APOD: Southern Cross to Eta Carinae (2019 Apr 26)

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APOD: Southern Cross to Eta Carinae (2019 Apr 26)

Post by APOD Robot » Fri Apr 26, 2019 4:07 am

Image Southern Cross to Eta Carinae

Explanation: Tracking along the southern Milky Way this beautiful celestial mosaic was recorded under dark Brazilian skies. Spanning some 20 degrees it actually starts with the dark expanse of the Coalsack nebula at the lower left, tucked under an arm of the Southern Cross. That compact constellation is topped by bright yellowish Gamma Crucis, a cool giant star a mere 88 light-years distant. A line from Gamma Crucis through the blue star at the bottom of the cross, Alpha Crucis, points toward the South Celestial Pole. Follow the Milky Way to the right and your gaze will sweep across IC 2948, popularly known as the Running Chicken nebula, before it reaches Eta Carinae and the Carina Nebula near the right edge of the frame. About 200 light-years across, the Carina Nebula is a star forming region much larger than the more northerly stellar nursery the Orion Nebula. The Carina Nebula lies around 7,500 light-years from Earth along the plane of the Milky Way.

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Re: APOD: Southern Cross to Eta Carinae (2019 Apr 26)

Post by Boomer12k » Fri Apr 26, 2019 4:37 am

Really nice image...lots to explore...

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Re: APOD: Southern Cross to Eta Carinae (2019 Apr 26)

Post by Ann » Fri Apr 26, 2019 8:04 am

Wow, what a treasure trove of southern delights!! Where do I start talking about them? Perhaps with the Jewel Box cluster (picture found here)?

Naah. The Jewel Box is, in comparison with all the other goodies here, a fairly run-of-the-mill circa 15 million-year-old young cluster, nothing special as such clusters go.

Evolutionary path of a solar-mass star.
Illustration: Lithopsian.
But let's start with Gamma Crucis, Gacrux! Gacrux is the red star at the top of the constellation Crux, here seen in a picture where it looks perhaps brighter in relation to the other stars of Crux than it really is. The fascinating thing about Gacrux is that it is an M-class giant, not one of the dime-a-dozen K-class giants like Pollux or Dubhe, and not one of the brilliant M-class supergiants, like Betelgeuse or Antares.

Look at the illustration at left of the evolutionary path of a solar-mass star. After our Sun has exhausted its core hydrogen, it is will leave the main sequence and expand prodigiously as its center contracts and heats up, while its outer atmosphere balloons enormously. At this stage, the Sun will ascend the red giant branch all the way to the top of it. I believe that this stage is relatively quick and quite dramatic.

But when the Sun has reached the top of the red giant branch, its core has grown hot enough that it can start fusing its core helium into carbon and oxygen. When this happens, the Sun's outer layers shrink, and the Sun will descend from its beastly red glory into the red clump stage of its evolutionary path. The red clump is where you will find all these boring K-type giants. Look at this picture of the Beehive Cluster, M44, by Bob Franke. See those weakly colored pale, pale orange stars? They are the modest red clump K-type core helium burning stars. Yawn.

When the Sun has reached its red clump stage and started fusing helium to oxygen and carbon in its core, it is going to stay in the red clump region for a relatively long time. The fact that the helium fusion can be produced by modest stars like the Sun, and that it can keep going for a relatively long time, is the reason why we see so many K-class pale orange giants everywhere in the sky. Because the red clump stars are K-class stars, while (perhaps all) the red giant branch stars and all the AGB stars are M-class ones.

Right. But when the Sun has exhausted its core helium, it will begin its second ascent, on the Asymptotic Giant Branch, which will take it to even brighter and redder and more monstrously swollen heights. And after reaching the top of the AGB branch, the Sun will get the Mira hiccups. And then, planetary nebula and white dwarf death is near for the Sun.
Jim Kaler wrote about Gacrux:

Gacrux's evolutionary -- ageing -- status is uncertain. With a mass perhaps three times solar or less, it may well have given up not just hydrogen fusion in its core (which it must do to become a giant in the first place), but may also have gone through its core helium-fusion stage. If that is the case, Gacrux is in the process of becoming a "second-ascent" giant, one brightening into the ethereal realm of the giant stars for the second time, a speculation reinforced by its variability. Perhaps one day it will appear to us as a full-blown pulsating variable like Mira in Cetus.
My point is that present-day Gacrux could be what the Sun will be in the future, when it becomes as red and bright and large as it will ever be.

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Re: APOD: Southern Cross to Eta Carinae (2019 Apr 26)

Post by orin stepanek » Fri Apr 26, 2019 11:49 am

The Yellowish (Golden} star Gamma Crucis, really stands out nicely in this Photo! :-D This Southern Cross area is really easy on the eyes! :thumb_up: :clap:
Last edited by orin stepanek on Fri Apr 26, 2019 8:28 pm, edited 1 time in total.
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Re: APOD: Southern Cross to Eta Carinae (2019 Apr 26)

Post by neufer » Fri Apr 26, 2019 11:57 am

Ann wrote:
Fri Apr 26, 2019 8:04 am

The fascinating thing about Gacrux is that it is an M-class giant, not one of the dime-a-dozen K-class giants like Pollux or Dubhe, and not one of the brilliant M-class supergiants, like Betelgeuse or Antares.

When the Sun has reached the top of the red giant branch, its core has grown hot enough that it can start fusing its core helium into carbon and oxygen. When this happens, the Sun's outer layers shrink, and the Sun will descend from its beastly red glory into the red clump stage of its evolutionary path. The red clump is where you will find all these boring K-type giants. Look at this picture of the Beehive Cluster, M44, by Bob Franke. See those weakly colored pale, pale orange stars? They are the modest red clump K-type core helium burning stars. Yawn.

When the Sun has reached its red clump stage and started fusing helium to oxygen and carbon in its core, it is going to stay in the red clump region for a relatively long time. The fact that the helium fusion can be produced by modest stars like the Sun, and that it can keep going for a relatively long time, is the reason why we see so many K-class pale orange giants everywhere in the sky. Because the red clump stars are K-class stars, while (perhaps all) the red giant branch stars and all the AGB stars are M-class ones.

Right. But when the Sun has exhausted its core helium, it will begin its second ascent, on the Asymptotic Giant Branch, which will take it to even brighter and redder and more monstrously swollen heights. And after reaching the top of the AGB branch, the Sun will get the Mira hiccups. And then, planetary nebula and white dwarf death is near for the Sun.
https://en.wikipedia.org/wiki/Nutty_Professor_II:_The_Klumps wrote:

<<After finding success with a DNA restructuring formula, Sherman Klump has created another formula which enables those who take it to find the Fountain of Youth. He has also met and fallen in love with a colleague, Denise Gaines, who has developed a method to isolate genetic material and later becomes his fiancée. Together, their work has enabled Wellman College to receive a $150 million award from a pharmaceutical firm to the excitement of Dean Richmond, who has grown to adore and respect Sherman. Despite his good fortune, Sherman has a major problem: the personality of his vanquished alter ego, Buddy Love, is still ingrained inside him and causes him to act out in the same crass manner Buddy does.

Sherman quickly works on a newer, much more potent formula while his mental faculties allow him to. Richmond confronts him about Buddy's actions, believing the two are working together. He leaves with Richmond and a tennis ball and head to the competing firm. Meanwhile, a worried Denise discovers what has happened and that Sherman's brain damage has progressed to almost eighty percent. Enlisting the help of Sherman's father Cletus, Denise goes after him. Sherman takes advantage of the canine DNA that crossed with Buddy's, and uses the tennis ball to play fetch. The ball is covered with the new formula, which takes Buddy back to an infantile state and eventually to a glowing mass of genetic material for Sherman to suck the genetic material back into his body through a straw, thus putting his DNA back together and returning him to normal. However, as Sherman chases what is left of Buddy, the glowing mass evaporates and thus Sherman cannot restore his intelligence.

Denise and Cletus arrive too late to save him, and seeing what has happened to Sherman, Denise breaks into tears. As they go to leave, Sherman takes a look at a fountain and remarks that it is "pretty". Seeing that the water is glowing, Denise realizes that the genetic material has reconstituted and that if Sherman drinks the water before it dissipates, he will be restored to normal. Sherman eventually drinks the water with the help of Denise and Cletus, and thus he is able to get his genetic makeup back in proper order.>>
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Re: APOD: Southern Cross to Eta Carinae (2019 Apr 26)

Post by NCTom » Fri Apr 26, 2019 12:02 pm

Thanks, Ann, for the explanation. You definitely keep the science from getting boring!

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Re: APOD: Southern Cross to Eta Carinae (2019 Apr 26)

Post by BDanielMayfield » Fri Apr 26, 2019 1:46 pm

I see what looks like several globular clusters in this wide panorama. How many GCs are found in this image, I wonder?
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Re: APOD: Southern Cross to Eta Carinae (2019 Apr 26)

Post by Wadsworth » Fri Apr 26, 2019 3:38 pm

Who else played 'Southern Cross' by Crosby, Stills, & Nash after seeing today's APOD?

--
When you see the Southern Cross for the first time,
You understand now why you came this way.
'Cause the truth you might be running from is so small,
But it's as big as the promise, the promise of a coming day.
--
So we cheated, and we lied, and we tested;
And we never failed to fail. It was the easiest thing to do.
You will survive being bested. Somebody fine, will come along make me forget about loving you.
And the southern cross..
--

Cheers.

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Re: APOD: Southern Cross to Eta Carinae (2019 Apr 26)

Post by Ann » Fri Apr 26, 2019 5:23 pm

NCTom wrote:
Fri Apr 26, 2019 12:02 pm
Thanks, Ann, for the explanation. You definitely keep the science from getting boring!
Thanks a lot, Tom! :D

I was going to talk about several of the objects in the Crux-Centaurus-Carina region, but researching and writing so much will drive me crazy. And many of the rest of you will get really tired of me, probably.

So I'll write about just one more object in today's APOD. A blue star, wouldn't you know it! :wink:

Cluster IC 2602 and its luminary Theta Carinae.
Photo: Fred Espenak.
Yes, but this blue star is special. Not because it is the brightest of the blue stars in the heavens - it isn't even an O-type star, for goodness sake - but because it is far too young for its cluster! It really is!!!

For you, Dino, Theta Carina wasn't there.

















Here's the deal. Theta Carina is a B0 spectral type star (or perhaps B0.5V), which is about as hot and bright as a normal hydrogen-fusing star can get without being an O-star. That means That Theta Carina must be massive, which in turn means it is going to use up its core hydrogen very fast, like all massive stars do. And since it is still happily fusing away hydrogen in its core, it must be young. Only about four times as old as humanity, or four million years old, according to Wikipedia. The dinosaurs never got to see it.

So Theta Carina is only four million years old. Yes, but the cluster it is sitting in is much older!
Wikipedia wrote:

IC 2602 is likely about the same age as the open cluster IC 2391,[4] which has a lithium depletion boundary age of 50 million years old,[5] though the accepted age from its HR-Diagram is about 13.7 million years.
Wikipedia wrote:

Theta Carinae is a single-lined spectroscopic binary with a 2.2 day period

The estimated age of the pair is 4 million years

and it appears much younger than the surrounding IC 2602 cluster.
Jim Kaler wrote:

Theta Car is in fact TOO bright. Clusters, born with an intact mass sequence of hydrogen-burners, die from the top down, high mass stars going first. The top of IC 2602's is considerably less massive than Theta. From the maximum general mass remaining, the cluster's age is set at 34 million years. Yet Theta is anomalously dated to be just a couple million years old.
Matter transfer in an Algol system. Copyright: MPL 3D
What's going on here? Theta Carina is like a happy toddler attending a class of bored teenagers!

The solution to the conundrum is that Theta Carina is a blue straggler, a star that has gained youth and power by stealing matter from others! Theta would be the perfect poster child for such stars, if well-known Algol in Perseus hadn't already grabbed that glory for itself. Except that Algol isn't even known as a blue straggler star, but of course it is one!
Jim Kaler wrote:

Algol is famed first as a prototype of the class of eclipsing double stars, of which thousands are known. (...) But Algol is equally famed for the "Algol paradox." The higher the mass of a star, the shorter its lifetime, as its fuel is used so much faster. The companion to Algol is the dying giant star. Yet carrying but 0.81 solar masses, it is the LESS massive of the two (the B star weighing in at 3.7 solar).

The only explanation is that the dim companion has lost a great deal of mass. The two stars are so close together, separated by only five percent the distance between the Earth and the Sun, that the brighter smaller star produces tides in the larger one. Matter then flows in from the large one (at a rate of around two hundred- millionths of a solar mass per year) to the small bright one, the effect directly observed through the stellar spectrum as the K giant is being stripped nearly to its core.
Theta Carina is a blue straggler like Algol, and it has stolen matter from a close companion like the primary star of Algol.
Wikipedia wrote about Theta Carina:

In this spectroscopic system, the primary star is probably a blue straggler, which is an unusual type of star created by merging or the interaction between two or more stars. The source of the mass transfer is likely to be the less massive secondary companion, and what is now is the primary star was probably originally the less massive component. The estimated age of the pair is 4 million years,[7] and it appears much younger than the surrounding IC 2602 cluster.[6]

The primary star is about 15 solar masses (M☉) and five solar radii (R☉).[6] Theta Carinae has an intensely hot outer radiating envelope with an effective surface temperature of 31,000 K.[9] Once the primary reaches around 11 million years old, the star will expand and will begin to transferring its outer surface mass back to its companion. Little is known about the companion star, but it is likely an F-type star with a luminosity less than 1% of the primary.
Photo: Denis Omelchenko/Shutterstock
So there you have it. Theta Carina is in all probability just as old as the other stars of the IC 2602 cluster. But Theta has stolen a lot of mass from its hapless companion, and all that fresh hydrogen that has been dumped on Theta acts as a youth elixir that allows this brash star to pose as an energetic baby among slightly tired teenagers.

And next time you read about an impossibly massive and hot star, ask yourself if this star couldn't be a blue straggler.

Ann
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Re: APOD: Southern Cross to Eta Carinae (2019 Apr 26)

Post by neufer » Fri Apr 26, 2019 6:03 pm

Ann wrote:
Fri Apr 26, 2019 5:23 pm

Theta has stolen a lot of mass from its hapless companion, and all that fresh hydrogen that has been dumped on Theta acts as a youth elixir that allows this brash star to pose as an energetic baby. And next time you read about an impossibly massive and hot star, ask yourself if this star couldn't be a blue straggler.
https://www.etymonline.com/word/straggle wrote:
<<straggle (v.) early 15c., "to wander from the proper path, stray, to rove from one's companions," perhaps from a Scandinavian source (compare dialectal Norwegian stragla "to walk laboriously"). Specifically of soldiers, "be dispersed, be apart from the main body," from 1520s.>>
Art Neuendorffer

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Re: APOD: Southern Cross to Eta Carinae (2019 Apr 26)

Post by bls0326 » Fri Apr 26, 2019 7:33 pm

Thanks Ann. Your posts made a very good APOD also very interesting!