Using observations from ESO’s VLT, astronomers were able for the first time to reconstruct the site of a flare on a solar-like star located 150 light years away - about ten million times further away from us than the Sun is. The study of this young star, BO Microscopii, will help scientists better understand the youth of our own star.

BO Microscopii is a young star with a mass about 90% of the mass of our Sun. It is located 150 light years away towards the Microscope constellation. 'Speedy Mic', as it is called, got its name because of its very fast rotation. The object rotates 66 times as fast as our Sun, which results in much stronger magnetic fields than ours.

Using a technique called ‘Doppler imaging’, the astronomers reconstructed images of the surface of the star, detecting the presence of several spots. A few are near the visible pole, while most spots are asymmetrically distributed at mid-latitudes.


One nine-hour rotation of Speedy Mic in fast motion as deduced from the UVES observations. Dark spots on the surface correspond to concentrations of magnetic fields. These fields partially extend to far above the surface, presumably supporting the large prominence loops. The small loop, colored red during the flare, marks the reconstructed flare site. Note that the shape and precise size of the shown loops are not constrained by the Doppler imaging. The scale at the bottom of the animation shows the relative size compared to the star.

Trying to see spots on its surface is thus as challenging as trying to directly obtain a photograph of the footsteps of Neil Armstrong on the Moon, and be able to see details in it.

This is impossible to achieve even with the best telescopes: to obtain an image with such amount of details, you would need a telescope with a 400 km wide mirror. Astronomers therefore use indirect imaging techniques, such as Doppler imaging. Doppler imaging makes use of the information contained in the slightly changing spectra observed as a star rotates. In this case, the astronomers obtained 142 spectra of the star with the UVES spectrograph on ESO’s VLT.

“The image we could secure of Speedy Mic is, given its distance, a real prowess, that allows us to localise for the first time ever the source of a flare and its surrounding,” says Uwe Wolter, lead author of the paper relating the discovery. The team is composed of Wolter, J. Robrade, and J. Schmitt (Hamburg Observatory, Germany), and J. Ness (Arizona State University, USA).

The X-ray observations indeed identified several flares, which are sudden and vast releases of energy. For one of them, the astronomers could pinpoint its origin on the surface of the star. The flare, lasting about 4 hours, was a hundred times more energetic than a large solar flare and considerably larger than solar coronal loops.

The surprising finding, the team says, was the location of the flare. Contrary to our Sun, the site of the observed flare does not correspond to the detected spots.

“Interestingly, the flare occurs on a rather inconspicuous portion of the star’s surface, away from the main concentration of activity in terms of dark spots,” explains Wolter.

Speedy Mic is a very young star: with an age of only about 30 million years, it is roughly 150 times younger than the Sun. “It is very likely that our young Sun was such a fast rotator as well,” says Wolter. “Studying Speedy Mic is thus like observing our own host star while still in its infancy and so, better understand how the eruptions on the young Sun affected the planets. These studies may also contribute to the understanding of current solar eruptions which can cause havoc in our telecommunications and power distributions.”

The team reports their results in the Astronomy and Astrophysics article, Doppler imaging an X-ray flare on the ultrafast rotator BO Mic - A contemporaneous multiwavelength study using XMM-Newton and VLT by. U. Wolter et al.).