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

Eta Carinae- A Naked Eye Enigma

25 Nov , 2009

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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.”

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Anaconda
Member
Anaconda
November 25, 2009 12:18 PM

“The problem is we don’t have a real honest-to-God model…”

DrFlimmer
Member
DrFlimmer
November 25, 2009 12:38 PM

Why is all the interesting stuff in the southern hemisphere? That is unfair!

But hopefully this beast blows up soon. That would be spectacular and we could test tons of models on it!

Savino
Member
Savino
November 25, 2009 1:53 PM

@DrFilmmer

Why it´s unfair? It´s more than fair!!!! You have all the good equipament for a reasonable price and we have the sky! smile

But I agree with you in one thing: I reeeeeally hope that it blows up in our lifetime.
And I hope that it makes some shadows even at daylight (two suns!!!!)

Ivan3man_At_Large
Member
Ivan3man_At_Large
November 25, 2009 2:02 PM

At the first paragraph, in the second line, that should be its (possessive form of the pronoun it, not “it’s”.

Ivan3man_At_Large
Member
Ivan3man_At_Large
November 25, 2009 2:18 PM

Dr. Kris Davidson:

We don’t understand it, and [we] don’t believe anyone who says they do. [Emphasis mine.]

Savino
Member
Savino
November 25, 2009 2:34 PM

@IVAN3MAN:
He is more than right, you need to proof that you have the knoledge to understand it, not simply say it.

Savino
Member
Savino
November 25, 2009 2:36 PM

Oops:
More then right.
Sorry, but something in english is pretty hard to understand! hehehe

DrFlimmer
Member
DrFlimmer
November 25, 2009 2:52 PM

@ Savino:

Enjoy your two shadows *grrr* wink Hopefully, it blows up that late in my life that I am able to seat myself into an airplane and jet down to the south. This is a MUST-see.
I guess, even tourism would benefit from such an event!

Ivan3man_At_Large
Member
Ivan3man_At_Large
November 25, 2009 2:58 PM

@ Savino,

Actually, you were right the first time. smile

Savino
Member
Savino
November 25, 2009 3:06 PM

@IVAN3MAN
Darn! Someday I will get it right!!! smile
Thanks for the tip!

Savino
Member
Savino
November 25, 2009 3:07 PM

@DrFlimmer:

Look at the bright side (or dark side, in this case), your backyard observation will not be damage by the “second sun” at nigt!

razz

Jon Hanford
Member
Jon Hanford
November 25, 2009 3:31 PM

A southern sky observer has ‘northern sky envy’ in the previous article: http://www.universetoday.com/2009/11/25/the-view-from-down-under/#comments .

Personally, that southern hemisphere view must be awesome. Magellanic clouds, Eta Car, the Coalsack, the Galactic Center, Cen A. I’m with Dr. Flimmer, gotta go south sometime (soon).

Jon Hanford
Member
Jon Hanford
November 25, 2009 3:33 PM

Oops, meant to link to article, not comments.

ND
Member
ND
November 25, 2009 3:56 PM

yeah, a trip to Australia and/or New Zealand would be fun. Long trip tho. Or some place like Argentina.

What sort of equipment to take though. Binoculars and and maybe a compact scope. They have small collapsible Newtonians.

Anaconda
Member
Anaconda
November 25, 2009 7:59 PM

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.

Yes, anybody that doesn’t recognize electromagnetism in deep-space would be inclined to say, “We don’t understand it, and don’t believe anyone who says they do.”

Those that consider electromagnetism have a different answer.

Ivan3man_At_Large
Member
Ivan3man_At_Large
November 25, 2009 8:48 PM

Whenever a thermonuclear bomb is detonated, the release of intense gamma rays from the fission/fusion reaction creates an electromagnetic pulse, not the other way around — entropy always increases, unless work is applied to the system.

Nexus
Member
November 25, 2009 10:00 PM

Anaconda,
I’ll let you in on a little secret. Astrophysicists DO consider electromagnetism. It’s one of the first things they look at in explaining astronomical observations- probably second only to gravity. You are wrongly assuming that, because they don’t immediately adopt the vague, insubstantial monument to confused thinking known as EU, that they must be ignoring electromagnetism altogether. In fact, the reason they don’t take up EU theory is that it’s demonstrably wrong.

DrFlimmer
Member
DrFlimmer
November 26, 2009 2:37 AM

@ Nexus:

It is worthless. I’ve told him that a gazillion times, and he just doesn’t care.

@ Savino:

I would accept the bright night sky. The second sun is only temporarily and will be gone a few month later.

@ ND and Jon Hanford:

A trip to the Atacama desert would also do the trick.
In fact, there is one reason why I regret becoming a theoretical astrophysicist. The astronomical institute of my university has its own mountain with its own telescope down there (about 30km from ESO). Dammit, if I were a “real” astronomer I would have been there by now, just like a colleague of mine who’s been there for 3 weeks recently.

Lawrence B. Crowell
Member
Lawrence B. Crowell
November 26, 2009 6:00 AM
There are researchers who run large numerical codes to model stellar systems, including supernova. I don’t know all the physics behind this, other than to say it is very complicated. The hourglass appearance of the nebula around the star is a dipole effect. The spherical primary physics is perturbed in a Bessel series of polynomials of higher order terms. For reasons I honestly do not understand the eruption of energy over a century ago assumed a large dipole moment. This might be due to a magnetic dipole moment, a Rayleigh-Taylor instability, … . 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… Read more »
Jon Hanford
Member
Jon Hanford
November 26, 2009 8:26 AM

Over the years, many models of the have been put forth attempting to reconcile observations of Eta Carina and make predictions based on these models. Models that include a companion star seem to be increasingly favored, but Eta Carina holds on to its secrets tightly. Computer modeling of this system by theoretical astrophysicists will be essential to our understanding of it (so hang in there, Dr Flimmer smile ).

@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.

wpDiscuz