Supernova Imposter 2009ip Finally Comes Clean

Discovery photo taken in August 2009 of the supernova imposter in the galaxy NGC 7259. It was 18th magnitude at the time. Credit: CHilean Automatic Supernovas sEarch

Polyjuice. Once swallowed, the magic potion of the Harry Potter movies allows the user to assume the appearance of any person for just one hour. Starting in 2009, astronomers have witnessed something of this “polyjuice factor” in a star in a galaxy 66 million light years away. With one difference. The change appears permanent.

On August 26, 2009 the team of astronomers at the CHilean Automatic Supernovas sEarch (CHASE) discovered what they first thought was a brand new supernova in the galaxy NGC 7259 in the constellation Piscis Austrinus the Southern Fish. It even got one of those cool supernova names – SN 2009ip. But further study of older pictures taken by the Hubble Space Telescope as well as follow up observations revealed that the speed of the material blasted away by the star as well as its intrinsic brightness didn’t match that of a supernova. Astronomers realized they were seeing an outburst of a bright blue star called a luminous blue variable or LBV instead.

Eta Carinae in the southern Milky Way is probably the most famous nearby LBV. A large eruption in 1843, when the star became the second brightest star in the sky, created the curious twin-lobed cloud of gas and dust called the Homunculus Nebula. Eta’s about 8000 light years from Earth. Credit: NASA/ESA

LBVs are brilliant, massive, extremely hot supergiant stars that burn their fuel rapidly and live short lives of several million years compared to the sun’s ~10 billion year lifetime. Just to give you an idea, our supernova imposter packs away 50 to 80 times the mass of the sun and blazes hundreds of thousands of times brighter. Radiation raging from the interiors of LBVs causes the stars to sputter and spew portions their atmosphere into space. Some slough off the equivalent of the sun’s mass in just 10,000 years. Spendthrifts of the universe.

Along with losing mass, an LBV’s light varies almost continuously from day to day with bigger variations over longer time spans caused by large outbursts that release lots of matter into an ever-expanding envelope centered on the star.

The LBV in NGC 7259 re-brightened in July this year and became much brighter in September and October as it evolved into a supernova. This picture was taken on October 8 when 2009ip was magnitude 13.5 – bright enough to see in a 6-inch telescope. Credit: Joseph Brimacombe

Continued observation of SN 2009ip turned up a second outburst in 2010. This was further confirmation that the star didn’t destroy itself in a supernova explosion after all but returned to shine another day.

Then in July It re-brightened again, but this time astronomers at several observatories, using spectrographs to tease apart the star’s light, discovered dramatic changes in its appearance. You know what they say – the third time’s the charm.

Not only was it much brighter than the earlier outbursts, but the hotheaded sun was blasting out matter at supernova-style speeds of over 8,000 miles per second. Additional details of the star’s spectrum or light fingerprint all pointed to one thing: 2009ip appears to have become a real supernova right before our eyes!

Its rapid surge in brightness indicates that high-speed material flung from the host star has crashed into the older envelope of matter shed by previous eruptions. What’s driving all this new activity? As described earlier, big stars are the gas-guzzlers of the universe, rapidly consuming every drop of nuclear fuel in their cores. The pressure from burning keeps gravity at bay, but when 2009ip’s needle hit empty, the fire went out and its core caved in to the force of gravity, creating a shock wave that ripped the behemoth to shreds. Bada boom! A star dies, a supernova is born.

During a core collapse or Type II supernova, a shock wave surges from core to surface, tearing the star apart. Sometimes a tiny, dense remnant called a neutron star remains after the explosion. Credit: ESO

Supernovas located in galaxies in the far southern sky are not easy to see from a northern place like Duluth, Minn., yet this one grew bright enough earlier this month to stand out clearly in my 15-inch scope. SN 2009ip is still hanging in there at magnitude 13.9, making it a fine showpiece for enterprising amateurs. To keep tabs on it and see more photos, I recommend a trip to David Bishop’s special page on the object. If you’d like to read a detailed analysis, check out this paper on the topic by a team of astronomers at the Universities of Arizona and California.

Since stars live exceptionally long lives far in excess of the human time scale, we normally have to observe thousands of them and piece the observations together using computer models to build a full picture of a stellar lifetime. Seeing 2009ip flirt with destruction and then finally detonate in the space of three years offers astronomers – amateur and professional – a rare glimpse of stellar evolution in real time.

10 Responses

  1. Tim Fleming

    A very interesting topic – thanks.

    I have a viewing question for you. I enjoy viewing Andromeda with binoculars. When viewing a region of the sky, just north and west of Altair, there appeared two potential fuzzy spots that could be galaxies? anything galaxies in that region that could be viewed with binoculars?

    Thanks and appreciate your daily blog.


    1. astrobob

      Hi Tim,
      While there are no galaxies visible in binoculars in that part of the sky, you did see two deep sky objects that belong to the Milky Way galaxy. From the position, it sounds like you observed the Dumbbell Nebula (a planetary nebula) in the small constellation of Vulpecula and the rich star cluster M71 in Sagitta. Both are visible in binoculars. Excellent spotting!

      1. Timothy Fleming

        Thanks for the information Bob. Have a great day. Know your blog is always a daily treat. I appreciate your effort, enthusiasm, and knowledge.

  2. lynn

    Hi Bob

    Could you help me out with some info on how the Impact Risk table works on the Jpl website because some of the impact date’s are in 2012, 2013 and so on, like the one 2005 TM173 that says the impact date is December 2012 but I presume it doesn’t work like that as I think we would be all talking about it lol, so can you explain then how it all works. Thanks Bob 🙂

    1. astrobob

      Hi Lynn,
      Yes, the numbers show impact potential only and are based on only 6 observations spanning 1.94 days – a very limited time period. Any possibility for an impact is considered, but in nearly every case those chances drop to zero once the orbit is defined. Almost all the asteroids in the Impact Risk Table ( have impact possibilities that will never be realized. Going back to 2005 TM173 (, if you look in the next column under DISTANCE, you’ll see that on Dec. 16, 2012 the asteroid will pass 125.8 Earth radii or 504,000 miles from Earth – very safe. At the far right, you’ll also see that this asteroid rates a big “0” on the Torino scale all the way through the year 2110. “0” is defined as “the likelihood of a collision is zero, or is so low as to be effectively zero.” In the entire list of 411 NEAs (Near-Earth Asteroids) all rate “0” on the Torino scale and only two rate a “1” or “extremely unlikely”. Here’s a link to the Torino scale:

  3. lynn

    Thank you very much Bob, no matter how much I tried to work it out it was becoming very confusing, but now you have explained it I get it all now. So thanks again 🙂

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