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Thread: Is life on a planet in an AGN jet possible?

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    Is life on a planet in an AGN jet possible?

    Many Active Galactic Nuclei (AGNs) have back-to-back jets, of highly relativistic particles. For some, these extend tens even hundreds of thousands of pc, as seen in the "double lobe" structures so common in the radio. And some jets are also visible in the optical and x-ray, e.g. M87.

    The jets may also play an important role in the formation of EELRs (Extended Emission Line Regions), a.k.a. voorwerpjes (named after the archetype, Hanny's Voorwerp).

    Suppose a star with a planetary system which includes an Earth-like planet in its Goldilocks zone finds itself in one of these jets.

    Would the jet sterilize the planet? Either "immediately" (i.e. within days/weeks), or "after a delay" (e.g. by causing the atmosphere to be removed or dramatically changed).

    Yes, if such a planet were within a dozen, or even a few hundred pc, of an AGN, chances are life would be tough, with or without being hosed by a jet. But what about much further out? Say ~10 kpc?

    Of course, our own Earth is hit by downstream jets ... every BL Lac object is us "looking down the barrel" of such a jet (though all such jets terminate a very long way from us, perhaps as much as an Mpc from their host AGNs). And it's possible that some of the UHECRs (ultra high energy cosmic rays) we detect come from such jets; ditto some of the PeV neutrinos IceCube has detected.

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    Not that it would help me to answer the question, but I'm curious: is there an objective definition of "sterilize"? I mean, I would assume that science has a pretty good idea of what would be fatal for our kind of planet and life, but how universally applicable is that?
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    A recent paper suggesting that living around an AGN is a bad thing because the radiation will cause the planet to lose its atmosphere and maybe more.

    https://arxiv.org/abs/1902.07950

    Comparative analysis of the influence of Sgr A* and nearby active galactic nuclei on the mass loss of known exoplanets

    Agata M. Wisłocka, Andjelka B. Kovačević, Amedeo Balbi (Submitted on 21 Feb 2019)

    The detailed evolution of exoplanetary atmospheres has been the subject of decade-long studies. Only recently, investigations began on the possible atmospheric mass loss caused by the activity of galactic central engines. This question has so far been explored without using available exoplanet data. The goal of this paper is to improve our knowledge of the erosion of exoplanetary atmospheres through radiation from supermassive black holes (SMBHs) undergoing an active galactic nucleus (AGN) phase. To this end, we extended the well-known energy-limited mass-loss model to include the case of radiation from AGNs. We set the fraction of incident power ϵ available to heat the atmosphere as either constant (ϵ=0.1 ) or flux dependent (ϵ=ϵ(F XUV ) ). We calculated the possible atmospheric mass loss for 54 known exoplanets (of which 16 are hot Jupiters residing in the Galactic bulge and 38 are Earth-like planets (EPs)) due to radiation from the Milky Way's (MW) central SMBH, Sagittarius A* (Sgr A*), and from a set of 107,220 AGNs generated using the 33,350 AGNs at z<0.5 of the Sloan Digital Sky Survey database. We found that planets in the Galactic bulge might have lost up to several Earth atmospheres in mass during the AGN phase of Sgr A*, while the EPs are at a safe distance from Sgr A* (>7 kpc) and have not undergone any atmospheric erosion in their lifetimes. We also found that the MW EPs might experience a mass loss up to ∼15 times the Mars atmosphere over a period of 50 Myr as the result of exposure to the cumulative extreme-UV flux F XUV from the AGNs up to z=0.5 . In both cases we found that an incorrect choice of ϵ can lead to significant mass loss overestimates.
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    Quote Originally Posted by slang View Post
    Not that it would help me to answer the question, but I'm curious: is there an objective definition of "sterilize"? I mean, I would assume that science has a pretty good idea of what would be fatal for our kind of planet and life, but how universally applicable is that?
    Excellent question!

    And I think it gets more complicated when you consider the difference between life getting started and live being extinguished.

    For example, we now know that there are bacteria (and archaea?) living quite comfortably several km below the surface, in "rocks". Some survive on "food" which trickles down from the surface, ..., and some lives entirely "off the land" (yes, an awful joke) by "eating rock". But could life get started deep underground? Perhaps there's still life deep underground on Mars?

    So, could deep life survive a planet losing its atmosphere (or nearly so)? Maybe. How about losing its water? Maybe not (especially if it also gets very hot, say >500K).

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    Quote Originally Posted by Roger E. Moore View Post
    A recent paper suggesting that living around an AGN is a bad thing because the radiation will cause the planet to lose its atmosphere and maybe more.

    https://arxiv.org/abs/1902.07950

    Comparative analysis of the influence of Sgr A* and nearby active galactic nuclei on the mass loss of known exoplanets

    Agata M. Wisłocka, Andjelka B. Kovačević, Amedeo Balbi (Submitted on 21 Feb 2019)

    The detailed evolution of exoplanetary atmospheres has been the subject of decade-long studies. Only recently, investigations began on the possible atmospheric mass loss caused by the activity of galactic central engines. This question has so far been explored without using available exoplanet data. The goal of this paper is to improve our knowledge of the erosion of exoplanetary atmospheres through radiation from supermassive black holes (SMBHs) undergoing an active galactic nucleus (AGN) phase. To this end, we extended the well-known energy-limited mass-loss model to include the case of radiation from AGNs. We set the fraction of incident power ϵ available to heat the atmosphere as either constant (ϵ=0.1 ) or flux dependent (ϵ=ϵ(F XUV ) ). We calculated the possible atmospheric mass loss for 54 known exoplanets (of which 16 are hot Jupiters residing in the Galactic bulge and 38 are Earth-like planets (EPs)) due to radiation from the Milky Way's (MW) central SMBH, Sagittarius A* (Sgr A*), and from a set of 107,220 AGNs generated using the 33,350 AGNs at z<0.5 of the Sloan Digital Sky Survey database. We found that planets in the Galactic bulge might have lost up to several Earth atmospheres in mass during the AGN phase of Sgr A*, while the EPs are at a safe distance from Sgr A* (>7 kpc) and have not undergone any atmospheric erosion in their lifetimes. We also found that the MW EPs might experience a mass loss up to ∼15 times the Mars atmosphere over a period of 50 Myr as the result of exposure to the cumulative extreme-UV flux F XUV from the AGNs up to z=0.5 . In both cases we found that an incorrect choice of ϵ can lead to significant mass loss overestimates.
    Very cool, thanks for posting this!

    By "radiation" the authors seem to be limited to "electromagnetic radiation" (specifically XUV), and it seems that living near an AGN is not healthy for children and other forms of life.

    Looking at AGN jets: every now and then the Sun blasts us with what is somewhat like an incredibly mild form of an AGN jet (in the form of solar flares). Our atmosphere suffers only a tiny bit. Unlike that of Mars (but why is Venus' atmosphere not eroded?).

    What if we were hit by a solar flare, only continuously? What if the solar flare were a million times more intense? What if the particle energies were not limited to mere MeV, but included TeV or even PeV ones? Yes, our magnetic field would offer some relief, but higher energy particles would laugh at it, right?

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    Quote Originally Posted by Jean Tate View Post
    What if we were hit by a solar flare, only continuously? What if the solar flare were a million times more intense? What if the particle energies were not limited to mere MeV, but included TeV or even PeV ones? Yes, our magnetic field would offer some relief, but higher energy particles would laugh at it, right?
    I looked this up a few years ago because I was creating a webpage showing what would happen to the solar system if a nearby white dwarf blew up as a Type I Supernova. It appeared to be the consensus from my sources (science papers) that the atmosphere would become less effective as the radiation barrage went on. Eventually, life would be wiped out because of the muon rain from cosmic rays.

    Here is the link to the (extinct but Wayback saved) webpage. It's not all that great, but the references are legit.

    https://web.archive.org/web/20131118...iningstar.html
    Last edited by Roger E. Moore; 2019-Mar-20 at 10:41 PM.
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    Quote Originally Posted by Roger E. Moore View Post
    I looked this up a few years ago because I was creating a webpage showing what would happen to the solar system if a nearby white dwarf blew up as a Type I Supernova. It appeared to be the consensus from my sources (science papers) that the atmosphere would become less effective as the radiation barrage went on. Eventually, life would be wiped out because of the muon rain from cosmic rays.

    Here is the link to the (extinct but Wayback saved) webpage. It's not all that great, but the references are legit.

    https://web.archive.org/web/20131118...iningstar.html
    Roger, can you substantiate the gamma radiation dose at the surface?

    It does not add up to me.

    The atmosphere is equivalent mass to 11 metres of water. Why would another 6 inches make any difference either way?

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    Cool material, Roger!

    SNe, and GRB, are covered in Phil Plait’s Death from the Skies. I no longer have a copy, so can’t do a compare and contrast.

    GRBs are deadly, out to several kpc; however, they are brief, so the dark side gets to repopulate the newly sterilized one (repopulation from deep life would be very slow). There’s a delayed sterilizer for SNe, particle radiation. For AGN jets this will surely the more deadly, if it lasts long enough. IIRC, typical AGN duty cycles are ~10,000 years ... long enough to erode an Earthly atmosphere, even at a distance of 100kpc, say? Of course, relative motion of a jet and a planet may reduce exposure to much less than 10k years ...

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    Quote Originally Posted by kzb View Post
    Roger, can you substantiate the gamma radiation dose at the surface? It does not add up to me. The atmosphere is equivalent mass to 11 metres of water. Why would another 6 inches make any difference either way?
    Here is one of my sources.

    https://web.archive.org/web/20131118...rs/snrisks.txt

    The real problem are muons, though.

    The webpage I created, what survives of it, was a shot at trying something that had not been done before: creating a science-based SF background for use with any sort of storytelling. The difference between it and anything like it was to be as authentic and accurate as possible in describing the effects, citing sources as often as possible. I linked to the sources, some of which have (of course) vanished or moved online. About half the links are still active, I think. Try them and see.


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    Last edited by Roger E. Moore; 2019-Mar-21 at 04:46 PM.
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    Quote Originally Posted by Roger E. Moore View Post
    Here is one of my sources.

    https://web.archive.org/web/20131118...rs/snrisks.txt

    The real problem are muons, though.

    The webpage I created, what survives of it, was a shot at trying something that had not been done before: creating a science-based SF background for use with any sort of storytelling. The difference between it and anything like it was to be as authentic and accurate as possible in describing the effects, citing sources as often as possible. I linked to the sources, some of which have (of course) vanished or moved online. About half the links are still active, I think. Try them and see.


    .
    Hi roger, I've looked at the link you gave (none of the others yet).

    The problem is he is looking at it from the perspective of multiples of the solar flux, but with no idea of what that means to us here on the Earth's surface.

    I suspect that the shielding of Earth's atmosphere, same mass per unit area as 3 feet of lead, helps us with X-ray and gamma dose rates very considerably.

    The lethality is not from direct radiation, it is from the supposed destruction of the ozone layer, which in turn lets in UV from the sun. So it would be the sun that killed us, not the gamma rays themselves.

    The UV kills off the plants and phytoplankton, so the base of the foodchain is gone. Animals then die from starvation not gamma radiation.

    On to the muons, which are a bit of an unknown to me. However I found this:

    https://arxiv.org/abs/1712.09367

    This paper estimates a muon dose rate of 1Sv per 30 years at the earth's surface, for a supernova at 50pc. This wouldn't be good for health but neither will it cause mass extinctions.

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    As I understood it, the shielding of the atmosphere became useless when cosmic rays created muons in the upper air. I pulled two references from the "Shining Star" page, below, which told me that the muon rain would last for years and would likely kill all life on Earth.

    http://www.nasa.gov/centers/goddard/...supernova.html
    "These results will appear in the Astrophysical Journal 2003, March 10, vol. 585. Co-authors include Barbara Mattson of NASA Goddard (via L3 Com Analytics Corporation) and Wan Chen of Sprint IP Design in Reston, Virginia." (Have not yet looked this paper up.)

    "The new calculations -- based on the NASA Goddard two-dimensional photochemical transport model -- show that a supernova within 26 light years from Earth could wipe out 47 percent of the ozone layer, allowing approximately twice the amount of cancer-causing ultraviolet radiation to reach the Earth's surface. Excessive UV radiation is harmful to both plants and animals, thus a doubling of UV levels would be a significant problem to life on Earth.

    "The gamma-ray irradiation would last 300 to 500 days. The ozone layer would then repair itself, but only to endure cosmic-ray bombardment shortly after, lasting at least 10 years. (Cosmic rays are electrically charged particles whose paths are influenced by magnetic fields, and the extent of such fields in the interstellar medium is not well understood.)

    "The calculations simultaneously point to the resilience of the ozone layer as well as its fragility in a violent Universe, said Dr. Claude Laird of the University of Kansas, who developed the gamma-ray and cosmic ray input code and performed the atmospheric model simulations. Although the ozone layer should recover relatively rapidly once the particle influx tapers off -- within about one to two years, the Goddard models show -- even this short period of time is sufficient to cause significant and lasting damage to the biosphere.

    "The atmosphere usually protects us from gamma rays, cosmic rays, and ultraviolet radiation, but there's only so much hammering it can take before Earth's biological defenses break down," he said.

    ===

    http://galileoandeinstein.physics.vi.../srelwhat.html (near bottom)
    Explains why short-lived muons can reach the Earth's surface en masse. Muons go through anything but can damage DNA.

    I would agree it would not be the gamma rays directly, but indirectly yes because of the damage to the atmosphere in producing poisonous nitrogen compounds.
    Last edited by Roger E. Moore; 2019-Mar-21 at 07:02 PM.
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    Quote Originally Posted by kzb View Post
    However I found this:

    https://arxiv.org/abs/1712.09367
    I have not seen this report before, but then I stopped updating the "Shining Star" webpage in 2010. Thank you for finding that. Let's see...

    "We note that muons will dominate the dose at the ground and the ocean (O'Brien et al., 1998; Simonsen et al., 2000; UNSCEAR Report, 1996). They produce the largest ionizing dose of any secondary component from cosmic rays (Marinho et al., 2014) and this effect will increase with depth in the ocean. Therefore it is appropriate to focus on the muon dose....

    "Figure 2 shows the values obtained for annual dose as function of depth. The solid black line without markers shows the typical annual dose at the present time. The dose from muons in the ocean exceeds the present dose for 10 kyr with open boundary conditions on the cosmic rays from the SN. It even exceeds the average dose from all sources at the Earth’s surface for up to 1 kyr depending on depth—for depths from 100 m to 1 km. Again, with the CR confining boundary of the Local Bubble, the dose can be expected to last longer....

    "There will also be a differential effect based on the size of organisms. Again, most natural radiation is not penetrating, and will constitute a surface effect. Muon irradiation will effectively penetrate any organisms, and so constitute a volume effect. Larger organisms are largely self-shielded from most external natural radiation sources, but not from muons. The larger the organism, the larger will be the relative increase in radiation dose...."

    I highlighted in bold the section that caught my attention the most. I am not sure I get the exact meaning, but the paper's authors appear to be saying that the muon radiation dose will be enormous. Anyone please correct me if I got that wrong, it's a little tricky to get.

    And shockwaves...

    One of the other points made in the "Shining Star" page was that there was not ONE major radiation event from a nearby supernova, but SEVERAL. The initial radiation burst is followed by a shower of cosmic rays, which travel a little slower than the speed of light. Following that extended blast come even more body slams as the shockwave from the supernova arrives. I will have to check the page again, but I believe there will be a forward shock of cosmic radiation from the blast wave's front, then a reverse shock of radiation as the shockwave passes. We get hit over and over for many decades, one muon rain after the other.


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    Last edited by Roger E. Moore; 2019-Mar-21 at 08:08 PM.
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    Three other sources for cosmic rays from supernova shockwaves.

    https://web.archive.org/web/20110830...omy/34782.html
    Tycho's Remnant Provides Shocking Evidence for Cosmic Rays (using Wayback Machine as original link is dead)

    http://adsabs.harvard.edu/abs/2005ApJ...634..376W
    Cosmic-Ray Acceleration at the Forward Shock in Tycho's Supernova Remnant: Evidence from Chandra X-Ray Observations

    http://cdsads.u-strasbg.fr/abs/2010ApJ...708..965Z
    Nonthermal Radiation of Young Supernova Remnants: The Case of RX J1713.7-3946


    .
    Last edited by Roger E. Moore; 2019-Mar-21 at 08:06 PM. Reason: added wayback machine link
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    Going back to the original question, "Is life on a planet in an AGN jet possible?"

    No.
    There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
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    Quote Originally Posted by Roger E. Moore View Post
    I

    "We note that muons will dominate the dose at the ground and the ocean (O'Brien et al., 1998; Simonsen et al., 2000; UNSCEAR Report, 1996). They produce the largest ionizing dose of any secondary component from cosmic rays (Marinho et al., 2014) and this effect will increase with depth in the ocean. Therefore it is appropriate to focus on the muon dose....

    "Figure 2 shows the values obtained for annual dose as function of depth. The solid black line without markers shows the typical annual dose at the present time. The dose from muons in the ocean exceeds the present dose for 10 kyr with open boundary conditions on the cosmic rays from the SN. It even exceeds the average dose from all sources at the Earth’s surface for up to 1 kyr depending on depth—for depths from 100 m to 1 km. Again, with the CR confining boundary of the Local Bubble, the dose can be expected to last longer....

    I highlighted in bold the section that caught my attention the most. I am not sure I get the exact meaning, but the paper's authors appear to be saying that the muon radiation dose will be enormous. Anyone please correct me if I got that wrong, it's a little tricky to get.

    .
    It doesn't mean the muon dose will be enormous. It is saying it is many times the current rate. If you look at Figure 2, the very maximum dose rate at 1 metre depth is about 25 mSv per year if I have interpreted the scale correctly.

    This is about the occupational exposure limit for radiation workers. It won't cause a mass die-off. In fact it is pretty trivial, because lower life forms are more resistant to radiation than humans, plus in the natural world few organisms live long enough to get cancer.

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    Quote Originally Posted by Roger E. Moore View Post
    A recent paper suggesting that living around an AGN is a bad thing because the radiation will cause the planet to lose its atmosphere and maybe more.

    https://arxiv.org/abs/1902.07950

    Comparative analysis of the influence of Sgr A* and nearby active galactic nuclei on the mass loss of known exoplanets

    Agata M. Wisłocka, Andjelka B. Kovačević, Amedeo Balbi (Submitted on 21 Feb 2019)
    From Section 5.1 of this paper:

    Previous studies, for example, Forbes & Loeb (2018), concluded
    that terrestrial planets at distances greater than  0:1 kpc
    from Sgr A* are not likely to be a ected with significant mass
    loss during the active phase of Sgr A*. Balbi & Tombesi (2017)
    estimated the cap at  1 kpc, with mass loss comparable to that
    of Earth’s current atmosphere at distances d  0:5 kpc.



    In other words these previous studies find the atmosphere loss becomes insignificant at distances more than 0.1 to 1 kpc from an AGN.

    This is no loss because we already know there will be few habitable planets within this radius of the galaxy centre. The stellar density is enough to destabilise Earth-like planetary orbits in this region.

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    Sadly I will have to leave off commentary for now, cannot find anything new to add to the discussion. This has been awesome fun, thank you!

    Still don't think you can have habitable planets near an AGN jet, though.
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    Here’s one reason why looking at particle radiation from SNe may not be all that helpful: the energy spectrum.

    Galactic comic rays have a well-defined energy spectrum (and composition), one that is - AFAIK - consistent with production by SNe and entrapment by galactic magnetic fields, up to the ankle. Being in a starburst galaxy would mean the energy curve would get shifted upward (and the composition remain ~the same). But I think an AGN jet could have a very different energy spectrum (and composition?); specifically, far more EeV particles.

    Perhaps this makes little difference? A planetary atmosphere would be eroded, in a geologically short time, in either scenario, no matter how the large surface reservoirs (e.g. oceans, icesheets)?

    Then there’s the gammas: AGN jets are accompanied by lots of gamma radiation, likely of energies of PeV and more, unlike that from SNe, or even GRBs. Will surely speed atmosphere erosion, and directly or indirectly, be lethal to life on (and just below) the surface.

    So I’m coming round to thinking that deep life would survive, at least until the atmosphere were gone.

    Or not: if life could survive in sub-surface oceans (e.g. Europa, Titan), could it survive an AGN jet (leave aside the question of whether life could arise in such an environment)?

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    Quote Originally Posted by Jean Tate View Post
    Here’s one reason why looking at particle radiation from SNe may not be all that helpful: the energy spectrum.

    Galactic comic rays have a well-defined energy spectrum (and composition), one that is - AFAIK - consistent with production by SNe and entrapment by galactic magnetic fields, up to the ankle. Being in a starburst galaxy would mean the energy curve would get shifted upward (and the composition remain ~the same). But I think an AGN jet could have a very different energy spectrum (and composition?); specifically, far more EeV particles.

    Perhaps this makes little difference? A planetary atmosphere would be eroded, in a geologically short time, in either scenario, no matter how the large surface reservoirs (e.g. oceans, icesheets)?
    An AGN jet might be even shorter-lived in its impact, either because of the duration of AGN "on" episodes (hobbyhorse alert!) or because
    of precession of the jet direction - or indeed, near the AGN, orbital motion of the star. Distance to the AGN will also matter due to jet width - in some distance ranges at least, AGN jets are narrow cones (sometimes becoming more cylindrical, probably as the magnetic-field geometry changes).

    Then there’s the gammas: AGN jets are accompanied by lots of gamma radiation, likely of energies of PeV and more, unlike that from SNe, or even GRBs. Will surely speed atmosphere erosion, and directly or indirectly, be lethal to life on (and just below) the surface.
    To the extent that what we observe from BL Lacertae objects represents what happens along the jet, indeed everything up to X-rays has a component that gets boosted by scattering with the relativistic-particle content up to really hard gamma rays, going way up into TeVs.
    This plot is scaled to energy per decade, showing that the upward-boosted component has comparable energy in gamma rays (and of course the energy per photon is vastly higher). Similarly to assessing the impact of a GRB on an atmosphere (or indeed the ISM), the ionization impact of one of these is rich, complex, and I'm sure I do not yet have an adequate handle on it.

    Up to how well we can estimate the magnetic fields, the unscattered photon spectrum tells us about the particles - for example, optical radiation from the jet of M87 comes mainly from electrons with relativistic gamma values near 106. The associated X-rays must come from particles with energy ~10,000x times greater.
    Attached Images Attached Images

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    Quote Originally Posted by ngc3314 View Post
    An AGN jet might be even shorter-lived in its impact, either because of the duration of AGN "on" episodes (hobbyhorse alert!) or because
    of precession of the jet direction - or indeed, near the AGN, orbital motion of the star. Distance to the AGN will also matter due to jet width - in some distance ranges at least, AGN jets are narrow cones (sometimes becoming more cylindrical, probably as the magnetic-field geometry changes).



    To the extent that what we observe from BL Lacertae objects represents what happens along the jet, indeed everything up to X-rays has a component that gets boosted by scattering with the relativistic-particle content up to really hard gamma rays, going way up into TeVs.
    This plot is scaled to energy per decade, showing that the upward-boosted component has comparable energy in gamma rays (and of course the energy per photon is vastly higher). Similarly to assessing the impact of a GRB on an atmosphere (or indeed the ISM), the ionization impact of one of these is rich, complex, and I'm sure I do not yet have an adequate handle on it.

    Up to how well we can estimate the magnetic fields, the unscattered photon spectrum tells us about the particles - for example, optical radiation from the jet of M87 comes mainly from electrons with relativistic gamma values near 106. The associated X-rays must come from particles with energy ~10,000x times greater.

    On your linked article, it tells us the TeV gammas interact with the upper atmosphere. in other words they do not penetrate to ground level. The interaction cross section must start to increase with energy at some point.

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    Guess what? A new paper on this very topic is here. And the paper says I am wrong.

    https://arxiv.org/abs/1903.09768

    Active Galactic Nuclei: Boon or Bane for Biota?

    Manasvi Lingam, Idan Ginsburg, Shmuel Bialy (Submitted on 23 Mar 2019)

    Active Galactic Nuclei (AGNs) emit substantial fluxes of high-energy electromagnetic radiation, and have therefore attracted some recent attention for their negative impacts on galactic habitability. In this paper, we propose that AGNs may also engender the following beneficial effects: (i) prebiotic synthesis of biomolecular building blocks mediated by ultraviolet (UV) radiation, and (ii) powering photosynthesis on certain free-floating planets and moons. We also reassess the harmful biological impact of UV radiation originating from AGNs, and find that their significance could have been overestimated. Our calculations suggest that neither the positive nor negative ramifications stemming from a hypothetical AGN in the Milky Way are likely to affect putative biospheres in most of our Galaxy. On the other hand, we find that a sizable fraction of all planetary systems in galaxies with either disproportionately massive black holes (∼10 9−10 M ⊙ ) or high stellar densities (e.g., compact dwarf galaxies) might be susceptible to both the beneficial and detrimental consequences of AGNs, with the former potentially encompassing a greater spatial extent than the latter.
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    Quote Originally Posted by Roger E. Moore View Post
    Guess what? A new paper on this very topic is here. And the paper says I am wrong.

    https://arxiv.org/abs/1903.09768

    Active Galactic Nuclei: Boon or Bane for Biota?

    Manasvi Lingam, Idan Ginsburg, Shmuel Bialy (Submitted on 23 Mar 2019)

    Active Galactic Nuclei (AGNs) emit substantial fluxes of high-energy electromagnetic radiation, and have therefore attracted some recent attention for their negative impacts on galactic habitability. In this paper, we propose that AGNs may also engender the following beneficial effects: (i) prebiotic synthesis of biomolecular building blocks mediated by ultraviolet (UV) radiation, and (ii) powering photosynthesis on certain free-floating planets and moons. We also reassess the harmful biological impact of UV radiation originating from AGNs, and find that their significance could have been overestimated. Our calculations suggest that neither the positive nor negative ramifications stemming from a hypothetical AGN in the Milky Way are likely to affect putative biospheres in most of our Galaxy. On the other hand, we find that a sizable fraction of all planetary systems in galaxies with either disproportionately massive black holes (∼10 9−10 M ⊙ ) or high stellar densities (e.g., compact dwarf galaxies) might be susceptible to both the beneficial and detrimental consequences of AGNs, with the former potentially encompassing a greater spatial extent than the latter.
    Yep that paper concludes we would be safe at 2 pc ! What did I tell you all.

    On the other hand it only seems to look at UV, not gammas and high energy particles.....

  23. #23
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    My trouble is that I can't help talking about things I know little about. I should stick to posting news, but... eh, being wrong isn't so bad, sometimes. You learn a lot.
    There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
    — Mark Twain, Life on the Mississippi (1883)

  24. #24
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    This seems to best go here. Made a couple of minor editorial changes by separating some abutted words.

    https://arxiv.org/abs/1903.12338

    High-Energy Photon and Particle Effects on Exoplanet Atmospheres and Habitability

    Jeremy J. Drake, et al. (Submitted on 29 Mar 2019)

    It is now recognized that energetic stellar photon and particle radiation evaporates and erodes planetary atmospheres and controls upper atmospheric chemistry. Key exoplanet host stars will be too faint at X-ray wavelengths for accurate characterization using existing generation and future slated X-ray telescopes. Observation of stellar coronal mass ejections and winds are also beyond current instrumentation. In line with the Committee on an Exoplanet Science Strategy recognition that holistic observational approaches are needed, we point out here that a full understanding of exoplanet atmospheres, their evolution and determination of habitability requires a powerful high-resolution X-ray imaging and spectroscopic observatory. This is the only capability that can: (1) characterize by proxy the crucial, difficult to observe, EUV stellar flux, its history and its variations for planet hosting stars; (2) observe the stellar wind; (3) detect the subtle Doppler signatures of coronal mass ejections.
    There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
    — Mark Twain, Life on the Mississippi (1883)

  25. #25
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    And another one that sounds like it belongs in this thread more than any other, replacing stellar radiation with AGN radiation.

    https://arxiv.org/abs/1904.01063

    Extreme hydrodynamic losses of Earth-like atmospheres in the habitable zones of very active stars

    C. P. Johnstone, M. L. Khodachenko, T. Lüftinger, K. G. Kislyakova, H. Lammer, M. Güdel (Submitted on 1 Apr 2019)

    In this letter, we calculate for the first time the full transonic hydrodynamic escape of an Earth-like atmosphere. We consider the case of an Earth-mass planet with an atmospheric composition identical to that of the current Earth orbiting at 1 AU around a young and very active solar mass star. To model the upper atmosphere, we used the Kompot Code, which is a first-principles model that calculates the physical structures of the upper atmospheres of planets, taking into account hydrodynamics and the main chemical and thermal processes taking place in the upper atmosphere of a planet. This model enabled us to calculate the 1D vertical structure of the atmosphere using as input the high-energy spectrum of a young and active Sun. The atmosphere has the form of a transonic hydrodynamic Parker wind, which has an outflow velocity at the upper boundary of our computational domain that exceeds the escape velocity. The outflowing gas is dominated by atomic nitrogen and oxygen and their ion equivalents and has a maximum ionization fraction of 20%. The mass outflow rate is found to be 1.8x10^9 g s^-1, which would erode the modern Earth's atmosphere in less than 0.1 Myr. This extreme mass loss rate suggests that an Earth-like atmosphere cannot form when the planet is orbiting within the habitable zone of a very active star. Instead, such an atmosphere can only form after the activity of the star has decreased to a much lower level. This happened in the early atmosphere of the Earth, which was likely dominated by other gases such as CO2. Since the time it takes for the activity of a star to decay is highly dependent on its mass, this is important for understanding possible formation timescales for planets orbiting low-mass stars.
    There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
    — Mark Twain, Life on the Mississippi (1883)

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