Humungous Flare From Sun’s Nearest Neighbor Breaks Records (Planetary Science)

Scientists have spotted the largest flare ever recorded from the sun’s nearest neighbor, the star Proxima Centauri. 

The research, which appears today in The Astrophysical Journal Letters, was led by CU Boulder and could help to shape the hunt for life beyond Earth’s solar system.

CU Boulder astrophysicist Meredith MacGregor explained that Proxima Centauri is a small but mighty star. It sits just four light-years or more than 20 trillion miles from our own sun and hosts at least two planets, one of which may look something like Earth. It’s also a “red dwarf,” the name for a class of stars that are unusually petite and dim. 

Proxima Centauri has roughly one-eighth the mass of our own sun. But don’t let that fool you. 

In their new study, MacGregor and her colleagues observed Proxima Centauri for 40 hours using nine telescopes on the ground and in space. In the process, they got a surprise: Proxima Centauri ejected a flare, or a burst of radiation that begins near the surface of a star, that ranks as one of the most violent seen anywhere in the galaxy. 

“The star went from normal to 14,000 times brighter when seen in ultraviolet wavelengths over the span of a few seconds,” said MacGregor, an assistant professor at the Center for Astrophysics and Space Astronomy (CASA) and Department of Astrophysical and Planetary Sciences (APS) at CU Boulder.

The team’s findings hint at new physics that could change the way scientists think about stellar flares. They also don’t bode well for any squishy organism brave enough to live near the volatile star.

“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.”

Active stars

Artist’s conception of a stellar flare as seen from the planet Proxima Centauri b, a potentially Earth-like world. (Credit: NRAO/S. Dagnello)

The star has long been a target for scientists hoping to find life beyond Earth’s solar system. Proxima Centauri is nearby, for a start. It also hosts one planet, designated Proxima Centauri b, that resides in what researchers call the “habitable zone”—a region around a star that has the right range of temperatures for harboring liquid water on the surface of a planet.

But there’s a twist, MacGregor said: Red dwarves, which rank as the most common stars in the galaxy, are also unusually lively.

“A lot of the exoplanets that we’ve found so far are around these types of stars,” she said. “But the catch is that they’re way more active than our sun. They flare much more frequently and intensely.”

To see just how much Proxima Centauri flares, she and her colleagues pulled off what approaches a coup in the field of astrophysics: They pointed nine different instruments at the star for 40 hours over the course of several months in 2019. Those eyes included the Hubble Space Telescope, the Atacama Large Millimeter Array (ALMA) and NASA’s Transiting Exoplanet Survey Satellite (TESS). Five of them recorded the massive flare from Proxima Centauri, capturing the event as it produced a wide spectrum of radiation.

“It’s the first time we’ve ever had this kind of multi-wavelength coverage of a stellar flare,” MacGregor. “Usually, you’re lucky if you can get two instruments.”

Crispy planet

The technique delivered one of the most in-depth anatomies of a flare from any star in the galaxy.

The event in question was observed on May 1, 2019 and lasted just 7 seconds. While it didn’t produce a lot of visible light, it generated a huge surge in both ultraviolet and radio, or “millimeter,” radiation. 

“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,” MacGregor said. 

Those millimeter signals, MacGregor added, could help researchers gather more information about how stars generate flares. Currently, scientists suspect that these bursts of energy occur when magnetic fields near a star’s surface twist and snap with explosive consequences.  

In all, the observed flare was roughly 100 times more powerful than any similar flare seen from Earth’s sun. Over time, such energy can strip away a planet’s atmosphere and even expose life forms to deadly radiation.

That type of flare may not be a rare occurrence on Proxima Centauri. In addition to the big boom in May 2019, the researchers recorded many other flares during the 40 hours they spent watching the star.

“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,” MacGregor said. 

The findings suggest that there may be more surprises in store from the sun’s closest companion. 

“There will probably be even more weird types of flares that demonstrate different types of physics that we haven’t thought about before,” MacGregor said.

Other coauthors on the new study include Steven Cranmer, associate professor in APS and the Laboratory for Atmospheric and Space Physics (LASP) at CU Boulder; Adam Kowalski, assistant professor in APS and LASP at CU Boulder, also of the National Solar Observatory; Allison Youngblood, research scientist at LASP; and Anna Estes, undergraduate research assistant in APS. 

The Carnegie Institution for Science, Arizona State University, NASA Goddard Spaceflight Center, University of Maryland, University of North Carolina at Chapel Hill, University of Sydney, CSIRO Astronomy and Space Science, Space Telescope Science Institute, Johns Hopkins University, the Center for Astrophysics | Harvard & Smithsonian and the University of British Columbia also contributed to this research. 

Featured image: Artist’s conception of a violent flare erupting from the star Proxima Centauri. (Credit: NRAO/S. Dagnello)

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Reference: Meredith A. MacGregor, Alycia J. Weinberger et al., “Discovery of an Extremely Short Duration Flare from Proxima Centauri Using Millimeter through Far-ultraviolet Observations”, The Astrophysical Journal Letters, Volume 911, Number 2, 2021. Link to paper

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Provided by University of Colorado Boulder

Introducing The Most Energetic Flare Star Of the Decade, “GT Mus” (Planetary Science / Astronomy)

A team of international astronomers reported that the RS CVn-type star GT Mus (HR4492, HD 101379+HD 101380) was the most active star in the X-ray sky in the last decade in terms of the scale of recurrent energetic flares. Their study recently appeared in Astrophysical Journal.

MAXI is an all-sky X-ray monitor that has been operating on the Japanese Experiment Module (JEM; Kibo) on the International Space Station (ISS) since 2009 August 15. It observes a large area of the sky once per 92 minute orbital cycle and makes it possible to search for transients effectively.

Among the MAXI-detected stellar flare sources, the RS CVn-type star GT Mus showed remarkably energies flared with energies up to ~ 10³⁸ erg repeatedly. So far, MAXI has detected flare candidates with the MAXI “nova-alert system” designed to detect transients from MAXI all-sky images in real time.

The quadruple system GT Mus (HR4492) consists of two binary systems named HD 101379 and HD 101380, located at (R.A., Dec.)(J2000) = (11h39m29s.497, −65°23’52”.0135) at a distance of 109.594 pc. The two binaries (HD 101379 and HD 101380) are separated by 0.23 arcsec, which is spatially resolved by speckle methods.

The RS CVn-type single-lined spectroscopic binary HD 101379 has a G5/8 giant primary with a radius of 16.56 R. This binary shows strong CaII H, CaII K, and variable Hα emissions. Moreover, it shows a periodic photometric variation of 61.4 days, which dominates any other variations of GT Mus. This 61.4 day variation may be attributed to a rotational modulation of one or more starspots on HD 101379. These features indicate high magnetic activity, which implies that the flare observed by MAXI may have originated on HD 101379.

The other system, HD 101380, is a binary consisting of an A0 and an A2 main-sequence star. In the folded V-band GT Mus light curve, a small dip is detected. It is interpreted to be due to an eclipse of this binary with a period of 2.75 day. No variations by spots have ever been observed. Thus, it is feasible to speculate that HD 101379 has higher chromospheric activity than HD 101380.

All of the reported MAXI flares from GT Mus so far have been detected by the MAXI “nova-alert system”. However, there is a real potential that some flares have been missed by this automated system. Given the current small number (23) in the MAXI stellar flare sample and the highly active nature of GT Mus, GT Mus provides a good opportunity to study the physical characteristics of stellar flares and their mechanism.

Now, Sasaki and colleagues carried out a detailed analysis of the MAXI data of GT Mus to search for Xray flares. They successfully detected 11 flares (including the three that have been already reported) in 8 yr of observations with Monitor of All-sky X-ray Image (MAXI) from 2009 August to 2017 August. All flared showed a total released energy of 10³⁸ erg or higher. They also performed a unified analysis for all of them and found that the detected flare peak luminosities were 1–4 × 10³³ erg s¯¹ in the 2.0–20.0 keV band for its distance of 109.6 pc.

Their timing analysis showed long durations (τr +τd) of 2–6 days with long decay times (τd) of 1–4 days. The released energies during the decay phases of the flares in the 0.1–100 keV band ranged 1–11 × 10³⁸ erg, which are at the upper end of the observed stellar flare. The released energies during whole duration time ranged 2–13 × 10³⁸ erg in the same band.

They also carried out X-ray follow-up observations for one of the 11 flares with Neutron star Interior Composition Explorer (NICER) on 2017 July 18 and found that the flare cooled quasi-statically. On the basis of a quasi-static cooling model, the flare loop length is derived to be 4 × 10¹² cm (or 60 R). This size is a 2–3 orders of magnitude larger than that of the typical solar flare loop of 10⁹–10¹⁰. While, the electron density is derived to be 1 × 10¹⁰ cm¯³, which is consistent with the typical value of solar and stellar flares (10¹⁰¯¹³ cm¯³). The ratio of the cooling timescales between radiative cooling (τrad) and conductive cooling (τcond) is estimated to be τrad ∼ 0.1 τcond from the temperature; thus radiative cooling was dominant in this flare.

Figure 1. Scatter plot of the X-ray to bolometric luminosity ratio (LX/Lbol) vs. Rossby number (Ro). Dots and plus signs are for late-type main-sequence single and binary stars, respectively. The solar symbol is for the Sun. Squares are for G- and K-type giant binaries. The star indicates GT Mus. © Sasaki et al.

Furthermore, for the first time, they plotted the G and K giant binary samples in the diagram of X-ray to bolometric luminosity ratio versus Rossby number (shown in fig 1) and obtained a consistent distribution with those for the low-mass stars. The Rossby number and log(LX/Lbol) of GT Mus are 0.614 and −3.5, respectively, which puts GT Mus in line with the relation derived from low-mass and giant binary stars in the diagram. It shows a considerably higher LX/Lbol than other giant binaries. This high X-ray fraction suggests that GT Mus is at a high magnetic activity level, which is consistent with what is inferred from its recurring large flares.

Featured image: R/B-band color composite image of GT Mus from the Second Digitized Sky Survey (DSS2), measuring 30 arcminutes across. © In-the-Sky

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Reference: Ryo Sasaki, Yohko Tsuboi, Wataru Iwakiri, Satoshi Nakahira, Yoshitomo Maeda, Keith C. Gendreau, Michael F. Corcoran, Kenji Hamaguchi, Zaven Arzoumanian, Craig Markwardt, Teruaki Enoto, Tatsuki Sato, Hiroki Kawai, Tatehiro Mihara, Megumi Shidatsu, Hitoshi Negoro, Motoko Serino, “The RS CVn type star GT Mus shows most energetic X-ray flares throughout the 2010s”, the Astrophysical Journal, 910(1), 23 Mar 2021. https://iopscience.iop.org/article/10.3847/1538-4357/abde38

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Researchers Reveal Effects of Magnetic Activity on Mass Transfer of Binary (Astronomy)

Algol-type binary systems consist of a B-A-F type main-sequence primary component and an F-G-K type giant or subgiant secondary component.

© Xiang Dong et al.

According to the explanation of the Algol paradox, the initially more massive component evolves to fill the Roche lobes first and transfer material to another component, which results in the inversion of mass ratio and the formation of the Algol-type systems. Hence, mass transfer plays an important role in the evolution of this kind of binary system.

A research team led by Prof. QIAN Shengbang from the Yunnan Observatories of the Chinese Academy of Sciences analyzed the magnetic activity of interacting binaries and revealed its effects on the mass transfer of the binary. The study was published in The Astronomical Journal on Dec. 23.

The researchers analyzed the binary system KIC 06852488. Its primary component is a δ Sct-type pulsating star in the main-sequence stage, and its secondary component is a late-type component with a strong magnetic activity.

They found that the variation of the two maxima in the light curve was related with a same cycle length ~2000 days and a 180°phase difference, and the variation of the secondary maxima coincided with the O-C curve of primary light minima.

“The variation of light curve of KIC 06852488 is strongly correlated with the variation of O-C curve,” said SHI Xiangdong, first author of the study.

After analyzing the Kepler and Transiting Exoplanet Survey Satellite (TESS) light curves, the researchers detected that this binary is a semi-detached system with a mass ratio 0.46. The secondary component is filling its critical Roche lobe.

“The variation of the O’Connell effect could be explained by an evolving hot spot on the primary component and an evolving cool spot on the secondary component, and their positions are almost symmetrical with the inner Lagrange L1 point,” said Prof. QIAN. This reveals that the mass transfer of the binary may be related to the magnetic activity.

The flares, pulsation of component, mass transfer and spot activity make the system a natural astrophysics laboratory for studying the interaction of binary mass transfer, stellar pulsation and magnetic activity.

Reference: Xiang-dong Shi, Sheng-bang Qian, Lin-jia Li, and Nian-ping Liu, “Flaring and Spot Activities on the Semi-detached Binary System KIC 06852488”, AJ 161 (46), 2020. https://iopscience.iop.org/article/10.3847/1538-3881/abccd7

Provided by Chinese Academy of Sciences

Scientists Developed Detector For Sun (Planetary Science)

Researchers from MIPT have developed a prototype detector of solar particles. The device is capable of picking up protons at kinetic energies between 10 and 100 megaelectronvolts, and electrons at 1-10 MeV. This covers most of the high-energy particle flux coming from the sun. The new detector can improve radiation protection for astronauts and spaceships, as well as advancing our understanding of solar flares. The research findings are reported in the Journal of Instrumentation.

Photo. Device prototype: (1) the body of the detector consisting of scintillation disks, (2) fiber optics in a protective coating, (3) control boards for managing offset voltage and data acquisition — developed at the Institute for Nuclear Research of the Russian Academy of Sciences, (4) prototype frame and stand for ground-based observations. ©Egor Stadnichuk et al./Journal of Instrumentation

As energy gets converted from one form to another in the active regions of the solar atmosphere, streams of particles — or cosmic rays — are born with energies roughly between 0.01-1,000 MeV. Most of these particles are electrons and protons, but nuclei from helium to iron are also observed, albeit in far smaller numbers.

The current consensus is that the particle flux has two principal components. First, there are the narrow streams of electrons in brief flares lasting from tens of minutes to several hours. And then there are the flares with broad shockwaves, which last up to several days and mostly contain protons, with some occasional heavier nuclei.

Despite the vast arrays of data supplied by solar orbiters, some fundamental questions remain unresolved. Scientists do not yet understand the specific mechanisms behind particle acceleration in the shorter- and longer-duration solar flares. It is also unclear what the role of magnetic reconnection is for particles as they accelerate and leave the solar corona, or how and where the initial particle populations originate before accelerating on impact waves. To answer these questions, researchers require particle detectors of a novel type, which would also underlie new spaceship security protocols that would recognize the initial wave of electrons as an early warning of the impending proton radiation hazard.

A recent study by a team of physicists from MIPT and elsewhere reports the creation of a prototype detector of high-energy particles. The device consists of multiple polystyrene disks, connected to photodetectors. As a particle passes through polystyrene, it loses some of its kinetic energy and emits light, which is registered by a silicon photodetector as a signal for subsequent computer analysis.

The project’s principal investigator Alexander Nozik from the Nuclear Physics Methods Laboratory at MIPT said: “The concept of plastic scintillation detectors is not new, and such devices are ubiquitous in Earth-based experiments. What enabled the notable results we achieved is using a segmented detector along with our own mathematical reconstruction methods.”

Part of the paper in the Journal of Instrumentation deals with optimizing the detector segment geometry. The dilemma is that while larger disks mean more particles analyzed at any given time, this comes at the cost of instrument weight, making its delivery into orbit more expensive. Disk resolution also drops as the diameter increases. As for the thickness, thinner disks determine proton and electron energies with more precision, yet a large number of thin disks also necessitates more photodetectors and bulkier electronics.

The team relied on computer modeling to optimize the parameters of the device, eventually assembling a prototype that is small enough to be delivered into space. The cylinder-shaped device has a diameter of 3 centimeters and is 8 centimeters tall. The detector consists of 20 separate polystyrene disks, enabling an acceptable accuracy of over 5%. The sensor has two modes of operation: It registers single particles in a flux that does not exceed 100,000 particles per second, switching to an integrated mode under more intense radiation. The second mode makes use of a special technique for analyzing particle distribution data, which was developed by the authors of the study and does not require much computing power.

“Our device has performed really well in lab tests,” said study co-author Egor Stadnichuk of the MIPT Nuclear Physics Methods Laboratory. “The next step is developing new electronics that would be suitable for detector operation in space. We are also going to adapt the detector’s configuration to the constraints imposed by the spaceship. That means making the device smaller and lighter, and incorporating lateral shielding. There are also plans to introduce a finer segmentation of the detector. This would enable precise measurements of electron spectra at about 1 MeV.”

References: E. Stadnichuka, T. Abramova, M. Zelenyi, A. Izvestnyy, A. Nozik, V. Palmin and I. Zimovets, “Prototype of a segmented scintillator detector for particle flux measurements on spacecraft”, 2020 • © Journal of Instrumentation, Volume 15, September 2020. https://iopscience.iop.org/article/10.1088/1748-0221/15/09/T09006

Provided by Moscow Institute Of Physics And Technology

A New Look At Sunspots (Astronomy)

NASA’s extensive fleet of spacecraft allows scientists to study the Sun extremely close-up – one of the agency’s spacecraft is even on its way to fly through the Sun’s outer atmosphere. But sometimes taking a step back can provide new insight.

One of the largest sunspots seen in early January 2014, as captured by NASA’s Solar Dynamics Observatory. An image of Earth has been added for scale. ©NASA/SDO

In a new study, scientists looked at sunspots – darkened patches on the Sun caused by its magnetic field – at low resolution as if they were trillions of miles away. What resulted was a simulated view of distant stars, which can help us understand stellar activity and the conditions for life on planets orbiting other stars.

“We wanted to know what a sunspot region would look like if we couldn’t resolve it in an image,” said Shin Toriumi, lead author on the new study and scientist at ?the Institute of Space and Astronautical Science at JAXA. “So, we used the solar data as if it came from a distant star to have a better connection between solar physics and stellar physics.”

Sunspots are often precursors to solar flares – intense outbursts of energy from the surface of the Sun – so monitoring sunspots is important to understanding why and how flares occur. Additionally, understanding the frequency of flares on other stars is one of the keys to understanding their chance of harboring life. Having a few flares may help build up complex molecules like RNA and DNA from simpler building blocks. But too many strong flares can strip entire atmospheres, rendering a planet uninhabitable.

To see what a sunspot and its effect on the solar atmosphere would look like on a distant star, the scientists started with high-resolution data of the Sun from NASA’s Solar Dynamics Observatory and JAXA/NASA’s Hinode mission. By adding up all the light in each image, the scientists converted the high-resolution images into single datapoints. Stringing subsequent datapoints together, the scientists created plots of how the light changed as the sunspot passed across the Sun’s rotating face. These plots, which scientists call light curves, showed what a passing sunspot on the Sun would look like if it were many light-years away.

“The Sun is our closest star. Using solar observing satellites, we can resolve signatures on the surface 100 miles wide,” said Vladimir Airapetian, co-author on the new study and astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “On other stars you might only get one pixel showing the entire surface, so we wanted to create a template to decode activity on other stars.”

The new study, published in the Astrophysical Journal, looked at simple cases where there is just one group of sunspots visible across the entire face of the Sun. Even though NASA and JAXA missions have continually gathered observations of the Sun for over a decade, these cases are quite rare. Usually there are either several sunspots – such as during the solar maximum, which we are now moving toward – or none at all. In all the years of data, the scientists only found a handful of instances of just one isolated sunspot group.

Studying these events, the scientists found the light curves differed when they measured different wavelengths. In visible light, when a singular sunspot appears at the center of the Sun, the Sun is dimmer. However, when the sunspot group is near the edge of the Sun, it’s actually brighter due to faculae – bright magnetic features around sunspots – because, near the edge, the hot walls of their nearly vertical magnetic fields become increasingly visible.

The scientists also looked at the light curves in x-ray and ultraviolet light, which show the atmosphere above the sunspots. As the atmospheres above sunspots are magnetically heated, the scientists found brightening there at some wavelengths. However, the scientists also unexpectedly discovered that the heating could also cause a dimming in the light coming from the lower temperature atmosphere. These findings may provide a tool to diagnose the environments of spots on the stars.

“So far we’ve done the best-case scenarios, where there’s only one sunspot visible,” Toriumi said. “Next we are planning on doing some numerical modeling to understand what happens if we have multiple sunspots.”

By studying stellar activity on young stars in particular, scientists can glean a view of what our young Sun may have been like. This will help scientists understand how the young Sun – which was overall more dim but active – impacted Venus, Earth and Mars in their early days. It could also help explain why life on Earth started four billion years ago, which some scientists speculate is linked to intense solar activity.

Studying young stars can also contribute to scientists’ understanding of what triggers superflares – those that are 10 to 1000 times stronger than the biggest seen on the Sun in recent decades. Young stars are typically more active, with superflares happening almost daily. Whereas, on our more mature Sun, they may only occur once in a thousand years or so.

Spotting young suns that that are conducive to supporting habitable planets, helps scientists who focus on astrobiology, the study of the origin evolution, and distribution of life in the universe. Several next generation telescopes in production, which will be able to observe other stars in x-ray and ultraviolet wavelengths, could use the new results to decode observations of distant stars. In turn, this will help identify those stars with appropriate levels of stellar activity for life – and that can then be followed up by observations from other upcoming high-resolution missions, such as NASA’s James Webb Space Telescope.

Provided by NASA/GODDARD SPACE FLIGHT CENTER