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Proxima Flare Captured at Multiple Wavelengths

I’ve been wanting to explore some of the observing campaigns for the Alpha Centauri system — their approach, design and early results — and we’ll start that early next week. But let’s home in first on an event within that system, a flare from Proxima Centauri that is fully 100 times more powerful than any flare ever detected from our own star. That Proxima was capable of major flares was already known in 2018 when, according to data from the Atacama Large Millimeter Array (ALMA), an earlier flare at millimeter wavelengths (233 GHz) was detected.

It was an interesting moment, captured in a paper on the work in Astrophysical Journal Letters (citation below). Lead author Meredith MacGregor, an assistant professor at the Center for Astrophysics and Space Astronomy (CASA) and Department of Astrophysical and Planetary Sciences (APS) at the University of Colorado Boulder, also found it provocative. “We had never seen an M dwarf flare at millimeter wavelengths before 2018, so it was not known whether there was corresponding emission at other wavelengths,” says the astronomer.

That led MacGregor to initiate a 40 hour observing campaign over the course of several months in 2019, this one involving nine instruments at various wavelengths, both on the ground and in space. The attention quickly paid off. In May of that year, five of the instruments detected a seven-second event, a flare that surged in both ultraviolet wavelengths (Hubble) and millimeter wavelengths (ALMA) and, according to MacGregor, brightened the star by a factor of 14,000 in the ultraviolet. No flare around a star other than the Sun has ever been observed across such a wide range of wavelengths. The effects near Proxima should be egregious. Adds MacGregor:

“Proxima Centauri’s planets are getting hit by something like this not once in a century, but at least once a day, if not several times a day. If there was life on the planet nearest to Proxima Centauri, it would have to look very different than anything on Earth. A human being on this planet would have a bad time.”

Image: Artist’s conception of the violent stellar flare from Proxima Centauri discovered by scientists in 2019 using nine telescopes across the electromagnetic spectrum, including the Atacama Large Millimeter/submillimeter Array (ALMA). Powerful flares eject from Proxima Centauri with regularity, impacting the star’s planets almost daily. Credit: S. Dagnello, NRAO/AUI/NSF.

This was the largest ultraviolet flare ever detected from Proxima, a red dwarf and thus representative of the most common stellar type in the galaxy. It’s widely understood that these are highly active stars, so that protective mechanisms during flare activity would have to evolve for life to survive. Evgenya Shkolnik (Arizona State University) notes the importance of working across wavelengths as we try to understand the nature of UV flaring in this environment:

“This research is a benchmark of how best to study flares from many angles. It reminds me of the old parable about the blind men and an elephant, where different people observe small parts of the elephant and conclude that one part is a snake, another a wall, another a tree. Only when they look at all the angles together, do they finally understand it is an elephant. This multiwavelength flare from Proxima Centauri is our first snapshot of the whole elephant.”

Image: Artist’s conception of a violent stellar flare erupting on neighboring star, Proxima Centauri, from the viewpoint of Proxima Centauri b. The flare is the most powerful ever recorded from the star, and is giving scientists insight into the hunt for life on planets in M dwarf star systems, many of which have unusually lively stars. Credit: S. Dagnello, NRAO/AUI/NSF.

The huge surge in ultraviolet and millimeter radiation marks a kind of activity that could strip planetary atmospheres as well as exposing surface life to dangerous levels of flux. Numerous other flares were detected during the course of the 40 hours of observation, but none so powerful as this. There is conceivably a driver for evolution here as well, with radiation enabling chemical reactions that may eventually become the precursors for life. Untangling these contradictory threads will require continued focus on flare activity and its effects.

From the paper:

Proxima Cen is a unique target given that it hosts a planet in the habitable zone but also produces anomalously powerful flares for its old age. Can a planet truly be habitable in this environment? It is clear that necessary pieces are missing from our current understanding of M dwarf flares in order to answer that question. We expect to learn much more as we synthesize the available data from this project and from future flare campaigns. This paper presents the results from just a few minutes of the available data. Many other flaring events are detected simultaneously across multiple facilities (including ALMA and HST) during the full 40-hour campaign. If the correlation between FUV [far ultraviolet] and millimeter flaring emission holds, there is potential for future all-sky millimeter surveys (e.g., the Atacama Cosmology Telescope, Naess et al. 2020) to be able to provide constraints on the high-energy radiation environment of exoplanet host stars and inform discussion of planetary habitability.

The current paper is MacGregor et al., “Discovery of an Extremely Short Duration Flare from Proxima Centauri Using Millimeter through Far-ultraviolet Observations,” Astrophysical Journal Letters Vol. 911, No. 2 (21 April 2021). Abstract / Preprint. The 2018 paper is MacGregor et al., “Detection of a Millimeter Flare from Proxima Centauri,” Astrophysical Journal Letters Vol. 855 L2 (1 March 2018). Full text.


Comments on this entry are closed.

  • Michael Fidler April 23, 2021, 10:16

    The UV light may have been recorded from reflecting off the three planets in orbit around Proxima Centauri. This depends on where they are in their orbit in relation to the flare and to earth and in the relative percent of illumination as in crescent or gibbous phase, etc. The increase in UV would be around 14 seconds after the flare for planet d and 23 seconds for planet b and around 12 minutes for planet c. Has anyone looked for this increase? It should be polarized and may show at different frequencies besides the ultraviolet wavelengths.

    The other possibility from the flare is a increase in the auroral activity do to magnetic reconnection in the planet’s magnetotail. This would occur later when the CME reaches the planets and should be visible at certain radio frequencies. The geomagnetic storm would cause a major disturbance in the 3 planet’s magnetospheres.

    By coincidence I just finished watching the movie Stowaway, those storms can be brutal! Still hoping life on the terminator of these planets can survive.

    • Alex Tolley April 23, 2021, 13:14

      OT. I just watched stowaway too. From the blurb, I didn’t know if it was like an update of “The Cold Equations”, a rework of Clarke’s SS “Breaking Strain” with the stowaway trying to get rid of the crew to survive, or a more conventional “let’s create O2” story. It was a mix of different ideas that focused on the people, rather than the technology. I thought it was quite good up until the rather sudden ending.

  • Henry Cordova April 23, 2021, 11:08

    Perhaps one of you can summarize for me what we know about flare events on M dwarfs…

    Are these eruptions common to all red dwarfs, or just a fraction of them? If so, what fraction? Does anyone know if these events occur throughout the lifetimes of these stars, or are they limited to some portion of their evolutionary history? How much variation is there in the severity or frequency of these events between stars; within any one star? Are these flares correlated in any way with the star’s mass?

    It appears this sort of outburst would be hazardous to any existing life on a planet of one of these dwarfs, and would certainly be an obstacle to the genesis or evolution of any life there,. What I am trying to assess is the degree to which these events can rule out or maintain the possibility of life, and intelligence, arising in these stars. Although they dominate the stellar population by their sheer numbers, long term stability, slow evolution and long lifetimes, do these flares disqualify them from inclusion in our astrobiology searches?

    I understand these considerations are well understood in the astronomical community, I just wondered if we had sufficient evidence to make worthwhile speculations or draw any conclusions yet.

  • Alex Tolley April 23, 2021, 11:09

    …potential for future all-sky millimeter surveys (…) to be able to provide constraints on the high-energy radiation environment of exoplanet host stars and inform discussion of planetary habitability.

    When we have characterized the conditions of Proximal b as a ground truth data point for models, we might be able to start to answer the question of whether M_dwarfs are good or bad stellar types for life. Does the flaring strip atmospheres and prevent life appearing on the planet, or does the faring aid life formation and where the long life of M_dwarfs encourage life to consistently appear. No doubt the story will prove complex, but evidence of likely conditions will inform us of where abiogenesis is most probable.

    Of course, this says little about colonization by technological civilizations, although if Proxima b has no atmosphere due to flares, then colonization seems unlikely in this case. With such information, we would probably have quickly ruled out the nature of the recent radio signals that appeared could have originated from the Proxima system, rather than speculating about a possible ETI origin.

    • Michael Fidler April 23, 2021, 19:12

      This is why any indication of an increase in the auroral activity on these 3 planets would give some idea as to the magnetic field around them. The Coronal Mass Ejection (CME) from the flare should of reached planet d in less then 1/2 hour and planet b in less then an hour and c in less then a day if they follow how our sun’s CME’s propagate. I would think they may be faster then that because of the M dwarfs lower mass. The question is if the CME’s weather was on the side the planets were on and if the frequencies from the intense auroral activity produced by the CME was being monitored.

  • Andrei April 23, 2021, 15:11

    “…an even like this at least once a day, if not several times a day. A human being on this planet would have a bad time.”
    Funny understatement, a human who is not sitting in a shielded bunker far underground with all kinds of protection would be stone dead. It would in fact be lethal to any life as we know of.
    Superflares do not happen daily though ss the main text might have us think. But a handful of times each year, or perhaps once a month.
    It’s still enough to deplete any ozone layer in a few years. And the UV part of such a flare would then hit anything living like a sledgehammer.
    Now Proxima is a red dwarf that happen to cough a lot in it’s high age. So all hope is not lost for habitable red dwarf planets. For the rare case of one unusually quiet red dwarf, that also got a large moon to prevent the planet from ending up with bound rotation toward the star – a planet might still be habitable. But with those two less likely requirements we should not hope too much of any discovery of such world in the near future.
    They will still not be any prime target for the search for life, even less for possible colonization. At midday the light will be like moonlight on Earth at best, and even if colonized when there will be so many other better choices, the inhabitants would regularly have to run for shelter even when that more quiescent primary have a ‘bad day’.

  • Steve Muise April 23, 2021, 23:54

    “If there was life on the planet nearest to Proxima Centauri, it would have to look very different than anything on Earth.”

    If some form of life can survive these conditions I’m not sure I’d want to run into it in a dark alley…

    • Michael Fidler April 24, 2021, 10:26

      A dark alley may be right or a dark canyon near the terminator of planet b since it is tidally locked. Like the ice at the moons south pole protected from the ravages of the flare and CME. A large magnetic field could be there because the low end mass is 1.17 but high end is 2.75, the latest estimate from; “Estimating Planetary Mass with Deep Learning”, “A mass for Proxima Centauri b found by this method is 1.6.”

      An ocean world for b is still possible and the distant planet c, being a super earth with a mass of 7 times earth could have be very warm ocean world with large deep ocean volcanoes warming it. The image for c from SPHERE is to bright and the current theory is a ring system is causing a brighter image in the infrared but that may be the tropical oceans glowing. We are still learning about our own earth’s undersea volcanoes and the huge amount of energy they unleash in the deep oceans.

      Underwater Volcanoes Generate Enough Energy to Power the Entire US, Study Finds. April 21, 2021


      Rapid heat discharge during deep-sea eruptions generates megaplumes and disperses tephra. Published: 21 April 2021


  • Alex Tolley April 24, 2021, 11:58

    We are still learning about our own earth’s undersea volcanoes and the huge amount of energy they unleash in the deep oceans.

    Underwater Volcanoes Generate Enough Energy to Power the Entire US

    This may sound like a lot, but it makes next to no impact on the temperature of earth’s oceans. How could it – they are not warming due to undersea volcanoes.

    Some numbers:

    The USA generates about 4000 TWh/y electrical energy.
    The USA consumes about 100 quadrillion BTU in primary fuels.

    4000 TWh ~= 3.5E18 calories
    100 quadrillion BTU ~= 2.5E22 calories

    The mass of Earth’s oceans are ~= 1.4E24 g

    As 1 calorie heats water by 1 deg C:

    USA electricity would add 2E-6 C
    USA energy consumption would add 2E-2 C

    IOW, just as observation suggests, undersea volcanoes don’t add any significant energy to Earth’s oceans. All the warming is due to insolation from the sun.

    Therefore, the idea that there can be a waterworld (with even larger volumes of ocean) orbiting a star but kept warm by deep ocean volcanoes makes no sense to me. It would require orders of magnitude more volcanic heat, which in turn would require orders of magnitude more heat transfer, which in turn requires orders of magnitude more radioactive decay to supply that heat.

    Now if the waterworld was fully insulated that heat could accumulate and warm the oceans. But not even a dense CO2 atmosphere is that insulating. So the energy loss radiated out to space will exceed that from the volcanic input.

    Dr. Ramses Ramirez is the expert, yet I have not yet seen any papers from him that show that such a waterworld can exist out beyond the edge of the HZ. I’m sure he could demonstrate the energy requirements that would be needed, but it seems most likely that such a world would have a thick ice crust and an atmosphere of gases that have not frozen out. CO2 would freeze out, leaving only gases like methane to add any greenhouse effect. Such a world would be very cold, at best a few C above freezing at depth, but most likely frozen everywhere except at the volcanic vents where hot/warm water would exist as a relatively small volume until heat losses equilibrated with inputs, surrounding this bubble of liquid water in ice.

    I’m open to evidence that I am wrong, but show me some numbers/model to validate the idea.

    • Patient Observer April 24, 2021, 19:57

      I probably lost the logic thread but would not Io be a self-heating water world? True, its heat originates tidal forces but still it is self-heating.

      Speaking of self-heating planets:

      In a new paper, two astrophysicists suggest dark matter could be detected by measuring the effect it has on the temperature of exoplanets, which are planets outside our solar system.

      This could provide new insights into dark matter, the mysterious substance that can’t be directly observed, but which makes up roughly 80% of the mass of the universe.

      Smirnov co-authored the paper with Rebecca Leane, a postdoctoral researcher at the SLAC National Accelerator Laboratory at Stanford University. It was published April 22, 2021 in the journal Physical Review Letters.

      Smirnov said that when the gravity of exoplanets captures dark matter, the dark matter travels to the planetary core where it “annihilates” and releases its energy as heat. The more dark matter that is captured, the more it should heat up the exoplanet.

      Color me skeptical. To isolate an anomalous temperate of a exoplanet when just getting an average temperature of that planet would be a technological feat seems utterly ridiculous. I suppose it would be a good idea to read the paper before making any further judgements.

    • Michael Fidler April 25, 2021, 7:19

      Yes, “Require orders of magnitude more heat transfer, which in turn requires orders of magnitude more radioactive decay to supply that heat.”
      A 7 earth mass planet in a sphere diameter of 1.7 earth diameter would seem to a lot hotter then earth. Take a look at the second chart from this article:
      Growth model interpretation of planet size distribution.
      The first purple mark above the seven mass planet is about were Proxima c would be at 1.7 earth radius. This has a 33 percent iron content and would also make for a much deeper gravity well then compared to earth. We are getting into the transition between super earths and mini Neptunes and as you know both Uranus and Neptune produce more heat internally then they receive from the sun. I hope the JWST can shed some more infrared light on this but for all we know planet c could be a 1 inch black hole with a large ring around it. ;-}
      It may make for a very interesting model with the figures we are seeing! (Pun intended)

      There is one thought I had this morning that puts this in a different light. At a distance of 1.5 AU, Proxima c would still be under intense bombardment from Proxima Centauri’s super flares and giant CME’s, they would be much worse then earths and would have dire effects on atmospheric evolution. The CME’s would cause huge electrical build up in the the planets atmosphere and surface from electrical conductive rocks. Since at that distance it would not be tidally locked a large magnetosphere would exist and bring the energy into the polar regions.
      Perhaps it would be better to call these planets Frankenstein worlds, and that feature may liven up things on them…

      • Alex Tolley April 25, 2021, 11:56

        Neptune (not a mini-Neptune) of ~b 17 Earth masses generates 2.6x the energy received from the sun. At 30 AU, the solar energy is just 1/900 th that received by the Earth. So the energy is 0.3% of the solar energy of the Earth, i.e. about 3x the Earth’s internal energy (see calculation elsewhere). If Neptune was at 1 AU, the solar energy would be far larger than the internal energy.

        A Water world would not be generating internal energy like Neptune, but I grant you that its internal heat may be up to an order of magnitude greater than the Earth’s internal heat. That still doesn’t create nearly enough to keep an ocean in a liquid state without a way to reduce energy loss to a very low level. A water world should have a liquid surface, allowing complex life to frolic at the surface, even if it cannot use the atmosphere to respire. A water world with a thick ice crust like Europa is not a water world as I understand it. AFAIK, if Europa was not in orbit around Jupiter, it would freeze solid.

        If one can extend the outer edge of HZ to allow super-Earths to have habitable, liquid water surfaces, the planetary scientists need to know this. I find it hard to believe that they have all ignored this possibility.

        • Michael Fidler April 25, 2021, 17:21

          Your logic is beyond me, comparing a super earth and Europa. As I have said before these type of planets have no examples in our solar system. The mass of the iron alone in such worlds would be 2 times the mass of the whole earth.

  • Alex Tolley April 24, 2021, 14:55

    To further the calculations:

    I estimate that insolation at 1 AU ~= 1.3E24 Cals.
    That is 100x the total energy consumption of the USA.

    Even at Jupiter, the insolation impinging on an Earth-size world ~= 5E22 calls.

    That suggests to me that the sun’s energy exceeds any volcanic heat.

    Now the flaw in my argument is assuming that the undersea volcanism is just enough to power the USA. It may well be far more than that. Or it may be a lot less. From the Vice article:

    “Our results constrain the rate of energy release (or power) and show that during the eruption the power output is sufficient to run the US for that period of time, probably on the order of hours/days (however long it lasts—we don’t know precisely),” said Ferguson in an email.

    This suggests that the power output per plume is large, but transient. How many of these plumes there are is not specified. The Nature article does not provide overall energy output answers either.

    However, this Nature article suggests that the total output of volcanic energy is a tiny fraction of the heat produced by energy generation in the USA.

    Volcanoes throw out only a tiny fraction of energy compared with that produced by mankind, say scientists who have used satellite measurements to do a survey of the Earth’s heat output.

    In 2001, the amount of heat energy produced by volcanoes was 1000 times less than the energy consumed by the United States, the researchers report in the current issue of Geology1. They assume that most of the man-made energy, which is used for everything from residential lighting and heating to manufacture and transport, will end up in the form of heat.

    This appears to reinforce my conclusion that volcanic energy release cannot maintain a waterworld out beyond the HZ. Solar output is the primary energy source, modified by the GHGs in the atmosphere, to keep a planet’s surface warm.

    • Patient Observer April 24, 2021, 20:14

      Sure, the heat from point sources such as volcano may be low but the total energy from the earth’s interior is estimated at about 47 TW. If I did the math correctly that works out to 411,000 TWh/year or approximately 1,000 times the energy release by the US economy.

      Per Wikepedia:
      Earth’s internal heat budget is fundamental to the thermal history of the Earth. The flow of heat from Earth’s interior to the surface is estimated at 47±2 terawatts (TW)[1] and comes from two main sources in roughly equal amounts: the radiogenic heat produced by the radioactive decay of isotopes in the mantle and crust, and the primordial heat left over from the formation of Earth.[2]

      AND nuclear fission at the earth’s core. I wonder why this rather important science fact is not more widely accepted and reported.

      • Alex Tolley April 25, 2021, 11:30

        47 TW = 4.7E13 W
        Area of Earth’s surface facing sun: 4E13 m^2
        Energy of sun ~= 1.3E3 W/,^2
        Energy from sun = 5E16 W

        Solar/Earth energy ~= 1000x

        This suggests we can ignore the internal source of energy as 99.9% of the energy warming the Earth’s surface is from the sun.

        The internal heat of the Earth is substantial. That is why homes can use geothermal energy for heating. Volcanic heat sources, such as in Iceland, can be used to create hydrogen for power. But overall, the Earth’s heat is not significant when we consider keeping planets warm beyond the HZ.

  • Scott G April 25, 2021, 13:12

    I still have hope for Proxima b. If it formed with a large amount of water (a reasonable assumption), it could still conceivably have a global ocean and thick atmosphere today.

    If that is the case (and assuming that it is in fact tidally locked to Proxima – but has the necessary heat transport mechanisms in place), then there’s really no reason why life couldn’t exist in quite clement conditions in the twilight zone or on the dark side with its sun perpetually just below the horizon.

    My point is that there’s still potentially a large swath of habitable living space on that planet that would be well protected from these massive stellar flares. Or maybe that’s just me hoping :)

  • andy April 26, 2021, 13:51

    It would be interesting to do similar studies of red dwarfs that appear “quiet”, in case they are also active in the less-studied (sub)millimeter range.

  • Geoffrey Hillend April 26, 2021, 16:35

    I recall I read somewhere online that a water world might not have plate tectonics because of the weight of the water. Without a carbon cycle, the result would be a carbon dioxide depleted atmosphere which might not be good for life. It’s a speculation though. Internal heating still might result in some kind of volcanism and CO2 in the atmosphere. Without recycling it would eventually be depleted?

    A water world exoplanet has more mass so the core should be hotter than Earth’s core due to gravitational contraction.

    The millimeter frequency radio waves are probably the result of the synchrotron radiation from fast moving electrons in the solar flares magnetic field. Fastmoving electrons emit EMR.

  • Afterthought April 27, 2021, 0:28

    Overinterpretation or false positive.