Generally speaking, once a star explodes, that’s pretty much it. It’s done.
But there are exceptions. In the 1870s, the star Eta Carina underwent a massive and violent outburst, releasing so much energy it was really a mini-supernova event. It ejected two monster blobs of gas — massing as much as the Sun! — at high velocity, and was temporarily the second brightest star in the sky, even though it’s 7000+ light years away.
Eta Car is one of the most massive stars in the sky, and one of the most massive stars possible, in fact. But how common are objects like Eta Car?
Maybe more common than we thought. In 2004, Japanese astronomer Koichi Itagaki discovered what he thought was a supernova in the galaxy UGC 4904, which is about 78 million light years away. The object faded rapidly, and was gone 10 days later.
Then, two years later, he saw another supernova in UGC 4904 — in the same spot! The image above shows the sequence of events.
That’s just too big a coincidence to be two separate stars, so they followed up with more observations. What Itagaki and his team found is that this was a single star that blew up, probably very much like Eta Car: it had a violent paroxysm, and then exploded two years later. Spectra revealed an overabundance of helium in the star, which is expected if you have a very high mass star. It was probably 50 - 100 times the mass of the Sun, and they don’t get much bigger.
Eta Car is a singular star in our Galaxy; we have not seen another like it (though there may be others on the other side of the Galaxy where they are hard to spot). Maybe every galaxy actively forming stars has one or two like it. But I doubt it — stars like this don’t live very long before exploding, so they are most likely rare (there is none in the Andromeda galaxy of which I am aware, or any other nearby spiral). So gaze upon that picture above, at that that little unassuming dot, and know that you are witnessing the passing of something rare and amazing, and violent and monstrous. And also know that while it’s almost 80 million light years away, we’ll have a front row seat to a similar catastrophe soon enough. Maybe tonight, maybe not for a thousand years, but in the life of a galaxy, it’ll be in the blink of an eye.
June 14th, 2007 at 7:24 pm
Your post made me curious about whether the age of the UGC 4904 star has been estimated to be at the time that it went kablooie. Does the high content of helium mean that it was pretty old, or does it mean that it had formed from the detritus of several other “old” stars?
June 14th, 2007 at 7:30 pm
Just a minor nitpick … Shouldn’t the name be Eta Carin[b]ae[/b]?
June 14th, 2007 at 8:00 pm
I truly hope that one day I will get to witness one of those rare astronomical events like a nova visible in the day, or a comet that is truly awesome to the naked eye (I did see one a few years ago, but it was viewable only in the most darkest locations and very dim even then), or one of those meteor showers that rains hundreds or thousands of meteors a minute.
Perhaps Eta Carin will go off in my lifetime … that looks like it would be a real treat.
June 14th, 2007 at 9:12 pm
Your estimated of Eta Car distance from earth is stated at 80 million light years. This seemed excessive to me so I entered “Eta Carinae distance from earth” in my google search engine and got a series of estimates ranging from 7,000 lightyears to 9,000 lightyears. Not close enough to do anything catastropic to Earth. Could you have meant 8,000 lightyears rather than 80 million lightyears?
June 14th, 2007 at 9:42 pm
Allan, the star in the picture is not Eta Carinae. He said the distance to the start in the picture above is about 80 million light years. Earlier, he mentioned it was part of the galaxy UGC 4904 (78 million LY). In the first paragraph, he describes Eta Carinae, a star in our own galaxy, as being 7000+ light years away. I think Phil got everything right.
June 15th, 2007 at 3:18 am
Eta Car is a singular star in our Galaxy…
Once a while there are reports that its binarity is confirmed… a companion could explain its observed periodicity. But IMHO it doesn’t feel right… Eta Carinae is supposed to be a lone superhypergiant.
June 15th, 2007 at 3:57 am
Kullat: “singular” here is being used to mean “one of a kind” (i.e., unlike almost any other stars), not “not part of a multiple star system”.
June 15th, 2007 at 5:31 am
Thanks BA. I am always greedy for more. Why is an abundance of helium expected in a very high mass star?
June 15th, 2007 at 6:04 am
Helium comes from the rapid fusing of hydrogen in these super massive stars. At the mass indicated, the life span would be measured in millions rather than billions, of years. It must have collected from a glob of mostly Hydrogen, rather than from the detritus of previous stars going blowy-uppy, which would have left traces of heavy metals in Eta-C.
I wonder how the metal traces may affect the evolution of stars. Perhaps they slow fusion rates, by acting as energy absorbers??? Just a thought,,,
Gary 7
June 15th, 2007 at 6:49 am
I’m missing something here. What is it that makes Eta Carinae singular? Its size is amazing, but obviously not unique. The fact that it blew off so much mass is awe-inspiring, but that’s an effect, not a quality. So what is it? I assume we must know something about the two monster stars recently discovered that tells us that they don’t match Eta C - and it wouldn’t just be the lack of an ejected nebula, since that could happen tomorrow, right?
Maybe I’m just reading too much into your statement, but I do feel that you’ve said something I just don’t understand.
June 15th, 2007 at 7:04 am
Brian/Gary;
I’m not certain, but I think an abundance of helium is expected because of the sheer size of the H-burning zone in these hyper-massive stars, and because of the upheavals expected in their evolution.
The presence of heavy elements causes these massive stars to blow off mass during the formation phase. I’m not clear on why that is, but I’ve seen it referenced several times. Something about the presence of heavy elements making the solar winds more efficient at carving out a hollow in the proto-stellar gas cloud.
Thats also why we think that Pop. III stars could get monstrously huge (perhaps up to about 500Msol) and why that’s not possible in Pop. II or Pop. I stars.
June 15th, 2007 at 7:05 am
Yes, I’m curious as well…what makes you set Eta Car apart from other luminous blue variables? I know little about this, but I thought it was just considered a singularly spectacular example of that class.
June 15th, 2007 at 10:13 am
To be strictly accurate, the previous major outburst of Eta Carinae was in the 1830’s and 1840’s, not the 1870’s. The star reached magnitude -1 (brighter than Canopus and only half a magnitude down on Sirius) in 1843.
June 15th, 2007 at 11:40 am
[…] I covered the double supernova here. Phil Plait from Bad Astronomy has a great description of it was well. […]
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