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Old 06-14-2018, 08:38 PM
EastUmpqua EastUmpqua is offline
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Type Ia Supernova

Cosmologists use Type Ia supernova as a standard candle to determine distance (e.g. to other galaxies). One white dwarf sucks mass from itís binary companion and undergoes runaway carbon fusion when it reaches a specific mass (the Chandrasekhar limit). Itís absolute magnitude is predictable. But now it looks like most Type Ia supernovas occur when two white dwarfs merge (astronomers canít find evidence of remnant companion stars). That would mean the absolute magnitude is variable. How much would this impact cosmology?
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Old 06-14-2018, 10:21 PM
Exapno Mapcase Exapno Mapcase is online now
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According to Wikipedia, it's long been known that they are formed from two white dwarfs and that "This type Ia category of supernovae produces consistent peak luminosity because of the uniform mass of white dwarfs that explode via the accretion mechanism." So there isn't a problem to explain.
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Old 06-15-2018, 12:12 AM
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I don't think you're reading that wikipedia article correctly (although it could be written more clearly). There are two mechanisms discussed, the accretion mechanism whereby a white dwarf gradually steals material from its neighbor ("single degenerate progenitor"), and the merger mechanism where two white dwarfs collide("double degenerate progenitor"). The statement you quoted says that supernovae _due to accretion_ have a uniform peak luminosity, but later says "double degenerate scenarios raise questions about the applicability of Type Ia supernovae as standard candles, since total mass of the two merging white dwarfs varies significantly, meaning luminosity also varies." It also says a merger of two white dwarfs is a "very rare event" but that statement is not cited and doesn't seem completely consistent with the discussion in the Double Degenerate Progenitor section. So EastUmpqua's question is valid, but I'd like to see where they have read that "most" type Ia events are mergers.
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Old 06-15-2018, 05:43 AM
dtilque dtilque is online now
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Here's a thread at another message board that should illuminate this topic: A Path to Superluminous type 1a's?

I haven't read all of it, but I did get that Type Ia's are not exactly standard candles, but rather standardizable candles. That is, they aren't all the exact same absolute brightness, but you can find out the brightness by examining the spectra and light curve. Also some Type Ia's are peculiar and can't be used for this purpose.
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Old 06-15-2018, 09:50 AM
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Quote:
Originally Posted by EastUmpqua View Post
But now it looks like most Type Ia supernovas occur when two white dwarfs merge (astronomers canít find evidence of remnant companion stars).
Which papers are you basing this on? I haven't really kept up with this field of astronomy.
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Old 06-15-2018, 07:30 PM
EastUmpqua EastUmpqua is offline
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From Wikipedia:
It has been estimated that single degenerate progenitors account for no more than 20% of all Type Ia supernovae.[22]

Double degenerate scenarios raise questions about the applicability of Type Ia supernovae as standard candles, since total mass of the two merging white dwarfs varies significantly, meaning luminosity also varies.

So I’m wondering that if our estimates of cosmological distance is off, how much would that effect our current understanding. Maybe it would be like your ruler is off by 1/32”. Or could that explain some of the gravitational anomalies that require dark matter to fix..
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Old 06-15-2018, 11:22 PM
Sam Stone Sam Stone is online now
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It wouldn't have any effect on dark matter estimates, since those aren't based on galaxy distances, but rather their rotational velocities. We can also see dark matter from gravitational lensing.

However, it could have a major impact on dark energy, since the data from type 1a supernovae are what we used to determine that the expansion of the universe is accelerating, which is what created the need for something causing the expansion..

Recent measurements that improved on the early distance measurements of type 1a Supernovae have already put a slight question mark on dark energy, as the new measurements show that a solution that doesn't require dark energy can be found within the error bars of measurement, but just barely. So anything that calls into question the accuracy of type 1a distance measurement could change a lot.
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Old 06-16-2018, 08:33 AM
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There are lots of different independent forms of evidence for dark matter. Some of them are cosmological, and some of them relate to some degree to 1a supernovae.

Nowadays, though, the best data for all matters cosmological (including both dark matter and dark energy) comes from the cosmic microwave background.
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Old 06-17-2018, 01:42 PM
EastUmpqua EastUmpqua is offline
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Planck's relation). This is the source of the alternative term relic radiation. The surface of last scattering refers to the set of points in space at the right distance from us so that we are now receiving photons originally emitted from those points at the time of photon decoupling.

Is our ‘surface of scattering’ necessarily representative of the entire universe?
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Old 06-17-2018, 03:51 PM
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Any point in the Universe should be, at least approximately, representative of the whole, because the Universe doesn't seem to contain any "special" points. Take enough points, widely-enough separated, and the approximation should be very good indeed.

And what got cut off from that post?
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Old 06-17-2018, 04:25 PM
EastUmpqua EastUmpqua is offline
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Would our perception of our surface of scattering be different if we weren’t in a galactic gravity well?

From the Wikipedia article on cosmic microwave background:

universe became transparent instead of being an opaque fog.[3] Cosmologists refer to the time period when neutral atoms first formed as the recombination epoch, and the event shortly afterwards when photons started to travel freely through space rather than constantly being scattered by electrons and protons in plasma is referred to as photon decoupling. The photons that existed at the time of photon decoupling have been propagating ever since, though growing fainter and less energetic, since the expansion of space causes their wavelength to increase over time (and wavelength is inversely proportional to energy according to Planck's relation). This is the source of the alternative term relic radiation. The surface of last scattering refers to the set of points in space at the right distance from us so that we are now receiving photons originally emitted from those points at the time of photon decoupling.
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Old 06-18-2018, 09:03 AM
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It would be, but only very slightly, and by an amount that we can easily calculate and compensate for in the unlikely event that that much precision is required. We may be in a gravity well, but we're not very deep in it.
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