Rethinking Thorne-Żytkow Object Formation (in Plain English) 

Thorne-Żytkow objects (TŻOs) are theoretical stars that are powered by a neutron star located at the very center. Neutron stars are very small, dense, bright objects composed of closely packed neutrons, and they are left behind after a star dies (specifically, after the star undergoes an explosion called a supernova). Traditional stars like our sun are powered by a chemical process called nuclear fusion, but TŻOs, on the other hand, are powered by the neutron star heating up the stellar material surrounding it, creating a disk called an accretion disk (see diagram below). This accretion disk is what gives the star enough energy to shine. Like I mentioned, TŻOs are theoretical stars and have not yet been observed. My research on this topic consists of changing the initial theoretical model for these objects, and we present a new model called a Thin-Envelope TŻO (or TETŻO, pronounced te-tzō). Specifically, I model an existing X-ray binary system called LMC X-4, which consists of a star and a neutron star, from how it exists today, up until its final fate that is over a million years from now (see diagram below for the full evolution of LMC X-4). Part of this model consists of a simulation I made that allows us to learn about the physical processes that LMC X-4 will experience when the star engulfs its neutron star companion . We find that the effects of the neutron star's accretion disk, along with the angular momentum present from the neutron star's inspiral, would ultimately cause a chain of events that would deviate from how these systems were initially envisioned (for example: the neutron star will likely collapse into a black hole, and the rate at which the accretion disk heats the stellar material will change the overall structure of the star). We call the resulting structure a Thin-Envelope TŻO, because the stellar material is a lot more diffuse, or thin, than before. Additionally, the object will have a shorter lifetime than what was originally theorized. We argue that many other X-ray binaries will evolve into a TETŻO, and not the original TŻO structure that was previously assumed. Additionally, we predict ways that they can be detected today, such as through ultra-long gamma ray bursts emitting as a jet from the black hole, which are some of the most powerful explosions of light known in the universe.

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PS: a commonly asked question is: how on earth (lol) can a black hole exist inside of a star!? The answer in a nutshell: even though the gravitational pull of a black hole is so strong that not even light can escape, this only happens when light and matter cross the black hole's event horizon, which is the point/boundary around a black hole where nothing can escape. The accretion disk (see TETŻO diagram below) exists and orbits outside of this boundary, and has so much energy it creates an outward force that pushes material away from the black hole, and subsequently allows photons to radiate outwards.