Our Sun behaves *unlike* stars of about same mass/composition

[Halbhh]

Our own star, the Sun, appears to be an unusual acting star for a long while now, unlike others of about the same mass and composition.

It's not been doing what similar stars generally do.

https://phys.org/news/2020-04-sun-similar-stars.html

"By cosmic standards the sun is extraordinarily monotonous. This is the result of a study presented by researchers from the Max Planck Institute for Solar System Research in the upcoming issue of Science. For the first time, the scientists compared the sun with hundreds of other stars with similar rotation periods. Most displayed much stronger variations. ...

[But not our sun]...over the past 9000 years. For this period of time, scientists find regularly recurring fluctuations of comparable strength as during recent decades. "However, compared to the entire lifespan of the Sun, 9000 years is like the blink of an eye," says MPS scientist Dr. Timo Reinhold, first author of the new study. After all, our star is almost 4.6 billion years old. "It is conceivable that the Sun has been going through a quiet phase for thousands of years and that we therefore have a distorted picture of our star," he adds."

Our sun is a weirdly 'quiet' star — and that's lucky for all of us | Space

"The astronomers narrowed down a collection of tens of thousands of stars by focusing on those with about the same surface temperature, surface gravity, age and metallicity as our sun. Then, they split these stars into two batches: one containing 369 stars that rotate every 20 to 30 days and one with 2,529 stars that scientists haven't been able to calculate a rotation period for. (The sun rotates every 24.5 days, but that spin likely wouldn't be detectable to alien astrophysicists using the same techniques humans have, so both of these groups of stars are important.)

"The researchers then analyzed both these groups of stars to understand their activity levels and how they compare with the sun. Stars with known rotation rates were on average much more active than our sun has been over the past 9,000 years — about five times more active.

Think on that for a minute. Our Sun behaves oddly unlike similar stars...and in a way that is very much to our advantage as modern humans.

Life on Earth can tolerate plenty of radiation induced mutations and evolution, but we as a species that already exists don't want a lot of mutations. (Most radiation induced mutations are of course harmful, but some non-cancerous instances that affect reproductive germ cells can create lasting new mutations)....

So, it doesn't seem it is life on Earth that needs our Sun to be acting so uniquely unlike other similar stars. .... No.

It doesn't seem anthropomorphic, in other words. It's not the inevitable correspondence it seems, where you'd need only this kind of star for us to be able to show up in the tree of life at some point naturally.... That's not this situation.

Rather, you'd need this kind of star (or......rather, this kind of unusual behavior, to be more exact.....) for us to flourish after we show up -- as we have.



heh heh

 

[Brightmoon]

9000 years isn’t long compared to the how the Hominidae have been here . Even the chimp/ bonobos and human split happened long before that at 7 million years

 

[Halbhh]

9000 years isn’t long compared to the how the Hominidae have been here . Even the chimp/ bonobos and human split happened long before that at 7 million years

Yup. But, modern human civilization on the other hand has a time frame much alike to that 9,000 years they were able to measure. (note they didn't say anything about older than 9,000 years; perhaps because their tree ring analysis didn't have older time frame specimens?)

-----

An additional interesting hypothesis that came to mind regarding the brightness variations: Those variations in total solar radiance might be large enough to affect the ability for a fixed location city to farm the same crops at that same location, over time --

Bigger changes in brightness could affect crops, not by total sunlight, but rather by weather pattern changes, that is changes in rainfall. And if so, then that would affect the viability and thus the stability of that city location, and the attendant progress possible to make by residing there in sufficient affluence to support researchers. Advancement needs a certain amount of stable and sufficient food and free time to take time to do experiments, research, etc.

 

[Halbhh]

I didn't give much background information above (and who wants to see a 1,000 word post?)... So, I'll lay out very brief background so interesting here.

Star radiance variance for these non-variable stars ('variable stars' are quite different, where the entire star shrinks and expand for example) -- stars like our sun (stars that are not variable stars) -- will be variance due to sunspots, which are regions that emit a lot less light than other regions.

Sunspots in turn show magnetic activity, that is, the magnetic energy of the star.

Magnetic activity though is caused by moving electric charge, and is in a star then generally from the the rotation of the star.

Stars with higher rotation (shorter rotational periods) we observed (for a long time now) to have a lot more flaring and sunspots.

Flares cause emissions of more radiation, of higher energies and intensities.

Ergo, a star that flares a lot bombards its planets with a lot more dangerous radiation than a star that flares little.

But, our Sun isn't acting like stars with similar mass and rotation, and for apparently at least 9,000 years (could be, or is likely to be, longer than just 9,000 yrs., but that wasn't yet analyzed) ....

...and that lack of magnetic activity/spots/variance/(and thus also flares of more intensity more often) is the thing that is so very interesting.

 

[The Barbarian]

From your source:

Then, they split these stars into two batches: one containing 369 stars that rotate every 20 to 30 days and one with 2,529 stars that scientists haven't been able to calculate a rotation period for.
...
Stars with known rotation rates were on average much more active than our sun has been over the past 9,000 years — about five times more active.

So not quite one-seventh of them were more active than our sun. A minority of them.

 

[Halbhh]

From your source:

Then, they split these stars into two batches: one containing 369 stars that rotate every 20 to 30 days and one with 2,529 stars that scientists haven't been able to calculate a rotation period for.
...
Stars with known rotation rates were on average much more active than our sun has been over the past 9,000 years — about five times more active.

So not quite one-seventh of them were more active than our sun. A minority of them.

I understand now the problem in clarity there. It's not a really clear wording.

They are saying that when they could measure at all the most key thing of all -- the rotation period -- then for those stars (all the stars of similar mass to the sun and similar composition and for which they could measure the most key thing, the rotation period), in that group our sun stands out as an exception for being unusually quiet (stable).

(!)

It's an accurate summary they made (of course) to say:

"We were very surprised that most of the sun-like stars are so much more active than the sun," Alexander Shapiro, a physicist at the Max Planck Institute for Solar System Research in Germany and a co-author on the new research, said in a statement

 

[Percivale]

I understand now the problem in clarity there. It's not a really clear wording.

They are saying that when they could measure at all the most key thing of all -- the rotation period -- then for those stars (all the stars of similar mass to the sun and similar composition and for which they could measure the most key thing, the rotation period), in that group our sun stands out as an exception for being unusually quiet (stable).

(!)

It's an accurate summary they made (of course) to say:

"We were very surprised that most of the sun-like stars are so much more active than the sun," Alexander Shapiro, a physicist at the Max Planck Institute for Solar System Research in Germany and a co-author on the new research, said in a statement

Is it easier to measure the rotation of a more active star?
What was the variability of the other group?

 

[Halbhh]

Is it easier to measure the rotation of a more active star?
What was the variability of the other group?

Good questions, and of course you can seek to find out. Stars that rotate very slowly for example (some do), theoretically are expected to have less magnetic field on average (magnetism only arises from moving charge is the long establish understanding, meaning of course non-neutral matter that is moving, and of course rotation is a largely consistent movement in an on-average consistent direction (the sun being plasma)). Thus less stellar rotation is expected to generally mean less stellar magnetic turbulence on average, thus theoretically less sun spots on average also. Now, from decades of reading astrophysics research reports though, I know that it's very common that theories are shown to be inadequate very often (often just incomplete vs the complex situation), when about something complex (like for instance stellar activity).

Note that here though, we are looking at a significantly large number of stars that we can see are very much similar to our sun...and seeing the surprising finding that those stars are observed to be far more active than our sun seems to have been in the last 9,000 years according to the way the researchers estimated our sun's activity during the last 9,000 years. It's not that they are a little more active. The factor is 5!

"The researchers then analyzed both these groups of stars to understand their activity levels and how they compare with the sun. Stars with known rotation rates were on average much more active than our sun has been over the past 9,000 years — about five times more active."

It's just an interesting thing, and of course to me interesting enough to keep my eye out for more research ongoing.