The seven hour explosion nobody could explain | Hacker News Reader

The seven hour explosion nobody could explain

phys.org

83 pointsmellosouls14 comments

The paper on which the article is based,

https://watermark02.silverchair.com/stag328.pdf?token=AQECAH...

mentions 3 three alternative interpretations for GRB 250702B:

1. Ultralong Collapsars: These stellar-engine models can explain long durations but struggle to account for the specific timing of this event. Specifically, they cannot easily produce a 12-hour gradual rise in X-rays followed by a multi-hour peak, as the jet would have to fight through a massive progenitor star while its power is still very low.

2. White Dwarf (WD) Tidal Disruptions: While an Intermediate Mass Black Hole (IMBH) disrupting a White Dwarf could theoretically provide the necessary gravity, the numbers do not add up for this specific burst. The timing between flares is too long for a WD scenario, and the total energy required would demand an unrealistically narrow jet. When physical constraints like detonation are factored in, this model is considered highly unlikely.

3. Micro-TDEs (Main Sequence star by a stellar-mass BH/NS): This is considered a competitive alternative that can explain the burst's sub-second variability and long duration. However, it faces two main issues: current afterglow data suggests the surrounding gas density matches an IMBH environment better than a micro-TDE environment, and the burst’s extreme energy would require very high jet efficiency or a very narrow beam.

If this were a scifi horror story, it would be that there was a high energy event so far away and so long ago that the protracted duration is due to red-shift. Those X-rays were actually unimaginably higher energy particles and the duration of the event was also brief but has gotten smeared over time by inflation.

That's actually not possible due to something called the GZK cutoff. Which is a weird phenomena that causes apparently empty space to turn somewhat cloudy for sufficiently high energy photons. Here is how it works.

If an electron and a positron meet, they turn into two very high energy photons.

Because physics is time reversible, if two high energy photons meet, they have a chance to turn into an electron-positron pair.

If an extremely high energy photon meets a low energy one, there is a moving reference frame in which they have the same energy, and are both high energy. Therefore they have a chance to turn into an electron-positron pair whose center of mass is in that reference frame.

The result is that if a photon is above something like 10^15 eV in energy, it can annihilate itself against any photon in the cosmic microwave background radiation (CMBR). There are lots of photons in the CMBR. Those collisions are sufficiently likely that such photons essentially cannot travel intergalactic distances.

If you go back to the early universe, the CMBR was much denser than it is today. Making the distance that such photons could reasonably travel even shorter then than it is today.

That said, no good storyteller should let inconvenient physical fact keep them from writing a good story.

Does that interaction cascade such that space is effectively even more opaque as the flux increases? Or could we inlist an even more unimaginable flux of high energy photons to clear the path and allow the observed x-rays to come out the other end of the very long path..?

My understanding is that it doesn't. Though if the energy gets high enough, you can start to get other particles out.

As for protecting one photon with a sheathe of other photons, the energy density required for that tube is absolutely insane. We're talking photons spaced the width of a proton apart, with very high energy. Even assuming that it could be assembled, the gravity from the leading edge of the tube is going to do "interesting things" to the rest of the tube. Maybe even black hole levels of interesting...

Source-paper (and nothing to do with this clickbait): [A milli-tidal disruption event model for GRB 250702B: main-sequence star disrupted by an IMBH](https://academic.oup.com/mnras/article/547/1/stag328/8488781)

Open & accessible

The article suggests that the event occurred in a different galaxy, but does not indicate which one, or how far away it is from us. Anyone know?

tldr: it was the office microwave.

(just kidding - probably a black hole)

You're referring to [1] which is certainly a fun (and instructive) story. But FRBs are pretty much the exact opposite to seven-hour events.

[1] https://www.nature.com/nature-index/news/its-the-microwave-h...

A black hole is, but what if something big fell into it?

3I/ATLAS first detected on: July 1 2025

Gamma ray burst that kept going for seven hours, fired three distinct bursts spread across an entire day: July 2 2025

just saying

This event originated in a different galaxy.

Obviously this was the distant alien civilization remotely beaming power to the probe they sent to our solar system :)

Thanks Avi, very cool!

Reply on news.ycombinator.com