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Time-Domain, transients and Multi-Messenger Astrophysics

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Time-Domain, transients and Multi-Messenger Astrophysics

Key scientific objectives

  1. Transient Astrophysical Phenomena

MOSAIC will enable spectroscopic follow-up and population studies of a wide range of explosive and transient events, including:

  • Supernovae: Thermonuclear (Type Ia) and core-collapse (Type II) supernovae, probing stellar evolution, chemical enrichment, and cosmological parameters.

  • Kilonovae: Neutron star mergers, key to understanding heavy element (r-process) nucleosynthesis.

  • Gamma-Ray Bursts (GRBs): Redshifts, environments, and progenitor properties.

  • Tidal Disruption Events (TDEs): Stars torn apart by supermassive black holes, probing accretion physics and black hole demography

  • Fast Blue Optical Transients (FBOTs): Rare, fast-evolving phenomena with unclear origins, potentially linked to exotic stellar endpoints or TDEs by intermediate black holes.

  • Fast Radio Burst (FRB)’s host Galaxies: Redshifts, star-formation rates, metallicities, and stellar populations to probe the physical conditions at their burst sites.

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Artist's representation of a tidal disruption event (a star being torn apart by a black hole). Credit: NASA / CXC / M. Weiss.
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Observation of the supernova remnant Tycho (SN 1572). Credit : X-ray : NASA/CXC/SAO, Infrared: NASA/JPL-Caltech ; Optical: MPIA, Calar Alto, O.Krause et al.
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Illustration of the most common type of gamma-ray burst: The core of a massive star (left) has collapsed, forming a black hole that sends a jet into space at nearly the speed of light. Radiation, including gamma rays, X-rays, visible light and radio waves, arises from hot ionised gas near the newborn black hole, collisions among shells of fast-moving gas within the jet, and from the leading edge of the jet as it sweeps up and interacts with its surroundings. Credit: NASA's Goddard Space Flight Center.

Examples of key questions

  • What are the progenitors of various types of transients?

  • How do the spectral features of gamma-ray burst (GRB) afterglows evolve, and what do they tell us about GRB and its surroundings?

  • What are the properties of the neutral gas in high-redshift galaxies probed by GRBs?

  • What are the spectral signatures of kilonovae, and do they confirm their role as major sites of heavy element nucleosynthesis (r-process)?

  • What are the mechanisms of accretion and ejection of matter during Tidal Disruption Events (TDEs)?

  • What are the properties of the host galaxies of fast radio bursts (FRBs)? 

  

  1. Time-Domain Astrophysics

MOSAIC’s high sensitivity and multiplexing capabilities will enable large-scale spectroscopic monitoring campaigns to study astrophysical variability across a wide range of timescales, from minutes to years:
  • Active Galactic Nuclei (AGN):
    • - "Changing-state" phenomena, probing accretion variability.
    • -  Reverberation mapping to constrain the geometry and kinematics of the broad-line region (BLR) and to estimate supermassive black hole masses.
  •  Variable Stars and Stellar Flares:
    • - Pulsating stars (e.g., Cepheids, RR Lyrae) to refine distance scaling and stellar structure models.
    • - Stellar flares and magnetic activity, with implications for stellar evolution and exoplanet habitability.
  • Cataclysmic Variables (CVs) and Novae:
    • - Evolution of the accretion disc and secondary star during quiescence and outburst phases of CVs.
    • - Nova eruptions, mapping ejecta composition, kinematics, and chemical enrichment.
  • Microlensing Events:
    • - Lens masses and stellar populations, including the search for isolated stellar compact objects.
  • X-ray Binaries (XRBs):
    • - Nature of the compact object (neutron star versus black hole) via spectroscopic studies of the companion star (measure of the system mass).
    • - Spectroscopic surveys of XRB candidates in the Milky Way, Magellanic Clouds, and nearby galaxies (e.g., M31, M33).
    • - Investigation of accretion states, disc winds, and jet launching via line variability and asymmetries.
  • Exoplanet Atmospheres and Transits:
    • - Transiting exoplanets to detect and characterise atmospheric composition through time-resolved spectroscopy.
  • Solar System Bodies and Small Bodies:
    • - Cometary outbursts and seasonal effects on icy bodies.

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An artist's representation of an active galactic nucleus (AGN) - Credit: NASA/CXC/M.Weiss
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Artist’s impression of an X-ray binary. Credits: ESA, NASA, and Felix Mirabel.

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Artist impression by Danielle Futselaar. The illustration shows the host star HIP 67522 and its orbiting planet HIP 67522 b. A powerful stellar flare erupts from the star, directed toward the planet. The image also visualises the star’s magnetic field lines, highlighting the magnetic connection between the star and the exoplanet.

Examples of key questions

  • What are the driving physical mechanisms behind the luminosity, variability or spectral changes of active galactic nuclei (AGN)?                        

  • How do the atmospheres of exoplanets change over time, and what can we learn about their composition and dynamics?

 

  1. Multi-Messenger Astrophysics

With the advent of gravitational wave and high-energy neutrino astronomy, MOSAIC will play a pivotal role in identifying and studying electromagnetic counterparts of multi-messenger events:

  • Gravitational Wave Follow-Up:

    • - Localising and characterising the optical/NIR counterparts of mergers involving neutron stars, stellar black holes, as detected by observatories such as LIGO, Virgo, and KAGRA.

    • - Localising and characterising the optical/NIR counterparts of supermassive black hole binaries, as detected by observatories such as LISA and PTA.

  • High-Energy Neutrino Counterparts: Spectroscopic identification of potential astrophysical (AGNs, starburst and star-forming Galaxies, supernova remnants, TDEs, GRBs…) counterparts associated with neutrino alerts from facilities like IceCube and KM3NeT.

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Simulations of two black holes that are going to merge. Image courtesy of SXS Lensing/Simulating eXtreme Spacetimes Collaboration.

 

Examples of key questions

  • What are the astrophysical sources of high-energy neutrinos, and are they linked to AGNs, GRBs, or other extreme phenomena?

  • What are the electromagnetic signatures of milli-parsec supermassive binaries (GW, LISA)?

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