The best way to measure dark energy just got better

Jan 13, 2011
A Type Ia supernova occurs when a white dwarf accretes material from a companion star until it exceeds the Chandrasekhar limit and explodes. By studying these exploding stars, astronomers can measure dark energy and the expansion of the universe. CfA scientists have found a way to correct for small variations in the appearance of these supernovae, so that they become even better standard candles. The key is to sort the supernovae based on their color. Credit: NASA/CXC/M. Weiss

(PhysOrg.com) -- Dark energy is a mysterious force that pervades all space, acting as a "push" to accelerate the Universe's expansion. Despite being 70 percent of the Universe, dark energy was only discovered in 1998 by two teams observing Type Ia supernovae. A Type 1a supernova is a cataclysmic explosion of a white dwarf star.

These supernovae are currently the best way to measure dark energy because they are visible across intergalactic space. Also, they can function as "standard candles" in distant galaxies since the intrinsic brightness is known. Just as drivers estimate the distance to oncoming cars at night from the brightness of their headlights, measuring the apparent brightness of a supernova yields its distance (fainter is farther). Measuring distances tracks the effect of dark energy on the expansion of the Universe.

The best way of measuring dark energy just got better, thanks to a new study of led by Ryan Foley of the Harvard-Smithsonian Center for Astrophysics. He has found a way to correct for small variations in the appearance of these supernovae, so that they become even better standard candles. The key is to sort the supernovae based on their color.

"Dark energy is the biggest mystery in physics and astronomy today. Now, we have a better way to tackle it," said Foley, who is a Clay Fellow at the Center. He presented his findings in a press conference at the 217th meeting of the American Astronomical Society.

The new tool also will help astronomers to firm up the cosmic distance scale by providing more accurate distances to faraway galaxies.

Type Ia supernovae are used as standard candles, meaning they have a known intrinsic brightness. However, they're not all equally bright. Astronomers have to correct for certain variations. In particular, there is a known correlation between how quickly the supernova brightens and dims (its light curve) and the intrinsic peak brightness.

Even when astronomers correct for this effect, their measurements still show some scatter, which leads to inaccuracies when calculating distances and therefore the effects of dark energy. Studies looking for ways to make more accurate corrections have had limited success until now.

"We've been looking for this sort of 'second-order effect' for nearly two decades," said Foley.

Foley discovered that after correcting for how quickly Type Ia supernovae faded, they show a distinct relationship between the speed of their ejected material and their color: the faster ones are slightly redder and the slower ones are bluer.

Previously, astronomers assumed that redder explosions only appeared that way because of intervening dust, which would also dim the explosion and make it appear farther than it was. Trying to correct for this, they would incorrectly calculate that the explosion was closer than it appeared. Foley's work shows that some of the color difference is intrinsic to the supernova itself.

The new study succeeded for two reasons. First, it used a large sample of more than 100 supernovae. More importantly, it went back to "first principles" and reexamined the assumption that Type Ia supernovae are one average color.

The discovery provides a better physical understanding of Type Ia and their intrinsic differences. It also will allow cosmologists to improve their data analysis and make better measurements of - an important step on the road to learning what this mysterious force truly is, and what it means for the future of the cosmos.

Explore further: An unprecedented view of two hundred galaxies of the local universe

Related Stories

$2.38 Million for Supernova Research

Sep 21, 2004

The Gordon and Betty Moore Foundation of San Francisco has awarded $2,377,000 to the University of California at Berkeley's Space Sciences Laboratory, in support of the Nearby Supernova Factory (SNfactory). ...

Supernovae mystery solved

Jun 30, 2010

(PhysOrg.com) -- Supernovae are gigantic stellar explosions that can be seen across the entire universe. Type Ia supernovae are a relatively homogeneous class of stellar explosions, which researchers use as ...

Where do supernovae come from?

Sep 17, 2010

(PhysOrg.com) -- Supernovae, the explosive deaths of massive stars, are among the most momentous events in the cosmos because they disburse into space all of the chemical elements that were produced inside ...

Origin of Key Cosmic Explosions Still a Mystery

Jul 12, 2010

(PhysOrg.com) -- When a star explodes as a supernova, it shines so brightly that it can be seen from millions of light-years away. One particular supernova variety - Type Ia - brightens and dims so predictably ...

Recommended for you

The origins of local planetary orbits

12 hours ago

A plutino is an asteroid-sized body that orbits the Sun in a 2:3 resonance with Neptune. They are named after Pluto, which also orbits the Sun twice for every three orbits of Neptune. It is thought that Pluto ...

Wild ducks take flight in open cluster

13 hours ago

The Wide Field Imager on the MPG/ESO 2.2-meter telescope at ESO's La Silla Observatory in Chile has taken this beautiful image, dappled with blue stars, of one of the most star-rich open clusters currently ...

Image: The Pillars of Creation

14 hours ago

The Pillars of Creation (seen above) is an image of a portion of the Eagle nebula (M16) taken by Hubble Space Telescope in 1995. It soon became one of the most iconic space images of all time. The Eagle nebula ...

User comments : 11

Adjust slider to filter visible comments by rank

Display comments: newest first

Nik_2213
5 / 5 (7) Jan 13, 2011
"... it went back to "first principles" and reexamined the assumption that Type Ia supernovae are one average colour."

And it paid off !! Well done !!

IIRC, a similar re-inspection recently discovered that Cepheids are not quite as 'constant' as thought, but change slightly as they age because they blow off material with each pulsation...
LarsKristensen
2 / 5 (13) Jan 13, 2011
Dark energy is not an energy but a mathematical function in a physical phenomenon.

When light redshifted it done by the original light will be redshifted. After an equally long time interval redshifted light will be redshifted instead. This makes the subsequent happening at the same time intervals, an accelerating redshift of the more redshifted light. The same phenomenon is known in the financial world, this phenomenon is called simply compounding. Here is the original money is raised through the compound interest increase in an accelerating movement.

The dark energy is not an energy and therefore should not be used as evidence for an accelerating universe. The dark energy is and remains simply a mathematical function in a physical phenomenon.

That scientists can bring himself to believe that "dark energy" is an energy that I can with my right mind does not comprehend.
deatopmg
2.3 / 5 (8) Jan 13, 2011
Here dark energy is spoken of as a fact. In fact, it (and dark matter) is/are a construct, i.e. fudge factor, to bolster an existing theory that without it/them cannot explain the observations.

Other more elegant theories that better describe the observations exist but they all require trashing the existing cosmic paradigm. Therefore, it'll take at least 2 generations for one of these to become predominate.
soulman
3.4 / 5 (5) Jan 13, 2011
Here dark energy is spoken of as a fact

Yup, that's what evidence is telling us.
In fact, it (and dark matter) is/are a construct, i.e. fudge factor, to bolster an existing theory that without it/them cannot explain the observations

Just because the two phenomena share the word 'dark' doesn't mean that they are linked. Certainly dark matter has been 'observed' through gravitational lensing and various other indirect evidence. There are currently no better alternatives.
Other more elegant theories that better describe the observations exist but they all require trashing the existing cosmic paradigm

Name them. If they truly did fit all observations better than current theories, then they would be mainstream. They don't, so they're not.
Therefore, it'll take at least 2 generations for one of these to become predominate

Time won't make these 'alternatives' more attractive, only better agreement with reality will.
Sten
not rated yet Jan 13, 2011
"fainter is further"?? Imagine how that could be otherwise.
LarsKristensen
2.3 / 5 (3) Jan 13, 2011
This dark energy is described as a fact.

Yup, that's what the evidence tells us.[/ q]

There is no evidence of dark energy. There is evidence that redshifted light is accelerating redshifted. Dark energy idea is a conclusion resulting from an attempt at understanding the acceleration redshift. The conclusion is no evidence.

Dark energy and dark matter should not be debated at the same time, it simply creates confusion.
soulman
3 / 5 (6) Jan 14, 2011
There is no evidence of dark energy.

That's laughable especially since you're posting in a thread which is actually about evidence for dark energy.
There is evidence that redshifted light is accelerating redshifted.

That didn't make sense, so I can't comment.

However, other evidence comes from CMB measurements which show the universe to be flat and for that to be the case, you need a certain amount of matter (dark or luminous). We can only account for some 30% of it, which means the remaining 70% goes towards dark energy. Then there's the ISW effect... So, yeah, no evidence.
more...
soulman
3 / 5 (6) Jan 14, 2011
Dark energy idea is a conclusion resulting from an attempt at understanding the acceleration redshift. The conclusion is no evidence.

Bull. You conveniently ignored the solid, observational evidence I gave you in the previous post.
Dark energy and dark matter should not be debated at the same time, it simply creates confusion.

And debates shouldn't be started and prosecuted by people ignorant of the facts. That leads to much greater confusion and muddy water.
LarsKristensen
2.5 / 5 (4) Jan 14, 2011
Dark energy is not dark matter.

These are two very different things.

Dark energy is raised conclusion is existent, because the redshifted light appears to be accelerating in its redshift, resulting in Type Ia supernovae.

Dark matter can not be observed visually using electromagnetic radiation, but only through its manifestation in influencing its surroundings with a gravitational effect.

Do not mix these two phenomena together. There are two very different worlds of difference.

The dark energy is a mathematical function in a physical phenomenon.

The dark matter is an apparent physical reality.
soulman
3 / 5 (4) Jan 14, 2011
Dark energy is not dark matter.

These are two very different things.

No shit. Have you even read anything I wrote?
mysticshakra
1.4 / 5 (7) Jan 14, 2011
There is no.dark anything, leave.your.religion at the.door. the big bang (originally a pejorative term) is a failure and amounts to asking for just one miracle. These ad hoc bandaids are to cover the.holes.in hour swiss.cheese. if the observations don't fit you throw.out the.theory. mud oftheoretical.physics and all of its dogmas need to be thrown in the fire.