Are AGNs or GRBs a greater danger for life on Earth?

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Discussion Overview

The discussion revolves around the potential dangers posed to life on Earth by gamma-ray bursts (GRBs) from Eta Carina and active galactic nuclei (AGNs) from the black hole at the Galactic center. Participants explore the implications of radiation levels and the calculations involved in assessing these threats.

Discussion Character

  • Homework-related, Technical explanation, Debate/contested

Main Points Raised

  • One participant estimates the danger of Eta Carina as a GRB compared to the Galactic center black hole, suggesting the GRB is more dangerous due to its proximity and energy output.
  • Another participant emphasizes that the danger to Earth depends on the radiation levels reaching it and supports calculations based on source strength and distance.
  • A participant questions the applicability of the inverse-square law for GRBs, prompting a discussion about the nature of radiation from such events.
  • Another participant suggests that the inverse-square law could still apply to both spherical and beamed radiation, raising considerations about relativistic jets.
  • One participant argues that Eta Carina is unlikely to pose a significant threat due to its rotational axis not being aligned with Earth and predicts it will more likely result in a supernova rather than a GRB. They also note that the supermassive black hole (SMBH) poses a remote threat due to a lack of significant material to accrete.

Areas of Agreement / Disagreement

Participants express differing views on the applicability of the inverse-square law to GRBs and the potential threat level of Eta Carina and the SMBH, indicating that multiple competing views remain without a consensus.

Contextual Notes

Some assumptions regarding the alignment of Eta Carina and the nature of its potential explosion are not fully explored, and the discussion includes unresolved considerations about the effects of beamed versus isotropic radiation.

Maitreya
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I've got a small homework question that goes:

Which would be more dangerous and why: Eta Carina exploding as a gamma-ray burst, or
the black hole at the Galactic centre accreting material at the same rate as a typical luminous
Seyfert galaxy?

I have simply estimated the flux from both of them given the average energy output of GRBs and AGNs, and their distance from the Su with inverse square law. Does it make sense that the GRB, closer and slightly more energetic is way more dangerous for life on Earth?
 
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The danger posed to Earth would be based on the radiation levels reaching earth.

Calculating the flux as a function of source strength and distance is the way to go.

Edit: Please refer to cross reference: WR104 Gamma Ray Burst
 
Last edited:
I don't think you can use the inverse-square law for a gamma-ray burst. Think about it for a moment and see if you agree.
 
Are you hinting something regarding the presence of relativistic jets? Doesn't the inverse square law work anyways, both for a spherical radiation and for a beamed one?
 
Not entirely, a beamed jet could be a danger. They appear to be collimated not unlike a laser beam due to intense magnetic fields of the star. It does not, however, appear Eta Carinae is much of a threat. Its rotational axis is not aligned with Earth and is unlikely to become a gamma burster, more likely a garden variety stellar collapse supernova. The SMBH is an even more remote threat. It has no significant 'food' source at present and that is unlikely to change for millions, if not billions of years.
 

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