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Institute of Astronomy

 

The landscape of binary core-collapse supernova progenitors and the late emergence of Wolf-Rayet winds

Recent IoA Publications - Thu, 03/07/2025 - 11:57
arXiv:2503.01993v2 Announce Type: replace Abstract: The majority of core-collapse supernova (CCSN) progenitors are massive stars in multiple systems, and their evolution and final fate are affected by interactions with their companions. These interactions can explain the presence of circumstellar material in many CCSNe, and the inferred low mass in stripped-envelope supernova progenitors. Through binary interactions, stars can gain mass, lose mass, or merge, impacting their final properties. Specific sub-types of binary interaction products have been investigated but few detailed full population models exist. Using thousands of detailed simulations with updated prescriptions for binary interactions and winds at Milky Way and Magellanic Clouds metallicities, we follow the evolution of single massive stars, primaries in interacting binaries and coalescence products following common envelope evolution. We also follow the evolution of the surviving secondary star, with a compact companion formed from the evolutionary end of the primary star or alone if the system was disrupted in the first supernova. The endpoints of our simulations map the rich landscape of CCSN progenitors, and provide detailed mass-loss history and progenitor structures. We identify an important evolutionary phase for stripped-envelope supernova progenitors, in which the wind mass-loss rate of stars stripped by binary interaction rapidly increases in their final evolutionary stages, after core helium burning. These strong winds would give rise to a Wolf-Rayet (WR) spectral appearance, though only for a few millennia, in contrast to hundreds of millennia for their more massive WR counterparts. Such lightweight WR stars in binaries can account for observed properties of type Ib/c supernovae.

The landscape of binary core-collapse supernova progenitors and the late emergence of Wolf-Rayet winds

Stars and stellar evolution - Thu, 03/07/2025 - 11:57
arXiv:2503.01993v2 Announce Type: replace Abstract: The majority of core-collapse supernova (CCSN) progenitors are massive stars in multiple systems, and their evolution and final fate are affected by interactions with their companions. These interactions can explain the presence of circumstellar material in many CCSNe, and the inferred low mass in stripped-envelope supernova progenitors. Through binary interactions, stars can gain mass, lose mass, or merge, impacting their final properties. Specific sub-types of binary interaction products have been investigated but few detailed full population models exist. Using thousands of detailed simulations with updated prescriptions for binary interactions and winds at Milky Way and Magellanic Clouds metallicities, we follow the evolution of single massive stars, primaries in interacting binaries and coalescence products following common envelope evolution. We also follow the evolution of the surviving secondary star, with a compact companion formed from the evolutionary end of the primary star or alone if the system was disrupted in the first supernova. The endpoints of our simulations map the rich landscape of CCSN progenitors, and provide detailed mass-loss history and progenitor structures. We identify an important evolutionary phase for stripped-envelope supernova progenitors, in which the wind mass-loss rate of stars stripped by binary interaction rapidly increases in their final evolutionary stages, after core helium burning. These strong winds would give rise to a Wolf-Rayet (WR) spectral appearance, though only for a few millennia, in contrast to hundreds of millennia for their more massive WR counterparts. Such lightweight WR stars in binaries can account for observed properties of type Ib/c supernovae.

Stunning image of a supernova reveals a dead star that exploded twice

Astronomy News - Thu, 03/07/2025 - 11:22

Pictures of a distant supernova remnant show two concentric rings, providing clear evidence that exploding white dwarf stars go boom twice in the blink of an eye

Interstellar visitor spotted hurtling through the solar system

Astronomy News - Thu, 03/07/2025 - 11:22

An object thought to have come from another star has been seen entering the solar system at high speed, and is expected to whip around the sun in the coming months

New Horizons images enable first test of interstellar navigation

Astronomy News - Thu, 03/07/2025 - 11:21

By looking at the shifting of stars in photos from the New Horizons probe, astronomers have calculated its position in the galaxy – a technique that could be useful for interstellar missions

Bioplastic habitats on Mars could be built from algae

Astronomy News - Thu, 03/07/2025 - 11:20

A lab experiment that simulated Mars conditions showed that green algae can grow in plastic containers made from the same algae, setting the stage for a self-sustaining system to build habitats on the planet

Interstellar comet hurtling through solar system named 3I/ATLAS

Astronomy News - Thu, 03/07/2025 - 11:20

An object from another star has been seen entering the solar system at high speed, and is expected to whip around the sun in the coming months

Carbonate formation and fluctuating habitability on Mars

Astronomy News - Thu, 03/07/2025 - 11:18

Nature, Published online: 02 July 2025; doi:10.1038/s41586-025-09161-1

A modelling study suggests that Mars had a desert-like climate with intermittent liquid-water oases regulated by a negative feedback among solar luminosity, liquid water and carbonate formation.

Tue 08 Jul 11:15: Optimizing Data Delivery and Scalable HI Profile Classification for the SKA Era: Infrastructure and Science Challenges at the Spanish SRC

Next External Talks - Thu, 03/07/2025 - 11:17
Optimizing Data Delivery and Scalable HI Profile Classification for the SKA Era: Infrastructure and Science Challenges at the Spanish SRC

This talk presents ongoing work at the Spanish SKA Regional Centre (esSRC) in the context of the SRC Net 0.1. The first part focuses on the development of efficient data delivery techniques from the distributed Rucio-based storage system to the SRC infrastructure and, ultimately, to user workspaces. Several approaches have been evaluated to support science-ready access, yet current solutions often involve unnecessary data duplication in user areas, resulting in increased usage of storage and computational resources. To address this, we have prototyped mechanisms based on file linking, caching, and data reuse, enabling more efficient access paths for users. While these methods show promising improvements in terms of performance and resource usage, challenges remain, particularly in terms of orchestration, scalability, and compatibility with existing workload managers. The second part presents advances in the automated classification of neutral hydrogen (HI) profiles using machine learning methods, building on previous work [Parra et al., 2024, arXiv:2501.11657]. We outline a roadmap for extending these techniques to handle the data volumes expected from the SKA Observatory. This includes developing scalable pipelines capable of ingesting and processing large spectral datasets in a reproducible and efficient manner, and adapting the classification models to cope with the diversity and complexity of the SKA data products.

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Molecular gas in a low-dust galaxy hints at how stars formed in the early Universe

Astronomy News - Thu, 03/07/2025 - 11:16

Nature, Published online: 02 July 2025; doi:10.1038/d41586-025-01979-z

The James Webb Space Telescope has detected molecular hydrogen in a nearby galaxy that has a very low proportion of metals. This implies that considerable quantities of molecular gas can form at low metallicities, and provides insight into similarly metal-poor galaxies in the early Universe.

Close-in planet induces flares on its host star

Astronomy News - Thu, 03/07/2025 - 11:16

Nature, Published online: 02 July 2025; doi:10.1038/s41586-025-09236-z

Planet-induced flares on HIP 67522, a 17 million-year-old G dwarf star with two known close-in planets, were detected.

How NASA’s SPHEREx Mission Will Share Its All-Sky Map With the World 

Astronomy News - Thu, 03/07/2025 - 11:15

5 min read

How NASA’s SPHEREx Mission Will Share Its All-Sky Map With the World  NASA’s SPHEREx mission will map the entire sky in 102 different wavelengths, or colors, of infrared light. This image of the Vela Molecular Ridge was captured by SPHEREx and is part of the mission’s first ever public data release. The yellow patch on the right side of the image is a cloud of interstellar gas and dust that glows in some infrared colors due to radiation from nearby stars. NASA/JPL-Caltech

NASA’s newest astrophysics space telescope launched in March on a mission to create an all-sky map of the universe. Now settled into low-Earth orbit, SPHEREx (Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer) has begun delivering its sky survey data to a public archive on a weekly basis, allowing anyone to use the data to probe the secrets of the cosmos.

“Because we’re looking at everything in the whole sky, almost every area of astronomy can be addressed by SPHEREx data,” said Rachel Akeson, the lead for the SPHEREx Science Data Center at IPAC. IPAC is a science and data center for astrophysics and planetary science at Caltech in Pasadena, California.

Almost every area of astronomy can be addressed by SPHEREx data.

Rachel Akeson

SPHEREx Science Data Center Lead

Other missions, like NASA’s now-retired WISE (Wide-field Infrared Survey Explorer), have also mapped the entire sky. SPHEREx builds on this legacy by observing in 102 infrared wavelengths, compared to WISE’s four wavelength bands.

By putting the many wavelength bands of SPHEREx data together, scientists can identify the signatures of specific molecules with a technique known as spectroscopy. The mission’s science team will use this method to study the distribution of frozen water and organic molecules — the “building blocks of life” — in the Milky Way.

This animation shows how NASA’s SPHEREx observatory will map the entire sky — a process it will complete four times over its two-year mission. The telescope will observe every point in the sky in 102 different infrared wavelengths, more than any other all-sky survey. SPHEREx’s openly available data will enable a wide variety of astronomical studies. Credit: NASA/JPL-Caltech

The SPHEREx science team will also use the mission’s data to study the physics that drove the universe’s expansion following the big bang, and to measure the amount of light emitted by all the galaxies in the universe over time. Releasing SPHEREx data in a public archive encourages far more astronomical studies than the team could do on their own.

“By making the data public, we enable the whole astronomy community to use SPHEREx data to work on all these other areas of science,” Akeson said.

NASA is committed to the sharing of scientific data, promoting transparency and efficiency in scientific research. In line with this commitment, data from SPHEREx appears in the public archive within 60 days after the telescope collects each observation. The short delay allows the SPHEREx team to process the raw data to remove or flag artifacts, account for detector effects, and align the images to the correct astronomical coordinates.

The team publishes the procedures they used to process the data alongside the actual data products. “We want enough information in those files that people can do their own research,” Akeson said.

One of the early test images captured by NASA’s SPHEREx mission in April 2025. This image shows a section of sky in one infrared wavelength, or color, that is invisible to the human eye but is represented here in a visible color. This particular wavelength (3.29 microns) reveals a cloud of dust made of a molecule similar to soot or smoke. NASA/JPL-Caltech This image from NASA’s SPHEREx shows the same region of space in a different infrared wavelength (0.98 microns), once again represented by a color that is visible to the human eye. The dust cloud has vanished because the molecules that make up the dust — polycyclic aromatic hydrocarbons — do not radiate light in this color. NASA/JPL-Caltech




During its two-year prime mission, SPHEREx will survey the entire sky twice a year, creating four all-sky maps. After the mission reaches the one-year mark, the team plans to release a map of the whole sky at all 102 wavelengths.

In addition to the science enabled by SPHEREx itself, the telescope unlocks an even greater range of astronomical studies when paired with other missions. Data from SPHEREx can be used to identify interesting targets for further study by NASA’s James Webb Space Telescope, refine exoplanet parameters collected from NASA’s TESS (Transiting Exoplanet Survey Satellite), and study the properties of dark matter and dark energy along with ESA’s (European Space Agency’s) Euclid mission and NASA’s upcoming Nancy Grace Roman Space Telescope.

The SPHEREx mission’s all-sky survey will complement data from other NASA space telescopes. SPHEREx is illustrated second from the right. The other telescope illustrations are, from left to right: the Hubble Space Telescope, the retired Spitzer Space Telescope, the retired WISE/NEOWISE mission, the James Webb Space Telescope, and the upcoming Nancy Grace Roman Space Telescope. NASA/JPL-Caltech

The IPAC archive that hosts SPHEREx data, IRSA (NASA/IPAC Infrared Science Archive), also hosts pointed observations and all-sky maps at a variety of wavelengths from previous missions. The large amount of data available through IRSA gives users a comprehensive view of the astronomical objects they want to study.

“SPHEREx is part of the entire legacy of NASA space surveys,” said IRSA Science Lead Vandana Desai. “People are going to use the data in all kinds of ways that we can’t imagine.”

NASA’s Office of the Chief Science Data Officer leads open science efforts for the agency. Public sharing of scientific data, tools, research, and software maximizes the impact of NASA’s science missions. To learn more about NASA’s commitment to transparency and reproducibility of scientific research, visit science.nasa.gov/open-science. To get more stories about the impact of NASA’s science data delivered directly to your inbox, sign up for the NASA Open Science newsletter.

By Lauren Leese
Web Content Strategist for the Office of the Chief Science Data Officer 

More About SPHEREx

The SPHEREx mission is managed by NASA’s Jet Propulsion Laboratory for the agency’s Astrophysics Division within the Science Mission Directorate at NASA Headquarters. BAE Systems in Boulder, Colorado, built the telescope and the spacecraft bus. The science analysis of the SPHEREx data will be conducted by a team of scientists located at 10 institutions in the U.S., two in South Korea, and one in Taiwan. Caltech in Pasadena managed and integrated the instrument. The mission’s principal investigator is based at Caltech with a joint JPL appointment. Data will be processed and archived at IPAC at Caltech. The SPHEREx dataset will be publicly available at the NASA-IPAC Infrared Science Archive. Caltech manages JPL for NASA.

To learn more about SPHEREx, visit:

https://nasa.gov/SPHEREx

Media Contacts

Calla Cofield
Jet Propulsion Laboratory, Pasadena, Calif.
626-808-2469
calla.e.cofield@jpl.nasa.gov

Amanda Adams
Office of the Chief Science Data Officer
256-683-6661
amanda.m.adams@nasa.gov

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Institute Coordinator

Vacancies - Thu, 03/07/2025 - 01:00

The Kavli Institute for Cosmology, Cambridge (KICC), affiliated with the Department of Physics, the Institute of Astronomy (IoA) and the Department of Applied Mathematics and Theoretical Physics (DAMTP), seeks to appoint an enthusiastic and highly organised Institute Coordinator. This is an exciting opportunity to join a vibrant scientific community and play a key role in the coordination of the Institute's academic and administrative activities.

The successful candidate will support the Director of KICC and oversee the smooth operation of the Institute's internal processes. You will be responsible for coordinating a diverse portfolio of activities including the administration of funding calls, recruitment of postdoctoral fellows, visitor programmes, scientific events, financial processes, and internal and external communications. You will also act as the first point-of-contact for KICC and provide a professional PA service to the Director.

This is a dynamic role requiring strong communication, organisational and interpersonal skills, the ability to manage competing priorities, and experience of working with minimal supervision. You will be liaising regularly with academic staff, visiting scientists, University departments, and external partners, and must be confident in building effective working relationships at all levels. Applicants should be educated to degree level, or have equivalent practical experience, and be proficient in the use of standard IT applications including Microsoft Office. Experience in event or project coordination and financial or HR processes would be an advantage.

Why Join Us?

At the University of Cambridge, we offer a rewarding and supportive work environment with:

  • Generous Leave: 36 days annually (including bank holidays, pro rata for part-time staff).
  • Career Development: Access to University training and annual development reviews.
  • Work-Life Balance: Hybrid working and a collaborative, inclusive culture.
  • Family-Friendly Policies: Extensive parental leave, workplace nurseries, and childcare support.
  • Financial Security: Competitive pay with annual increases and a generous pension scheme.
  • Exclusive Perks: Travel benefits and discounts at over 2,000 retailers.
  • Join a world-class institution committed to research, innovation, and your personal growth.

Informal enquiries about the role may be directed to the IoA Departmental Administrator via departmental.administrator@ast.cam.ac.uk.

If you have any questions regarding the application process, please contact HR@ast.cam.ac.uk.

While the role is ideally suited to being filled on a full-time basis, we are open to considering part-time or job share arrangements, with a minimum of 0.8 FTE.

Click the 'Apply' button below to register an account with our recruitment system (if you have not already) and apply online.

Closing Date: Thursday, 24 July 2025 at 23:59 BST

Please note, should we receive a high volume of applications for this vacancy, we reserve the right to close the advert earlier than the stated closing date. Conversely, we may also extend the closing date if necessary to ensure a robust and inclusive recruitment process.

Interview Date: Week commencing 11 August 2025

Please ensure that you outline how you match the criteria for the post and why you are applying for this role on the online application form.

Please include details of your referees, including email address and phone number, one of which must be your most recent line manager.

Please quote reference LG46508 on your application and in any correspondence about this vacancy.

The University actively supports equality, diversity and inclusion and encourages applications from all sections of society.

The University has a responsibility to ensure that all employees are eligible to live and work in the UK.

Fewer Companions in the Crowd: The Low Close Binary Fraction in Globular Clusters from Gaia RVS

Recent IoA Publications - Wed, 02/07/2025 - 12:00
arXiv:2507.00131v1 Announce Type: new Abstract: In dense environments like globular clusters (GCs), dynamical interactions can disrupt or harden close binaries, nonetheless, detailed comparisons with field binary fractions remain limited. Here, we present an analysis of the close binary fraction in a carefully selected sample of field stars and 10 GCs using Gaia Radial Velocity Spectrometer (RVS) data, which is among the largest samples of GCs analysed using multi-epoch spectroscopy to date. By assessing the peak-to-peak variations of the sources' radial velocity (RV), we estimate the close binary fractions through a method that fits the distribution as the product of two Gaussian distributions. By applying the same RV-variability method to both cluster members and field stars, we ensure a homogeneous and inclusive comparison between the two environments. Despite matching stellar parameters between the field and GC samples, our findings confirm that GCs possess a significantly lower close binary fraction than field stars. Interestingly, we do not detect any clear trend of binary fraction with cluster metallicity; metal-rich and metal-poor GCs are uniformly binary-poor (within uncertainties). We discuss possible interpretations, including dynamical hardening in dense environments and the effects of common envelope evolution, which may lead to companion accretion or merger events.

Fewer Companions in the Crowd: The Low Close Binary Fraction in Globular Clusters from Gaia RVS

Near-field cosmology - Wed, 02/07/2025 - 12:00
arXiv:2507.00131v1 Announce Type: new Abstract: In dense environments like globular clusters (GCs), dynamical interactions can disrupt or harden close binaries, nonetheless, detailed comparisons with field binary fractions remain limited. Here, we present an analysis of the close binary fraction in a carefully selected sample of field stars and 10 GCs using Gaia Radial Velocity Spectrometer (RVS) data, which is among the largest samples of GCs analysed using multi-epoch spectroscopy to date. By assessing the peak-to-peak variations of the sources' radial velocity (RV), we estimate the close binary fractions through a method that fits the distribution as the product of two Gaussian distributions. By applying the same RV-variability method to both cluster members and field stars, we ensure a homogeneous and inclusive comparison between the two environments. Despite matching stellar parameters between the field and GC samples, our findings confirm that GCs possess a significantly lower close binary fraction than field stars. Interestingly, we do not detect any clear trend of binary fraction with cluster metallicity; metal-rich and metal-poor GCs are uniformly binary-poor (within uncertainties). We discuss possible interpretations, including dynamical hardening in dense environments and the effects of common envelope evolution, which may lead to companion accretion or merger events.

Orbit and atmosphere of HIP 99770 b through the eyes of VLTI/GRAVITY

Recent IoA Publications - Wed, 02/07/2025 - 11:50
arXiv:2507.00117v1 Announce Type: new Abstract: Context: Inferring the likely formation channel of giant exoplanets and brown dwarf companions from orbital and atmospheric observables remains a formidable challenge. Further and more precise directly measured dynamical masses of these companions are required to inform and gauge formation, evolutionary, and atmospheric models. We present an updated study of HIP 99770 b based on observations conducted with VLTI/GRAVITY. Aims: Combining the new data with previous observations from the literature, we characterise HIP 99770 b to better constrain its orbit, dynamical mass, and atmospheric properties, as well as to shed light on its likely formation channel. Methods: We ran a renewed orbit fit to further constrain the dynamical mass of the companion and the orbit solution. We also analysed the GRAVITY K-band spectrum, placing it into context with literature data, and extracting magnitude, age, spectral type, bulk properties and atmospheric characteristics of HIP 99770 b. Results: We detected the companion at a radial separation of $417\,\mathrm{mas}$ from its host. The new orbit fit yields a dynamical mass of $17_{-5}^{+6}\,\mathrm{M}_\mathrm{Jup}$ and an eccentricity of $0.31_{-0.12}^{+0.06}$. We also find that additional relative astrometry epochs in the future will not enable further constraints on the dynamical mass due to the dominating relative uncertainty on the Hipparcos-Gaia proper motion anomaly. The publication of Gaia DR4 will likely ease this predicament. We find that the companion is consistent with spectral type L8 and exhibits a potential metal enrichment in its atmosphere. Conclusions: These results do not yet allow for a definite inference of the companion's formation channel. Nevertheless, the new constraints on its bulk properties and the additional GRAVITY spectrum presented here will aid future efforts to determine the formation history of HIP 99770 b.

Orbit and atmosphere of HIP 99770 b through the eyes of VLTI/GRAVITY

Planetary systems - Wed, 02/07/2025 - 11:50
arXiv:2507.00117v1 Announce Type: new Abstract: Context: Inferring the likely formation channel of giant exoplanets and brown dwarf companions from orbital and atmospheric observables remains a formidable challenge. Further and more precise directly measured dynamical masses of these companions are required to inform and gauge formation, evolutionary, and atmospheric models. We present an updated study of HIP 99770 b based on observations conducted with VLTI/GRAVITY. Aims: Combining the new data with previous observations from the literature, we characterise HIP 99770 b to better constrain its orbit, dynamical mass, and atmospheric properties, as well as to shed light on its likely formation channel. Methods: We ran a renewed orbit fit to further constrain the dynamical mass of the companion and the orbit solution. We also analysed the GRAVITY K-band spectrum, placing it into context with literature data, and extracting magnitude, age, spectral type, bulk properties and atmospheric characteristics of HIP 99770 b. Results: We detected the companion at a radial separation of $417\,\mathrm{mas}$ from its host. The new orbit fit yields a dynamical mass of $17_{-5}^{+6}\,\mathrm{M}_\mathrm{Jup}$ and an eccentricity of $0.31_{-0.12}^{+0.06}$. We also find that additional relative astrometry epochs in the future will not enable further constraints on the dynamical mass due to the dominating relative uncertainty on the Hipparcos-Gaia proper motion anomaly. The publication of Gaia DR4 will likely ease this predicament. We find that the companion is consistent with spectral type L8 and exhibits a potential metal enrichment in its atmosphere. Conclusions: These results do not yet allow for a definite inference of the companion's formation channel. Nevertheless, the new constraints on its bulk properties and the additional GRAVITY spectrum presented here will aid future efforts to determine the formation history of HIP 99770 b.

A New Alloy is Enabling Ultra-Stable Structures Needed for Exoplanet Discovery

Astronomy News - Wed, 02/07/2025 - 11:44

7 min read

A New Alloy is Enabling Ultra-Stable Structures Needed for Exoplanet Discovery

A unique new material that shrinks when it is heated and expands when it is cooled could help enable the ultra-stable space telescopes that future NASA missions require to search for habitable worlds.

Advancements in material technologies are needed to meet the science needs of the next great observatories. These observatories will strive to find, identify, and study exoplanets and their ability to support life. Credit: NASA JPL

One of the goals of NASA’s Astrophysics Division is to determine whether we are alone in the universe. NASA’s astrophysics missions seek to answer this question by identifying planets beyond our solar system (exoplanets) that could support life. Over the last two decades, scientists have developed ways to detect atmospheres on exoplanets by closely observing stars through advanced telescopes. As light passes through a planet’s atmosphere or is reflected or emitted from a planet’s surface, telescopes can measure the intensity and spectra (i.e., “color”) of the light, and can detect various shifts in the light caused by gases in the planetary atmosphere. By analyzing these patterns, scientists can determine the types of gasses in the exoplanet’s atmosphere.

Decoding these shifts is no easy task because the exoplanets appear very near their host stars when we observe them, and the starlight is one billion times brighter than the light from an Earth-size exoplanet. To successfully detect habitable exoplanets, NASA’s future Habitable Worlds Observatory will need a contrast ratio of one to one billion (1:1,000,000,000).

Achieving this extreme contrast ratio will require a telescope that is 1,000 times more stable than state-of-the-art space-based observatories like NASA’s James Webb Space Telescope and its forthcoming Nancy Grace Roman Space Telescope. New sensors, system architectures, and materials must be integrated and work in concert for future mission success. A team from the company ALLVAR is collaborating with NASA’s Marshall Space Flight Center and NASA’s Jet Propulsion Laboratory to demonstrate how integration of a new material with unique negative thermal expansion characteristics can help enable ultra-stable telescope structures.

Material stability has always been a limiting factor for observing celestial phenomena. For decades, scientists and engineers have been working to overcome challenges such as micro-creep, thermal expansion, and moisture expansion that detrimentally affect telescope stability. The materials currently used for telescope mirrors and struts have drastically improved the dimensional stability of the great observatories like Webb and Roman, but as indicated in the Decadal Survey on Astronomy and Astrophysics 2020 developed by the National Academies of Sciences, Engineering, and Medicine, they still fall short of the 10 picometer level stability over several hours that will be required for the Habitable Worlds Observatory. For perspective, 10 picometers is roughly 1/10th the diameter of an atom.

NASA’s Nancy Grace Roman Space Telescope sits atop the support structure and instrument payloads. The long black struts holding the telescope’s secondary mirror will contribute roughly 30% of the wave front error while the larger support structure underneath the primary mirror will contribute another 30%.

Credit: NASA/Chris Gunn

Funding from NASA and other sources has enabled this material to transition from the laboratory to the commercial scale. ALLVAR received NASA Small Business Innovative Research (SBIR) funding to scale and integrate a new alloy material into telescope structure demonstrations for potential use on future NASA missions like the Habitable Worlds Observatory. This alloy shrinks when heated and expands when cooled—a property known as negative thermal expansion (NTE). For example, ALLVAR Alloy 30 exhibits a -30 ppm/°C coefficient of thermal expansion (CTE) at room temperature. This means that a 1-meter long piece of this NTE alloy will shrink 0.003 mm for every 1 °C increase in temperature. For comparison, aluminum expands at +23 ppm/°C.

While other materials expand while heated and contract when cooled, ALLVAR Alloy 30 exhibits a negative thermal expansion, which can compensate for the thermal expansion mismatch of other materials. The thermal strain versus temperature is shown for 6061 Aluminum, A286 Stainless Steel, Titanium 6Al-4V, Invar 36, and ALLVAR Alloy 30.

Because it shrinks when other materials expand, ALLVAR Alloy 30 can be used to strategically compensate for the expansion and contraction of other materials. The alloy’s unique NTE property and lack of moisture expansion could enable optic designers to address the stability needs of future telescope structures. Calculations have indicated that integrating ALLVAR Alloy 30 into certain telescope designs could improve thermal stability up to 200 times compared to only using traditional materials like aluminum, titanium, Carbon Fiber Reinforced Polymers (CFRPs), and the nickel–iron alloy, Invar.

The hexapod assembly with six ALLVAR Alloy struts was measured for long-term stability. The stability of the individual struts and the hexapod assembly were measured using interferometry at the University of Florida’s Institute for High Energy Physics and Astrophysics. The struts were found to have a length noise well below the proposed target for the success criteria for the project. Credit: (left) ALLVAR and (right) Simon F. Barke, Ph.D.

To demonstrate that negative thermal expansion alloys can enable ultra-stable structures, the ALLVAR team developed a hexapod structure to separate two mirrors made of a commercially available glass ceramic material with ultra-low thermal expansion properties. Invar was bonded to the mirrors and flexures made of Ti6Al4V—a titanium alloy commonly used in aerospace applications—were attached to the Invar. To compensate for the positive CTEs of the Invar and Ti6Al4V components, an NTE ALLVAR Alloy 30 tube was used between the Ti6Al4V flexures to create the struts separating the two mirrors. The natural positive thermal expansion of the Invar and Ti6Al4V components is offset by the negative thermal expansion of the NTE alloy struts, resulting in a structure with an effective zero thermal expansion.

The stability of the structure was evaluated at the University of Florida Institute for High Energy Physics and Astrophysics. The hexapod structure exhibited stability well below the 100 pm/√Hz target and achieved 11 pm/√Hz. This first iteration is close to the 10 pm stability required for the future Habitable Worlds Observatory. A paper and presentation made at the August 2021 Society of Photo-Optical Instrumentation Engineers conference provides details about this analysis.

Furthermore, a series of tests run by NASA Marshall showed that the ultra-stable struts were able to achieve a near-zero thermal expansion that matched the mirrors in the above analysis. This result translates into less than a 5 nm root mean square (rms) change in the mirror’s shape across a 28K temperature change.

The ALLVAR enabled Ultra-Stable Hexapod Assembly undergoing Interferometric Testing between 293K and 265K (right). On the left, the Root Mean Square (RMS) changes in the mirror’s surface shape are visually represented. The three roughly circular red areas are caused by the thermal expansion mismatch of the invar bonding pads with the ZERODUR mirror, while the blue and green sections show little to no changes caused by thermal expansion. The surface diagram shows a less than 5 nanometer RMS change in mirror figure. Credit: NASA’s X-Ray and Cryogenic Facility [XRCF]

Beyond ultra-stable structures, the NTE alloy technology has enabled enhanced passive thermal switch performance and has been used to remove the detrimental effects of temperature changes on bolted joints and infrared optics. These applications could impact technologies used in other NASA missions. For example, these new alloys have been integrated into the cryogenic sub-assembly of Roman’s coronagraph technology demonstration. The addition of NTE washers enabled the use of pyrolytic graphite thermal straps for more efficient heat transfer. ALLVAR Alloy 30 is also being used in a high-performance passive thermal switch incorporated into the UC Berkeley Space Science Laboratory’s Lunar Surface Electromagnetics Experiment-Night (LuSEE Night) project aboard Firefly Aerospace’s Blue Ghost Mission 2, which will be delivered to the Moon through NASA’s CLPS (Commercial Lunar Payload Services) initiative. The NTE alloys enabled smaller thermal switch size and greater on-off heat conduction ratios for LuSEE Night.

Through another recent NASA SBIR effort, the ALLVAR team worked with NASA’s Jet Propulsion Laboratory to develop detailed datasets of ALLVAR Alloy 30 material properties. These large datasets include statistically significant material properties such as strength, elastic modulus, fatigue, and thermal conductivity. The team also collected information about less common properties like micro-creep and micro-yield. With these properties characterized, ALLVAR Alloy 30 has cleared a major hurdle towards space-material qualification.

As a spinoff of this NASA-funded work, the team is developing a new alloy with tunable thermal expansion properties that can match other materials or even achieve zero CTE. Thermal expansion mismatch causes dimensional stability and force-load issues that can impact fields such as nuclear engineering, quantum computing, aerospace and defense, optics, fundamental physics, and medical imaging. The potential uses for this new material will likely extend far beyond astronomy. For example, ALLVAR developed washers and spacers, are now commercially available to maintain consistent preloads across extreme temperature ranges in both space and terrestrial environments. These washers and spacers excel at counteracting the thermal expansion and contraction of other materials, ensuring stability for demanding applications.

For additional details, see the entry for this project on NASA TechPort.

Project Lead: Dr. James A. Monroe, ALLVAR

The following NASA organizations sponsored this effort: NASA Astrophysics Division, NASA SBIR Program funded by the Space Technology Mission Directorate (STMD).

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Tue 01 Jul 13:15: Double black hole mergers in nuclear star clusters: eccentricities, spins, masses, and the growth of massive seeds

IoA Institute of Astronomy Talk Lists - Tue, 01/07/2025 - 14:02
Double black hole mergers in nuclear star clusters: eccentricities, spins, masses, and the growth of massive seeds

We investigate the formation of intermediate-mass black holes (IMBHs) through hierarchical mergers of stellar-origin black holes (BHs), as well as BH mergers formed dynamically in nuclear star clusters. Using a semi-analytical approach that incorporates probabilistic, mass-function–dependent double-BH (DBH) pairing, binary–single encounters, and a mass-ratio–dependent prescription for energy dissipation in hardening binaries, we find that IMB Hs with masses of order 10²–10⁴ M⊙ can be formed solely through hierarchical mergers on timescales of a few hundred Myr to a few Gyr. Clusters with escape velocities ≳ 400 km s⁻¹ inevitably form high-mass IMB Hs. The spin distribution of IMB Hs with masses ≳ 10³ M⊙ is strongly clustered at χ ≈ 0.15, while for lower masses it peaks at χ ≈ 0.7. Eccentric mergers are more frequent for equal-mass binaries containing first- and second-generation BHs. Metal-rich, young, dense clusters can produce up to 20 of their DBH mergers with eccentricity ≥ 0.1 at 10 Hz, and ~ 2–9 of all in-cluster mergers form at > 10 Hz. Nuclear star clusters are therefore promising environments for the formation of highly eccentric DBH mergers, detectable with current gravitational-wave detectors. Clusters of extreme mass (∼ 10⁸ M⊙) and density (∼ 10⁸ M⊙ pc⁻³) can have about half of their DBH mergers with primary masses ≥ 100 M⊙. The fraction of in-cluster mergers increases rapidly with increasing escape velocity, approaching unity for Vesc ≳ 200 km s⁻¹. The cosmological DBH merger rate from nuclear clusters varies from ≲ 0.01 to 1 Gpc⁻³ yr⁻¹, where the large uncertainties stem from cluster initial conditions, number-density distributions, and the redshift evolution of nucleated galaxies.

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Tue 01 Jul 13:15: Double black hole mergers in nuclear star clusters: eccentricities, spins, masses, and the growth of massive seeds

Next Wednesday Seminars - Tue, 01/07/2025 - 14:02
Double black hole mergers in nuclear star clusters: eccentricities, spins, masses, and the growth of massive seeds

We investigate the formation of intermediate-mass black holes (IMBHs) through hierarchical mergers of stellar-origin black holes (BHs), as well as BH mergers formed dynamically in nuclear star clusters. Using a semi-analytical approach that incorporates probabilistic, mass-function–dependent double-BH (DBH) pairing, binary–single encounters, and a mass-ratio–dependent prescription for energy dissipation in hardening binaries, we find that IMB Hs with masses of order 10²–10⁴ M⊙ can be formed solely through hierarchical mergers on timescales of a few hundred Myr to a few Gyr. Clusters with escape velocities ≳ 400 km s⁻¹ inevitably form high-mass IMB Hs. The spin distribution of IMB Hs with masses ≳ 10³ M⊙ is strongly clustered at χ ≈ 0.15, while for lower masses it peaks at χ ≈ 0.7. Eccentric mergers are more frequent for equal-mass binaries containing first- and second-generation BHs. Metal-rich, young, dense clusters can produce up to 20 of their DBH mergers with eccentricity ≥ 0.1 at 10 Hz, and ~ 2–9 of all in-cluster mergers form at > 10 Hz. Nuclear star clusters are therefore promising environments for the formation of highly eccentric DBH mergers, detectable with current gravitational-wave detectors. Clusters of extreme mass (∼ 10⁸ M⊙) and density (∼ 10⁸ M⊙ pc⁻³) can have about half of their DBH mergers with primary masses ≥ 100 M⊙. The fraction of in-cluster mergers increases rapidly with increasing escape velocity, approaching unity for Vesc ≳ 200 km s⁻¹. The cosmological DBH merger rate from nuclear clusters varies from ≲ 0.01 to 1 Gpc⁻³ yr⁻¹, where the large uncertainties stem from cluster initial conditions, number-density distributions, and the redshift evolution of nucleated galaxies.

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Categories: Talks