From ALMA [The Atacama Large Millimeter/submillimeter Array] (CL): “Record-breaking Stellar Flare from Nearby Star Recorded in Multiple Wavelengths for the First Time”

From European Southern Observatory (EU)/National Astronomy Observatory of Japan (JP)/National Radio Astronomy Observatory (US) ALMA [The Atacama Large Millimeter/submillimeter Array] (CL)

21 April, 2021

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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: NRAO/S. Dagnello.

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Artist’s conception of a violent stellar flare erupting on neighboring star, Proxima Centauri. 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: NRAO/S. Dagnello.

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have spotted a flare from Earth’s nearest neighboring star, Proxima Centauri, that is 100 times more powerful than any similar flare seen from the Sun. The flare, which is the largest ever recorded from the star, has revealed the inner workings of such events to astronomers, and could help to shape the hunt for life beyond the Solar System.

Stellar flares occur when the release of magnetic energy in stellar spots explodes in an intense burst of electromagnetic radiation that can be observed across the entire electromagnetic spectrum, from radio waves to gamma rays. This is the first time that a single stellar flare, other than those that occur on the Sun, has been observed with such complete wavelength coverage. The study was precipitated by the serendipitous discovery of a flare from Proxima Centauri in 2018 ALMA archival data.

“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,” said Meredith MacGregor, an assistant professor at the Center for Astrophysics and Space Astronomy (CASA) and Department of Astrophysical and Planetary Sciences (APS) at University of Colorado (US), and the lead author on the study.

To better understand the flares on Proxima Centauri— a red dwarf star located roughly four light-years or 20 trillion miles from Earth— a team of astronomers observed the star for 40 hours over the course of several months in 2019 using nine telescopes on the ground and in space.

In May 2019, Proxima Centauri ejected a violent flare that lasted just seven seconds, but generated a surge in both ultraviolet and millimeter wavelengths. The flare was characterized by a strong, impulsive spike never before seen at these wavelengths. The event was recorded by five of the nine telescopes involved in the study, including the Hubble Space Telescope (HST) in ultraviolet, and ALMA in millimeter wavelengths.

“The star went from normal to 14,000 times brighter when seen in ultraviolet wavelengths over the span of a few seconds,” said MacGregor, adding that similar behavior was captured in millimeter wavelengths by ALMA at the same time.

“In the past, we didn’t know that stars could flare in the millimeter range, so this is the first time we have gone looking for millimeter flares,” said MacGregor, adding that the new observations could help researchers gather more information about how stars generate flares, which can have an impact on nearby life.

Powerful flares from our Sun are uncommon, occurring only a few times in a solar cycle. According to MacGregor, that’s not the case on Proxima Centauri. “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,” said MacGregor.

The star is prominent in discussions surrounding the prospect for life around red dwarf stars because of its proximity to Earth, and because it is host to Proxima Centauri b, a planet that resides in the star’s habitable zone.

“If there was life on the planet nearest to Proxima Centauri, it would have to look very different than anything on Earth,” MacGregor said. “A human being on this planet would have a bad time.”

Future observations will focus on unveiling the many secrets behind Proxima Centauri’s flares in the hopes of uncovering the internal mechanisms that cause such powerful outbursts.

“We want to see what surprises this star has in store for us to help us understand the physics of stellar flaring,” said MacGregor.

Additional Information

The results of the study are reported today in The Astrophysical Journal Letters.

Author lists and affiliation:

Meredith A. MacGregor1, Alycia J. Weinberger2, R. O. Parke Loyd3, Evgenya Shkolnik3, Thomas Barclay4,5, Ward S. Howard6, Andrew Zic7,8, Rachel A. Osten9,10, Steven R. Cranmer1,12, Adam F. Kowalski1,11, Emil Lenc8, Allison Youngblood12, Anna Estes1, David J. Wilner13, Jan Forbrich13,14, Anna Hughes15, Nicholas M. Law6, Tara Murphy7, Aaron Boley15, and Jaymie Matthews15

1 Department of Astrophysical and Planetary Sciences, University of Colorado, 2000 Colorado Avenue, Boulder, CO 80309, USA
2 Earth & Planets Laboratory, Carnegie Institution for Science, Washington, DC 20015, USA
3 School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, USA
4 NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
5 University of Maryland, Baltimore County, Baltimore, MD 21250, USA
6 Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
7 Sydney Institute for Astronomy, School of Physics, University of Sydney, NSW 2006, Australia
8 CSIRO Astronomy and Space Science, Epping, NSW 1710, Australia
9 Space Telescope Science Institute, Baltimore, MD 21218 USA
10 Center for Astrophysical Sciences, Johns Hopkins University, Baltimore, MD 21218, USA
11 National Solar Observatory, University of Colorado Boulder, Boulder, CO 80303, USA
12 Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80303, USA
13 Center for Astrophysics Harvard & Smithsonian, Cambridge, MA 02138, USA
14 Centre for Astrophysics Research, University of Hertfordshire, AL10 9AB, UK
15 Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1, Canada

Regarding the telescopes involved:

“We executed a multi-wavelength campaign to monitor Proxima Cen for ∼ 40 hours between April–July 2019 simultaneously at radio through X-ray wavelengths. This paper presents the first results from this observing campaign, highlighting an extremely short duration flaring event observed on 2019 May 1 UTC by the Australian Square Kilometre Array Pathfinder (ASKAP), ALMA, the TESS – Transiting Exoplanet Survey Satellite, the Las Campanas Observatory Irénée du Pont Telescope — Las Campanas Observatory, and the National Aeronautics and Space Administration(US)/European Space Agency [Agence spatiale européenne] [Europäische Weltraumorganisation] (EU) Hubble Space Telescope(HST). Details on the data reduction and analysis are provided in the Appendix. Several other telescopes including Evryscope-South, The Las Cumbres Observatory Global Telescope (LCOGT) 1m, the Neil Gehrels Swift Observatory, and NASA Chandra X-ray Observatory (US) were involved in the full campaign but were not observing at the time of this event. This observing campaign aligned with TESS observations in Sectors 11 and 12. Several other analyses incorporating the available TESS data from this time period have been previously published by Vida et al. (2019) and Zic et al. (2020). However, the campaign presented here is unique in the multi-wavelength observations obtained simultaneously. Indeed, this is the first time that a stellar flare has been observed with such complete wavelength coverage (spanning millimeter to FUV wavelengths) and high time resolution (1 sec integrations with ALMA and HST) enabling unique insights into the process of flaring on M dwarfs. “


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The Atacama Large Millimeter/submillimeter Array (ALMA) (CL) , an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA is funded in Europe by the European Organization for Astronomical Research in the Southern Hemisphere (ESO), in North America by the U.S. National Science Foundation (NSF) in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and in East Asia by the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Academia Sinica (AS) in Taiwan.

ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), which is managed by Associated Universities, Inc. (AUI) and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

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