Universe's 'standard candles' are white dwarf mergers

Oct 04, 2011
A small section of the Subaru Deep Field image showing some of the galaxies and supernovae used in the study. Credit: NAOJ

(PhysOrg.com) -- The largest survey to date of distant exploding stars is giving astronomers new clues to what’s behind the Type Ia supernovae they use to measure distances across the cosmos.

These stellar explosions helped astronomers conclude more than a decade ago that dark energy is accelerating the expansion of the universe. But what caused them was a mystery. Many astronomers thought white dwarf stars were pulling matter from their normal stellar companions and growing so fat they exploded.

But the new study by American, Israeli and Japanese astronomers using Subaru and Keck telescopes in Hawaii instead suggests that many, if not most, of the Type Ia supernovae result when two white dwarf stars merge and annihilate in a thermonuclear explosion.

“The nature of these events themselves is poorly understood, and there is a fierce debate about how these explosions ignite,” said Dovi Poznanski, one of the main authors of the paper and a post-doctoral fellow at the University of California, Berkeley, and Lawrence Berkeley National Laboratory.

“The main goal of this survey was to measure the statistics of a large population of supernovae at a very early time, to get a look at the possible star systems,” he said. “Two merging can explain well what we are seeing.”

Poznanski, Tel-Aviv University graduate student Or Graur and their colleagues will report their findings in the October 2011 issue of the journal Monthly Notices of the Royal Astronomical Society (MNRAS).

The results do not place in jeopardy the conclusion that the expansion of the universe is accelerating, said coauthor Alex Filippenko, UC Berkeley professor of astronomy.

“As long as Type Ias explode in the same way, no matter what their origin, their intrinsic brightnesses should be the same, and the distance calibrations would remain unchanged,” he said.

Evidence that Type Ia supernovae are caused by the merger of two white dwarfs the so-called double-degenerate theory has been accumulating over the past two years, based on surveys by the Hubble Space Telescope and others.

“The tide is definitely turning, and these are the best data yet to support the double-degenerate theory,” Filippenko said.

White dwarfs are dense, compact stars formed from normal stars like the sun once they exhaust their nuclear fuel and compress under their own weight.

The new, largest-ever survey using the Subaru Telescope in Hawaii accumulated a sample of 150 distant supernovas that exploded between 5 and 10 billion years ago.

The finding, when combined with previous surveys of closer Type Ia supernovae, suggests that astronomers surveying Type Ia supernovae may be seeing a mixture of single- and double-degenerates.

“There are no good answers yet, and it could be that we are seeing a mix of the two types of explosions,” Poznanski said.

Though the two-faced nature of Type Ia supernovae still allows them to be used as calibratable candles to measure cosmic distance, Filippenko said, it might affect attempts to “quantify in detail the history of the expansion rate of the . The subtle differences between single- and double-degenerate models could introduce a systematic error that we’ll need to account for.”

The team found that Type Ia supernovae were five times more common 5-10 billion years ago than today, probably because there were more young stars back then rapidly evolving into white dwarfs. Moreover, this study allowed the team to more accurately determine the production of iron over cosmic time, as Type Ia supernovae create iron through nuclear reactions when they explode.

To find their distant sample, the international team of astronomers exploited the enormous light collecting power of the Subaru Telescope’s Suprime-Camera on four separate occasions. They pointed the ground-based telescope, located atop Hawaii’s Mauna Kea volcano, toward a single field in the sky that was approximately the size of the full moon. Each run yielded about 40 supernovae among 150,000 galaxies.

Then they used the Keck telescopes on Mauna Kea to observe the galaxies where these explosions occurred. These observations were crucial for pinpointing the distance of these events.

Future observations with the Hyper Suprime-Camera, which will be mounted on the Subaru Telescope, will be able to discover even larger and more distant supernova samples to test this conclusion.

Explore further: Can astronomy explain the biblical Star of Bethlehem?

More information: Read the paper at: arxiv.org/abs/1102.0005

Provided by W. M. Keck Observatory

4.7 /5 (7 votes)

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Sanescience
5 / 5 (3) Oct 04, 2011
"As long as Type Ias explode in the same way..."

I keep getting a sense of a growing "hedge".

As is frequently the case with science, what was obvious has become "complicated".

Nor have I seen explanations that convince me that a number of issues might not effect their luminosity average values. Like levels of "haze" gasses in earlier vs. later galaxies. Or the spin orientation of the star effecting it's observed luminosity (similar to how quasars are believed to be able to be so bright) being more or less jumbled the farther back in time you go. Or that a-symmetric explosions might be more common if triggered by in falling planets instead of smooth accumulation of gas from a companion star.

When ever "science" says something is understood but doesn't have the details, beware.
Callippo
1 / 5 (1) Oct 04, 2011
As long as Type Ias explode in the same way.
Is there a (good) reason for such assumption at all? Why the collision of two small stars should make the same flash, like the collision of large ones?
omatumr
1 / 5 (7) Oct 04, 2011
dark energy is accelerating the expansion of the universe


Accelerating expansion of the universe is a discovery worthy of a Nobel Prize

www.canada.com/te...e/Faster expanding universe work wins physics Nobel/5499804/story.html

Because it confirms that neutron repulsion [1] causes neutrons to be emitted faster from smaller fragments of parent neutron stars - as water evaporates faster from smaller water droplets - in our infinite cosmos [2].

1. "Neutron repulsion", APEIRON Journal, in press (2011)

http://arxiv.org/...2.1499v1

2. "Is the Universe Expanding?", Journal of Cosmology 13, 4187-4190 (2011)

http://journalofc...g102.htm

With kind regards,
Oliver K. Manuel
Former NASA Principal
Investigator for Apollo
http://myprofile....anuelo09
malapropism
not rated yet Oct 04, 2011
So if there are 2 putative populations of Type 1a supernovae (single-degenerate and double-degenerate) would this show up in spectra with the double-degenerate class being higher in metal content than others?

(I don't know the answer but am interested, if anyone who knows this stuff can give a reply. Thanks.)
jsdarkdestruction
4.2 / 5 (5) Oct 04, 2011
Oliver, do you not know of phase 2 of the plan? see kissinger and nixon knew about neutron repulsion and it being the main source of the suns and the universes power but chairman mao did not. as the world all followed their lead in the conspiracy they said it was to prevent nuclear war. however under the guise of that the united states had different reasons. as the climatoligists/scientists destroy our economy and power while funneling money to third world nations for supportung the scam the chinese will soon grow too strong and overpopulated for anyone but the us to even have a chance of stopping the chinese from taking over the world, at that moment neutron repulsion will be officially "discovered" and cheap easy neutron repulsion energy will be used both to power production of weapons and supplies and as weapons of mass destruction themselves in neutron repulsion bombs. saving the united states and allowing us to finally take over the whole world without looking like the bad guys...

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