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The Galaxy's Brightest Explosions Go Nuclear With an Unexpected Trigger (sciencemag.org) 29

Posted by BeauHD from the cause-and-effect dept.
sciencehabit writes: Type Ia supernovae, a bright and long-lasting brand of stellar explosion, play a vital role in cosmic chemical manufacturing, forging in their fireballs most of the iron and other metals that pervade the universe. The explosions also serve as "standard candles," assumed to shine with a predictable brightness. Their brightness as seen from Earth provides a cosmic yardstick, used among other things to discover "dark energy," the unknown force that is accelerating the expansion of the universe. Astronomers have long thought that the blasts come from white dwarfs, burnt out stars once like our Sun, reignited after stealing material from a companion red giant. But evidence is mounting that other mechanisms may be causing white dwarfs to explode, making their standard candle status a puzzle.
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The Galaxy's Brightest Explosions Go Nuclear With an Unexpected Trigger More

The Galaxy's Brightest Explosions Go Nuclear With an Unexpected Trigger

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  • Easy evaluation (Score:5, Insightful)

    by moxrespawn ( 6714000 ) on Friday June 05, 2020 @03:09AM (#60147944)

    "But the extreme speed of the white dwarfs suggested a different scenario, in which the fleeing dwarfs had delivered the sparks, from close orbits around the doomed stars. When they blew up, these partners were flung away like shots from a biblical sling."

    Bible mentioned, article summarily dismissed.

    But I'll look up and contemplate twins (stars) anyway, while I have my half/double a loaf of French bread for breakfast.

    • Need some Lithium? https://www.nasa.gov/feature/l... [nasa.gov]
    • Slings were actually used in the Biblical timeperiod (and actually uses until very late also). Many people are most familiar with slings in that context; the story of David and Goliath is particularly well known. The Bible is a useful cultural touchstone to get people to understand what one is talkng about. It is a mistake to go from a mention of "biblical" to then decide that there must be somehthing wrong with the article. Heck, I read not too long ago an article that referenced polyjuice potion from Har

      • Thanks. I suppose I assumed that most would know I am theist (having been one of the more vocal ones here for years), so I didn't explicitly end with "/sarcasm".

        Yes, dismissing the scientific content because of the bible reference would be stupid. But many here actually will, the "conflict thesis" is popular here.

        • Thanks. I suppose I assumed that most would know I am theist (having been one of the more vocal ones here for years), so I didn't explicitly end with "/sarcasm".

          Yes, dismissing the scientific content because of the bible reference would be stupid. But many here actually will, the "conflict thesis" is popular here.

          Oh great, another imagined persecution. You imagine that people will dismiss it because of a passing bible reference, that's not something that actually happened. As long as you get to feel like a victim! Just like the Romans throwing the Christians to the lions [uq.edu.au], the persecution is mostly in your imagination.

      • Slings were actually used in the Biblical timeperiod (and actually uses until very late also).

        They're still a routine tool of protest in Middle Eastern countries today. Why they're not used more often in, for example, this weeks protests, I don't know.

        • Two reasons: First, the actual set of rioting here has been very small. This really is mostly protesting. Second, using a sling effectively actually requires a lot of practice. If one doesn't know what one is doing then one can easily hurt one's self or one's allies with a sling.

  • The Galaxy's Brightest Explosions Go Nuclear With an Unexpected Trigger

    Nuclear??? ...Supernovas??? Ok, which one of you has been allowing Blindseer to press the big red button again?

  • It may be strange to say it (Score:4, Insightful)

    by t4eXanadu ( 143668 ) on Friday June 05, 2020 @08:58AM (#60148522)

    I love when Astronomy and Cosmology theories turn out to be wrong, almost as much as when evidence is gathered in their support (and in the long run, most will be discarded). This is how scientific thought advances. In the sciences, ignorance is not necessarily a bad thing. Recently, many people seem to misunderstand how science works, claiming failure is some kind of indictment of scientists. That is not how science works. It is built on the back of previous misconceptions and failures. It shows that the universe is always stranger and more complex than our puny minds wish it to be. That's not to say we can't ever get it right. We owe the whole of our technological advancement to prior scientific research. The mysteries of the nature are what drives science, keeps us in awe, and motivates scientists to better understand. It's a beautiful thing.

  • Double-degenerate model, not exactly new (Score:3, Informative)

    by Shag ( 3737 ) on Friday June 05, 2020 @12:44PM (#60149260) Journal

    And by virtue of being not exactly new, not exactly surprising.

    The underlying math for a type Ia supernova is that at about 1.4 solar masses, a white dwarf can't maintain equilibrium and will collapse and detonate. We call this the Chandrasekhar limit, since he did the math.

    One way of increasing the mass of a white dwarf until it reaches that limit is by having it siphon mass off a larger companion in a binary star system. To the extent that this works, and with a little bit of a fudge factor for stars rotating at different speeds, type Ia supernovae are relatively "standard candles" cosmologically.

    But we have found type Ia supernovae that are "too bright," indicating that they had a greater mass when they detonated. So how do you suddenly get a white dwarf of, say, 1 solar mass, to way more than 1.4 solar masses? Easy, just have it collide with another one the same size. Ta-da, kaboom. We've seen and studied a number of these already.

    The "double-degenerate" model has been put forth as a likely explanation for super-Chandrasekhar-mass, superluminous type Ia's for at least a decade or so. Google finds papers.

    (Full disclosure: associate member of the Nearby Supernova Factory at Lawrence Berkeley National Library, 2007-2016)

    • Another complicating factor - which people have known about since the late 80s, if not earlier - is that there seems to be a small relationship between Type-Ia brightness and the metallicity of the progenitor. Which shouldn't surprise anyone - the degenerate electron pressure that supports a white dwarf depends somewhat on the mass of the particles, which includes the nuclei. Have more heavy nuclei and the pressures will be different, and the mass at which the bang goes off would be different.

      Nonetheless,

      • Nonetheless, supernovae in galaxies in which we can also see Cepheids still show a good low variance trend in brightness/ distance that the dark matter/ dark energy deductions don't change significantly.

        Except assumptions about the regularity and reliability of Cepheids are also crap. Under the standard assumptions, the Milky Way would have to be shaped like a Pringles chip, but there is no such distortion in the distribution of distances in the Gaia data, including for Cepheids close enough to be measured by Gaia. A whole lot of things are going to have to be reexamined because of Gaia satellite data.

        We live in in the most exciting times in the history of astrophysics. When SpaceX finally stops blowing

    • The underlying math for a type Ia supernova is that at about 1.4 solar masses, a white dwarf can't maintain equilibrium and will collapse and detonate. We call this the Chandrasekhar limit, since he did the math.

      One way of increasing the mass of a white dwarf until it reaches that limit is by having it siphon mass off a larger companion in a binary star system.

      Having read the article (I know, I know), it's become quite clear that the red giant with white dwarf companion scenario basically never happens. It's not just uncommon, it's extremely rare. Even allowing for the possibility that we're not very good at finding systems like that, they're still damn rare.

      The dynamically driven double-degenerate double detonation model from 2010 is for sub-Chandrasekhar-mass, not super. It's fusion shockwave induced, not gravity induced. And it looks like at least 75% of a

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