Eta Carinae- A Naked Eye Enigma

by Mike Simonsen on November 25, 2009

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Credit: X-ray: NASA/CXC/GSFC/M.Corcoran et al.; Optical: NASA/STScI

Credit: X-ray: NASA/CXC/GSFC/M.Corcoran et al.; Optical: NASA/STScI

Eta Carinae is a beast of a star. At more than 100 solar masses and 4 million times the luminosity of our Sun, eta Car balances dangerously on the edge of stellar stability and it’s ultimate fate: complete self-destruction as a supernova. Recently, Hubble Space Telescope observations of the central star in the eta Carinae Nebula have raised an alert on eta Car among the professional community. What they discovered was totally unexpected.

“It used to be, that if you looked at eta Car you saw a nebula and then a faint little core in the middle” said Dr. Kris Davidson, from the University of Minnesota. “Now when you look at it, it’s basically the star with a nebula. The appearance is completely different. The light from the star now accounts for more than half the total output of eta Car. I didn’t expect that to happen until the middle of this century. It’s decades ahead of schedule. We know so little about these very massive objects, that if eta Car becomes a supernova next Thursday we should not be very surprised.”

In 1843, eta Carinae underwent a spectacular eruption, making it the second brightest star in the sky behind Sirius. During this violent episode, eta Car ejected 2 to 3 solar masses of material from the star’s polar regions. This material, traveling at speeds close to 700 km/s, formed two large, bipolar lobes, now known as the Homunculus Nebula. After the great eruption, Eta Car faded, erupted again briefly fifty years later, then settled down, around 8th magnitude. Davidson picks up the story from there.

This light curve depicts the visual apparent brightness of Eta Car from 1822 to date. It contains visual estimates (big circles), photographic (squares), photoelectric (triangles) and CCD (small circles) observations. All of them have been fitted for consistency of the whole data. Red points are recent observations from La Plata (Feinstein 1967; Fernández-Lajús et al., 2009, 2010). Used by permission.

This light curve depicts the visual apparent brightness of Eta Car from 1822 to date. It contains visual estimates (big circles), photographic (squares), photoelectric (triangles) and CCD (small circles) observations. All of them have been fitted for consistency of the whole data. Red points are recent observations from La Plata (Feinstein 1967; Fernández-Lajús et al., 2009, 2010). Used by permission.

“Around 1940, Eta suddenly changed its state. The spectrum changed and the brightness started to increase. Unfortunately, all this happened at a time when almost no one was looking at it. So we don’t know exactly what happened. All we know is that by the 1950’s, the spectrum had high excitation Helium lines in it that it didn’t have before, and the whole object, the star plus the Homunculus, was gradually increasing in brightness. In the past we’ve seen three changes of state. I suspect we are seeing another one happening now.”

During this whole time eta Car has been shedding material via its ferocious stellar winds. This has resulted in an opaque cloud of dust in the immediate vicinity of the star. Normally, this much dust would block our view to the star. So how does Davidson explain this recent, sudden increase in the luminosity of eta Carinae?

“The direct brightening we see is probably the dust being cleared away, but it can’t be merely the expansion of the dust. If it’s clearing away that fast, either something is destroying the dust, or the stellar wind is not producing as much dust as it did before. Personally, I think the stellar wind is decreasing, and the star is returning to the state it was in more than three hundred years ago. In the 1670’s, it was a fourth magnitude, blue, hot star. I think it is returning to that state. Eta Carinae has just taken this long to readjust from its explosion in the 1840’s.”

After 150 years what do we really know about one of the great mysteries of stellar physics? “We don’t understand it, and don’t believe anyone who says they do,” said Davidson.  “The problem is we don’t have a real honest-to-God model, and one of the reasons for that is we don’t have a real honest-to-God explanation of what happened in 1843.”

Can amateur astronomers with modest equipment help untangle the mysteries of eta Carinae? Davidson think so, “The main thing is to make sure everyone in the southern hemisphere knows about it, and anyone with a telescope, CCD or spectrograph should have it pointed at eta Carinae every clear night.”

Anaconda November 26, 2009 at 9:48 AM

@ Nexus:

Please…the responses to my continuing comments on this website are of such a obvious hostile nature as to be remarkable.

(Anybody with the slightest objectivity can see that.)

Initially, the responses were hostile to any mention of “electromagnetism” in space, even near-space here in the solar system.

That has stopped because the recent scientific evidence is unambiguous regarding the solar system and a grudging admission has taken its place.

Although, a “line in the sand” has been drawn outside the solar system by the usual suspects.

Even today, while magnetism has been duly noted in association with all deep-space structures as Hannes Alfven, 1970 Nobel Prize winner in physics, predicted in 1960:

“The earth, the sun and many stars possess general magnetic fields. It is possible that interstellar clouds are magnetized, that spiral arms have regular magnetic fields, and that galaxies also have general magnetic fields. Even if the views of different authors are still conflicting, it seems reasonably certain that interstellar matter is usually magnetized. This makes is likely that there should be some very general process which produces magnetic fields in fluid bodies as different as the earth’s fluid interior, the stars, and interstellar matter. The energy required for magnetization can easily be drawn from the kinetic energy of internal motions, but the difficulty is to find a workable mechanism from the production of magnetic fields.” (Alfvén, H. “On the Origin of Cosmic Magnetic Fields”, Royal Institute of Stockholm, October 28, 1960).”:

The electric fields and electric currents giving rise to these magnetic fields are remarkably absent from discussion in the peer-reviewed literature. If these ‘electric’ causes were discussed widely then the obvious hostility expressed here would be absent and a more productive “give and take” discussion could emerge.

(Nexus, your comment is meant as a dismissal, not as an invitation for more wide-ranging discussion.)

DrFlimmer is one of the worst offenders on this account. Constantly attempting to re-write the record when earlier statements (of his and others) about the absence of ‘electricity’ are no longer tenable.

This post with its confession is an invitation for wide-ranging discussion as are my two previous comments, here, but as is generally the case, the usual suspects want nothing to do with wide-ranging discussion and take refuge in their established belief system.

(Instead of DrFlimmer making a false claim, he could have discussed electromagnetism, that he didn’t speaks louder than his empty claims to the contrary.)

Hon. Salacious B. Crumb November 26, 2009 at 10:40 AM

Using any spectroscope on the star and the nebulosity will reveal a bright-line spectrum typically seen in many hot stars or bright planetary nebulae. Brightest of these lines is the greenish-blue Hydrogen-beta, and this makes the nebula most prominent using an Hydrogen-beta filter. Other lines are seen not normally seen in astronomical objects. Three lines in the same region of the spectrum are seen being highly ionised Iron (Fe) lines, a broad line in the violet, and two other in the yellow corresponding to ionised nitrogen (N II) and helium He I. All these lines, except the Iron ones, are also seen in planetary nebulae.
Eta Carinae IS a known binary or single star. This was firstdiscovered by Augusto Damineli of the University of Sao Paulo in Brazil. By analysis of the star’s spectrum, every 5.5 years (the orbital period of the stars, whose orbit seems to be reasonably elliptical) Eta Carina ultraviolet and x-ray output undergoes a short-term change. In the x-rays the flux increases steadily, then plunges, followed by a slow recovery. In the ultraviolet, several dark emission lines on the star’s spectrum disappear. Damineli has been able to trace this cycle back through the five or six decades, and was first to successfully predicted an output event in December 1997, where the x-ray output plummeted and the UV emission faded, according to his predictions. Such an event was observed in 2003-04 and
Based on this cycle, astronomers propose a binary star theory that would explain previous eruptions as a result of the orbital interactions of two stars. Although not all scientists agree on this theory, most agree that the star’s powerful x-ray emission is propelled by the collision of two dense stellar winds, emanating either from the two stars as the close interacting binary system or from the fast and slow stellar wind from the single star.
If the star was only brightening in the visual wavelengths, it might be explained that Eta is shedding an outer layer in response to radiation pressure whereby the star’s outer layers cool and its output shifts from ultraviolet to visual wavelengths, however, this is not what is observed. Brightening is occurring across the entire electromagnetic spectrum, implying an intrinsic brightening of one of the Eta Carina stars. Two choices remain – expel the envelope around the stars or just go “boom!” as Supernova Type II.
Evidence of this envelope is seen in infrared wavelengths. Eta and its nebula are the brightest objects in the sky beyond our solar system. The mid-infrared emission of Eta Carinae originates in dust ejected by the star during giant mass-loss events within the past several hundred years.

Eta is also a unique source of x-rays. The outer horseshoe shaped ring has a temperature of about three million degrees Kelvin. It is about two light years in diameter and was probably caused by an outburst that occurred more than one or two thousand years ago. The whole blue core area is hotter than the ring, and the inner white region is hottest and contains the variable star Eta itself.

At radio wavelengths Eta Carinae produces the brightest known stellar wind. A recent increase in radio emission has occurred because cool gas close to the star has been excited by a blast of radiation.

I think the largest puzzle is to understanding this star is that we do not know what caused Eta Carinae’s 1840′s Great Eruption, when it rose as a first magnitude star.

Each night when I look at the sky, I always look at Eta Carina to see if it has brightened. Presently it is a reddish 4th to 4.5 magnitude, and has brightened in several decades. The biggest question is what will it do next.

******************
As to alternative comments and “personal theories” here, most of it is totally irrelevant.

Towards any new responders here, the individual known Anaconda has been generally black banned as a troll in this group. As said by others before, just ignore him, please.

Thanks

IVAN3MAN November 26, 2009 at 11:13 AM

@ Hon. Salacious B. Crumb,

Actually, the correct term is blackballed, not “black banned”.

Hon. Salacious B. Crumb November 26, 2009 at 11:40 AM

The term “black ban” means Union members not allowed to work for or at an employer or work site. The term is non-racist.

ND November 26, 2009 at 11:43 AM

Nexus,

You can’t win with a dishonest and belligerent crank like Anaconda who plays the innocent victim at every turn projects on to everyone else his failings. We’ve tried for a long time under the misguided and naive idea that he could learn. Alas no. And responding to him turned into a habit. Time to cut the cord.

Anaconda November 26, 2009 at 11:50 AM

Crumb:

Your rendition, paraphrased from an unnamed source, proves my point — no consideration of electromagnetic forces — and your parting shot also proves my point in that it’s manifest hostility.

What is interesting about your rendition is that an electromagnetic analysis & interpretation can readily be derived from the observations & measurements you provide.

IVAN3MAN November 26, 2009 at 11:57 AM

Anaconda:

It’s the variability that makes it so difficult to pin down — the gravity “only” model doesn’t account for the variability expressed by this nebula.

Notice another “hourglass” shape.

Yeah, so what? As well as Eta Carinae, there is an unusual shape located in the Carina Nebula: how does the “Electric Universe” hypothesis “account for the variability expressed by this nebula“, then?

Anaconda November 26, 2009 at 12:06 PM

@ ND:

You’re a joke, you’ve been unplacably hostile since you linked a ScienceDaily article claiming so-called “dark” matter was “discovered” 70 years ago.

Which was manifestly false (but you didn’t know any better — wannabe parrot that you are).

That I pointed out your ignorance for others to see was my offense.

You are a wannabe — stay over at Bad Astronomy where you can chip in and your ignorance will go unremarked.

Anaconda November 26, 2009 at 12:11 PM

@ Ivan3Man: Similar to the “fingers of god” in the Eagle nebula, if not one of the “fingers” themselves.

This is likely a plasma flow, but let’s stay on topic — oh, forgot, you guys don’t like this post because your model has no answers…

Anaconda November 26, 2009 at 12:31 PM

Correction: “Pillars of Creation” in the Eagle nebula.

ND November 26, 2009 at 12:33 PM

IVAN3MAN++

Jon Hanford November 26, 2009 at 12:50 PM

@ HSB Crumb: Thanks for that earlier post summarizing where we stand on current Eta Carinae research. I remember reading papers on the colliding wind models vs. fast-slow winds from a single star.

“We don’t understand it, and don’t believe anyone who says they do”. I don’t think any astrophysicist familiar with Eta Carinae would say this in the first place. We do have SOME ideas.

HSB Crumb writes: “Each night when I look at the sky, I always look at Eta Carina to see if it has brightened. ” If I was in a favorable locale, I’d do the same. Lucky SOB :)

DrFlimmer November 26, 2009 at 2:38 PM

LBC:

I frankly don’t know the specifics. Maybe Dr. Flimmer can comment further. I took an elementary astrophysics course as an undergraduate and only learned the hydrostatic model of a star. This is the “first order” model.

Jon Hanford:

Computer modeling of this system by theoretical astrophysicists will be essential to our understanding of it (so hang in there, Dr Flimmer :) ).

Thanks a lot for the flowers, but sorry, guys. Don’t put too much hope in me. I have not yet finished my studies, so please be patient with me. My Master’s thesis will be about Blazer spectra, so I am actually no expert for stars and supernovae!
My knowledge about stars is not much more than yours, LBC. In fact, I’m glad to know this model at all ;) .
HSB Crumb seems to be the better expert. Indeed, very interesting comment! You don’t have any recent papers about the topic, do you, HSB Crumb? ;) (I mean, can you recommend some? I don’t want to skip through all the available papers at ADS or arxiv ;) )

@Dr Flimmer, sign me up for the Atacama desert excursion. It would be nice to see the construction of ALMA by day and taking in those dark southern skies at night.

Couldn’t agree more with you. Maybe there will be a time……. one should not stop dreaming ;)

Lawrence B. Crowell November 26, 2009 at 3:36 PM

Dr. Flimmer, I thought you might have a bit more to say. I am really a bit of an astrophysics sophmore at best. My bit is largely general relativity which connects up with astrophysics of course. I also wrote that in part for Anaconda, for these problems in astrophysics involve a range of physics: shock waves, hydrodynamics, acoustical physics, radiative transport, thermodynamics (and I give half a bet for nonequilibrium thermo), gravitation and of course his favority E&M.

These are complex systems that are not at all in a nice state of equilibrium, or hydrostationarity.

Happy T-day, LC

Olaf November 26, 2009 at 3:44 PM

Oops someone used the dirty word again: “electromagnetism ”

I also try to avoid using those word at my work but it is hard to avoid it if your work has something to do with R&D and electronics.

Anyway, the EU model can’t explain Eta Carinae with electromagnetism only so they don’t know. Therefor the standard model must be true. (Yes EU logic!)

Astrofiend November 26, 2009 at 9:28 PM

Anaconda Says:
November 26th, 2009 at 9:48 am

You really are too much Anaconda. You honestly do believe that astronomers and physicists hate the idea of electromagnetism in space, don’t you? Grudgingly accept it? They invented the idea you moron!

If physicists find the idea so repugnant, and try to suppress it at every turn, then why was I able to study plasma astrophysics at uni, a subject solely concerned with um, plasma astrophysics? Why does my physics department offer a subject called space physics, a subject almost entirely to do with solar system electromagnetic effects? What about advanced electromagnetic theory as a subject, which has a significant component dedicated to space and astronomy-based physics? Why, when I go to the physics section of my library, is there shelves filled with volumes after volumes of work done on electromagnetism and electromagnetic effects in astronomy?

You don’t even know enough about your ‘own’ subject to know that physicists have been working on these things for a very long time. Mainstream physicists. Every physicist! I think the problem is that you have only a popular-level understanding of your own topic. You simply cannot understand the work that has already been done. I would bet many many dollars that you can’t even deal with the basic math of electromagnetism. How’s your vector calculus and ability at working with the MHD equations? Non-existent I should imagine, because you never really seem to interested in showing any details behind you ideas, just spouting off about hourglass shapes here and there, like it is somehow self-evident that some wisp of gas vaguely resembling a bipolar flow proves every piece of rubbish you have ever spouted beyond doubt. “It’s electromagnetism!” you say. Duh – that’s what hundreds of papers have stated already, only they realise that it goes beyond the simplistic and flat out wrong ideas of EU in complexity, and acknowledge openly that they don’t have the full answer yet.

Wake up and smell the defeat Anaconda – far greater physicists than you have worked on, and continue to work on, problems in electromagnetism and astronomy. It is due to their work that we find ourselves where we are today, and it will be because of them that we make progress in science for tomorrow. I am just delighted that you will be there to see it going forward, always moving further away from your own archaic conception of how you would dearly like things to be.

PS feel free not to respond. I probably won’t be botherd to check back, and I almost certainly won’t be bothered replying to you again. I’m a little bored right now.

Hon. Salacious B. Crumb November 26, 2009 at 10:26 PM

Several here might be interested in the history of the Eta Carinae Nebula and the historically relationship to it and eta Car itself.

http://homepage.mac.com/andjames/NGC3372.htm

Hon. Salacious B. Crumb November 26, 2009 at 10:41 PM

Towards the references, there are so many i don’t know where to start. The best explanation of the April-May 2003 event appears in the AAVSO Alert Notice 301 of the AAVSO

http://www.aavso.org/publications/alerts/alert301.shtml

You can search the AAVSO database ifor observational n the left under “Pick a star” – inserting “Eta car.”

Hon. Salacious B. Crumb November 26, 2009 at 10:46 PM

Another interesting article on observations and explaining the recent spectra brightness variations is;

Martin, J.C.; “Eta Carinae’s Brightness Variations Since 1998: HST Observations of the Central Star

http://arxiv.org/abs/astro-ph/0401254

ND November 27, 2009 at 12:43 AM

plasma astrophysics taught at a mainstream university science department?! That’s ideologically unpossible!!!

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