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Powerful flare from star Proxima Centauri detected with ALMA

81 points by autocorr 9y ago

TheSpiceIsLife 9y ago
> “Nor is there any information yet that indicates the star has a rich planetary system like ours.” Could it just be that, if there are any planets around Proxima Centauri, they don't transit the star as observed from Earth? Or is there other data suggesting the absence of planets?
- goodcanadian 9y ago
  I think the implication is that the stellar activity cleared the dust from the system preventing planets from forming.
- KodiakLabs 9y ago
  The passing of exoplanets (planets outside or solar system) if front of the host star is not the only way to detect the planets. The most common method used to be the Radial Velocity method. Essentially, planets and stars orbit a common center of mass (which often lies witching the star’s radius). This effect essentially wobbles the parent star. Because we know the constituents of the star and it’s spectrum, this wobble causes a period red and blue shift (the Doppler effect). From the magnitude of this effect you can describe a lot of the planet’s orbit, but not everything. For example: you can describe the minimum mass of the planet but not the actual mass. I’m not sure if the have used the radial velocity method of this star, but assume they would have.
  - kazagistar 9y ago
    You can't see a doppler shift if the pole of the orbit is facing sol, right? So there are still systems with invisible planets.
    - roywiggins 9y ago
      You can measure the position of the star in the sky and use that to detect systems that are "face on" to us (with the axis pointing at us) but it's harder. http://www.planetary.org/explore/space-topics/exoplanets/astrometry.html http://www.planetary.org/explore/space-topics/exoplanets/ast...
      - martinpw 9y ago
        Sounds like 'harder' is an understatement - according to that article no planets have been discovered with this technique, and it is unlikely to yield any discoveries any time soon. (Technique is to directly observe the star wobbling in space rather than measure doppler shifts.)
    - KodiakLabs 9y ago
      You are correct. A component of the velocity of the wobble has to be in the line of sight. If not, it would be an edge case.
- fjfaase 9y ago
  In the abstract, it says that they conclude this from the absent of "quiescent excess emission". I do not know what this exactly means, could not find an explaination for it, but maybe it is a technical term for "light echo" or something related to it. If a star suddenly becomes 1000x brighter, one would expect that after some time, planets and dust would also light up after the star has returned to normal brightness. https://en.wikipedia.org/wiki/Light_echo https://en.wikipedia.org/wiki/Light_echo
  - kwoff 9y ago
    The web page links to a journal article that you have to pay for, but you can find the freely-readable version of the full article at https://arxiv.org/abs/1802.08257 https://arxiv.org/abs/1802.08257 . Section 4.2 discusses dust emission. The original paper they're correcting is at https://arxiv.org/abs/1711.00578 https://arxiv.org/abs/1711.00578 (section 3.2). This paper concludes that the previous paper had wrong assumptions because a flare happened during their measurement, so they didn't need to hypothesize that there is a dust belt (at least the 2 inner ones; they didn't have info about the far outer belt) to account for the supposed "excess emission".
- bonzini 9y ago
  Planetary systems are more rare around binary systems and planets are smaller too (making them harder to detect). Proxima Centauri is the smallest star in a triple system.
bhaavan 9y ago
How do we know that the sun is immune from such solar activity and will not have flares of such magnitude?
- DougWebb 9y ago
  We don't. At the end of the last ice age there was a strange period we call the Younger Dryas, during which we had a major extinction event and drastic temperature swings. There are several theories about the cause, including a massive solar event. I did a quick search and found the article below about it: http://www.spacedaily.com/reports/Did_A_Massive_Solar_Proton_Event_Fry_The_Earth_999.html http://www.spacedaily.com/reports/Did_A_Massive_Solar_Proton...
  - valuearb 9y ago
    I’m assuming next time we can just stay indoors for two days?
    - chiph 9y ago
      You know that crazy prepper neighbor who spent last fall putting a shelter in his backyard? Yeah, he'll be fine. For the old folks like me - there's roughly a 1:100 conversion between sieverts and rem. So an anticipated 3-6 sieverts over 2 days is 300-600 rem, which is fatal to nearly everyone.
      - valuearb 9y ago
        What if I have a metal roof?
      - Tuna-Fish 9y ago
        But the radiation mostly comes in form of electrons, protons or nucleii of heavier elements, not neutrons or gamma/xray. A really thin sheet of metal would reliably stop that. I think the effect of the direct radiation would indeed be blocked by the typical roof and walls. The part where the prepper has an advantage is dealing with the indirect effects -- such bombardment would (temporarily) collapse the geomagnetic field and fill the uppermost reaches of atmosphere with dust. That would cause massive effects on the climate.
danbruc 9y ago
“March 24, 2017, was no ordinary day for Proxima Cen,” said Meredith MacGregor [...] Nitpicking, but the not so ordinary day for Proxima Centauri was two or three days before New Year's Eve 2012 due to its distance. Maybe just some fireworks set off prematurely.
- raattgift 9y ago
  ( Aside: link to preprint: https://arxiv.org/abs/1802.08257 https://arxiv.org/abs/1802.08257 ) tl;dr: parochialism is convenient Practically anyone doing real astronomy will use a well-defined continuous Earth-centric (or solar-system barycentric) timescale for a variety of reasons including reproducibility within the solar system (after all, astronomers on Earth only have other Earth-bound/near-Earth astronomers to communicate with at present) and the uncertainties in (spacetime) position of astronomical objects dwarfing the precision of local timescales (e.g. TT or TAI). Describing observables at one timestamp (a form of gauge fixing) is convenient, but pushes the uncertainty into the spatial slice thus fixed, and a suitable choice of coordinates can push most of that uncertainty into one of the three spacelike axes. Since there is a gauge freedom -- meaning you can choose to slice up the spacetime position arbitrarily -- you would be perfectly free to use coordinates fixed on the observed object as you are doing, but that's incovenient for discussing the relationship between a distant object and a closer one, and because uncertainties in spacetime position for astronomical objects are commonplace and demand revision when new data provides a better estimate of position. Concretely, you say "two or three days", capturing the uncertainty in distance to Prox. Cen. That's rather worse than the sub-second errors in the ALMA timestamp data (e.g. JD 2457836.8349, one of the timestamps in the preprint). Moreover, further observation of the alpha Cen. system will almost inevitably reduce uncertainties in position of Prox. Cen., which raises the question of whether one should go back and revise any timestamps like your "two or three days before New Year's Eve 2012" as better data enable better retrodiction of its position relative to Earth. Fixing a Gregorian-like date on a set of spacetime coordinates originating on an event at a celestial object is a false de-parochialization; that is, it's no more general. If there are astronomers on Proxima b, it would be a stunning coincidence if their start-of-year aligned with our start-of-year on that orbit (and we don't know enough about the rotation of Proxima b to talk about their local length-of-day). Astronomers elsewhere in the galaxy (and in particular in our future) are unlikely to be helped by swapping observations-at-JD-xxxyyy for a best guess of local-to-event observables inferred by retrodiction from those same Earth-bound observations.
davidgrenier 9y ago
I hope they're ok.
batuhanw 9y ago
Does that mean Proxima B is unhabitable?
- raattgift 9y ago
  That would depend on Prox Cen b's atmosphere and magnetic field, and we don't know much about either. At the top of its atmosphere (if it has one at all; otherwise, at the surface) Prox Cen b would get about 500x more EUV/X-Ray radiation in an average day than we get at the top of Earth's atmosphere, so putting Earth into an orbit whose periastron is similar to Prox Cen B's average orbital distance would not be good news for many of Earth's near-surface organisms. The planet is in such a tight orbit around Prox Cen that it may not have any atmosphere thanks to erosion by the stellar wind. However, it might have a sufficiently strong magnetic field that erosive loss is checked. It also might not be a rocky planet rather than something like a small Neptune, with a deep atmosphere. Finally, Venus's magnetic field is negligible, and Venus is rocky, yet it has a thick atmosphere; Prox Cen b could be like a big Venus, for all we know so far. Venus is pretty interesting: https://link.springer.com/article/10.1007/s11214-017-0362-8 https://link.springer.com/article/10.1007/s11214-017-0362-8 Maybe someday we'll have similar (well, almost certainly strictly superior) probes around Prox Cen b.

81 points by autocorr 9y ago

> “Nor is there any information yet that indicates the star has a rich planetary system like ours.” Could it just be that, if there are any planets around Proxima Centauri, they don't transit the star as observed from Earth? Or is there other data suggesting the absence of planets?

goodcanadian 9y ago
I think the implication is that the stellar activity cleared the dust from the system preventing planets from forming.
KodiakLabs 9y ago
The passing of exoplanets (planets outside or solar system) if front of the host star is not the only way to detect the planets. The most common method used to be the Radial Velocity method. Essentially, planets and stars orbit a common center of mass (which often lies witching the star’s radius). This effect essentially wobbles the parent star. Because we know the constituents of the star and it’s spectrum, this wobble causes a period red and blue shift (the Doppler effect). From the magnitude of this effect you can describe a lot of the planet’s orbit, but not everything. For example: you can describe the minimum mass of the planet but not the actual mass. I’m not sure if the have used the radial velocity method of this star, but assume they would have.
- kazagistar 9y ago
  You can't see a doppler shift if the pole of the orbit is facing sol, right? So there are still systems with invisible planets.
  - roywiggins 9y ago
    You can measure the position of the star in the sky and use that to detect systems that are "face on" to us (with the axis pointing at us) but it's harder. http://www.planetary.org/explore/space-topics/exoplanets/astrometry.html http://www.planetary.org/explore/space-topics/exoplanets/ast...
    - martinpw 9y ago
      Sounds like 'harder' is an understatement - according to that article no planets have been discovered with this technique, and it is unlikely to yield any discoveries any time soon. (Technique is to directly observe the star wobbling in space rather than measure doppler shifts.)
  - KodiakLabs 9y ago
    You are correct. A component of the velocity of the wobble has to be in the line of sight. If not, it would be an edge case.
fjfaase 9y ago
In the abstract, it says that they conclude this from the absent of "quiescent excess emission". I do not know what this exactly means, could not find an explaination for it, but maybe it is a technical term for "light echo" or something related to it. If a star suddenly becomes 1000x brighter, one would expect that after some time, planets and dust would also light up after the star has returned to normal brightness. https://en.wikipedia.org/wiki/Light_echo https://en.wikipedia.org/wiki/Light_echo
- kwoff 9y ago
  The web page links to a journal article that you have to pay for, but you can find the freely-readable version of the full article at https://arxiv.org/abs/1802.08257 https://arxiv.org/abs/1802.08257 . Section 4.2 discusses dust emission. The original paper they're correcting is at https://arxiv.org/abs/1711.00578 https://arxiv.org/abs/1711.00578 (section 3.2). This paper concludes that the previous paper had wrong assumptions because a flare happened during their measurement, so they didn't need to hypothesize that there is a dust belt (at least the 2 inner ones; they didn't have info about the far outer belt) to account for the supposed "excess emission".
bonzini 9y ago
Planetary systems are more rare around binary systems and planets are smaller too (making them harder to detect). Proxima Centauri is the smallest star in a triple system.

bhaavan 9y ago

How do we know that the sun is immune from such solar activity and will not have flares of such magnitude?

DougWebb 9y ago
We don't. At the end of the last ice age there was a strange period we call the Younger Dryas, during which we had a major extinction event and drastic temperature swings. There are several theories about the cause, including a massive solar event. I did a quick search and found the article below about it: http://www.spacedaily.com/reports/Did_A_Massive_Solar_Proton_Event_Fry_The_Earth_999.html http://www.spacedaily.com/reports/Did_A_Massive_Solar_Proton...
- valuearb 9y ago
  I’m assuming next time we can just stay indoors for two days?
  - chiph 9y ago
    You know that crazy prepper neighbor who spent last fall putting a shelter in his backyard? Yeah, he'll be fine. For the old folks like me - there's roughly a 1:100 conversion between sieverts and rem. So an anticipated 3-6 sieverts over 2 days is 300-600 rem, which is fatal to nearly everyone.
    - valuearb 9y ago
      What if I have a metal roof?
    - Tuna-Fish 9y ago
      But the radiation mostly comes in form of electrons, protons or nucleii of heavier elements, not neutrons or gamma/xray. A really thin sheet of metal would reliably stop that. I think the effect of the direct radiation would indeed be blocked by the typical roof and walls. The part where the prepper has an advantage is dealing with the indirect effects -- such bombardment would (temporarily) collapse the geomagnetic field and fill the uppermost reaches of atmosphere with dust. That would cause massive effects on the climate.

danbruc 9y ago

“March 24, 2017, was no ordinary day for Proxima Cen,” said Meredith MacGregor [...] Nitpicking, but the not so ordinary day for Proxima Centauri was two or three days before New Year's Eve 2012 due to its distance. Maybe just some fireworks set off prematurely.

raattgift 9y ago
( Aside: link to preprint: https://arxiv.org/abs/1802.08257 https://arxiv.org/abs/1802.08257 ) tl;dr: parochialism is convenient Practically anyone doing real astronomy will use a well-defined continuous Earth-centric (or solar-system barycentric) timescale for a variety of reasons including reproducibility within the solar system (after all, astronomers on Earth only have other Earth-bound/near-Earth astronomers to communicate with at present) and the uncertainties in (spacetime) position of astronomical objects dwarfing the precision of local timescales (e.g. TT or TAI). Describing observables at one timestamp (a form of gauge fixing) is convenient, but pushes the uncertainty into the spatial slice thus fixed, and a suitable choice of coordinates can push most of that uncertainty into one of the three spacelike axes. Since there is a gauge freedom -- meaning you can choose to slice up the spacetime position arbitrarily -- you would be perfectly free to use coordinates fixed on the observed object as you are doing, but that's incovenient for discussing the relationship between a distant object and a closer one, and because uncertainties in spacetime position for astronomical objects are commonplace and demand revision when new data provides a better estimate of position. Concretely, you say "two or three days", capturing the uncertainty in distance to Prox. Cen. That's rather worse than the sub-second errors in the ALMA timestamp data (e.g. JD 2457836.8349, one of the timestamps in the preprint). Moreover, further observation of the alpha Cen. system will almost inevitably reduce uncertainties in position of Prox. Cen., which raises the question of whether one should go back and revise any timestamps like your "two or three days before New Year's Eve 2012" as better data enable better retrodiction of its position relative to Earth. Fixing a Gregorian-like date on a set of spacetime coordinates originating on an event at a celestial object is a false de-parochialization; that is, it's no more general. If there are astronomers on Proxima b, it would be a stunning coincidence if their start-of-year aligned with our start-of-year on that orbit (and we don't know enough about the rotation of Proxima b to talk about their local length-of-day). Astronomers elsewhere in the galaxy (and in particular in our future) are unlikely to be helped by swapping observations-at-JD-xxxyyy for a best guess of local-to-event observables inferred by retrodiction from those same Earth-bound observations.

davidgrenier 9y ago

I hope they're ok.

batuhanw 9y ago

Does that mean Proxima B is unhabitable?

raattgift 9y ago
That would depend on Prox Cen b's atmosphere and magnetic field, and we don't know much about either. At the top of its atmosphere (if it has one at all; otherwise, at the surface) Prox Cen b would get about 500x more EUV/X-Ray radiation in an average day than we get at the top of Earth's atmosphere, so putting Earth into an orbit whose periastron is similar to Prox Cen B's average orbital distance would not be good news for many of Earth's near-surface organisms. The planet is in such a tight orbit around Prox Cen that it may not have any atmosphere thanks to erosion by the stellar wind. However, it might have a sufficiently strong magnetic field that erosive loss is checked. It also might not be a rocky planet rather than something like a small Neptune, with a deep atmosphere. Finally, Venus's magnetic field is negligible, and Venus is rocky, yet it has a thick atmosphere; Prox Cen b could be like a big Venus, for all we know so far. Venus is pretty interesting: https://link.springer.com/article/10.1007/s11214-017-0362-8 https://link.springer.com/article/10.1007/s11214-017-0362-8 Maybe someday we'll have similar (well, almost certainly strictly superior) probes around Prox Cen b.