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From symmetry

Better 'cosmic candles' to illuminate dark energy

Using a newly identified set of supernovae, researchers have found a way to measure distances in space twice as precisely as before. Photo courtesy of NASA/CXC/U.Texas

Researchers have more than doubled the precision of a method they use to measure long distances in space—the same one that led to the discovery of dark energy.

In a paper published in Science, researchers from the University of California, Berkeley, SLAC National Accelerator Laboratory, the Harvard-Smithsonian Center for Astrophysics and Lawrence Berkeley National Laboratory explain that the improvement allows them to measure astronomical distances with an uncertainty of less than 4 percent.

The key is a special type of Type Ia supernovae.

Type Ia supernovae are thermonuclear explosions of white dwarfs — the very dense remnants of stars that have burned all of their hydrogen fuel. A Type Ia supernova is believed to be triggered by the merger or interaction of the white dwarf with an orbiting companion star.

"For a couple of weeks, a Type Ia supernova becomes increasingly bright before it begins to fade," says Patrick Kelly, the new study's lead author from the University of California, Berkeley. "It turns out that the rate at which it fades tells us about the absolute brightness of the explosion."

If the absolute brightness of a light source is known, its observed brightness can be used to calculate its distance from the observer. This is similar to a candle, whose light appears fainter the farther away it is. That's why Type Ia supernovae are also referred to as astronomical "standard candles."

The 2011 Nobel Prize in physics went to a trio of scientists who used these standard candles to determine that our universe is expanding at an accelerating rate. Scientists think this is likely caused by an unknown form of energy they call dark energy.

Measurements using these cosmic candles are far from perfect, though. For reasons that are not yet understood, the distances inferred from supernova explosions seem to be systematically linked to the environments the supernovae are located in. For instance, the mass of the host galaxy appears to have an effect of 5 percent.

In the new study, Kelly and his colleagues describe a set of Type Ia supernovae that allow distance measurements that are much less dependent on such factors. Using data from NASA's GALEX satellite, the Sloan Digital Sky Survey and the Kitt Peak National Observatory, they determined that supernovae located in host galaxies that are rich in young stars yield much more precise distances.

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Manuel Gnida

In Brief

Science Next Door April newsletter now online

The April edition of "Science Next Door," Fermilab's monthly community newsletter, is now available online. View it or subscribe to get the latest about the laboratory's public events, including tours, lectures, arts events and volunteer opportunities.

In the News

These are the most beautiful science labs in the world

From Gizmodo, March 25, 2015

Editor's note: Fermilab makes the list.

Who said that laboratories, research centers and other science institutions have to be boring places? Believe me, architects are doing their bests when it comes to designing the headquarters of such facilities. The following 22 images prove that I am right.

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Director's Corner

Welcome, DUNE

Fermilab Director
Nigel Lockyer

Significant progress has been made on the new international neutrino collaboration. Last week, scientists from 148 institutions around the world chose DUNE (Deep Underground Neutrino Experiment) as the name of the experiment that will use the Long-Baseline Neutrino Facility (LBNF) neutrino beam. And, the group elected André Rubbia, ETH Zurich, and Mark Thomson, University of Cambridge, as the collaboration's spokespeople. Congratulations to both André and Mark.

The DUNE collaboration, which includes participation from Asia, Europe, and North and South America, represents a significant milestone in the implementation of P5 report recommendations. More than 700 scientists from 23 countries currently belong to the collaboration, and the group seeks further international partners to participate in this world-class experiment.

From April 16 to 18, the first DUNE collaboration meeting will be held at Fermilab, when funding agencies and research institutions come together for the first time. In the meantime, much work is already in progress.

The collaboration is assembling work groups that will tackle different tasks, with the goal of defining the final design for the first 10-kiloton underground detector in South Dakota. CERN will build two large prototype detectors to advance the engineering aspects of liquid-argon technology. Here at Fermilab, DUNE scientists will soon be able to take data with a smaller, 35-ton liquid-argon prototype detector. In July, funding agencies will review the updated project plans for LBNF/DUNE.

At the same time, we are working with the Department of Energy to advance cavern excavation plans for the detector in South Dakota. This spring, DOE will release its draft environmental assessment of LBNF and hold public meetings at Fermilab and in South Dakota. In addition, discussions are happening with other funding agencies about how they can benefit from the neutrino program at Fermilab and contribute to the construction of the DUNE detectors.

Thank you to the all the individuals and organizations who have helped us get to this point. There is still much work to be done, but we have made excellent progress on the world's most ambitious neutrino experiment.

Photo of the Day

Canis latrans

A coyote kindly pauses by Bullrush Pond for the camera. Photo: Mark Kaletka, CCD
In the News

Dark matter is apparently 'darker' than we thought

From The Washington Post, March 27, 2015

A new study published Thursday in Science suggests that dark matter might be able to zip through the universe without slowing or dragging because particles of it don't even interact with each other.

Based on what we can observe about the universe, galaxies should be tearing themselves apart. That's where so-called dark matter comes in: It's a term for the as-of-yet unobserved matter that must be bulking up cosmos, giving galaxies the gravity they need to spin at the rates they do without falling to pieces. But even though we haven't caught dark matter (so named because it doesn't interact with light the way normal matter does — not absorbing or reflecting it — though it does bend light with a weird lensing effect) in a straightforward observation, scientists can learn about it based on the effects it has on more typical, observable forms of matter.

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