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SUMMARY:A FISSION FLASH IN THE INNER CRUST OF AN EXPLODING LOW-MASS NEUTRO
 N STAR
DTSTART;VALUE=DATE-TIME:20261029T064500Z
DTEND;VALUE=DATE-TIME:20261029T070000Z
DTSTAMP;VALUE=DATE-TIME:20261102T005338Z
UID:indico-contribution-6189@cern.ch
DESCRIPTION:Speakers: Anton Ignatovskiy (MIPT\, NRC "Kurchatov Institute")
 \nAmong the scenarios for the evolution of various astrophysical objects i
 n which the conditions necessary for the r‑process to occur can be reali
 zed\, the process of neutron star mergers in a close binary system is curr
 ently considered the main one [1]. This scenario largely depends on the ma
 sses of the objects included in the system and can develop in different wa
 ys: 1) If neutron stars have approximately the same mass\, a merger occurs
 \, accompanied by the ejection of neutron‑rich matter in the equatorial 
 plane and in the wind from the hot\, massive neutron star [2]\; 2) If the 
 masses of the neutron stars differ significantly\, the evolution of the ne
 utron star system follows a stripping scenario [3]\, in which\, in particu
 lar\, the nucleosynthesis of heavy elements proceeds differently [4\,5].\n
 The first ideas about the merger of a neutron star (NS) and a black hole a
 ssociated with short gamma-ray bursts (GRB) were put forward by Lattimer a
 nd Schramm [6].   The scenario of the merger of two neutron stars was deve
 loped by Clark and Eardley [3]. In the last paper not only the merging of 
 two neutron stars was discussed\, but also proposed a stripping scenario i
 nvolving the loss of mass by a minimum mass star.\nIn both scenarios\, two
  neutron stars orbiting each other must come closer due to the loss of ang
 ular momentum caused by the emission of gravitational waves. What is the d
 ifference between the merger and tidal disruption mechanisms? The merger m
 echanism is as follows: having approached each other to a sufficient dista
 nce\, the neutron stars merge into a single object — a black hole or a r
 apidly rotating neutron star — over several orbits. At the same time\, p
 art of the matter may be ejected from the system due to tidal interaction.
  Furthermore\, due to the extreme acceleration of the rotation of the matt
 er and its heating\, a highly collimated ejection of matter can form — a
  jet — and part of the matter of the merged neutron star can evaporate i
 n the form of a wind. This picture of neutron star mergers is currently ge
 nerally accepted\, although many of its details remain unclear.\nThe funda
 mental difference between the stripping mechanism and a rapid merger lies 
 in the prolonged (many orbits of the binary system) transfer of matter fro
 m one star to the other. Note that for this scenario to be realized\, a su
 fficient asymmetry in the masses of the components of the binary system is
  required. As the neutron stars approaches\, the component with the smalle
 r mass first fills its Roche lobe\, since it has a larger radius\, and beg
 ins to transfer mass to the more massive companion through the inner Lagra
 nge point. The asymmetry of the system increases\, and the distance betwee
 n the stars increases due to the approximate conservation of the system’
 s angular momentum. However\, the transfer does not stop (it is stable) du
 e to the loss of angular momentum through the emission of gravitational wa
 ves and the increase in the radius of the NS with the smaller mass.  \nAs 
 a result of the exchange\, the mass of the heavier star (M1) increases\, w
 hile its radius remains approximately constant or decreases\, and the mass
  of the lighter NS (M2) decreases while its radius increases. When M2 reac
 hes the value corresponding to the minimum possible mass of the NS (about 
 0.1 solar masses)\, an explosion occurs\, which leads to the destruction o
 f the low‑mass NS.\nThis report examines the nucleosynthesis of heavy nu
 clei under the influence of neutrons (the r‑process) in the inner crust 
 of a low‑mass neutron star (LMSN)\, which loses mass due to the transfer
  of matter onto a more massive companion neutron star (the stripping scena
 rio) and explodes upon reaching a hydrodynamically unstable configuration 
 [7].  \nIt has been shown that the schock wave generated during the destru
 ction of the MMNZ heats the outer shell of the inner core to high temperat
 ures\, and the r‑process transforms into explosive nucleosynthesis. Sinc
 e the cross‑sections of induced fission increase by orders of magnitude 
 when the temperature rises to values of T9>5\, and given the persistently 
 high neutron density\, an instantaneous (t~3–5 ms) fission flash of the 
 actinides formed in the r‑process occurs. The composition of the resulti
 ng fission product nuclei largely depends on the model of the mass distrib
 ution of fission products and represents a new initial composition for the
  r‑process\, which resumes after further expansion of the matter and a d
 rop in temperature.\nThe work was carried out as part of fulfilling the st
 ate assignment of the National Research Center “Kurchatov Institute”.\
 nLITERATURE\n1. J. J. Cowan\, et al. // Rev. Mod. Phys. 2021. V. 93. id. 1
 5002.\n2. S. Rosswog\, Philosophical Transactions of the Royal Society A. 
 2013\, V. 371\, № 1992\, 20120272.\n3. J. P. A. Clark and D. M. Eardley 
 // Astrophys. J. 1977. V. 215. P. 311.\n4. I.V. Panov\, A.V. Yudin // Astr
 onomy Letters. 2020. V. 46. P. 518.\n5. A. Yudin\, N. Kramarev\, I. Panov\
 , A. Ignatovskiy // Particles. 2023. V. 6. P. 784. \n6. J.M. Lattimer\, D.
 N. Schramm //  Astrophys. Lett. 1974. V. 192. P. 145.\n7. S. I. Blinnikov\
 , D. K. Nadyozhin\, N. I. Kramarev\, A. V. Yudin // Astronomy Reports. 202
 1. V. 65. P. 385.\n\nhttps://indico.particle.mephi.ru/event/626/contributi
 ons/6189/
LOCATION: Conference Hall 2
URL:https://indico.particle.mephi.ru/event/626/contributions/6189/
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