A very large eruption from a young sun-like star suggests that young planets must exist in a fairly violent environment.
A team of scientists from the Center for Astrophysics (CfA) used the Submillimeter Array (SMA), a set of telescopes on Maunakea in Hawaii, to observe the young star HD 283572. The team watched as the brightness of HD 283572 increased hundreds of times. for a few hours. This eruption was seen as one of the most powerful flares ever seen.
Located about 400 light-years away, HD 283572 is about 1.4 times the size of the sun – but just under 3 million years old, it is a thousand times younger than our star, which is about 4.6 billion years old. That means that when astronomers saw HD 283572, they saw it at the same stage of life that the sun was in when it started forming planets, like Earth.
As a result, these results may indicate that planets must have had turbulent conditions to form, including the planets of the solar system.
“We were surprised to see an extremely bright flare from an ordinary young star,” team leader and CfA scientist Joshua Bennett Lovell said in a statement. “Any potential planets developing in this system would be wasted by the intense power of the flare. I don’t want to grow up there!”
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Young stars are strictly wound springs
Stellar flares like the ones observed by Lovell and his colleagues are thought to be created as stars rotate and interact with their magnetic fields.
Just as the termination of a spring stores too much kinetic energy that must be released, the magnetic energy stored in these termination magnetic fields must be relaxed. In the case of stars, this sends bursts of accelerated particles erupting through their surfaces and out into space.
Stellar flares accompanying this eruption of stellar material, or plasma, can increase a star’s brightness by thousands or hundreds of times and across a range of light wavelengths. However, seeing such flares is still challenging because these events are essentially random, so there is no clear idea of when to point a telescope at a star to catch its next streak.
This was certainly the case for HD 283572, which was seen dormant before its massive eruption.
“Every time we sent the SMA back to the star after this flare, we saw nothing,” explained Lovell. “Our results confirm that these flare events are rare at millimeter wavelengths, but can be extremely powerful for stars at this young age.”
Over a period of 9 hours, the energy of the HD 283572 flare reached levels millions of times greater than the energy released by similar flares measured in the vicinity of the solar system.
“This was a massive event, equivalent to expending the Earth’s entire nuclear arsenal in a millisecond, over and over again, for almost half a day!” SMA Project Scientist and staff member Garrett Keating said in the statement. “If we account for the wavelengths of light from the star that were not detected by the SMA, we expect that it could be much more energetic.”
The team only saw one flare from HD 283572, so we can’t be sure right now what triggered the massive explosion.
“Flares at these wavelengths are rare, and we didn’t expect to see anything but a faint glow of planet-forming dust,” Keating said. “It’s a real puzzle, and there are a range of mechanisms that could be at work. Interactions with unseen companion stars or planets or periodic spotting activity are two possibilities, but there’s no doubting how powerful this incident.”
Flares like these are so powerful that they can remove atmospheres as they develop around young planets that are forming.
The discovery of such an energetic flare at this critical period in the life of the planetary system gives scientists a clue about the type of pressure that Earth and its sibling planets would have been under when it was forming around 4.5 billion years ago. The results could also hint at what could be suffering from extra-solar planets or “exoplanets” in earlier stages of their current life.
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The team behind this research is continuing to monitor HD 283572 to find out how often the young star erupts and to see if this flaring could affect the growth of planetary atmospheres in the young planets around her.
In addition, the new SMA campaign will study other young stars like HD 283572 to determine their typical properties and flare frequencies. By combining the SMA data with longer wavelength observations, the team said they also hope to better understand the physics of these flares and the processes that lead to them.
The team’s findings have been accepted for publication in The Astrophysical Journal Letters, and a peer-reviewed paper is available on arXiv.