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Moon dust 'rarer than gold' arrives in UK from China

Astronomy News - Fri, 09/05/2025 - 10:42

First Moon samples collected in nearly 50 years and loaned by China for the first time are now in the UK.

Tue 20 May 11:15: A 21-cm Cosmologist’s Journey: From Cambridge to North America and Back Again

Next External Talks - Thu, 08/05/2025 - 21:22
A 21-cm Cosmologist’s Journey: From Cambridge to North America and Back Again

In this talk, I’ll take you on a whistle-stop tour of my journey in 21-cm cosmology – from my PhD days in Cambridge to fellowship and research scientist positions in the USA and Canada. I’ll discuss the significance of 21-cm cosmology in understanding the Universe’s first billion years and describe key projects I’ve worked on, including the SKA , HERA, EDGES , and REACH . Along the way, I’ll share some personal highlights from my time in North America, including adventures in national parks and snow sports.

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Categories: Talks

Fri 11 Jul 11:30: Title to be confirmed

IoA Institute of Astronomy Talk Lists - Thu, 08/05/2025 - 17:58
Title to be confirmed

Abstract not available

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Wed 14 May 13:40: Gravitational Phase-Space Turbulence: the Small-Scale Limit of the Cold-Dark-Matter Power-Spectrum

IoA Institute of Astronomy Talk Lists - Thu, 08/05/2025 - 16:41
Gravitational Phase-Space Turbulence: the Small-Scale Limit of the Cold-Dark-Matter Power-Spectrum

The matter power spectrum is one of the fundamental quantities in the study of large-scale structure in cosmology. In this talk, I will describe its small-scale asymptotic limit, and give a theoretical argument to the effect that, for cold dark matter, P(k) has a universal asymptotic scaling with the wave-number k, for k >> k_nl, viz. P(k) ~ k^(-3). I will explain how gravitational collapse drives a turbulent phase-space flow of the quadratic Casimir invariant, where the linear and non-linear time scales are balanced, and how this balance dictates the k dependence of the power spectrum. The coldness of the dark-matter distribution function — its non-vanishing only on a 3-dimensional sub-manifold of phase-space — underpins the analysis. I will show Vlasov-Poisson simulations that support the theory, and if time permits, also describe a stationary-phase technique for deriving an equivalent result. 

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Wed 14 May 13:40: Gravitational Phase-Space Turbulence: the Small-Scale Limit of the Cold-Dark-Matter Power-Spectrum

Next Wednesday Seminars - Thu, 08/05/2025 - 16:41
Gravitational Phase-Space Turbulence: the Small-Scale Limit of the Cold-Dark-Matter Power-Spectrum

The matter power spectrum is one of the fundamental quantities in the study of large-scale structure in cosmology. In this talk, I will describe its small-scale asymptotic limit, and give a theoretical argument to the effect that, for cold dark matter, P(k) has a universal asymptotic scaling with the wave-number k, for k >> k_nl, viz. P(k) ~ k^(-3). I will explain how gravitational collapse drives a turbulent phase-space flow of the quadratic Casimir invariant, where the linear and non-linear time scales are balanced, and how this balance dictates the k dependence of the power spectrum. The coldness of the dark-matter distribution function — its non-vanishing only on a 3-dimensional sub-manifold of phase-space — underpins the analysis. I will show Vlasov-Poisson simulations that support the theory, and if time permits, also describe a stationary-phase technique for deriving an equivalent result. 

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Fri 16 May 13:00: Modified gravity and the atomic world

Next External Talks - Thu, 08/05/2025 - 13:47
Modified gravity and the atomic world

The existence of dark energy and dark matter hint that there is more to gravity than meets the eye.  A wide range of new theories, exhibiting a new scalar particle with a property called screening, indicate small-scale tests as the most promising route towards detection of new particles.  Atomic physics is especially promising.  I will discuss how pairs of atomic clocks are capable of searching for equivalence-principle violating scalar couplings to Standard Model particles, which hold the potential to detect quintessence, ultralight dark matter, and modified gravity.  Similarly, atom interferometry and atomic spectroscopy provide a window to detect new forces associated with new screened scalars as well.

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DAmodel: Hierarchical Bayesian Modelling of DA White Dwarfs for Spectrophotometric Calibration

Stars and stellar evolution - Thu, 08/05/2025 - 12:14
arXiv:2412.08809v2 Announce Type: replace Abstract: We use hierarchical Bayesian modelling to calibrate a network of 32 all-sky faint DA white dwarf (DA WD) spectrophotometric standards ($16.5 < V < 19.5$) alongside three CALSPEC standards, from 912 \r{A} to 32 $\mu$m. The framework is the first of its kind to jointly infer photometric zeropoints and WD parameters (surface gravity $\log g$, effective temperature $T_{\text{eff}}$, extinction $A_V$, dust relation parameter $R_V$) by simultaneously modelling both photometric and spectroscopic data. We model panchromatic Hubble Space Telescope Wide Field Camera 3 (HST/WFC3) UVIS and IR photometry, HST/STIS UV spectroscopy and ground-based optical spectroscopy to sub-percent precision. Photometric residuals for the sample are the lowest yet yielding $<0.004$ mag RMS on average from the UV to the NIR, achieved by jointly inferring time-dependent changes in system sensitivity and WFC3/IR count-rate nonlinearity. Our GPU-accelerated implementation enables efficient sampling via Hamiltonian Monte Carlo, critical for exploring the high-dimensional posterior space. The hierarchical nature of the model enables population analysis of intrinsic WD and dust parameters. Inferred spectral energy distributions from this model will be essential for calibrating the James Webb Space Telescope as well as next-generation surveys, including Vera Rubin Observatory's Legacy Survey of Space and Time and the Nancy Grace Roman Space Telescope.

DAmodel: Hierarchical Bayesian Modelling of DA White Dwarfs for Spectrophotometric Calibration

Recent IoA Publications - Thu, 08/05/2025 - 12:14
arXiv:2412.08809v2 Announce Type: replace Abstract: We use hierarchical Bayesian modelling to calibrate a network of 32 all-sky faint DA white dwarf (DA WD) spectrophotometric standards ($16.5 < V < 19.5$) alongside three CALSPEC standards, from 912 \r{A} to 32 $\mu$m. The framework is the first of its kind to jointly infer photometric zeropoints and WD parameters (surface gravity $\log g$, effective temperature $T_{\text{eff}}$, extinction $A_V$, dust relation parameter $R_V$) by simultaneously modelling both photometric and spectroscopic data. We model panchromatic Hubble Space Telescope Wide Field Camera 3 (HST/WFC3) UVIS and IR photometry, HST/STIS UV spectroscopy and ground-based optical spectroscopy to sub-percent precision. Photometric residuals for the sample are the lowest yet yielding $<0.004$ mag RMS on average from the UV to the NIR, achieved by jointly inferring time-dependent changes in system sensitivity and WFC3/IR count-rate nonlinearity. Our GPU-accelerated implementation enables efficient sampling via Hamiltonian Monte Carlo, critical for exploring the high-dimensional posterior space. The hierarchical nature of the model enables population analysis of intrinsic WD and dust parameters. Inferred spectral energy distributions from this model will be essential for calibrating the James Webb Space Telescope as well as next-generation surveys, including Vera Rubin Observatory's Legacy Survey of Space and Time and the Nancy Grace Roman Space Telescope.

Mon 09 Jun 14:00: Title to be confirmed

Next External Talks - Thu, 08/05/2025 - 12:11
Title to be confirmed

Abstract not available

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Categories: Talks

Mon 12 May 14:00: On the role of magnetic fluctuations in low magnetic Prandtl number plasmas

Next External Talks - Thu, 08/05/2025 - 11:55
On the role of magnetic fluctuations in low magnetic Prandtl number plasmas

Magnetic fields on small scales are ubiquitous in the universe. For example, the fluctuating magnetic fields in star-forming regions of galaxies are more than twice the strength of the magnetic fields coherent over large scales. On the solar surface, magnetic fields are mostly concentrated in medium and small-scale structures, while the proportion comprising the mean field strength is even lower than in galaxies. The generation mechanisms of the fluctuating magnetic fields are not fully understood. One possibility is the so-called small-scale dynamo (SSD), the other is tangling of the large-scale field structures through turbulence acting on them. In the interstellar medium of galaxies, the resistivity is much lower than the viscosity, such that magnetic instabilities are easier to excite relative to the turbulence. SSD in such high magnetic Prandtl number (Pm, i.e. the ratio between viscosity and resistivity) conditions has therefore been predicted to be easily excited. In the Sun and cool stars, Pm is much lower, namely in the range of 1e-6 to 1e-3. Both theoretically and especially numerically, SSD is more difficult to excite at such very low magnetic Prandtl numbers. Indeed, some recent numerical studies has indicated that the threshold for SSD excitation should systematically increase with decreasing Pm, concluding that SSD would be impossible in the Sun and cool stars.

Accelerating the magnetohydrodynamics solvers with graphics processing units has recently opened an avenue to numerically study low-Pm flows. With these tools we have been able to perform simulations that approach the solar Pm-values, studying both kinematic and non-linear regimes. Contrary to earlier findings, the SSD turns out not only to be possible for Pms down to 0.0031, but even to become increasingly easy to excite for Pm below approximately 0.05. We relate this behaviour to the known hydrodynamic phenomenon, referred to as the bottleneck effect. Extrapolating our results to solar values of Pm indicates that an SSD would be possible under such conditions. The saturation strength of the SSD is of the order of the turbulent kinetic energy independent of the Pm, when the magnetic Reynolds number (Rm) is moderate (up to a few thousands). For higher Rm the saturation strength rapidly diminishes and reaches levels of order of magnitude lower than turbulent kinetic energy, casting a new doubt of the SSD being important in the Sun and stars. Even higher resolution studies, however, would be required to verify this robustly. For such calculations, however, extraordinary resources/quantum computers are required.

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Early and Extensive Ultraviolet Through Near Infrared Observations of the Intermediate-Luminosity Type Iax Supernovae 2024pxl

Stars and stellar evolution - Thu, 08/05/2025 - 11:53
arXiv:2505.04610v1 Announce Type: new Abstract: We present ultraviolet (UV) through near-infrared (NIR) photometric and spectroscopic observations of the nearby SN 2024pxl, the third Type Ia supernova (SN Ia) in NGC 6384. SN 2024pxl is a Type Iax supernova (SN Iax) with an intermediate luminosity ($M_r = -16.99\pm0.32$ mag) and an average SN Iax light curve decline rate. SN 2024pxl was discovered $\sim$3 days after first light, and the rising light curve follows a single power law that is inconsistent with significant interaction with a companion star or circumstellar material. Our extensive NIR photometric coverage is comparable to that of the well-observed SNe Iax 2005hk and 2012Z, and we demonstrate that the $J-H$ colors of SNe Iax differ from normal SNe Ia and appear to be more homogeneous as a class. Spectroscopically, we report the earliest-ever NIR spectrum of a SN Iax as measured from maximum light ($t\approx-9$ days): a featureless continuum with similarities to a $\sim$9,000 K blackbody, and the line velocities are consistent with a mixed-ejecta structure, with C, Si, and Fe having similar velocities and velocity evolutions. We find a tentative correlation between the $H$-band break Co II velocity $\sim$20 days post-peak and absolute magnitude, with more luminous SNe Iax showing faster Co II velocities. Our observations suggest that SN 2024pxl resulted from the thermonuclear disruption of a CO white dwarf star that undergoes deflagration burning.

Early and Extensive Ultraviolet Through Near Infrared Observations of the Intermediate-Luminosity Type Iax Supernovae 2024pxl

Recent IoA Publications - Thu, 08/05/2025 - 11:51
arXiv:2505.04610v1 Announce Type: new Abstract: We present ultraviolet (UV) through near-infrared (NIR) photometric and spectroscopic observations of the nearby SN 2024pxl, the third Type Ia supernova (SN Ia) in NGC 6384. SN 2024pxl is a Type Iax supernova (SN Iax) with an intermediate luminosity ($M_r = -16.99\pm0.32$ mag) and an average SN Iax light curve decline rate. SN 2024pxl was discovered $\sim$3 days after first light, and the rising light curve follows a single power law that is inconsistent with significant interaction with a companion star or circumstellar material. Our extensive NIR photometric coverage is comparable to that of the well-observed SNe Iax 2005hk and 2012Z, and we demonstrate that the $J-H$ colors of SNe Iax differ from normal SNe Ia and appear to be more homogeneous as a class. Spectroscopically, we report the earliest-ever NIR spectrum of a SN Iax as measured from maximum light ($t\approx-9$ days): a featureless continuum with similarities to a $\sim$9,000 K blackbody, and the line velocities are consistent with a mixed-ejecta structure, with C, Si, and Fe having similar velocities and velocity evolutions. We find a tentative correlation between the $H$-band break Co II velocity $\sim$20 days post-peak and absolute magnitude, with more luminous SNe Iax showing faster Co II velocities. Our observations suggest that SN 2024pxl resulted from the thermonuclear disruption of a CO white dwarf star that undergoes deflagration burning.

Key Portion of NASA’s Roman Space Telescope Clears Thermal Vacuum Test

Astronomy News - Thu, 08/05/2025 - 11:16

One half of NASA’s nearly complete Nancy Grace Roman Space Telescope just passed a lengthy test to ensure it will function properly in the space environment.

This photo shows half of the NASA’s Nancy Grace Roman observatory — the outer barrel assembly, deployable aperture cover, and test solar arrays — fully deployed in a thermal chamber at NASA’s Goddard Space Flight Center in Greenbelt, Md., for environmental testing. Credit: NASA/Sydney Rohde

“This milestone tees us up to attach the flight solar array sun shield to the outer barrel assembly, and deployable aperture cover, which we’ll begin this month,” said Jack Marshall, who leads integration and testing for these elements at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Then we’ll complete remaining environmental tests for the flight assembly before moving on to connect Roman’s two major assemblies and run the full observatory through testing, and then we’ll be ready to launch!”

Prior to this thermal testing, technicians integrated Roman’s deployable aperture cover, a visor-like sunshade, to the outer barrel assembly, which will house the telescope and instruments, in January, then added test solar panels in March. They moved this whole structure into the Space Environment Simulator test chamber at NASA Goddard in April.

There, it was subjected to the hot and cold temperatures it will experience in space. Next, technicians will join Roman’s flight solar panels to the outer barrel assembly and sunshade. Then the structure will undergo a suite of assessments, including a shake test to ensure it can withstand the vibrations experienced during launch.

This photo captures the installation of the test solar panels for NASA’s Nancy Grace Roman Space Telescope, which took place in March. One panel is lifted in the center of the frame on its way to being attached to the outer barrel assembly at right. The deployable aperture cover is stowed on the front of the outer barrel assembly, and the other half of the observatory — the spacecraft and integrated payload assembly, which consists of the telescope, instrument carrier, and two instruments — appears at the left of the photo.Credit: NASA/Jolearra Tshiteya

Meanwhile, Roman’s other major portion — the spacecraft and integrated payload assembly, which consists of the telescope, instrument carrier, and two instruments — will undergo its own shake test, along with additional assessments. Technicians will install the lower instrument sun shade and put this half of the observatory through a thermal vacuum test in the Space Environment Simulator.

“The test verifies the instruments will remain at stable operating temperatures even while the Sun bakes one side of the observatory and the other is exposed to freezing conditions — all in a vacuum, where heat doesn’t flow as readily as it does through air,” said Jeremy Perkins, an astrophysicist serving as Roman’s observatory integration and test scientist at NASA Goddard. Keeping the instrument temperatures stable ensures their readings will be precise and reliable.

Technicians are on track to connect Roman’s two major parts in November, resulting in a complete observatory by the end of the year. Following final tests, Roman is expected to ship to the launch site at NASA’s Kennedy Space Center in Florida for launch preparations in summer 2026. Roman remains on schedule for launch by May 2027, with the team aiming for launch as early as fall 2026.

This infographic shows the two major subsystems that make up NASA’s Nancy Grace Roman Space Telescope. The subsystems are each undergoing testing prior to being joined together this fall.Credit: NASA’s Goddard Space Flight Center

To virtually tour an interactive version of the telescope, visit:

https://roman.gsfc.nasa.gov/interactive

The Nancy Grace Roman Space Telescope is managed at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, with participation by NASA’s Jet Propulsion Laboratory in Southern California; Caltech/IPAC in Pasadena, California; the Space Telescope Science Institute in Baltimore; and a science team comprising scientists from various research institutions. The primary industrial partners are BAE Systems Inc. in Boulder, Colorado; L3Harris Technologies in Rochester, New York; and Teledyne Scientific & Imaging in Thousand Oaks, California.

By Ashley Balzer
NASA’s Goddard Space Flight Center, Greenbelt, Md.

​​Media Contact:
Claire Andreoli
NASA’s Goddard Space Flight Center
301-286-1940

Share Details Last Updated May 07, 2025 EditorAshley BalzerContactAshley Balzerashley.m.balzer@nasa.govLocationNASA Goddard Space Flight Center Related Terms Explore More 6 min read NASA’s Roman Mission Shares Detailed Plans to Scour Skies Article 2 weeks ago 6 min read Team Preps to Study Dark Energy via Exploding Stars With NASA’s Roman Article 2 months ago 6 min read How NASA’s Roman Space Telescope Will Illuminate Cosmic Dawn Article 10 months ago

Soviet-era spacecraft likely to crash back to Earth

Astronomy News - Thu, 08/05/2025 - 11:14

The spacecraft was meant to go to Venus but has been stuck in orbit for more than 50 years.

Mon 12 May 14:00: On the role of magnetic fluctuations in low magnetic Prandtl number plasmas

Next External Talks - Wed, 07/05/2025 - 14:28
On the role of magnetic fluctuations in low magnetic Prandtl number plasmas

Magnetic fields on small scales are ubiquitous in the universe. For example, the fluctuating magnetic fields in star-forming regions of galaxies are more than twice the strength of the magnetic fields coherent over large scales. On the solar surface, magnetic fields are mostly concentrated in medium and small-scale structures, while the proportion comprising the mean field strength is even lower than in galaxies. The generation mechanisms of the fluctuating magnetic fields are not fully understood. One possibility is the so-called small-scale dynamo (SSD), the other is tangling of the large-scale field structures through turbulence acting on them. In the interstellar medium of galaxies, the resistivity $\eta$ is much lower than the viscosity $\nu$, such that magnetic instabilities are easier to excite relative to the turbulence. SSD in such high magnetic Prandtl number (Pm=$\nu/\eta$) conditions has therefore been predicted to be easily excited. In the Sun and cool stars, Pm is much lower, namely in the range of $10>6;">$$10{-3}$. Both theoretically and especially numerically, SSD is more difficult to excite at such very low magnetic Prandtl numbers. Indeed, some recent numerical studies had indicated that the threshold for SSD excitation should systematically increase with decreasing Pm, concluding that SSD would be impossible in the Sun and cool stars.

Accelerating the magnetohydrodynamics solvers with graphics processing units has recently opened an avenue to numerically study low-Pm flows. With these tools we have been able to perform simulations that approach the solar Pm-values, studying both kinematic and non-linear regimes. Contrary to earlier findings, the SSD turns out not only to be possible for Pms down to 0.0031, but even to become increasingly easy to excite for Pm below $\simeq 0.05$. We relate this behaviour to the known hydrodynamic phenomenon, referred to as the bottleneck effect. Extrapolating our results to solar values of Pm indicates that an SSD would be possible under such conditions. The saturation strength of the SSD is of the order of the turbulent kinetic energy independent of the Pm, when the magnetic Reynolds number (Rm) is moderate (up to a few thousands). For higher Rm the saturation strength rapidly diminishes and reaches levels of order of magnitude lower than turbulent kinetic energy, casting a new doubt of the SSD being important in the Sun and stars. Even higher resolution studies, however, would be required to verify this robustly. For such calculations, however, extraordinary resources/quantum computers are required.

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Categories: Talks

Thu 15 May 16:00: The different merger and evolutionary histories of the Milky Way and Andromeda (M31)e to be confirmed

IoA Institute of Astronomy Talk Lists - Wed, 07/05/2025 - 12:52
The different merger and evolutionary histories of the Milky Way and Andromeda (M31)e to be confirmed

The Milky Way experienced a major satellite merger 10 Gyr ago which altered, but did not destroy, the early high-alpha disk and created both an accreted and an in situ inner halo. The low-alpha disk that formed subsequently became bar-unstable 8 Gyr ago, creating the b/p bulge that also contains the inner high-alpha disk stars. M31 experienced a similar major satellite merger 3 Gyr ago which greatly heated and mixed the pre-existing high-metallicity disk, and also caused a massive inflow of gas and the formation of a dynamically hot secondary inner disk. Such a merger is consistent with the wide-spread star formation event 2-4 Gyr ago seen in disk colour-magnitude diagrams, and with the major substructures and metal-rich stars in the inner halo of M31 , when comparing photometric and recent spectroscopic data with available models. The merged satellite must have had a broad metallicity distribution and would have been the third most massive galaxy in the Local Group before the merger.

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Thu 15 May 16:00: The different merger and evolutionary histories of the Milky Way and Andromeda (M31)e to be confirmed

Next Colloquia - Wed, 07/05/2025 - 12:52
The different merger and evolutionary histories of the Milky Way and Andromeda (M31)e to be confirmed

The Milky Way experienced a major satellite merger 10 Gyr ago which altered, but did not destroy, the early high-alpha disk and created both an accreted and an in situ inner halo. The low-alpha disk that formed subsequently became bar-unstable 8 Gyr ago, creating the b/p bulge that also contains the inner high-alpha disk stars. M31 experienced a similar major satellite merger 3 Gyr ago which greatly heated and mixed the pre-existing high-metallicity disk, and also caused a massive inflow of gas and the formation of a dynamically hot secondary inner disk. Such a merger is consistent with the wide-spread star formation event 2-4 Gyr ago seen in disk colour-magnitude diagrams, and with the major substructures and metal-rich stars in the inner halo of M31 , when comparing photometric and recent spectroscopic data with available models. The merged satellite must have had a broad metallicity distribution and would have been the third most massive galaxy in the Local Group before the merger.

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Mon 12 May 13:00: DESI DR2: Survey overview and cosmological constraints from DR2 Baryon Acoustic Oscillation measurements Zoom link: https://cam-ac-uk.zoom.us/j/86165819179?pwd=uITeMzHyCpzVlUmVufdGEJXudF0dsy.1

Next External Talks - Wed, 07/05/2025 - 11:01
DESI DR2: Survey overview and cosmological constraints from DR2 Baryon Acoustic Oscillation measurements

The Dark Energy Spectroscopic Instrument (DESI) is undertaking a five-year survey spanning 14,000 square degrees of the sky, with the goal of mapping 40 million extragalactic redshifts. These observations aim to refine our understanding of the universe’s expansion history through Baryon Acoustic Oscillations (BAO) and the growth of cosmic structure via Full Shape analyses. In 2025, the DESI collaboration released BAO cosmology results from the Data Release 2 (DR2) sample, assembled from the first three years of data taking (2021 – 2024). This presentation will introduce the instrument and the survey and review the BAO measurements derived from DR2 . I will discuss the consistency of BAO constraints with other probes—-CMB (including the latest ACT DR6 CMB data) and supernovae—-and present cosmological constraints on dark energy and neutrino masses. I will conclude by providing an outlook on upcoming DESI analyses.

Zoom link: https://cam-ac-uk.zoom.us/j/86165819179?pwd=uITeMzHyCpzVlUmVufdGEJXudF0dsy.1

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NASA’s IXPE Reveals X-ray-Generating Particles in Black Hole Jets

Astronomy News - Wed, 07/05/2025 - 10:03

5 min read

Preparations for Next Moonwalk Simulations Underway (and Underwater)

The blazar BL Lacertae, a supermassive black hole surrounded by a bright disk and jets oriented toward Earth, provided scientists with a unique opportunity to answer a longstanding question: How are X-rays generated in extreme environments like this?

NASA’s IXPE (Imaging X-ray Polarimetry Explorer) collaborated with radio and optical telescopes to find answers. The results (preprint available here), to be published in the journal Astrophysical Journal Letters, show that interactions between fast-moving electrons and particles of light, called photons, must lead to this X-ray emission. 

This artist’s concept depicts the central region of the blazar BL Lacertae, a supermassive black hole surrounded by a bright disk and a jet oriented toward Earth. The galaxy’s central black hole is surrounded by swirls of orange in various shades representing the accretion disk of material falling toward the black hole. While black holes are known for pulling in material, this accretion process can result in the ejection of jets of electrons at nearly the speed of light. The jet of matter is represented by the cone of light that starts at the center of the black hole and widens out as it reaches the bottom of the image. It is streaked with lines of white, pink and purple which represent helix-shaped magnetic fields. We can observe these jets in many wavelengths of light including radio, optical, and X-ray. NASA’s Imaging X-ray Polarimetry Explorer (IXPE) recently collaborated with radio and optical telescopes to observe this jet and determine how the X-rays are generated in these types of celestial environments.NASA/Pablo Garcia

Scientists had two competing possible explanations for the X-rays, one involving protons and one involving electrons. Each of these mechanisms would have a different signature in the polarization of X-ray light. Polarization is a property of light that describes the average direction of the electromagnetic waves that make up light.

If the X-rays in a black hole’s jets are highly polarized, that would mean that the X-rays are produced by protons gyrating in the magnetic field of the jet or protons interacting with jet’s photons. If the X-rays have a lower polarization degree, it would suggest that electron-photons interactions lead to X-ray production.  

IXPE, which launched Dec. 9, 2021, is the only satellite flying today that can make such a polarization measurement. 

“This was one of the biggest mysteries about supermassive black hole jets” said Iván Agudo, lead author of the study and astronomer at the Instituto de Astrofísica de Andalucía – CSIC in Spain. “And IXPE, with the help of a number of supporting ground-based telescopes, finally provided us with the tools to solve it.”

Astronomers found that electrons must be the culprits through a process called Compton Scattering. Compton scattering (or the Compton effect) happens when a photon loses or gains energy after interacting with a charged particle, usually an electron. Within jets from supermassive black holes, electrons move near the speed of light. IXPE helped scientists learn that, in the case of a blazar jet, the electrons have enough energy to scatter photons of infrared light up to X-ray wavelengths. 

BL Lacertae (BL Lac for short) is one of the first blazars ever discovered, originally thought to be a variable star in the Lacerta constellation. IXPE observed BL Lac at the end of November 2023 for seven days along with several ground-based telescopes measuring optical and radio polarization at the same time. While IXPE observed BL Lac in the past, this observation was special. Coincidentally, during the X-ray polarization observations, the optical polarization of BL Lac reached a high number: 47.5%. 

“This was not only the most polarized BL Lac has been in the past 30 years, this is the most polarized any blazar has ever been observed!” said Ioannis Liodakis, one of the primary authors of the study and astrophysicist at the Institute of Astrophysics – FORTH in Greece. 

IXPE found the X-rays were far less polarized than the optical light. The team was not able to measure a strong polarization signal and determined that the X-rays cannot be more polarized than 7.6%. This proved that electrons interacting with photons, via the Compton effect, must explain the X-rays. 

The fact that optical polarization was so much higher than in the X-rays can only be explained by Compton scattering.

Steven Ehlert

Project Scientist for IXPE at Marshall Space Flight Center

“The fact that optical polarization was so much higher than in the X-rays can only be explained by Compton scattering”, said Steven Ehlert, project scientist for IXPE and astronomer at the Marshall Space Flight Center. 

“IXPE has managed to solve another black hole mystery” said Enrico Costaastrophysicist in Rome at the Istituto di Astrofísica e Planetologia Spaziali of the Istituto Nazionale di Astrofísica. Costa is one of the scientists who conceived this experiment and proposed it to NASA 10 years ago, under the leadership of Martin Weisskopf, IXPE’s first principal investigator. “IXPE’s polarized X-ray vision has solved several long lasting mysteries, and this is one of the most important. In some other cases, IXPE results have challenged consolidated opinions and opened new enigmas, but this is how science works and, for sure, IXPE is doing very good science.”

What’s next for the blazar research?

“One thing we’ll want to do is try to find as many of these as possible,” Ehlert said. “Blazars change quite a bit with time and are full of surprises.”

More about IXPE

IXPE, which continues to provide unprecedented data enabling groundbreaking discoveries about celestial objects across the universe, is a joint NASA and Italian Space Agency mission with partners and science collaborators in 12 countries. IXPE is led by NASA’s Marshall Space Flight Center in Huntsville, Alabama. BAE Systems, Inc., headquartered in Falls Church, Virginia, manages spacecraft operations together with the University of Colorado’s Laboratory for Atmospheric and Space Physics in Boulder. Learn more about IXPE’s ongoing mission here:

https://www.nasa.gov/ixpe

Elizabeth Landau
NASA Headquarters
elizabeth.r.landau@nasa.gov
202-358-0845

Lane Figueroa
Marshall Space Flight Center, Huntsville, Ala.
lane.e.figueroa@nasa.gov
256.544.0034 

Share Details Last Updated May 06, 2025 EditorBeth RidgewayContactElizabeth R. Landauelizabeth.r.landau@nasa.govLocationMarshall Space Flight Center Related Terms Explore More 4 min read NASA’s Chandra Diagnoses Cause of Fracture in Galactic “Bone” Article 5 days ago 4 min read NASA Marshall Fires Up Hybrid Rocket Motor to Prep for Moon Landings Article 2 weeks ago 6 min read NASA’s Chandra Releases New 3D Models of Cosmic Objects Article 3 weeks ago Keep Exploring Discover Related Topics

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Black Holes

Black Holes Black holes are among the most mysterious cosmic objects, much studied but not fully understood. These objects aren’t…

Tue 13 May 13:00: Deciphering giant planet formation

IoA Institute of Astronomy Talk Lists - Wed, 07/05/2025 - 09:56
Deciphering giant planet formation

The multitude of detected exoplanets and their diversity never cease to fascinate us, while the statistical trends emerging from these detections present promising opportunities to delve into the past of planetary systems, all the way back to their formation. In this talk, I will give an overview of my group’s recent observational and theoretical results on the formation of gas giants. Owing to their large gravitational influence these planets cannot be overlooked in the evolution of planetary systems towards a life-harbouring system such as our own. Results of RV and direct imaging surveys in recent years revealed that gas giants are not a common outcome of planet formation, and that their most frequent hosts – the intermediate-mass stars (IMSs) seem to hold the answers to their formation.

We investigate the formation of giant planets using the pebble-accretion driven planet formation simulations, exploring a range of different formation conditions. In this work, and in contrast to common approaches in the literature, we implement stellar-mass dependent time evolution of luminosity on the pre-main sequence, and find that this makes a significant difference to giant planet formation outcomes. We successfully reproduce the giant planet occurrence rates as a function of stellar mass, found by RV surveys. This work revealed that mass accretion rate is the key parameter in determining whether a star will likely host a giant planet in its future planetary system.

Our large surveys of pre-main sequence star candidates led to the first unbiased sample of such IMSs, and the result that their protoplanetary discs are dispersed faster than discs around low mass stars, a devastating prospect for giant planet formation unless it happens very fast (e.g., via GI). This is in stark contrast with the observational examples of massive discs actively forming planets at 5-6Myr of age. Our work shows that late gas accretion, as seen in some of those sources, must be the dominant mechanism that sustains the mass reservoir of these older protoplanetary discs. Our surveys, and follow-up with ALMA also allowed a unique insight in the elusive transition state from protoplanetary to debris discs and origin of gas in debris discs.

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