XMM-Newton Detects X-ray Superflare from Ultracool Dwarf | Astronomy – Sci-News.com
Using data from the European Photon Imaging Camera (EPIC) onboard ESA’s XMM-Newton X-ray observatory, astronomers have detected for the first time a powerful X-ray flare from an ultracool dwarf of spectral class L. Designated 3XMM J033158.9-273925 (hereafter J0331-27), the tiny star is located approximately 783 light-years away. In a matter of minutes, it released over 10 times more energy of even the most intense flares suffered by the Sun.
An artist’s impression of an L dwarf star, a star with so little mass that it is only just above the boundary of actually being a star, caught in the act of emitting an enormous superflare of X-rays, as detected by ESA’s XMM-Newton X-ray space observatory. Image credit: ESA.
Flares are released when the magnetic field in a star’s atmosphere becomes unstable and collapses into a simpler configuration.
In the process, it releases a large proportion of the energy that has been stored in it.
This explosive release of energy creates a sudden brightening — the flare — and this is where the new observations present their biggest puzzle.
“This is the most interesting scientific part of the discovery, because we did not expect L-dwarf stars to store enough energy in their magnetic fields to give rise to such outbursts,” said Dr. Beate Stelzer, an astronomer in the Institut für Astronomie und Astrophysik Tübingen and INAF – Osservatorio Astronomico di Palermo.
Energy can only be placed in a star’s magnetic field by charged particles, which are also known as ionized material and created in high-temperature environments.
As an L dwarf, however, J0331-27 has a low surface temperature for a star — just 2,100 K compared to the roughly 6,000 K on the Sun.
Astronomers did not think such a low temperature would be capable of generating enough charged particles to feed so much energy into the magnetic field. So the conundrum is: how a superflare is even possible on such a star.
“That’s a good question. We just don’t know — nobody knows,” Dr. Beate said.
Understanding the similarities and differences between this new — and so far unique — superflare on the L dwarf and previously observed flares, detected at all wavelengths on stars of higher mass is now a priority for the team. But to do that, they need to find more examples.
Stars that flare more frequently release less energy each time, while this L dwarf seems to release energy very rarely but then in a really big event.
Why this might be the case is still an open question that needs further investigation.
“The discovery of this L dwarf superflare is a great example of research based on the XMM-Newton archive, demonstrating the mission’s enormous scientific potential. I look forward to the next surprise,” said Dr. Norbert Schartel, XMM-Newton project scientist for ESA.
The findings were published in the journal Astronomy & Astrophysics.
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Andrea De Luca et al. 2020. EXTraS discovery of an X-ray superflare from an L dwarf. A&A 634, L13; doi: 10.1051/0004-6361/201937163
