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
The brightness of Proxima Centauri as observed by ALMA over the two minutes of the event on March 24, 2017. The massive stellar flare is shown in red, with the smaller earlier flare in orange, and the enhanced emission surrounding the flare that could mimic a disk in blue. At its peak, the flare increased Proxima Centauri’s brightness by 1,000 times. The shaded area represents uncertainty. Credit: Meredith MacGregor, Carnegie
Artist animation of a red dwarf star similar to 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. Vimeo
An artist’s impression of a flare from Proxima Centauri,
modeled after the loops of glowing hot gas seen in the largest solar
flares. An artist’s impression of the exoplanet Proxima b is shown in
the foreground. Proxima b orbits its star 20 times closer than the Earth
orbits the Sun. A flare 10 times larger than a major solar flare would
blast Proxima b with 4,000 times more radiation than the Earth gets
from our Sun’s flares. Credit: Roberto Molar Candanosa / Carnegie Institution for Science, NASA/SDO, NASA/JPL
Contacts:
Charles Blue,
NRAO Public Information Officer
(434) 296-0314;
cblue@nrao.edu
Meredith MacGregor,
Carnegie Institution for Science
(202) 478-8846;
mmacgregor@carnegiescience.edu
Alycia Weinberger,
Carnegie Institution for Science
(202) 478-8852
aweinberger@carnegiescience.edu
Powerful Flare from Star Proxima Centauri Detected with ALMA
Puts habitability of nearby system into question
Space weather emitted by Proxima Centauri, the star closest to our
sun, may make that system rather inhospitable to life after all.
Using data from the Atacama Large Millimeter/submillimeter Array (ALMA),
a team of astronomers discovered that a powerful stellar flare erupted
from Proxima Centauri last March. This finding, published in the Astrophysical Journal Letters,
raises questions about the habitability of our solar system’s nearest
exoplanetary neighbor, Proxima b, which orbits Proxima Centauri.
At its peak, the newly recognized flare was 10 times brighter than
our sun’s largest flares, when observed at similar wavelengths. Stellar
flares have not been well studied at the millimeter and submillimeter
wavelengths detected by ALMA, especially around stars of Proxima
Centauri’s type, called M dwarfs, which are the most common in our
galaxy.
“March 24, 2017, was no ordinary day for Proxima Cen,” said Meredith
MacGregor, an astronomer at the Carnegie Institution for Science,
Department of Terrestrial Magnetism in Washington, D.C., who led the
research with fellow Carnegie astronomer Alycia Weinberger. Along with
colleagues from the Harvard-Smithsonian Center for Astrophysics, David
Wilner and Adam Kowalski, and Steven Cranmer of the University of
Colorado Boulder — they discovered the enormous flare when they
reanalyzed ALMA observations taken last year.
The flare increased Proxima Centauri’s brightness by 1,000 times over
10 seconds. This was preceded by a smaller flare; taken together, the
whole event lasted fewer than two minutes of the 10 hours that ALMA
observed the star between January and March of last year.
Stellar flares happen when a shift in the star’s magnetic field
accelerates electrons to speeds approaching that of light. The
accelerated electrons interact with the highly charged plasma that makes
up most of the star, causing an eruption that produces emission across
the entire electromagnetic spectrum.
“It’s likely that Proxima b was blasted by high energy radiation
during this flare,” MacGregor explained, adding that it was already
known that Proxima Centauri experienced regular, although smaller, X-ray
flares. “Over the billions of years since Proxima b formed, flares like
this one could have evaporated any atmosphere or ocean and sterilized
the surface, suggesting that habitability may involve more than just
being the right distance from the host star to have liquid water.”
An earlier paper that also used the same ALMA data interpreted its
average brightness, which included the light output of both the star and
the flare together, as being caused by multiple disks of dust
encircling Proxima Centauri, not unlike our own solar system’s asteroid
and Kuiper belts.
But when MacGregor, Weinberger, and their team looked at the ALMA
data as a function of observing time, instead of averaging it all
together, they were able to see the transient explosion of radiation
emitted from Proxima Centauri for what it truly was.
“There is now no reason to think that there is a substantial amount
of dust around Proxima Cen,” Weinberger said. “Nor is there any
information yet that indicates the star has a rich planetary system like
ours.”
The National Radio Astronomy Observatory is a facility of the
National Science Foundation operated under cooperative agreement by
Associated Universities, Inc.
# # #
This research is presented in a paper titled “Detection of a
millimeter flare from Proxima Centauri,” by M. MacGregor, et al.,
published in the Astrophysical Journal Letters. [https://doi.org/10.3847/2041-8213/aaad6b; preprint: http://arxiv.org/abs/1802.08257]
The Atacama Large Millimeter/submillimeter Array (ALMA), an
international astronomy facility, is a partnership of the European
Organisation for Astronomical Research in the Southern Hemisphere (ESO),
the U.S. National Science Foundation (NSF) and the National Institutes
of Natural Sciences (NINS) of Japan in cooperation with the Republic of
Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in
cooperation with the National Research Council of Canada (NRC) and the
Ministry of Science and Technology (MOST) in Taiwan and by NINS in
cooperation with the Academia Sinica (AS) in Taiwan and the Korea
Astronomy and Space Science Institute (KASI).
ALMA construction and operations are led by ESO on behalf of its
Member States; by the National Radio Astronomy Observatory (NRAO),
managed by Associated Universities, Inc. (AUI), on behalf of North
America; and by the National Astronomical Observatory of Japan (NAOJ) on
behalf of East Asia. The Joint ALMA Observatory (JAO) provides the
unified leadership and management of the construction, commissioning and
operation of ALMA.
This research was supported in part by a National Science Foundation
Astronomy and Astrophysics Postdoctoral Fellowship under Award No.
1701406.
The Carnegie Institution for Science (carnegiescience.edu) is a
private, nonprofit organization headquartered in Washington, D.C., with
six research departments throughout the U.S. Since its founding in 1902,
the Carnegie Institution has been a pioneering force in basic
scientific research. Carnegie scientists are leaders in plant biology,
developmental biology, astronomy, materials science, global ecology, and
Earth and planetary science.
Contacts:
Charles Blue,
NRAO Public Information Officer
(434) 296-0314;
cblue@nrao.edu
Meredith MacGregor,
Carnegie Institution for Science
(202) 478-8846;
mmacgregor@carnegiescience.edu
Alycia Weinberger,
Carnegie Institution for Science
(202) 478-8852
aweinberger@carnegiescience.edu
