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Can an entire star pass through the event horizon of a black hole unharmed? is a one sentence HNQ with an amazing (to me at least) answer: for supermassive black holes larger than roughly 100 million solar masses (they can get way bigger than that) a star like our Sun can probably pass through the event horizon "unharmed", or at least not tidally disrupted and spaghettified.

@ProfRob's answer there links to Suvi Gezari's April 21, 2021 preprint Tidal Disruption Events which includes the interesting figure shown below, which I am trying to understand.

Question(s):

  1. Does this mean that for the conditions external to all possible triangles (above, below, left and right of the overlapping triangular areas of all start types that one wants to consider) spaghettification is not likely to happen and there is "safe passage" of the star through the event horizon (or the event horizon into the star), otherwise known as being eaten alive as ProfRob points obliquely as:

...suggesting indeed that more massive black holes are able to swallow stars whole.

  1. On the left sides of the triangles, this really suggest that the black hole can "gracefully" enter the star without tidally disrupting it? The star would continue to look like a roughly spherical star, but being eaten alive from within?

Figure 1: Allowable region for the tidal disruption of stars representative of different evolutionary states https://arxiv.org/abs/2104.14580

Figure 1: Allowable region for the tidal disruption of stars representative of different evolutionary states, a 0.6M☉ carbon oxygen white dwarf (CO WD), a 0.17M☉ helium white dwarf (He WD), a 1M☉ main-sequence star (MS), and a 1.4M☉ red giant (RG), bounded by the conditions that Rp < RT, R* < RS, and RT > RS for a TDE to be observable, as a function of black hole mass (MBH) and β is the strength of the tidal encounter (β ≡ RT/Rp). Diagram inspired by Rosswog, Ramirez-Ruiz & Hix (2009).

Rosswog S, Ramirez-Ruiz E, Hix WR. 2009. Astrophys. J. 695:404–419 (open access, and arXiv).

If I'm not mistaken, the variables are:

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  • $\begingroup$ Pretty sure there is disruption in the mass range given by the base of the triangle for each type of star. $\endgroup$
    – ProfRob
    Jun 8, 2021 at 9:39
  • $\begingroup$ @ProfRob Yes, I tried to cover that with "Does this mean that for the conditions external to all possible triangles (above, below, left and right of the overlapping triangular areas of all start types that one wants to consider)..." My meaning was that for a given star type, all possible triangles would span all possible ages and masses and metallicities and rotation rates and anything else. If there's a non-awkward wording to say all that please feel free to edit, I've run out of space words for the day :-) $\endgroup$
    – uhoh
    Jun 8, 2021 at 11:08
  • $\begingroup$ @PM2Ring as I have point out in my question in item 2, on the left sides of the triangle the figure indicates "$R_{star} > R_{Schwarzschild}$, BH enters star" and presumably this would apply to any triangle representing a given star. When outside and to the left of the spaghettification triangle for a given star, I'm asking if the black hole enters gracefully and then starts eating the star from within. $\endgroup$
    – uhoh
    Jun 8, 2021 at 12:04
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    $\begingroup$ Sorry, I misunderstood. I didn't notice that you were talking about small BHs entering larger stars. $\endgroup$
    – PM 2Ring
    Jun 8, 2021 at 12:12
  • $\begingroup$ @PM2Ring it's a cool figure, while it looks deceptively simple it's had me scratching my head for a while trying to get a handle on the story it's telling. $\endgroup$
    – uhoh
    Jun 8, 2021 at 12:16

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