Sinister Security: ALMA

Powerful Flare from Star Proxima Centauri Detected with ALMA

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Space weather emitted by Proxima Centauri, the star closest to our stars (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.

ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 meters

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.”

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.

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.

Credit: nrao.edu

Potential Building Block Of Life Found In Very Young Star System

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Two teams of researchers report today that they have detected a prebiotic molecule—a potential building block of life—around newly formed sun-like stars. The molecule, methyl isocyanate, has a structure that is chemically similar to a peptide bond, which is what holds amino acids together in proteins.

The finding suggests that quite complex organic molecules may be created very early in the evolution of star systems.

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“It shows the level of complexity you can get to before planets form is pretty high. A lot of [spectral] lines were detected which gives confidence that it’s real. It’s a safe detection.” says astrochemist Karin Oberg of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, who was not involved in the studies.

Methyl isocyanate has become a target for astrochemists ever since the European Space Agency’s Rosetta mission detected the molecule on the comet 67P/Churyumov-Gerasimenko 2 years ago. Comets are thought to have survived unchanged since the early days of the solar system, so the discovery of methyl isocyanate suggested it had been present on the comet since then and didn’t form on a planet.

Although the detection on 67P/Churyumov-Gerasimenko is now questioned by some, methyl isocyanate was also detected in two star-forming clouds, Orion KL and Sagittarius B2(N), in 2015 and 2016, but these are hot environments full of very massive stars, very unlike the situation of the early Sun.Top of FormBottom of Form Undaunted, researchers began to study more sun-like sources. One group was already surveying a clutch of very young stars known as IRAS 16293-2422.

“We thought, why not look [for methyl isocyanate] in our source,” says team member Niels Ligterink of Leiden Observatory in the Netherlands.

The instrument of choice for such studies is the Atacama Large Millimeter/Submillimeter Array (ALMA), a collection of 66 dishes high in the Chilean Andes. ALMA focuses on the region of the spectrum between radio waves and infrared light, the range of frequencies at which complex molecules emit light when they undergo various transitions. Because the molecules are so complex, there are many possible transitions, each emitting photons of a specific frequency.

So a molecule such as methyl isocyanate will emit a characteristic fingerprint of photons that will appear as spikes or lines in the spectrum detected from the gas cloud. The challenge for astronomers is to identify that fingerprint among the forest of spectral lines from all the other chemicals in the cloud.

Ligterink’s team combed through data they had collected from IRAS 16293-2422 using ALMA in 2014 and 2015 and found 43 clearly identifiable lines from methyl isocyanate. The other team, led by Rafael Martín-Doménech of the Center for Astrobiology (INTA-CSIC) in Madrid, Spain, used new and archived data to find another eight lines in a different frequency range. The two teams report their results in the latest issue of the Monthly Notices of the Royal Astronomical Society.

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Both teams then tried to figure out how methyl isocyanate might have formed in such a very cold and inhospitable environment. In a protoplanetary cloud around a young star there would be tiny grains of rocky material that would provide a surface on which chemicals could react.

Ligterink says his team filled a vacuum chamber with a gas mixture of isocyanic acid and methane and chilled it to 15 kelvin, freezing the gases onto a gold surface. They then illuminated the surface with intense ultraviolet light, as you might get from a young sun-like star. The infrared spectrum of the resulting gas, as well as mass spectrometry, showed clear signs of methyl isocyanate.

In space, many other molecules would also be present, says Ligterink, such as water, carbon monoxide, and carbon dioxide. More experiments are needed to ensure these would not block the reaction.

Martín-Doménech says that their chemical modeling of the cloud suggests that reactions on dust grains would not have produced enough of the molecules.

“There must be more reactions in the gas phase to get the abundances we observed,” he says.

Oberg says that although methyl isocyanate is not the most complex organic molecule that’s been detected in star-forming clouds, it’s interesting because it is so similar to a key part of proteins. But she warns about jumping to the conclusion that newly formed planets are seeded with the entire key ingredient for life.

“We don’t know the chemical process. We don’t know if methyl isocyanate is crucial and we don’t know how peptides form,” she says. Although such studies are finding ever more complex molecules ahead of planet formation, “the link to how life forms on planets is unknown.”

The two teams and others will continue to scour gas clouds for other complex organic molecules to fill out the picture of life formation. Martín-Doménech says the holy grail for these searches is amino acids, in particular the simplest one: glycine. Amino acids, the building blocks of proteins, are more complex than the likes of methyl isocyanate and likely to exist in smaller quantities that would be harder to detect. So glycine would be a big prize. Says Martín-Doménech:

“Then you are just one step from proteins.”

Sinister Security

Powerful Flare from Star Proxima Centauri Detected with ALMA

Potential Building Block Of Life Found In Very Young Star System

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