The Explosive Universe

picture-1.pngMany things are in the pipeline for production. In the past 24 hours I have recorded numerous different interviews and tidbits with people working on supernovae, in science reporting, and astronomy education. I have so much material I’m not quite sure when I’ll find the time to edit it together, but time will be made, and Astronomy Cast will have some great new material in weeks to come.

Today’s press conferences spanned a wide gamut, talking about everything from dwarf galaxies to disk formation to, I kid you not, hot chocolate. The highlight for me was the press conference on new supernovae results. As often happens at these things, three very different results on the same broad class of objects were presented together.

In brief:

  • Dr. Stephen P. Reynolds (North Carolina State University) presented results obtained using the Chandra showing that Kepler’s Supernova Remnant (see image above, credit NASA/ESA/JHU/R.Sankrit & W.Blair) resulted from a Type Ia supernovae (the type of supernova created by an exploding white dwarf). In this case of forensic astronomy, they learned that it is possible for exploding white dwarfs to be surrounded by the type of circumstellar material normally associated with higher mass stars going through a period of mass loss via stellar winds. This implies that perhaps larger mass stars are able to loss enough mass to become white dwarfs. If these stars occur in binary star systems, they can gravitationally steal mass from a companion star until they become so fat they explode as supernovae. It has been unclear for a long time what limits there are on which stars can become white dwarfs. We can say with certainty the sun will become one because it is so small there are no other options. This is true of everything up to a couple solar masses. Above this limit however, it is possible for a star to become a neutron star or perhaps even, for the largest stars, a black hole or a supernova that leaves behind nothing at all. ‘Possible’ and ‘certain’, however, are words with different meaning. Now it appears that some larger than previously expected stars are becoming white dwarfs. This has the neat implication that type 1a supernovae may have been able to occur earlier in the universe than was previously expected, allowing Iron, which is created in the explosion, to get distributed around the universe earlier than expected. This means planets may have been able to also form earlier than expected. And, that means, life may also have been able to start forming earlier than previously expected. I’ll explain why that is cool in a later blog entry.
  • supernova1.jpgDr. Nathan Smith (University of California Berkeley) reported on the discovery of 3 luminous blue variables (LBV) that have surrounding ring structures similar to those seen around the famous Supernova 1987 A. In pre-supernova images of this star it was discovered that SN1987a’s progenitor star was a LBV. This result was a bit shocking because LBVs were supposed to go through a red supergiant phase before going SN, and no one was quite sure how to explain this discrepancy between theory and data (and some really Rube Goldberg theories I won’t go into were made up to fit the situation). The three LBVs that Smith and the research team he works with discovered all resemble SN 1987a’s progenitor (see image at right of HD168625. credit: NASA, JPL-Caltech, Nathan Smith/UC Berkeley), and they believe that perhaps stellar evolution has a never before suspected branch, and that in certain situations LBVs just go supernova. This adds a new branch to the possible paths of stellar evolution, and this result also has neat implications for the future of the nearby LBV Eta Carina. While it was previously believed this star would have to go through one more evolutionary stage before it exploded (becoming a Wolf-Rayet Star), it is now believed Eta Carina may just explode. Boom. While not harmful to life on Earth, this explosion could destroy all the satellites around our planet. While I’d love it if Eta Carina exploded in my lifetime, I have to admit the economic implications are a bit scary. (And it will be hard to study if all the on-orbit observatories bite the dust.)
  • ssc2007-01a_200.jpgDr. Nicolas Flagey (Institut d’Astrophysique Spatiale, Orsay, France) discussed how the beloved “Pillars of Creation” in the Eagle Nebula may actually not exist anymore. The Eagle Nebula is located roughly 7000 light years away. They have found evidence that in the year 6000BC a supernova exploded, sending shockwaves through the nebula. They estimate the shockwave encountered the Pillars of Creation in 4000 BC, causing them to crumble apart, with the densest material forming stars while the less dense material was dispersed by the shock. Because of the travel time of light, that original supernova may have been observed in 1000 AD, and in roughly 3000 AD future astronomers will be around to find out if this papers results are correct, as they do or do not observe the falling of the pillars. Today we see the supernovae shockwave as red in the image at right (credit: NASA/JPL-Caltech/N. Flagey (IAS/SSC) & A. Noriega-Crespo (SSC/Caltech))
  • I’m sure that Phil Plait, an expert on SN1987a, will be blogging about the results later, so keep an eye on Bad Astronomy.

    In a completely separate press conference, Dr. Michael Ireland (CalTech) announced that it has been discovered that the giant star Mira, a favorite variable for amateur astronomers, is contributing to the formation of a disk around its companion star. As material streams off of Mira, lost to its stellar wind, its companion gravitationally pulls it into a disk. This may be a new way to create a new planetary disk in an old system.

    And here is where I admit that I missed the earliest press conference of the morning because I had a breakfast meeting with Dr. Sarah Maddison of Swinburne Astronomy Online. She is a great lady and we did a great little interview, but it means I missed a bit of news. Luckily, one of the other reports, Govert Schilling, was there to cover it. Check out his story at Science Now.

    There is so much more I want to write, but there are also people to interview, and I can’t do both at once, so this is it for now.


  1. Paul January 10, 2007 at 3:01 pm #

    I have a question about how stars form. I’m confused about the answers I’ve read or heard about. Some people say that stars “condense” from molecular space gas. As they do, they heat up and ignite. Others say they “collapse” from gas. Still others say that the gas is “compressed” by a nearby supernova.

    It seems that there are problems with all of these scenarios. I read that for collapse or condensation to take place, until a critical density is reached, gas pressure is greater than gravity and the the proto star will never be able to form.

    As for the compression theory, it reminds me of Tokamak, the attempt to design a magnetic bottle to hold in a hot plasma so that fusion can be sustained. If I remember correctly, designing a “leak-free” bottle is a major hurdle. But even assuming that they can do it, it is hard to imagine a supernova applying directed pressure on all sides so that no gas “leaks” out and a new star is formed. And even this does not explain the very first stars.

    Can you help explain how stars are formed?


  2. Pamela January 11, 2007 at 11:24 pm #

    Hey Paul, I answered this in the next entry. Cheers, Pamela

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