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Eta Carinae- A Naked Eye Enigma

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.”

Comments on this entry are closed.

  • DrFlimmer November 27, 2009, 5:10 AM

    @ ND:

    Believe it or not, I attended a course named exactly that way in the last semester, too.

    @ HSBC:

    Thanks a lot. I will start looking at the links right now :)

  • Anaconda November 27, 2009, 8:00 AM

    @ Astrofiend:

    Great ! Then let’s discuss plasma and electromagnetism as possibilities instead of spending so much time dismissing it.

    You spend several paragraphs disparaging me and Plasma Cosmology, but not one iota on the possibility of electromagnetism being involved in Eta Carinae.

    Your copious words are entirely empty of specifics or relevant content to the post at hand.

    Prove your statements by discussing electromagnetism in relation to Eta Carinae or any other deep-space structure as the posts come up.

    That’s the “proof’s in the pudding” response I would respect and would prove me wrong.

    Can you prove me wrong?

    Or are you just an empty suit, Astrofiend?

    That’s right, “all hat and no cattle.”

  • Hon. Salacious B. Crumb November 27, 2009, 1:06 PM

    Anaconda’s desperate attempts in trying to engage individuals here is an illusion, and is certainly not genuine. From his history in expressing irrelevant alternative comments and stating his “personal theories” here, it is clear all he wants to do is spread hearsay instead of discussing the issues presented in the news story at hand.
    Towards any here, the individual known Anaconda has been pointed out by the writers here as a TROLL, and have suggested we just ignore him – and perhaps he’ll have the sense to go away for good.
    There is no need to “prove him wrong” or even correct in his views, In the end this treatment he has brought on himself.

    IMO, the only way he can redeem himself is through improving his own behaviour, instead of trying to corrupt others or highjack the discussion to his own ends. Until he discuss the issues in a rational and logical manner, he should be ignored or discussed in the third person.Engaging him only encourages his poor behaviour, and unless responders are willing to ignore this individual, we will only perpetuate the same old rhetorical nonsense.

    There is a great saying. “‘For things to change, i must change.” And this importantly applies to this individual.

    I’d suggest he should be encouraged to do so.

    Until then, I recommend we just ignore him – for all our sakes.

    Thanks

  • Hon. Salacious B. Crumb November 27, 2009, 1:10 PM

    Sorry for the shouting. I forgot to close the HTML tag!

    Pity I can’t edit it!

  • Hon. Salacious B. Crumb November 27, 2009, 1:25 PM

    At the moment Eta Carina is in the news.

    I.e. Sky &Telescope “A Rouge Star Gone Wild”
    at http://www.skyandtelescope.com/news/75160377.html

    (Perhaps Anaconda might like to place his “personal theories” there instead. He might get a warmer response?)

  • Hon. Salacious B. Crumb November 27, 2009, 1:41 PM

    I found an interesting article entitled “Eta Carinae: The 2003.5 Observing Campaign”, which examples the multi-wavelength observation of eta Car during 2003.

    It has lots of information and references (some as links), that gives some idea of the efforts being taken to learn about this remarkable star and nebulous object. http://lheawww.gsfc.nasa.gov/users/corcoran/eta_car/2003.5/

    No magnetic field mumbo-jumbo, just good ol’ solid evidence.

  • Anaconda November 27, 2009, 4:12 PM

    Crumb wrote: “…it is clear all he wants to do is spread hearsay…”

    Don’t you mean “heresy” :-)

  • Anaconda November 27, 2009, 4:35 PM

    Just because I appreciate the irony of being accused of “heresy” in the scientific domain:

    http://www.thunderbolts.info/tpod/2005/arch05/051005eta-carinae.htm

    Sometimes in Science, a good case of “heresy” leads towards the pathway of reality…you never know.

    Crumb, the NASA link is superb, the X-ray & gamma ray observations as outlined in the relevant graph are similar to the energy profile of a lightning bolt…an electric discharge.

  • Hon. Salacious B. Crumb November 27, 2009, 4:54 PM

    hearsay

    “…information received from other people that one cannot adequately substantiate; rumor.”

  • IVAN3MAN November 28, 2009, 3:41 AM

    I second the Hon. Salacious B. Crumb’s comment, above, referring to the likes of Anaconda, and, in addition, I suggest everyone to read this before commenting further:
    FORUM NOTICE.

  • Hon. Salacious B. Crumb November 28, 2009, 6:09 AM

    Ta!
    IVANMAN

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