Multi-messenger astrophysics

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Discussions around tools and discoveries in the novel domain of multi-messenger and time domain astrophysics. We'll highlight recent publications, discuss tools to faciliate observations and generally talk about the cool science behind the most violent explosions in the universe.

  1. Hunting for Radio Ghosts: The Search for Persistent Sources Near FRBs

    6H AGO

    Hunting for Radio Ghosts: The Search for Persistent Sources Near FRBs

    In this episode, we explore a new study utilizing the powerful MeerKAT telescope to investigate the environments of Fast Radio Bursts (FRBs). While some repeating FRBs are known to be accompanied by "Persistent Radio Sources" (PRSs)—compact, glowing radio beacons—it remains unclear if one-off FRBs share this feature. We discuss how researchers targeted 25 well-localised one-off FRBs to hunt for these elusive radio sources. The team detected radio emission coincident with 14 of these bursts. However, the mystery deepens: were these detections the sought-after PRSs, or simply the radio signature of star formation within the host galaxies? Tune in to learn about the difference between repeating and one-off FRB environments, the discovery of a variable radio source, and why future high-resolution observations with telescopes like e-MERLIN are critical to solving this puzzle. Key Takeaways: The Mission: Searching for Persistent Radio Sources (PRSs) associated with 25 one-off FRBs using the MeerKAT telescope.The Findings: Radio emission was detected at 14 FRB positions, often aligning with the host galaxy's optical structure.The Verdict: Current data suggests the radio emission is likely driven by star formation rather than compact central engines, though one source showed intriguing variability. Reference Article: Mfulwane, L. L., et al. "A MeerKAT search for persistent radio sources towards twenty-five localised Fast Radio Bursts." arXiv preprint arXiv:2602.07716. Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: MeerKAT (NRF/SARAO)

    16 min
  2. The JWST Forges: Witnessing the Birth of Quasars

    5D AGO

    The JWST Forges: Witnessing the Birth of Quasars

    In this episode, we explore a breakthrough discovery from the James Webb Space Telescope (JWST) regarding the mysterious population of objects known as "Little Red Dots" (LRDs). Characterized by a unique V-shaped spectral energy distribution and broad emission lines, LRDs are thought to host supermassive black holes, yet they strangely lack the X-ray signatures of typical Active Galactic Nuclei (AGNs). We discuss a new study identifying two exceptional LRDs—dubbed "Forge I" and "Forge II"—at redshifts of $z \approx 2.9$. Unlike previously known LRDs, the Forges emit intense X-rays and radio waves, suggesting the dense gas envelopes typically hiding these black holes are finally dispersing. This discovery places the Forges as a "missing link" in cosmic evolution, capturing the brief, transitional moment when a dusty Little Red Dot evolves into a luminous quasar. **Key Topics Covered:** * **What are Little Red Dots?** Understanding the compact, red objects found by JWST that host super-Eddington accreting black holes. * **The Anomalies:** Introducing Forge I and Forge II, which break the mold by showing strong X-ray and radio emission. * **The "Cocoon" Breaking:** How the hybrid properties of the Forges suggest their dense gas envelopes are clearing out, allowing high-energy photons to escape. * **Evolutionary Fate:** Evidence that LRDs are a short-lived phase that eventually transitions into standard quasars or AGNs. **Reference:** Fu, S., Zhang, Z., Jiang, D., et al. (2025). *Discovery of two little red dots transitioning into quasars*. arXiv preprint. Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: Nature volume 649, pages574–579 (2026)

    15 min
  3. STONKS: How XMM-Newton is Finding Faint Transients

    JAN 30

    STONKS: How XMM-Newton is Finding Faint Transients

    In this episode, we explore the dynamic and violent universe revealed by the STONKS pipeline (Search for Transient Object in New observations using Known Sources). While the name might remind you of internet finance memes, this system is a serious tool for the XMM-Newton space telescope. We discuss how researchers are using STONKS to detect long-term X-ray transients in the Galactic plane that are too faint for standard wide-field survey instruments to see. Join us as we break down the first results from a multi-year survey of the Galaxy, identifying 70 astrophysical sources that change in brightness over time. From waking magnetars to flaring stars, we look at what these faint signals tell us about the most extreme physical environments in the cosmos. Key Topics Discussed: What is STONKS? A near-real-time detection system that compares new XMM-Newton observations against archival data to spot variability.The Advantage: Unlike survey missions (like Swift or eROSITA), STONKS utilizes long exposure times to find variable sources at fluxes several orders of magnitude lower than other systems.Major Discoveries: A Magnetar Candidate: The detection of a potential magnetar (4XMM J175136.9-275858) caught at the onset of a massive outburst, increasing in brightness by nearly two orders of magnitude.Exotic Stars: The identification of a $\gamma$-Cas analogue (HD 162718) and new candidates for Cataclysmic Variables (CVs).New Detections: Of the 70 sources analyzed, 23 were detected in X-rays for the very first time.The Future: How systematic analysis of archival data is opening a new window into stellar evolution and compact objects like black holes and neutron stars. Reference Material "STONKS first results: Long-term transients in the XMM-Newton Galactic plane survey", Robbie Webbe, E. Quintin, N. A. Webb, Gabriele Ponti, Tong Bao, Chandreyee Maitra, Shifra Mandel, Samaresh Mondal, Astronomy & Astrophysics manuscript no. aa57789-25, January 28, 2026. Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: ESA

    15 min
  4. The Spectroscopic Revolution: Multi-Messenger Astronomy and the WST

    JAN 19

    The Spectroscopic Revolution: Multi-Messenger Astronomy and the WST

    In this episode, we explore the **Wide-field Spectroscopic Telescope (WST)**, a proposed 12-meter class facility that aims to revolutionize our understanding of the cosmos in the 2030s and 2040s. While imaging surveys like LSST and Euclid provide a "video" of the sky, the WST provides the physical "voice" needed to interpret those images through high-speed, massive-scale spectroscopy. **Key Topics Covered:** * **The Technological Leap:** Discover how the WST’s unique design allows for **simultaneous Multi-Object Spectroscopy (MOS) and Integral Field Spectroscopy (IFS)**, featuring a 12-meter aperture and a massive 3.1 square degree field of view. * **The "Spectroscopic Alert" Era:** How the WST will close the gap between millions of nightly photometric alerts and our limited capacity to follow them up, turning spectroscopy into a primary discovery tool for supernovae, exocomets, and binary black holes. * **Mapping the Milky Way:** Learn how "chemical tagging" will allow astronomers to reconstruct the history of our galaxy by analyzing the chemical fingerprints of millions of stars. * **Cosmology and the Cosmic Web:** Exploring the "Dark Universe," from measuring the mass of neutrinos to charting the expansion of the universe using the 3D topology of the Lyman-alpha forest. * **Multi-Messenger Synergies:** How the WST will work alongside gravitational wave detectors (LISA, Einstein Telescope) and neutrino observatories (IceCube-Gen2) to pinpoint the most violent events in the universe. **Featured Reference:** 1. **Mainieri, V., Anderson, R. I., Brinchmann, J., et al. (2024). *The Wide-field Spectroscopic Telescope (WST) Science White Paper*.** This foundational document provides a comprehensive overview of the facility's **12-meter aperture**, its unique simultaneous **Multi-Object Spectroscopy (MOS) and Integral Field Spectroscopy (IFS)** capabilities, and its broad science cases ranging from cosmology to Galactic archaeology. 2. **Melo, A., Sanchez-Saez, P., Ivanov, V. D., et al. (2025). *Spectroscopic Alerts for the Time-Domain Era*.** This article introduces the paradigm-shifting concept of **"Spectroscopic Alerts,"** which are real-time notifications triggered by physical changes in a source's spectrum, allowing the WST to act as a primary **discovery instrument** for transient phenomena. 3. **Schüssler, F., Bisero, S., Cornejo, B., et al. (2026). *Multi-Messenger Studies with High-Energy Neutrinos and Gamma Rays: The WST Opportunity*.** This reference highlights the WST's role in **multi-messenger astrophysics**, specifically its ability to rapidly survey large sky areas to classify the electromagnetic counterparts of **high-energy neutrinos** and very-high-energy **gamma rays**. Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: G.Gausachs/WST

    16 min
  5. Asymmetric Blasts: Inside the Ejecta of GRB 180728A / SN 2018fip

    JAN 16

    Asymmetric Blasts: Inside the Ejecta of GRB 180728A / SN 2018fip

    In this episode, we dive into the fascinating discovery of **GRB 180728A**, one of the nearest and most energetic long-duration gamma-ray bursts ever recorded at a low redshift. While most nearby bursts are low-energy events, this explosion released a massive **$2.5 \times 10^{51}$ erg of isotropic energy**, placing it in a rare class of cosmological powerhouses found right in our relative "backyard". We explore the detailed analysis of its associated supernova, **SN 2018fip**, and what it reveals about the complex nature of stellar collapses. **Key Topics Covered:** * **A Rare High-Energy Event:** Learn why GRB 180728A is significant, sitting at a redshift of **z = 0.1171** and ranking as one of the most energetic nearby bursts after the famous GRB 030329 and the record-breaking "BOAT" (GRB 221009A). * **The Supernova Mystery:** Despite the high energy of the gamma-ray burst itself, the associated supernova SN 2018fip was **intrinsically fainter** than many typical events, showing that the energy of a burst doesn't always correlate with the brightness of its supernova. * **The Shape of the Blast:** Discover why researchers believe this wasn't a simple spherical explosion. The sources suggest a **two-component ejecta** model: a narrow, high-velocity component (> 20,000 km/s) and a slower, more massive inner component. * **The Neighborhood:** We take a look at the **host galaxy**—a low-mass, blue, star-forming irregular dwarf galaxy typical for these types of cosmic events. * **Advanced Observations:** Insights into how astronomers used instruments like the **X-shooter** on the Very Large Telescope to track the explosion for 80 days. **Featured Reference:** Rossi, A., Izzo, L., Maeda, K., et al. (2026). **"GRB 180728A and SN 2018fip: the nearest high-energy cosmological gamma-ray burst with an associated supernova."** *Astronomy & Astrophysics*. Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: Anna Serena Esposito

    12 min
  6. The Superkilonova Symphony: Merging Stars Inside Exploding Ones (AT2025ulz and S250818k)

    JAN 12

    The Superkilonova Symphony: Merging Stars Inside Exploding Ones (AT2025ulz and S250818k)

    In this episode, we dive into a groundbreaking discovery that may have revealed a brand-new category of cosmic explosion: the Superkilonova. On August 18, 2025, gravitational-wave detectors picked up a signal, S250818k, indicating a merger between two neutron stars—but with a twist. The estimated "chirp mass" was surprisingly low, suggesting that at least one of the objects was below the mass of our Sun, a finding that challenges standard models of stellar evolution. The Optical Mystery: The Zwicky Transient Facility (ZTF) quickly identified a matching optical transient, AT2025ulz, in the same region. While its first week of behavior looked like a classic "kilonova" (the expected glow from a neutron star merger), it soon evolved into something much more complex. Spectroscopic and photometric data eventually showed it was most similar to a Type IIb stripped-envelope supernova, which is the explosion of a massive star that has lost most of its outer hydrogen. The Superkilonova Theory: How can an event be both a neutron star merger and a supernova? The researchers explore a fascinating theoretical model known as a Superkilonova. In this scenario, a rapidly spinning massive star collapses, and its core either fissions into two pieces or its surrounding disk fragments into subsolar-mass neutron stars. These fragments then merge almost immediately inside the supernova explosion. Key Highlights: A "Veritable Symphony": The potential for a single event to produce gravitational waves from a merger while simultaneously displaying the light of a core-collapse supernova.New Stellar Pathways: If confirmed, this proves that neutron stars can form via accretion-disk fragmentation, or it might even be evidence of primordial black holes.Multimessenger Challenges: Why scientists need more than just light to solve these puzzles, relying instead on a "panchromatic dataset" including X-rays, radio waves, and gravitational strain. Article Reference Kasliwal, M. M., et al. (2025). "ZTF25abjmnps (AT2025ulz) and S250818k: A Candidate Superkilonova from a Subthreshold Subsolar Gravitational-wave Trigger." The Astrophysical Journal Letters, 995:L59 (18pp). Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: Caltech/K. Miller and R. Hurt (IPAC)

    17 min
  7. MeerKAT’s Deep Gaze: Unveiling the Radio Ghosts of V4641 Sgr

    JAN 9

    MeerKAT’s Deep Gaze: Unveiling the Radio Ghosts of V4641 Sgr

    In this episode, we dive into a groundbreaking discovery made with the **MeerKAT radio telescope**: a massive, symmetric **"bow-tie" shaped radio structure** surrounding the black hole system **V4641 Sgr**. While this microquasar has been known since 1999 for its erratic outbursts and superluminal jets, this new research reveals the long-term impact these black holes have on their galactic neighborhoods, stretching across nearly **35 parsecs (about 114 light-years)** of space. **Key Topics Discussed:** * **The System:** V4641 Sgr is a low-mass X-ray binary (LMXB) featuring a **6.4 solar mass black hole** and a B-type stellar companion. It is famous for its "superluminal" jets that appear to move faster than the speed of light due to their orientation and velocity. * **The "Bow-Tie" Discovery:** Using deep imaging techniques, astronomers found a faint, diffuse radio structure that mirrors the size and position of extended X-ray emission recently detected by the XRISM satellite. * **Particle Acceleration:** The sources suggest the radio and X-ray emission are likely caused by **synchrotron radiation**. This implies that electrons are being accelerated to energies of **more than 100 TeV**—even tens of parsecs away from the central black hole. * **The Proper Motion Mystery:** Interestingly, the black hole is slightly offset from the center of the bow-tie. The researchers explain this through the **proper motion of the system**; by tracing the black hole's path backward, they estimate it was at the center of this structure roughly **10,000 years ago**. * **The Gamma-Ray Disconnect:** While large-scale gamma-ray "bubbles" have also been detected around this system, they are oriented differently and are much larger than the radio bow-tie. We explore why these different "colors" of light reveal different chapters of the black hole's history. **Why This Matters:** This discovery adds V4641 Sgr to a growing list of **"microquasars"**—stellar-mass black holes that act as smaller-scale analogs to the supermassive black holes found in the centers of galaxies. It reinforces the idea that these systems are significant contributors to **galactic cosmic rays** and powerful drivers of change in the interstellar medium. *** ### **Reference** Grollimund, N., Corbel, S., Fender, R., et al. (2026). **"Large-scale radio bubbles around the black hole transient V4641 Sgr."** *Astronomy & Astrophysics*, manuscript no. aa57124-25. Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: N. Grollimund et al.

    16 min
  8. Breaking the Redshift Barrier: H.E.S.S. and the Distant Blazar PKS 0346−27

    JAN 6

    Breaking the Redshift Barrier: H.E.S.S. and the Distant Blazar PKS 0346−27

    In this episode, we dive into a groundbreaking discovery in high-energy astrophysics: the detection of the blazar PKS 0346−27 at a redshift of $z = 0.991$. This makes it one of the most distant objects ever detected in very-high-energy (VHE) gamma-rays ($E > 100$ GeV). We explore how the H.E.S.S. (High Energy Stereoscopic System) telescopes in Namibia managed to capture this elusive signal despite the thick "fog" of Extragalactic Background Light (EBL) that usually absorbs such distant photons. Key Discussion Points: The Record-Breaking Detection: Why reaching a redshift of approximately 1 is a major milestone for gamma-ray astronomy and what it tells us about the evolution of the universe.A Tale of Two Flares: The strange two-day delay between the high-energy flare caught by the Fermi-LAT satellite and the very-high-energy flare detected by H.E.S.S..The Physics of the Jet: We break down the debate between leptonic and hadronic models. While electrons are the usual suspects, the data from PKS 0346−27 strongly favors a proton-synchrotron model, even though it requires jet power that temporarily exceeds the source’s Eddington limit.Multi-Wavelength Cooperation: How a global team used data from H.E.S.S., Fermi-LAT, the Swift Observatory, and the ATOM telescope to build a complete picture of this cosmic event.The "Synchrotron Mirror" Hypothesis: Exploring how stationary clouds near the black hole might be reflecting radiation back into the jet to create "orphan" VHE flares. Technical Insight: The researchers found that a traditional leptonic model (based on electrons) would require "implausible" parameters, such as a Doppler factor exceeding 80, to explain the flare. This push toward hadronic models suggests that relativistic protons may play a much larger role in the most powerful jets in the universe than previously confirmed. Featured Article: H.E.S.S. Collaboration, et al. (2026). "H.E.S.S. detection and multi-wavelength study of the $z \sim 1$ blazar PKS 0346−27." Astronomy & Astrophysics manuscript no. 0346. Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: Stefan Schwarzburg

    16 min
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Discussions around tools and discoveries in the novel domain of multi-messenger and time domain astrophysics. We'll highlight recent publications, discuss tools to faciliate observations and generally talk about the cool science behind the most violent explosions in the universe.

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