`Less active than similar stars`

James Marshall
May 4, 2020

The researchers compared data from similar stars with historical data on solar activity.

The stellar brightness variations due to bright and dark spots rotating across our line of sight are generally of much lower amplitude though. This finding has made many experts believe that the sun is going through a quiet phase for several millennia. The extent to which solar activity (and thus the number of sunspots and the solar brightness) varies can be reconstructed using various methods - at least for a certain period of time.

To understand what the sun was doing before those records begin, scientists can interpret a host of data types, like levels of specific elements in tree rings and ancient ice.

"After all, our star is nearly 4.6 billion years old", said lead author Dr. Timo Reinhold, a scientist in the Max-Planck-Institut für Sonnensystemforschung.

"Nine thousand years in the lifetime of a star 4.5 billion years old is like less than three-quarters of an hour in the life of a 40-year-old human", Professor Horner said.

"These other stars could represent some other phase of the Sun that we just haven't lived long enough to see". These data showed that the sun has not been much more active than it is now.

Be thankful that the sun is truly weird, as researchers have learned by contrasting its action and that of comparable stars.

"We've chosen those stars we think are solar like on the basis they are about the same mass, they're about the same temperature, they're about the same age, they're about the same composition, but what we're learning is that there is more to it than that", Professor Horner said. A star's rotation contributes to the creation of its magnetic field in a dynamo process in its interior.

The researchers scoured this huge sample and selected those stars that rotate once around their own axis within 20 to 30 days. The Sun needs about 24.5 days for this. In the end, they came up with 369 Sun-like stars to study.

In a pulsating star, the light variation has an intrinsic cause: the star literally pulses in and out, becoming larger then smaller, brighter then fainter, with a regularly repeating pattern of changing brightness.

The sun seems to be much less active than similar stars in terms of brightness fluctuations caused by sunspots and other phenomena - scientists say a "boring" personality that is not necessarily a bad thing for us compatriots. By quantifying the brightness variations of the stars, the authors found that most were more active than the Sun, often being five times more variable than the Sun was over the last 140 years. Alexander Shapiro of MPS, who heads the research group "Connecting Solar and Stellar Variabilities".

However, it is not possible to determine the rotation period of all the stars observed by the Kepler telescope. Viewed through the Kepler telescope, even the Sun would not reveal its rotation period. Still, the team of researchers also analyzed over 2,500 stars similar to the Sun with unknown orbit periods, which showed that their glow changed a lot less. These results allow two interpretations.

But while the Sun's calmness reminded Professor Horner of the ultimate movie midlife slacker, the "Dude" from The Big Lebowski, we just haven't got enough data to know if this is the norm, he said. They therefore concluded that most stars of the same type as the Sun are more active than the Sun. There is, however, no cause for concern. For the foreseeable future, there is no indication of such solar "hyperactivity".

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