Mysterious stars that incite their stellar companions to explode in spectacular supernovas have just been revealed — these culprits can be bloated red giants, researchers say.

Supernovas are exploding stars that are bright enough to briefly outshine all the stars in their galaxies. They can occur when one star sheds gas onto a dying star known as a white dwarf, the dim fading core of a star that was once about the size of our sun.

Eventually, all this extra gas increases the white dwarf's mass enough to trigger runaway nuclear reactions that detonate the white dwarf.

The nature of the white dwarfs' companion stars in these explosions, which are a rare type of stellar conflagration dubbed a Type 1a supernova, is hotly debated, since researchers have not directly observed these companions. To learn more, astronomers used observatories in California, Hawaii, Arizona and the Canary Islands to investigate the supernova PTF 11kx, which is about 675 million light-years away. [Amazing Photos of Supernova Explosions]

Red giant star trigger
The scientists observed the complex shells of gas closely surrounding this supernova in very fine detail. This material from the white dwarf's companion star yielded insights regarding the identity of its source.

"We really saw for the first time detailed evidence of the progenitor for a Type 1a supernova," study lead author Benjamin Dilday, an astronomer at Las Cumbres Observatory Global Telescope Network in Goleta, Calif., told SPACE.com.

The researchers suggest the companion was a red giant star, much like what our sun is expected to become in about 5 billion years. As this red giant swelled with age, this matter poured on its white dwarf companion, occasionally triggering explosions known as novas. Enough material eventually poured onto this white dwarf to set off a far more powerful supernova. The researchers estimate that novas give rise to more than one-tenth of a percent of all type 1a supernovas, but less than 20 percent.

Past evidence suggested that only merging white dwarfs could cause Type 1a supernovas. The new findings suggest these kinds of explosions can involve many different kinds of stars.

"It is a total surprise to find that thermonuclear supernovae, which all seem so similar, come from different kinds of stars," said study author Andy Howell at Las Cumbres Observatory Global Telescope Network. "It is like discovering that some humans evolved from apelike ancestors, and others came from giraffes."

The new study also suggests that studying smaller star explosions called novas, which don't entirely destroy the star, might also shed light on Type 1a supernovas.

"We may be able to gain a better understanding of supernova 1a progenitor systems in general," Dilday said.

Cosmic candles in the night
Type 1a supernovas are ideal for measuring cosmic distances. They always erupt from white dwarfs of certain masses, and so always have the same relative brightness.

This predictability makes them extraordinarily valuable in figuring out how far away their host galaxies are — scientists compare how bright they know these explosions should be with how bright they appear to calculate the distance of the supernovas and their galaxies.

Knowing the distance of far-flung galaxies helps astronomers better understand how the universe evolved, and as such, learning more about Type 1a supernovas could help shed light on cosmic mysteries such as the dark energy that is apparently causing our universe's expansion to accelerate, Dilday said.

The scientists detailed their findings in the Aug. 24 issue of the journal Science.

• Top 10 Star Mysteries
• 7 Surprising Things About the Universe
• Stars: Formation, Classification and Constellations

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14 Comments

1. 1. jtdwyer 05:29 PM 8/23/12

   The article states:
   "Past evidence suggested that only merging white dwarfs could cause Type 1a supernovas. The new findings suggest these kinds of explosions can involve many different kinds of stars."
   
   This seems to conflict with all other type Ia SNe information I've seen.
   
   http://en.wikipedia.org/wiki/Type_Ia_supernova
   "Consensus model" section states:
   "There are several means by which a supernova of this type can form, but they share a common underlying mechanism. When a slowly-rotating,[2] carbon-oxygen white dwarf accretes matter from a companion, it cannot exceed the Chandrasekhar limit of about 1.38 solar masses..."
   It is this accretion process that consistently produces type Ia SNe as the swelling mass reaches about 1.38 solar masses - producing supernovae of consistent source luminosity and presumedly allowing their use as a 'standard candle'.
   
   The same Wikipedia entry section "Double degenerate progenitors" concludes:
   "Double degenerate scenarios [merging white dwarfs] raise questions about the applicability of Type Ia supernovae as standard candles, since total mass of the collapsing star made by the two white dwarfs vary on a great range, meaning luminosity also varies."
   
   http://news.sciencemag.org/sciencenow/2012/08/scienceshot-no-star-left-behind.html?ref=hp
   references two recent research reports, one in the "Astrophysical Journal", the other in "Nature", and concludes with the statement:
   "... hinting that more Type Ia supernovae may stem from double white dwarfs than astronomers had thought."
   
   This space.com report seems confusing if not completely confused...

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2. 2. vinodkumarsehgal 08:56 AM 8/24/12

   To jtdwyer
   
   You are refering to links of wikipedia which states that Type IA supernova may be formed by the accretion of matter by a white dwarf (rotating) from a neighboring white dwarf.
   
   This article states that Type IA SN may be formed by either
   i) Merging of two white dwarfs
   ii) Accretion of matter by a white dwarf from a red giant.
   
   in any case, common condition for the formation of a Type I A SN is increase in the mass of a white dwarf either due to accretion of matter from a white dwarf or red giant OR merging of white dwarf with another neighboring white dwarf.
   
   Distance between stars is very large in the range of light years. Closest star to our Sun is Proxima Centuri which is about 4.2 light years.
   
   In view of large distances, how a white dwarf can accrete matter from a neighboring white dwarf or red giant Or merge with another white dwarf?

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3. 3. jtdwyer in reply to vinodkumarsehgal 11:11 AM 8/24/12

   Nonsense! Where is it stated that, as you said:
   "Type IA supernova may be formed by the accretion of matter by a white dwarf (rotating) from a neighboring white dwarf?"
   
   It's stated in the first paragraph under
   http://en.wikipedia.org/wiki/Type_Ia_supernova#Formation
   "One model for the formation of this category of supernova is a close binary star system. The progenitor binary system consists of main sequence stars, with the primary possessing more mass than the secondary. Being greater in mass, the primary is the first of the pair to evolve onto the asymptotic giant branch, where the star's envelope expands considerably. If the two stars share a common envelope then the system can lose significant amounts of mass, reducing the angular momentum, orbital radius and period. After the primary has degenerated into a white dwarf, the secondary star later evolves into a red giant and the stage is set for mass accretion onto the primary. During this final shared-envelope phase, the two stars spiral in closer together as angular momentum is lost. The resulting orbit can have a period as brief as a few hours. If the accretion continues long enough, the white dwarf may eventually approach the Chandrasekhar limit."
   
   http://en.wikipedia.org/wiki/Binary_stars#Research_findings
   "It is estimated that approximately 1/3 of the star systems in the Milky Way are binary or multiple, with the remaining 2/3 consisting of single stars."

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4. 4. vinodkumarsehgal 05:30 AM 8/25/12

   To jtdwyer
   "Being greater in mass, the primary is the first of the pair to evolve onto the asymptotic giant branch, where the star's envelope expands considerably."
   
   "After the primary has degenerated into a white dwarf, the secondary star later evolves into a red giant and the stage is set for mass accretion"
   
   What does evolution of primary into asymptotic giant branch and expansion of its envelope means? Does it not mean a main sequence star may evolve into a red giant. Subsequently, on loss of matter from its outer layers or accretion of matter into its core, its core may change into a white dwarf.
   In the formation of a red giant also, on combustion of all the H and He, its outer layer expands due to loss of hydrostatic equilibrium in the star.
   
   I mean to say is red giant not an intermediate stage between a main sequence star and a white dwarf?
   
   After the conversion of secondary into a red giant and on accretion of its matter by primary or/and loss of matter from its outer layers to space in the form of dust , will secondary not convert into a white dwarf. So eventually will it not be two white dwarfs in close vicinity if primary does not explodes into a SN? If there is more loss of angular momentum, white dwarfs may merge and explode into into SN. That is what the following para of this article is stating
   
   "Past evidence suggested that only merging white dwarfs could cause Type 1a supernovas."
   
   I understand that our Sun shall swallow to a red giant after about 5 billion years and then its core will convert into a white dwarf when matter from outer layers of red giant will be lost.
   
   One thing more which neither this article nor wikilink is mentioning. Can a white dwarf, which is highly dense object with high gravitation, draw some interstellar matter/dust from adjoining space?
   
   
   
   
   

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5. 5. jtdwyer 07:14 AM 8/25/12

   Since I'm not a working astrophysicist, to answer your questions I have to go to web sources for verification. A good place to start would be http://en.wikipedia.org/wiki/Asymptotic_giant_branch
   or
   http://en.wikipedia.org/wiki/Stellar_evolution
   
   In the previously referenced entry under the section http://en.wikipedia.org/wiki/Type_Ia_supernova#External_links
   the first entry is a very good explanation of the Ia SN process, and how that relates to studies indicating that expansion of the universe is accelerating: http://www.pha.jhu.edu/~bfalck/SeminarPres.html
   
   In answering your questions, I would do a little research on the web to ensure that my response was as correct and complete as I could make it. While I learn a great deal from that research, it takes quite a bit of time. Since you have so many questions, I suggest that you research them on the web and answer them yourself.

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6. 6. patrick 07:22 AM 8/25/12

   Ref.Mr.vinodkumarsehgal-interesting to read your well detailed explanations ...Read this, it has a in-depth interlocking relationship for your comment's-"Supernovae of the Same Brightness, Cut From Vastly Different Cosmic Cloth Berkeley Lab researchers make historic observation of rare Type 1a Supernova" .

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7. 7. vinodkumarsehgal 09:32 AM 8/25/12

   To Mr Parick and jtdwyer
   
   Thanks for providing the reference link of Berkley Lab http://crd.lbl.gov/news-and-publications/news/2012/ptfkx11/. I have read the article.
   This article on Berkley sites provides more clarity and details, based upon empirical observations, on the formation of SN PTF 11 Kx than the present article in SA.
   
   One thing about which I am not clear is if a SN can be formed without any companion star in the form of red giant or white dwarf? What I mean to say if it is possible that a main sequence star without any binary pair, having adequate mass, may explode into a SN in the following chain :
   i) On exhaustion of combustible H and He, core may collapse into a white dwarf
   ii) Outer layers may expand into a red giant
   iii) White dwarf may have feed of matter from outer layers of same red giant.
   iv) At one stage of feed, thermo-nuclear reactions may again commence and white dwarf may explode into a SN.
   
   If you have confirmed knowledge on above concept, please share with me

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8. 8. jtdwyer in reply to vinodkumarsehgal 10:08 AM 8/25/12

   I see you haven't read the Wikipedia sources I directed you to - look it up yourself!

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9. 9. tecton47 12:38 PM 8/25/12

   Sometimes the best method to employ during a scientific endeavor is to abandon some preconceived notions and start over. I am not a trained cosmologist or astronomer, I'm just very interested in our universe and the amazing events and discoveries happening in it. The article makes it sound as if the white dwarf and the red giant are close enough for this accretion process to proceed unimpeded. At some point wouldn't the gases sloughed off by the red giant be dispersed by the "solar winds" of nearby stars? If the white dwarf is collecting the material it must be in miniscule amounts and I would assume that this process would take millions - if not billions - of years to reach the point of critical mass. Given this time frame it might be worth considering that the white dwarf going supernova is caused more by fundamental changes in its internal structure and less so by the accretion theory. Since astronomers have yet to actually view a pair of stars that would help validate this theory the actual explanation could be something far different than the accretion theory. Or maybe the accretion is just one factor in the process leading up to a Type 1a SN. Back in February I was fortunate enough to spend some time with Dr. Neil Degrasse Tyson but we mainly discussed the growing number of exoplanets and his remake of the "Cosmos" series by Carl Sagan. If I'd had the option of monopolizing his time there would've been a number of things I would've enjoyed discussing with him, including this suject. The nature of science is to ask a question, have someone provide a likely answer which will likely lead new questions and so on. If the debate is insular then it's easy to become mired in a fixed mindset and not considering the possibilities past the boundaries of a trapezoid (I'm tired of the phrase "thinking outside of the box.") It would benefit the people seeking the correct answer to an explanation for the white dwarf/red giant supernovae to abandon some accepted ideas and reconsider their entire approach.

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10. 10. jtdwyer in reply to tecton47 03:47 PM 8/25/12

    Please see:
    http://en.wikipedia.org/wiki/Type_Ia_supernova
    
    It shows an image of a supernova remnent that hasn't been blown away by anything for >400 years. You might find some other answers there. Follow the links...

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11. 11. Quinn the Eskimo 09:34 PM 8/25/12

    This boils down quite well. Children, remember where we parked the Star.
    
    Dad
    
    
    

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12. 12. jtdwyer in reply to Quinn the Eskimo 07:06 AM 8/26/12

    I told ya that old clunker's gonna blow up!

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13. 13. tecton47 in reply to jtdwyer 12:41 PM 8/27/12

    Thanks jtdwyer, I'll check that out. If my "solar wind" theory fails to hold water then I'm still curious about the distance factor and the incredibly slow accretion rate governed by that distance.

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14. 14. biggus56 06:29 AM 8/28/12

    Roche lobes and Lagrangian points.

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