Universe's Rate of Expansion Called into Question

posted by cmn32480 on Wednesday April 15 2015, @01:44PM

from the not-your-momma's-chevy-nova dept.

Science Daily has an intriguing article, "Accelerating universe? Not so fast", which notes the discovery that type Ia supernovae, which are used as a 'standard candle' for measuring distances in the universe, actually come in two different subtypes. Though nearly indistinguishable in normal optical frequencies, the differences became apparent when examined in the ultraviolet. The significance is two type IA supernovae having the same luminosity may actually be located at different distances from us. This, in turn, calls into question how fast the universe is expanding.

So, if I measured the brightness of a "100-watt bulb" at 1km, and then measure another "100-watt bulb" and find it to have the same brightness, I would assume that it, too, was 1km away. Apparently some "100-watt bulbs" are dimmer than others — and, according to the inverse square law, would be closer to me than 1 km.

I've been unable to determine how much a difference this would cause in our estimation of the rate of the expansion of the universe. Also, I suspect this might affect our 3-D maps of the universe and what is located where. How will it affect the current thinking about "dark energy"? How much of an impact are we looking at here? What else might be affected?

[Continued after the break]

From the article:

The team, led by UA (University of Arizona) astronomer Peter A. Milne, discovered that type Ia supernovae, which have been considered so uniform that cosmologists have used them as cosmic "beacons" to plumb the depths of the universe, actually fall into different populations. The findings are analogous to sampling a selection of 100-watt light bulbs at the hardware store and discovering that they vary in brightness.
"We found that the differences are not random, but lead to separating Ia supernovae into two groups, where the group that is in the minority near us are in the majority at large distances -- and thus when the universe was younger," said Milne, an associate astronomer with the UA's Department of Astronomy and Steward Observatory. "There are different populations out there, and they have not been recognized. The big assumption has been that as you go from near to far, type Ia supernovae are the same. That doesn't appear to be the case."
The discovery casts new light on the currently accepted view of the universe expanding at a faster and faster rate, pulled apart by a poorly understood force called dark energy.
[...] "The idea behind this reasoning," Milne explained, "is that type Ia supernovae happen to be the same brightness -- they all end up pretty similar when they explode. Once people knew why, they started using them as mileposts for the far side of the universe.
"The faraway supernovae should be like the ones nearby because they look like them, but because they're fainter than expected, it led people to conclude they're farther away than expected, and this in turn has led to the conclusion that the universe is expanding faster than it did in the past."

An abstract is available, article is paywalled.

Because of the slightly different colors for these groups, NUV-red SNe will have their extinction underestimated using common techniques. This, in turn, leads to underestimation of the optical luminosity of the NUV-blue SNe Ia, in particular, for the high-redshift cosmological sample. Not accounting for this effect should thus produce a distance bias that increases with redshift and could significantly bias measurements of cosmological parameters.

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