — and its age, Bedin 1 is the astronomical equivalent of a living fossil from the early Universe.

The discovery of Bedin 1 was a truly serendipitous find. Very few Hubble images allow such faint objects to be seen, and they cover only a small area of the sky. Future telescopes with a large field of view, such as the WFIRST telescope, will have cameras covering a much larger area of the sky and may find many more of these galactic neighbours.

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Notes

[1] While similar to dwarf elliptical galaxies in appearance and properties, dwarf spheroidal galaxies are in general approximately spherical in shape and have a lower luminosity.

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More Information

The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

The results were presented in the letter The HST Large Programme on NGC 6752. I. Serendipitous discovery of a dwarf galaxy in background, published in the journal Monthly Notices of the Royal Astronomical Society: Letters.

The international team of astronomers that carried out this study consists of L. R. Bedin (INAF-Osservatorio Astronomico di Padova, Italy), M. Salaris (Liverpool John Moores University, UK), R. M. Rich (University of California Los Angeles, USA), H. Richer (University of British Columbia), J. Anderson (Space Telescope Science Institute, USA), B. Bettoni (INAF-Osservatorio Astronomico di Padova, Italy), D. Nardiello (Università di Padova, Italy), A. P. Milone (Università di Padova, Italy), A. F. Marino (Università di Padova, Italy), M. Libralato (Space Telescope Science Institute, USA), A. Bellini (Space Telescope Science Institute, USA), A. Dieball (University of Bonn, Germany), P. Bergeron (Université de Montréal, Canada), A. J. Burgasser (University of California San Diego, USA), D. Apai (University of Arizona, USA).

Image credit: NASA, ESA, Bedin et al.

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Links

• Images of Hubble
• Hubblesite release
• Science paper

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Contact

L. R. Bedin
INAF-Osservatorio Astronomico di Padova
Padua, Italy
Tel: +49 8293 413
Email: luigi.bedin@oapd.inaf.it

Mathias Jäger
ESA/Hubble, Public Information Officer
Garching, Germany
Tel: +49 176 62397500
Email: mjaeger@partner.eso.org

Source: ESA/Hubble/News

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Thousands of Stars Observed Turning into Crystals for the First Time

Crystalized White Dwarf

Credit: University of Warwick/Mark Garlick)

Austin, Texas — The first direct evidence of crystallized white dwarf stars has been discovered by an international team of researchers that includes an astronomer at The University of Texas at Austin. Predicted half a century ago, the direct evidence of these stars will be published tomorrow in the journal Nature.

Observations have revealed that these stars have a core of solid carbon and oxygen due to a phase transition during their lifecycle, similar to water turning into ice. This phase transition slows their cooling in multiple ways, making them potentially billions of years older than previously thought.

The discovery, led by Pier-Emmanuel Tremblay of the U.K.’s University of Warwick, is largely based on observations taken with the European Space Agency’s Gaia satellite.

Almost all stars end up as white dwarfs, and some of them are among the oldest stars in the universe. They are useful to astronomers because their predictable cooling rate allows them to be used as cosmic clocks to estimate the ages of groups of stars. They are the leftover cores of red giant stars, after these huge stars have died and shed their outer layers. They are then constantly cooling as they release their stored-up heat over billions of years.

The Gaia satellite has enabled the selection of a sample of white dwarfs with precise luminosities and colors that is significantly larger and more complete than any previous survey. For the study, the team selected 15,000 white dwarfs within about 300 light-years of Earth.

White dwarfs get fainter and redder as they cool, which leads to a predictable distribution of white dwarfs in a plot of brightness versus color. The astronomers identified a pile-up in this plot, an excess in the number of stars at specific colors and luminosities. When compared with evolutionary models of white dwarfs, the pile-up strongly coincides with the phase in their development in which latent heat is predicted to be released in large amounts, resulting in a slowdown of their cooling process. It is estimated that in some cases these stars have slowed their aging by as much as 2 billion years.

Bart Dunlap, a postdoctoral fellow with UT Austin’s Wootton Center for Astrophysical Plasma Properties, working with JJ Hermes, made the discovery independently of the Warwick team and later joined forces with Tremblay. Hermes, a former UT graduate student, is now an assistant professor at Boston University.

“More than 50 years ago, Hugh Van Horn, an astronomer at the University of Rochester, predicted that we should see a crystallization sequence because of a slowdown in cooling when white dwarfs crystallize, but at the time, the data weren’t good enough to check this prediction,” Dunlap said. “Gaia finally made it possible to see what he predicted, and it really pops out in the data.”

Just as liquid water releases extra energy when it changes into ice — this energy is known as latent heat — the dense plasmas in the interiors of white dwarfs were predicted to release enough energy to noticeably slow their trek toward cool, faint stellar embers.

“All white dwarfs will crystallize at some point in their evolution, although more massive white dwarfs go through the process sooner,” said Tremblay, who led the study. “This means that billions of white dwarfs in our galaxy have already completed the process and are essentially metallic crystal spheres in the sky.”

This includes our own sun, which will become a crystal white dwarf in about 10 billion years.

Crystallization is the process of a material becoming a solid state in which its atoms form an ordered structure. Under the extreme pressures in white dwarf cores, atoms are packed so densely that their electrons become unbound, leaving a conducting electron gas governed by quantum physics, and positively charged nuclei in a fluid form. When the core cools to about 10 million degrees, the dense carbon oxygen plasma is cool enough that the fluid begins to solidify, forming a crystalline core at its heart.

“These results are really telling us a lot about the amount of pent-up energy these stars can release while cooling off,” Dunlap said.

The astronomers say they should have access to even better data from Gaia by 2021.

Media Contact:

Rebecca Johnson, 
Communications Mgr.
UT Austin McDonald Observatory
512-475-6763

Science Contacts:

Dr. Bart Dunlap, 
Postdoctoral Fellow
UT Austin Wootton Center for Astrophysical Plasma Properties & McDonald Observatory
501-940-2110

Dr. JJ Hermes, 
Assistant Professor of Astronomy
Boston University
512-517-2442

Source: UT Austin McDonald Observatory/News

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