MPA/RIKEN: Radioactive Elements in Cas A Suggest Neutrino-Driven Explosion

[bystander]

Radioactive Elements in Cassiopeia A Suggest Neutrino-Driven Explosion
National Research and Development Institute of Applied Chemistry, Japan (RIKEN) |
Max Planck Institute for Astrophysics (MPA) | 21 Jun 2017

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Stars exploding as supernovae are the main sources of heavy chemical elements in the Universe. In particular, radioactive atomic nuclei are synthesized in the hot, innermost regions during the explosion and can thus serve as probes of the unobservable physical processes that initiate the blast. Using elaborate computer simulations, a team of researchers from the Max Planck Institute for Astrophysics (MPA) and RIKEN in Japan were able to explain the recently measured spatial distributions of radioactive titanium and nickel in Cassiopeia A, a roughly 340 year old gaseous remnant of a nearby supernova. The computer models yield strong support for the theoretical idea that such stellar death events can be initiated and powered by neutrinos escaping from the neutron star left behind at the origin of the explosion.

Massive stars end their lives in gigantic explosions, so-called supernovae. Within millions of years of stable evolution, these stars have built up a central core composed of mostly iron. When the core reaches about 1.5 times the mass of the Sun, it collapses under the influence of its own gravity and forms a neutron star. Enormous amounts of energy are released in this catastrophic event, mostly by the emission of neutrinos. These nearly massless elementary particles are abundantly produced in the interior of the new-born neutron star, where the density is higher than in atomic nuclei and the temperature can reach 500 billion degrees Kelvin.

The physical processes that trigger and drive the explosion have been an unsolved puzzle for more than 50 years. One of the theoretical mechanisms proposed invokes the neutrinos, because they carry away more than hundred times the energy needed for a typical supernova. As the neutrinos leak out from the hot interior of the neutron star, a small fraction of them is absorbed in the surrounding gas. This heating causes violent motions of the gas, similar to those in a pot of boiling water. When the bubbling of the gas becomes sufficiently powerful, the supernova explosion sets in as if the lid of the pot was blown off. The outer layers of the dying star are then expelled into circumstellar space, and with them all the chemical elements that the star has assembled by nuclear burning during its life. But also new elements are created in the hot ejecta of the explosion, among them radioactive species such as titanium (⁴⁴Ti with 22 protons and 22 neutrons) and nickel (⁵⁶Ni with 28 neutrons and protons each), which decay to stable calcium and iron, respectively. The radioactive energy thus released makes the supernova shine bright for many years. ...

Production and Distribution of ⁴⁴Ti and ⁵⁶Ni in a Three-
Dimensional Supernova Model Resembling Cassiopeia A - A. Wongwathanarat et al

• Astrophysical Journal 842(1):13 (2017 Jun 10) DOI: 10.3847/1538-4357/aa72de
  arXiv.org > astro-ph > arXiv:1610.05643 > 14 Oct 2016 (v1), 13 Jun 2017 (v3)

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Writing for Business by Ivy Wigmore

• A fraction is or a fraction are?

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Although fraction is singular, it’s referring to multiple initiatives so,
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[BDanielMayfield]

Massive stars end their lives in gigantic explosions, so-called supernovae. Within [Over ?] millions of years of stable evolution, these stars have built up a central core composed of mostly iron. When the core reaches about 1.5 times the mass of the Sun, it collapses under the influence of its own gravity and forms a neutron star. Enormous amounts of energy are released in this catastrophic event, mostly by the emission of neutrinos. These nearly massless elementary particles are abundantly produced in the interior of the new-born neutron star, where the density is higher than in atomic nuclei and the temperature can reach 500 billion degrees Kelvin.

The physical processes that trigger and drive the explosion have been an unsolved puzzle for more than 50 years. One of the theoretical mechanisms proposed invokes the neutrinos, because they carry away more than [one, two ...?] hundred times the energy needed for a typical supernova. As the neutrinos leak out from the hot interior of the neutron star, a small fraction of them is [are] absorbed in the surrounding gas. This heating causes violent motions of the gas, similar to those in a pot of boiling water. When the bubbling of the gas becomes sufficiently powerful, the supernova explosion sets in as if the lid of the pot was blown off. The outer layers of the dying star are then expelled into circumstellar space, and with them all the chemical elements that the star has assembled by nuclear burning during its life. But also new elements are created in the hot ejecta of the explosion, among them radioactive species such as titanium (⁴⁴Ti with 22 protons and 22 neutrons) and nickel (⁵⁶Ni with 28 neutrons and protons each), which decay to stable calcium and iron, respectively. The radioactive energy thus released makes the supernova shine bright for many years. ...

How Big would a supernova be if all the neutrinos were absorbed?