
Powerful flare from star Proxima Centauri detected with ALMA - autocorr
https://public.nrao.edu/news/2018-alma-flare-proxima/
======
danbruc
_“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
( 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.

~~~
danielvf
We don’t know exactly how far away the stars are, so when we convert earth
time to star local time, we are being less accurate. Better to keep times
stored local to earth, and let distances get more accurate as we learn more.

~~~
raattgift
Sure, that's one of the points I made.

There isn't really any more precise timekeeping equipment available to us than
atomic clocks here on (and near) Earth, so using those are expedient.

In principle we could measure the spectra of the relic fields, but with
current technology we can't do that for the cosmic neutrino background, and
while the cosmic microwave background (CMB) is an attractive option (we have
lots of instruments measuring it in excruciatingly fine detail) its utility as
a quasi-universal clock is based on picking out an ideal observer who sees no
non-cosmological redshift (i.e., no contributions from proper motion or local
gravitation), and such an observer isn't really physical. Converting local
measurements of the CMB to an ideal observer's in a way which achieves
precision approaching that of our terrestrial atomic timescales depends on
understanding our own local (~ Mpc scale) environment better than we do today.

(Probably we will get there by using CMB observations to steer local
oscillators, much as we do in atomic clocks, H2 masers, and so forth, and use
those steered oscillators to predict CMB spectrum on the (well-supported)
assumption that it is that of an ideal blackbody with a certain temperature).

However, we'll still record actual observations at local CMB temperature
(perhaps recording what the "universal" CMB temperature would be if we were a
"universal" observer). We are still stuck with the problem of position of the
observed object, since we cannot directly observe the CMB temperature at an
event like this flare.

In other words, the coordination (or if you like, localization) problem here
isn't solved by switching to a different set of coordinates. Indeed, a
different set of coordinates might make things worse (which was the thrust of
what you replied to, and essentially what you write yourself).

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

~~~
DougWebb
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...](http://www.spacedaily.com/reports/Did_A_Massive_Solar_Proton_Event_Fry_The_Earth_999.html)

~~~
valuearb
I’m assuming next time we can just stay indoors for two days?

~~~
chiph
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.

~~~
Tuna-Fish
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.

~~~
valuearb
Famine would be the other problem the prepped would have an advantage in. One
would expect the deaths of many farm animals, and it would take a few years to
recover production.

~~~
anoncoward111
In my opinion, it would be difficult for the US to enter a widespread (5%
population starve to death) famine.

The amount of dried, preserved, high calorie, long shelf life food that we
have staggering. Crackers, soups, noodles, pasta, dehydrated soy/meat etc.

The only two reasons someone could starve to death is if companies
deliberately hid supply of food for fun, or if they refused to eat those types
of food for about 60 days, upon which most people die from acute starvation.

Malnutrition is more complex but vitamins exist.

------
TheSpiceIsLife
> “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?

~~~
KodiakLabs
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
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
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/ast...](http://www.planetary.org/explore/space-
topics/exoplanets/astrometry.html)

~~~
martinpw
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.)

------
davidgrenier
I hope they're ok.

------
batuhanw
Does that mean Proxima B is unhabitable?

~~~
raattgift
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.

