HEAPOW: A Breakthrough (2012 May 21)

[bystander]

HEAPOW: A Breakthrough (2012 May 21)

In any class some are brighter than others. This is also true for supernovae, the final, tremendous explosion of an evolved star. For some reason, a small subset of supernovae seems to be about ten times brighter than normal. Such was the case for an explosion detected at earth in 2010, which occurred in a distant irregular galaxy called UCG 5189A. This supernova, dubbed SN 2010jl, was about 10 times more luminous that your typical massive star core-collapse supernova. The unusual class of super-bright supernovae (if it really is a class) has been a puzzle to astronomers, and has raised uncomfortable questions about our understanding of the process by which a massive star dies. Three explanations have been presented: that these superluminous supernovae represent the formation of a strange neutron star with a super magnetic field; or that these stars are so massive they produce a weird "pair-instability" supernova; or these superluminous explosions occur in unusually dense circumstellar cocoons, which produces an enhanced interaction with the supernova blast wave. The image above of UCG 5189A is a composite of X-ray observations by the Chandra Observatory (purple) and an optical image by HST (in red, green, and blue). SN 2010jl is the bright white source on the left side of the image. Two Chandra X-ray observations of SN 2010jl in December 2010 and October 2011, were, literally, quite revealing. The later Chandra X-ray observations showed a dramatic decrease in the amount of X-ray absorption suffered by the supernova. This is the first time that a supernova breakout from its circumstellar cocoon was seen in "real time" (if you can call observing an event that actually occurred 160 million years ago "real time") and provides some evidence to support the blast-wave/thick circumstellar cocoon hypothesis as the source of these superluminous supernovae.

CXC: SN 2010jl: A Supernova Cocoon Breakthrough
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Author: Dr. Michael F. Corcoran

[neufer]

Actual Hubble line should diverge upward EVEN MORE if
distant hypernovae (w/large negative M's) are accounted for

.

Why hasn't the unusual class of super-bright supernovae
(a.k.a., hypernovae) raised uncomfortable questions
about our understanding of Dark Energy

(Specifically: whether these most distantly observed
hypernovae are in fact so numerous & so bright that
Dark Energy Ω_Λ is more than the presumed 70% )

http://www.scientificamerican.com/artic ... er-powered

http://www.scientificamerican.com/artic ... ang-theory

http://www.scientificamerican.com/artic ... -supernova

[Ann]

Okay, forgive me if I'm wrong. But my understanding is that astronomers came to the conclusion that dark energy exists partly because distant supernovae turned out to be fainter than expected, not brighter.

Now astronomers have found a few super-bright supernovae. That's fascinating. But in what way does it rock the foundation of dark energy?

Ann

[neufer]

Okay, forgive me if I'm wrong. But my understanding is that astronomers came to the conclusion that dark energy exists partly because distant supernovae turned out to be fainter than expected, not brighter.

Now astronomers have found a few super-bright supernovae. That's fascinating. But in what way does it rock the foundation of dark energy?

The idea is that there must have been more of these massive low metallicity super-bright supernovae
early in the Universe's evolution (i.e., at high z) than there are today (i.e., at low z).

Since these hypernovae are intrinsically brighter than expected:

1) their "relative dimness" must be even greater than expected and
2) their distances must likewise be greater than the assumed "10% to 15% farther out than expected."

<<The two teams, both of which have members in Europe, Latin America, Australia, and the United States, collected their supernova data with increasing efficiency over the last few years, expecting to find out by how much gravity was slowing cosmic expansion. Early this year, both teams announced that their expectations had been turned upside down: The relative dimness of the supernovae showed that they are 10% to 15% farther out than expected even in a universe with little matter, indicating that the expansion has accelerated over billions of years. At year's end, with dozens of supernovae analyzed, published, or in press, those conclusions stand.

That finding resurrects a mysterious repulsion that counteracts gravity, with lambda as the most likely candidate. There were earlier hints, from theories of cosmic evolution and observations of the large-scale structure of the universe, that the cosmos holds little mass and that there might be a lambda, but the idea was generally considered outlandish. Now lambda is respectable once more, and Einstein is proved right, albeit for reasons he could not have foreseen. In fact lambda appears to be dominant in the universe: In the simplest theoretical picture, the supernova data imply that 70% of the universe's energy is in the form of lambda and only 30% is matter.>>

[Ann]

Okay. Sorry. I thought you were trying to argue that dark energy can't be real if supernovae aren't perfect standard candles. Several people seem to try to make that point, or at least that's my impression.

Your point seems to be that dark energy might be even stronger than the current standard model says it is.

Ann

[neufer]

You(r) point seems to be that dark energy might be even stronger than the current standard model says it is.

Precisely.