Jittering jets in stripped-envelope core-collapse supernovae

Introduction to the show: ident: Astrophysics Radio. Generated commentary on the latest astrophysics papers.

Vera: Today's paper: "Jittering jets in stripped-envelope core-collapse supernovae".

Jocelyn: The gist The study finds that all models in the initial mass range of MZAMS = 12M⊙ to MZAMS = 40M⊙, regardless of whether they have hydrogenrich, hydrogen-stripped,

Vera: First, who's behind it and why it matters.

Title and authors: Jocelyn: Moving on to the summary of "Jittering jets in stripped-envelope core-collapse supernovae." This paper really zeroes in on those pre-collapse convective and velocity fluctuations we discussed, specifically in progenitors that have lost most of their hydrogen and helium.

Subrahmanyan: It’s important to remember they are focusing on the stripped-envelope CCSN progenitors because that’s where the physics gets interesting for the JJEM, as earlier studies hadn't fully explored this area.

Vera: The summary is basically reiterating that in all their tested models, regardless of whether they started with a hydrogenrich envelope or an H stripped envelope or a He plus hydrogen stripped envelope, there is at least one significant strong convective zone in the inner core.

Jocelyn: So it’s not just for some specific initial conditions; it’s a general feature across the mass range from MZAMS = 12Msun to MZAMS = 40Msun <ref:2510.02203#pg1>.

Subrahmanyan: That broad coverage is what makes this result relevant for structure formation, because it suggests that core physics in these massive stars is consistently leading toward a specific type of explosion pathway.

Vera: They also emphasize how the lower overall mass in stripped-envelope models leads to lower densities and temperatures in the outer core layers, which results in less complete burning of the Si plus S layers at the onset of collapse.

Jocelyn: And they point out that because these gradients are steeper near the core’s edge, they end up being more prone to convection, which is what drives those fluctuations.

Subrahmanyan: So we have a chain here: stripping leads to different density profiles, which leads to steeper gradients, and that steep gradient triggers the robust inner core convection that feeds the JJEM.

Vera: And they also looked at angular momentum seed perturbations using the specific angular momentum parameter j equals vconv, where r is the radius of the layer and vconv is the convective velocity according to mixing length theory.

Jocelyn: That specific parameter j equals vconv is what they are using to quantify those fluctuations, and they found that in all models except for MZAMS = 40Msun with H plus He removed envelope, there is at least one layer with j greater than or equal to two times ten to the power of fifteen centimeters squared per second inside the mass coordinate that forms a neutron star.

Subrahmanyan: That threshold, that two times ten to the power of fifteen centimeters squared per second, is what they identify as being large enough j(m) for these inner convective zones to facilitate the JJEM.

Vera: They also looked at how this moves things around; in massive envelope-removed stars, the inner convective zones with large enough j equals vconv to facilitate the JJEM tend to move toward lower mass coordinates.

Jocelyn: So as you strip more material, those crucial angular momentum seed perturbations are being pushed into regions closer to where a neutron star forms.

Subrahmanyan: That’s a key result because it shows how the core structure is evolving dynamically in response to the progenitor evolution, which is something we need to keep an eye on for structure formation.

The paper's summary: Vera: Now let’s talk about what this paper suggests as improvements or next steps for the study of "Jittering jets in stripped-envelope core-collapse supernovae." The authors are pointing out several things they think we need to do next.

Jocelyn: They highlight that the current numerical codes can’t resolve the small scale magnetic field reconnection, and they can't simulate the JJEM directly because of that.

Subrahmanyan: That’s a big limitation, because simulating those jets requires resolving very small-scale physics, which is what limits our tools right now for studying the source of angular momentum in intermittent accretion disks.

Vera: So they are essentially saying that simulations for the powering of the explosion and the shaping of the ejecta, like those done by Papish and Soker or Akashi and Soker or Abdikamalov and Beniamini, differ from the tools used to study angular momentum in intermittent accretion disks.

Jocelyn: They suggest that some JJEM studies focus on demonstrating that pre-collapse core convection zones exhibit large fluctuations in both velocity and angular momentum, which are characterized by significant variations in magnitude and direction.

Subrahmanyan: And those fluctuations are amplified by instabilities above the neutron star, for example, Abdikamalov et al. or Kazeroni and Abdikamalov or Buellet et al.

Vera: So the paper points toward needing more sophisticated modeling of those instabilities above the NS to fully amplify these stochastic angular momentum fluctuations before they seed any accretion disks.

Jocelyn: That seems like a logical next step, because if you can model that amplification better, maybe you can start to see those intermittent accretion disks forming.

Subrahmanyan: And if those disks form, then the whole picture of the explosion mechanism shifts toward something more complex than just a simple jet launch.

The paper's improvements: Vera: So to wrap up our discussion on this paper, we’ve established that there is at least one significant strong convective zone in the inner core for all models in the initial mass range of MZAMS = 12Msun to MZAMS = 40Msun, regardless of whether they have hydrogenrich, hydrogen-stripped, or helium plus hydrogen stripped envelopes <ref:2510.02203#pg1,at least one significant strong convective zone in the inner core>.

Jocelyn: And we’ve seen that this convection is robust and it facilitates the JJEM by showing a significant angular momentum parameter j equals vconv greater than or equal to two times ten to the power of fifteen centimeters squared per second inside the mass coordinate that forms a neutron star.

Subrahmanyan: The implication is that according to this study on "Jittering jets in stripped-envelope core-collapse supernovae," there is at least one significant strong convective zone in the inner core for all models, which can facilitate the JJEM.

Vera: This result strengthens the claim that according to the JJEM, there are no failed CCSNe and that all massive stars explode.

Jocelyn: It’s a small step toward showing those intermittent accretion disks might actually forming, even though they don't show them yet in this specific work.

Subrahmanyan: It’s a strong piece of evidence for the JJEM, but it doesn't prove that the intermittent accretion disks are actually forming yet.

Vera: We’ve examined the paper "Jittering jets in stripped-envelope core-collapse supernovae" and found that this robust convection is present and sufficient to seed perturbations for the JJEM.

Jocelyn: That’s a small step in demonstrating the robust convection in the inner core of stripped-envelope CCSN progenitors.

Subrahmanyan: It’s progress in establishing the JJEM as a primary explosion mechanism, but it doesn't show that those intermittent accretion disks actually form yet.

Vera: We have done our part with this paper on "Jittering jets in stripped-envelope core-collapse supernovae."

Conclusion: Vera: So we’ve been looking at "Jittering jets in stripped-envelope core-collapse supernovae," and the main thing here is that they found there’s at least one significant strong convective zone in the inner core for all models, from MZAMS = 12Msun up to MZAMS = 40Msun <ref:2510.02203#pg1,at least one significant strong convective zone in the inner core>.

Jocelyn: Right, so regardless of whether you stripped hydrogen or both hydrogen and helium off these stars, that convection feature is there.

Subrahmanyan: That’s what they found in all models, which is important because it suggests this core physics keeps happening across that whole mass range.

Vera: And they linked that convection to the jittering-jets explosion mechanism by finding a specific angular momentum parameter j equals vconv greater than or equal to two times ten to the power of fifteen centimeters squared per second inside the mass coordinate that forms a neutron star.

Jocelyn: Two times ten to the power of fifteen, that’s what they are using as their threshold for what’s needed to facilitate those jet launches.

Subrahmanyan: That specific number is what they identified as being large enough j(m) for the inner convective zones to facilitate the JJEM.

Vera: They also looked at how this angular momentum moves, and they saw that in massive envelope-removed stars, those inner convective zones with that large j equals vconv tend to move toward lower mass coordinates.

Jocelyn: So as you strip more material off these progenitors, the critical angular momentum seed perturbations are being pushed into regions closer to where a neutron star forms.

Subrahmanyan: That’s a key result because it shows how the core structure is evolving dynamically in response to progenitor evolution, which is something we need to keep an eye on for structure formation.

Vera: The implication for us observing this stuff is that according to the JJEM, there are no failed CCSNe and that all massive stars explode.

Jocelyn: That’s a strong claim based on their findings in "Jittering jets in stripped-envelope core-collapse supernovae."

Subrahmanyan: It’s progress in establishing the JJEM as a primary explosion mechanism, but it doesn't show that those intermittent accretion disks actually form yet.

Vera: They did do examine the timing of the processes, and they found that the Fe/Si interface is accreted about zero point one to zero point three seconds before the Si/O interface in most models.

Jocelyn: So those convective regions, including that Fe/Si interface and Si/O interface, are all accreted before the neutrino-driven mechanism revives the stalled shock.

Subrahmanyan: That’s a crucial comparison for differentiating between two different explosion mechanisms.

Vera: It’s a small step toward showing those intermittent accretion disks might actually forming, even though they don't show them yet in this specific work.

Jocelyn: So it’s a good piece of evidence for the JJEM, but it doesn't show that the intermittent accretion disks are actually forming yet.

Subrahmanyan: We should look at how those instabilities above the neutron star amplify those initial perturbations to see if we can get a better picture of those disks.

Vera: That’s what we’re going to look at next, so keep an eye on that amplification process.