Marshmallow Star Near a Black Hole: The Edge of Life and Destruction ✛ ✦

Original: "Bridging Roche Lobe Overflow and micro-TDEs: The Runaway Evolution of Eccentric Mass Transfer in Star-Black Hole Binaries"
· Tian-Shun Chen, Dong Lai
arXiv:2606.04966v1 · 2026-06-03 · CC BY 4.0 · 1 min
Scientists have figured out why some stars, captured in a black hole's embrace, are completely torn apart, while others lose only part of their material and continue circling for decades.

Marshmallow over a campfire: hold it too close — it puffs up and burns; pull it back — it just toasts, losing a bit of crust. That’s how a star like the Sun (made of hydrogen and helium) behaves as it circles a black hole. At the point of closest approach, the hole’s gravity tears gas away. Simulations have revealed a sharp boundary. When the distance falls to about 3.45 critical radii, an avalanche begins. The star loses mass, its outer layers swell, becoming even more vulnerable — and within a few orbits it is destroyed, producing a brilliant flare. At that moment, entropy (a measure of energy dispersal; introduced by Ludwig Boltzmann) grows irreversibly. But if the distance is slightly larger, the mass loss slightly expands the orbit. The star, as if recoiling, pushes itself away from doom. The process becomes slow and prolonged: such pairs can exist for decades. This links two scenarios — quiet feeding of the hole and catastrophic disruption. Predictions will be tested with the help of spectroscopy, photometry, and the James Webb Space Telescope. The ideas of Karl Schwarzschild and Subrahmanyan Chandrasekhar about matter in strong gravity are now being realized in computer models.

The destruction of a star by a black hole is sometimes called 'spaghettification'. In the described simulations, the star not only stretches into a thread but also first puffs up several times, like a marshmallow over a fire.

r_{\rm tide} = R_* \left(\frac{M_{\rm BH}}{M_*}\right)^{1/3}
Characteristic distance inside which the star will inevitably be torn apart.
R_L \approx 0.462 \, r_p \left( \frac{M_*}{M_*+M_{\rm BH}} \right)^{1/3}
The region within which matter is gravitationally bound to the star; when the star overflows this region, gas begins to stream onto the black hole.
Scientists
Subrahmanyan ChandrasekharRoger PenroseStephen HawkingFritz ZwickyJacob BekensteinKarl Schwarzschild
Concepts
mass transfer donor star binary stellar evolution eccentric black hole binary intermediate mass black hole tidal disruption event hills mechanism stellar evolution tidal migration exoplanets around red dwarfs massive star pair instability supernova transit starburst rossby wave asteroid belt helium flash hubble flow brown dwarf desert microquasar