Proxima Centauri just released a flare so powerful it was visible to the unaided eye

Artist’s impression of a flaring red dwarf star, orbited by
an exoplanet. Credit: NASA, ESA, and G. Bacon (STScI)

Since its discovery was announced in August of 2016, Proxima
b has been an endless source of wonder and the target of many
scientific studies. In addition to being the closest
extra-solar planet to our Solar System, this terrestrial
planet also orbits within Proxima Centauri’s circumstellar
habitable zone (aka. “Goldilocks Zone”). As a result,
scientists have naturally sought to determine if this planet
could actually be home to extra-terrestial life.


Many of these studies have been focused on whether or not
Proxima b could retain an atmosphere and liquid water on its
surface in light of the fact that it orbits an M-type (red
dwarf) star. Unfortunately, many of these studies have revealed
that this is not likely due to flare activity. According to a
new study by an international team of scientists, Proxima
Centauri released a superflare that was so powerful, it would
have been lethal to any life as we know it.

The study, titled “The First Naked-Eye Superflare Detected from
Proxima Centauri”, recently appeared online. The team was led
by Howard Ward, a Ph.D. candidate in physics and astronomy at
the UNC Chapel Hill, with additional members from the NASA
Goddard Space Flight Center, the University of Washington, the
University of Colorado, the University of Barcelona and the
School of Earth and Space Exploration at Arizona State
University.

As they indicate in their study, would be one of the greatest
potential threats to planetary habitability in a system like
Proxima Centauri. As they explain:

“[W]hile ozone in an Earth-like planet’s atmosphere can shield
the planet from the intense UV flux associated with a single
superflare, the atmospheric ozone recovery time after a
superflare is on the order of years. A sufficiently high flare
rate can therefore permanently prevent the formation of a
protective ozone layer, leading to UV radiation levels on the
surface which are beyond what some of the hardiest-known
organisms can survive.”

In addition stellar flares, quiescent X-ray emissions and UV
flux from a red dwarf star can would be capable of stripping
planetary atmospheres over the course of several billion years.
And while multiple studies have been conducted that have
explored low- and moderate-energy flare events on Proxima, only
one high-energy event has even been observed.

Artist impression of a red dwarf star like Proxima Centauri,
the nearest star to our sun. New analysis of ALMA
observations reveal that Proxima Centauri emitted a powerful
flare that would have created inhospitable conditions for
planets in that system. Credit: NRAO/AUI/NSF; D. Berry

This occurred on March of 2016, when Proxima Centauri emitted a
superflare that was so bright, it was visible to the naked eye.
This flare was observed by the Evryscope, an array of
telescopes – funded through the National Science Foundation’s
Advanced Technologies and Instrumentation (ATI) and Faculty
Early Career Development (CAREER) programs – that is pointed at
every part of the accessible sky simultaneously and
continuously.

As the team indicates in their study, the March 2016 superflare
was the first to be observered from Proxima Centauri, and was
rather powerful:

“In March 2016 the Evryscope detected the first-known Proxima
superflare. The superflare had a bolometric energy of 10^33.5
erg, ~10× larger than any previously-detected flare from
Proxima, and 30×larger than any optically measured Proxima
flare. The event briefly increased Proxima’s visible-light
emission by a factor of 38× averaged over the Evryscope’s
2-minute cadence, or ~68× at the cadence of the human eye.
Although no M-dwarfs are usually visible to the naked-eye,
Proxima briefly became a magnitude-6.8 star during this
superflare, visible to dark-site naked-eye observers.”

The superflare coincided with the three-month Pale Red Dot
campaign, which was responsible for first revealing the
existence of Proxima b. While monitoring the star with the
HARPS spectrograph – which is part of the 3.6 m telescope at
the ESO’s La Silla Observatory in Chile – the campaign team
also obtaining spectra on March 18th, 08:59 UT (just 27 minutes
after the flare peaked at 08:32 UT).

The team also noted that over the last two years, the Evryscope
has recorded 23 other large Proxima flares, ranging in energy
from 10^30.6 erg to 10^32.4 erg. Coupled with rates of a single
superflare detection, they predict that at least five
superflares occur each year. They then combined this data with
the high-resolution HARPS spectroscopy to constrain the
superflare’s UV spectrum and any associated coronal mass
ejections.

The team then used the HARPS spectra and the Evryscope flare
rates to create a model to determine what effects this star
would have on a nitrogen-oxygen atmosphere. This included how
long the planet’s protective ozone layer would be able to
withstand the blasts, and what effect regular exposure to
radiation would have on terrestrial organisms.

Proxima Centauri just released a flare so powerful it was visible to the unaided eye
Artist’s impression of Proxima b, which was discovered using
the Radial Velocity method. Credit: ESO/M. Kornmesser

“[T]he repeated flaring is sufficient to reduce the ozone of an
Earth-like atmosphere by 90 percent within five years. We
estimate complete depletion occurs within several hundred kyr.
The UV light produced by the Evryscope superflare therefore
reached the surface with ~100× the intensity required to kill
simple UV-hardy microorganisms, suggesting that life would
struggle to survive in the areas of Proxima b exposed to these
flares.”

Essentially, this and other studies have concluded that any
planets orbiting Proxima Centauri would not be habitable for
very long, and likely became lifeless balls of rock a long time
ago. But beyond our closest neighboring star system, this study
also has implications for other M-type star systems. As they
explain, are the most common
in our galaxy – roughly 75 percent of the population – and
two-thirds of these experience active flare
activity.

As such, measuring the impact that superflares have on these
worlds will be a necessary component to determining whether or
not exoplanets found by future missions are habitable. Looking
ahead, the team hopes to use the Evryscope to examine other
star systems, particularly those that are targets for the
upcoming Transiting Exoplanet Survey Satellite (TESS) mission.

“Beyond Proxima, Evryscope has already performed similar
long-term high-cadence monitoring of every other Southern TESS
planet-search target, and will therefore be able to measure the
habitability impact of stellar activity for all Southern
planetsearch-target M-dwarfs,” they write. “In conjunction with
coronal-mass-ejection searches from long- wavelength radio
arrays like the [Long Wavelength Array], the Evryscope will
constrain the long-term atmospheric effects of this extreme
stellar activity.”

For those who hoped that humanity might find evidence of
extra-terrestrial life in their lifetimes, this latest study is
certainly a letdown. It’s also disappointing considering that
in addition to being the most common type of star in the
universe, some research indicates that stars may be the most likely place to
find terrestrial planets. However, even if two-thirds of these
stars are active, that still leaves us with billions of
possibilities.

It is also important to note that these studies help ensure
that we can determine which exoplanets are potentially
habitable with greater accuracy. In the end, that will be the
most important factor when it comes time to decide which of
these systems we might try to explore directly. And if this
news has got you down, just remember the worlds of the immortal
Carl Sagan: “The universe is a pretty big place. If it’s just
us, seems like an awful waste of space.”

Explore further:

Proxima Centauri’s no good, very bad day

More information: The First Naked-Eye Superflare
Detected from Proxima Centauri. arxiv.org/pdf/1804.02001.pdf


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