Young stars spotted blasting gamma rays for the first time

Fermi telescope's observations revealed that the gamma-ray radiation is originating from a class of stars called T Tauri. 
Mrigakshi Dixit
Artist's impression of a T Tauri star: system formed by a central star and a circumstellar disk
Artist's impression of a T Tauri star: system formed by a central star and a circumstellar disk

INAF-OAPa/S. Orlando 

For the first time, a young, sun-like star has been observed spewing high-energy gamma radiation. 

This observation was carried out by an international team of astronomers utilizing the data from the powerful Fermi satellite telescope, which explores the universe in gamma rays.

This telescope's observations revealed that the gamma-ray radiation is originating from a class of stars called T Tauri. 

The first observational evidence

Gamma radiation is one of the most intense forms of light known to exist in the universe.

Despite its high intensity, this sort of radiation is difficult to detect using a ground-based telescope. This is where the high-sensitive Fermi satellite comes into play. Fermi has been regularly monitoring the sky since its launch in 2008. 

According to the official release from the Royal Astronomical Society, this thorough monitoring has indicated that the sources of around 30 percent of gamma-ray detections remain unknown to date. 

Ph.D. student Agostina Filócomo and a team of researchers set out to discover the source of some of the already discovered gamma rays. 

They were able to track that a large number of gamma rays seem to be originating from star-forming areas. 

Among them, the three unidentified gamma-ray sources detected at distinct time intervals were found to be originating from the young star-forming region NGC 2071, which is based 1,350 light years from Earth. This is located in the molecular cloud Orion B's northern hemisphere.

Megaflares are a possible source

The researchers investigated T Tauri stars in this formation to determine the source of these unexplained gamma-ray bursts.

As per the study release, T Tauri stars have a central star surrounded by a planet-forming disk of stellar gas and dust. This class of stars stands out as they exhibit varying brightness and are mostly located around active star formation zones.

The team identified as many as 58 T Tauri stars developing in NGC 2071. Therefore, these are the only known objects in this region that could be emitting gamma rays.

The study hypothesizes that the gamma-ray was produced by intense flare events known as "megaflares" of these stars. 

These flares are caused by the abrupt release of stored magnetic energy in the form of electromagnetic bursts. “Megaflares can span several stellar radii and last a few hours,” noted the release. Even our Sun produces solar flares but on a far lesser scale. 

Filócomo explained in the release: “This observational evidence is essential for understanding the origin of sources that have previously remained unknown for more than a decade, which is unquestionably a step forward in astronomy. It is also critical to comprehend the processes that occur during the early phases of star formation: if a T Tauri star produces gamma-ray radiation, it will affect the gas conditions of the protoplanetary disk and, consequently, the evolution of planet formation. The discovery of this phenomenon serves to understand how not only the Sun but also our home planet, Earth, were formed and evolved.”

The study is published in the Monthly Notices of the Royal Astronomical Society.

Study abstract:

NGC 2071 is a star-forming region that overlaps with three γ-ray sources detected by the Fermi Space Telescope. We propose that strong flare activity in T Tauri stars could produce γ-ray emission in a way that makes them a counterpart to some unidentified sources detected by the Large Area Telescope aboard the Fermi satellite. We have performed a spectral and temporal analysis for two Fermi data sets: the first 2 yr and the entire 14 yr of observations. We have found that the γ-ray source is detectable at 3.2σ above the background at energies above 100 GeV during the first 2 yr of observation. The analysis of the expected frequency of the highest energy flares occurring in T Tauri stars is consistent with our estimate. In addition, we have determined the minimum energy of the flare that would produce γ-ray emission, which is ∼5 × 1037 erg. This agreement becomes a hard observational constraint supporting previous hypotheses about rare flares as the origin of unidentified γ-ray sources in star-forming regions.

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