Kiril Maltsev

Massive stars undergoing iron-core collapse at the end of their evolution terminate their lives either in successful or failed supernovae (SNe). The most frequent outcomes are successful explosions, producing Type II or Type Ibc SNe. Though some stars fail to explode and continue to collapse until a black hole is formed. In this work, we formulate an explosion condition for the neutrino-heating driven SN mechanism (and for its failure) using multiple variables characterizing stellar structure at the onset of iron-core infall. We find that the final fates of massive stars are largely pre-determined already at the end of core-helium burning, and derive a simple core-collapse SN recipe applicable at this stage. The SN recipe predicts the remnant type (neutron star vs. black hole) given the carbon-oxygen core mass and metallicity, while distinguishing hydrogen-rich envelope retaining vs. envelope-stripped stars. Our explodability formalism connects to theory of massive star evolution through the advanced burning phases, is in good agreement with 3D core-collapse SN simulation outcomes and consistent with a number of observational constraints from transient astronomy.
doi:10.1051/0004-6361/202554931

In-progress work. Details to follow.

• Does the prediction of singularity formation in stellar gravitational collapse indicate the breakdown of General Relativity theory?
  doi:10.1142/9789811269776_0298
• Do classical-limit Schwarzschild black holes transcend the laws of thermodynamics?
  doi:10.1134/S1063772921100218

Using photometry data from Gaia DR3, we conduct a census of OB-type stars in the local Milky Way to identify and characterize a population of 105,971 massive star systems within 2 kpc from Earth. Our census of OB-type stars, the most complete that has been conducted so far, unveils a complex view of the young stellar populations across the thin disk, with prominent large-scale features such as the Cepheus Spur, the Giant Oval Cavity, and a segment of the Sagittarius-Carina spiral arm all visible. Their inhomogeneous spatial distribution implies that massive star formation has taken place clustered across a few highly concentrated regions. We identify over 4,200 core-collapse SN progenitor candidate stars within 2 kpc, but predict none of those within the innermost 100 pc to explode within the next 1 Myr - an event that could be harmful to Earth's biosphere. Finally, we identify more BH progenitors to collapse within the next 1 Myr than SNe to explode, despite the former's much scarcer number - which could be indicative of a recent massive star formation burst having taken place in the local Milky Way.
doi:10.48550/arXiv.2607.07068

In-progress work. Details to follow.

Core-collapse supernova explosions in the local Milky Way are rare events primarily for the reason that the number of massive stars above the zero-age-main-sequence (ZAMS) mass threshold for ignition of core-neon burning and evolution through the advanced burning phases is scarce. Their abundance is determined during star formation by the stellar Initial Mass Function (IMF). The canonical IMF models of Salpeter (1955), Kroupa et al. (2001) and Chabrier (2003) predict that the high-mass tail ($\text{M}$_ZAMS > 1 solar mass) of the IMF is characterized by a single slope parameter, α, which remains stationary across the entire high-mass range. The high-mass IMF of local-field stars is little constrained observationally, and its improved understanding will allow us to refine estimates of supernova explosion rates, chemical enrichment and stellar feedback efficiencies, which are important for many astrophysical studies.
When comparing observations of local-field stars to stellar evolution models to infer their $\text{M}$_ZAMS, interpolation of model catalogs for the iterative optimization-based parameter estimation is costly and therefore cannot be used to process large sample sizes.
To remedy this, we constuct an efficient deep-learning based surrogate model of stellar evolution, trained on evolutionary tracks pre-computed with the detailed stellar evolution code MESA while generalizing predictions over a continuous parameter space: it traces stellar evolution from the zero-age-main-sequence up to the end of core-helium burning while covering a mass range from red dwarves to 300 solar-mass stars. Its main advantage over classical interpolation of stellar model catalogs is the speed-up, as it casts millions of predictions within tens of seconds on a 4-core CPU, while keeping the predictive errors orders of magnitude below typical observational uncertainties. doi:10.1051/0004-6361/202347118

The merger of two NSs results either in prompt collapse to a BH or in a quasi-stable hypermassive neutron star (HMNS). The HMNS is supported by differential rotation, thermal effects and repulsive nuclear forces, and continues to emit gravitational waves (GWs) until it either stabilizes or undergoes a delayed collapse to a BH. One of the methods for ground-based detection of GWs emitted from cosmic HMNSs is the matched-filtering technique. It requires efficient GW template models that predict gravitational waveforms in the time- or frequency-domain as a function of astrophysical source parameters. The templates are scanned through the interferometry data in order to identify GW signals in a noisy background. In this work, we constructed a template model for the GW emission from HMNSs remaining quasi-stable for at least 17 ms after the merger, as a function of astrophysical source parameters, using numerical relativity simulations and supervised learning techniques. The template model is fast, accurate and noise-robust enough to in future be used for signal searches in the interferometry data of the Advanced LIGO detector network at design sensitivity as well as of next-generation detectors. Under Advanced LIGO conditions, we confirmed the earlier prediction that the main GW properties (in particular, the dominant and subdominant peak oscillation frequencies) can be reliably reconstructed up to a source luminosity distance of approximately 12 Mpc, and further found that signal detection is achievable even in the case that the Equation-of-State (EoS) model adopted in the search template only crudely replicates the actual EoS at source.
doi:10.1103/PhysRevD.111.023002

In-progress work. Details to follow.