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The atmosphere of the sun has a strange cool spot amid its many layers. The outer atmosphere is super-heated to millions of degrees, while the surface is about 6,000 degrees Celsius. Sandwiched in between is a 4,000-degree C layer. Astronomers have found a similar cool layer in the atmosphere of the nearby star Alpha Centauri A.
Scientists have discovered that the sun and its nearest twin star, Alpha Centauri A, share an odd solar quirk: a puzzling cool layer in their wispy, hot atmospheres.
The different temperatures of the sun's layers have long intrigued solar scientists. The outer atmosphere, or corona, is millions of degrees hotter than the sun's surface, or photosphere, where temperatures are about 10,000 degrees Fahrenheit (5,537 degrees Celsius).
But the temperatures don't simply rise the further away you get from the surface. There is actually a cooler layer sandwiched between the photosphere and the corona called the chromosphere, where temperatures dip as low as 7,300 degrees F (4,000 degrees C).
Now scientists have found a similarly cool layer around Alpha Centauri A using the European Space Agency's Herschel space observatory to look at the nearby star in far-infrared light.
"The study of these structures has been limited to the sun until now, but we clearly see the signature of a similar temperature inversion layer at Alpha Centauri A," study leader René Liseau of the Onsala Space Observatory in Sweden said in a statement. [Alpha Centauri Stars Explained (Infographic)]
Scientists believe the extreme heating of the sun's corona is likely related to the twisting of magnetic field lines that give rise to explosions known as solar flares. Studying Alpha Centauri A could help scientists better understand the atmospheric phenomenon, especially since the star is almost a twin to the Sun in mass, temperature, chemical composition and age.
"Detailed observations of this kind for a variety of stars might help us decipher the origin of such layers and the overall atmospheric heating puzzle," Liseau said.
The discovery may also help astronomers better estimate the amount of dust in the cold debris disks surrounding sunlike stars, the scientists said. The research is detailed in a recent edition of the journal Astronomy & Astrophysics.
The three stars of the Alpha Centauri system are the nearest to Earth beyond the sun. The two main stars are the binary pair Alpha Centauri A and Alpha Centauri B. They are about 4.37 light-years from Earth.
The third star, a faint red dwarf named Proxima Centauri, is the closest at just 4.22 light-years from Earth.
In 2012, astronomers announced the discovery of an Earth-size alien planet orbiting Alpha Centauri B.
The European Space Agency's Herschel observatory used to make the new Alpha Centauri A discovery is the largest infrared space telescope ever launched into space. The observatory launched in May 2009 to map the universe in the far-infrared and submillimeter light wavelengths.
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The one thing I'd add to the story; astronomer's excitement (thanks to new tech and tools) that allow us to, for the first time, get a sense of this level of detail in a star's makeup. We've assumed that the Sun is a "typical" star, but it's sure nice to get some confirming data!
Michael - Would I be correct in saying that the reason why Alpha Centauri A is very similar to our Sun is that both these stars were formed in the same stellar nursery XX billion years ago? I never thought about it that way until now, but 4 light year apart is right next door when talking about stars. So would it make sense that they would have coalesced out of the same dust and other building blocks? So while our Sun still might not be a "typical" star, it should be the same as those right around us, since it came out of the same starting material.
Hi Mark!
Alpha Cent is about 25% older than our Sun (rather large error bar, but almost certainly older), and just happens to be a near neighbour in our times. We can very precisely measure a star's motion, and can with great accuracy predict that Alpha Cent will be closest to Sun (& Earth too, of course) in the year 29,700, and continue moving past us until it will no longer be a naked-eye star in about 100,000 years.
Alpha Centauri and our Sun are two ships passing in the night....
We do not know of ANY stars that are our Sun's siblings, formed at the same time from the same stellar nursery (nebulae). Like all families, over many many years siblings move apart, and since the other sibs never bothered to send us their forwarding e-mail addy we don't know where any of them are. The search continues....
Cheers! ~Michael (Astronomy.FM★Radio)
Good Morning, Michael! Thank you very much for the explanation. I didn't know that the stars in our own Galaxy moved around so much in relation to each other. That's a real interesting tidbit that we haven't yet found any other stars that appear to have been formed out of the same primordial material as our Sun. If we say that Alpha Centauri A is like our Sun, what factors do we look for to say that another star formed like our Sun? Is it all spectroscopy? So much has been discovered since I left Grad school in the early '80's. I alway appreciate your comments and observations on these hard science stories.
All the best.
(Sorry - I'm offline for a bit - will reply tomorrow / Thursday)
Hey again Mark! Sorry for the tardy response.
Short answer - yes on the spectroscopy.
Longer answer, Part The First: It's frankly astonishing that we know what stars are made of. This is summed up rather well by a quote from French philosopher Auguste Comte, who said in 1835:
It's not that Comte didn't want to know; he thought that it would always be beyond our technical grasp to grok that knowledge.
Science marched on, and as often happens, put to bed the "never say never" idea with new discoveries. Only 14 years later German physicist August Kirchhoff discovered that the chemical composition of a gas could be figured out from its electromagnetic spectrum. (I just skipped over a couple of key discoveries by Robert Bunsen (birthday party on March 30th; you're invited!) and one of my favs, Joseph von Fraunhofer.)
Once spectroscopy was figured out in the lab it didn't take long to use the same technique on a telescope; first targeting the Sun (big and bright, so easy to discern with the tech of the day), and once techniques improved used to examine the much fainter stars.
Spectral Trivia: Helium (named after the Greek word for sun, "helios") was discovered in the Sun's spectrum, and then in that of other stars, before it was discovered here on Earth. It was a "cosmic mystery element" that took chemistry a while to nail down.
Longer answer, Part The Second: Stars are born from immensely hugely vast really really big nebulae; gargantuan expanses of gas and small bits of matter (astronomers call it "dust"), such as the Eagle Nebula:
http://www.spacetelescope.org/static/archives/fitsimages/screen/martin_kornmesser_1.jpg
An external event, such as a distant supernova, may compress the nebular material enough for localized gravity to do its thing (gravity always sucks), eventually leading to the formation of brand-new baby stars:
http://scienceblogs.com/startswithabang/files/2012/10/heic0702a_H.jpeg
(They are so CUTE when they're babies!)
After that looooong buildup, here's the key point - stars born from the same nebula have the same composition, and the same spectra. There is some change over time as a star busily turns hydrogen into heavier elements, as stars are wont to do, but the underlying chemical makeup is enough of a fingerprint to mark a star's origin. It's rather like how someone's accent can give away the region of their birth, even after living abroad for many years (something I know of first-hand).
So, to find our Sun's siblings, all we need to do is sift through the spectra of lots and lots (and LOTS!) of stars to find another with the same "accent". (Yes, it sounds like a huge project, but that's what grad students are for!)
Determining stellar spectra is the bread and butter of astronomical investigation. I think that Comte would be overjoyed to have had his prediction found to be so wrong; judging from his other writings he seemed to be a right fine fellow.
OK, first of all, I truly hope that part of your profession involves inspiring our youth into the sciences. You just went through two lesson plans that would blow some undergrad's hair back if they had the least interested in astronomy and what exists beyond our atmosphere. I was trained as an Analytical Chemist, so my first lab experiments involved putting various organic solvents in between optical salt crystals in a Perkin Elmer IR spectrometer. I am ashamed to say that I recently went on one of the Kitt Peak overnight tours, and I didn't focus on what they were doing with spectroscopy. With the way everything goes to some 4K CMOS linear sensor (or whatever the standard is now), I probably walked right by it without "seeing" the instrument itself.
My first visit to the KSC Visitor Center in 1974 (junior in HS) netted me a NASA pamphlet about interstellar spectroscopy and how they had measured OH and simple alcohols in nebulas. I can honestly say that's what led me down the road to Chemistry in college. I just never got much of a training in astronomy, even though it interests me to this day. I saw a golden star and a blue star last year with my naked eye through a small scope, but just couldn't tell you what or where they were.
Thanks again Michael for keep the flame alight! I can tell by your vocabulary (I grok) that you've read all the classics along the way. Don't dog the poor grad students too bad....!!
ye gods; michael has written a stoked ripper book fer crying out loud! [i like it!]
Thanks Knight; yer too kind!
Small world, Mark - we may have crossed paths at KSC! I think that I still have that same pamphlet around here somewhere....
I worked at at the National Solar Observatory / McMath-Pierce Solar Scope on Kitt Peak as a grad student; it was my first "real" astronomy gig, and incredibly fun! Since I was working days I got to "bum around" the other domes at night, which was way cool.
Thanks for the encouragement to "go forth and bug the kids!" (Get off my lawn!) As a condition of my grant I am required to do four public outreach events a year; last year I did 77 - elementary, middle, and high schools, as well as community groups and star parties "at the dome". I've got a couple of regular public radio gigs, too, so I keep pretty busy.
Thanks for the kind words, gents! I'll see both you "down the Vine!"
It's a challenge as I hate kids, kittens, and chocolate (in that order).
Ah, yes. The "funny looking building". They wouldn't let us in that one. Don't know why, since it was dark!!!
Michael, keep up the good work, and as we say down here (slightly paraphrased), "Copy that, see you over the hill on the Vine"