Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

'Zombie' stars key to measuring dark energy

01.07.2011
"Zombie" stars that explode like bombs as they die, only to revive by sucking matter out of other stars. According to an astrophysicist at UC Santa Barbara, this isn't the plot for the latest 3D blockbuster movie. Instead, it's something that happens every day in the universe –– something that can be used to measure dark energy.

This special category of stars, known as Type Ia supernovae, help to probe the mystery of dark energy, which scientists believe is related to the expansion of the universe.


This is a Chandra X-ray image of Tycho's supernova remnant. This Type Ia sueprnova was observed by Tycho Brahe in 1572, and today is just an expanding ball of gas. Astronomers used to have to wait years for a close, bright supernova to learn about them. Today big surveys are discovering supernovae by the thousands. Credit: NASA/Chandra X-ray Observatory

Andy Howell, adjunct professor of physics at UCSB and staff scientist at Las Cumbres Observatory Global Telescope Network (LCOGT), wrote a review article about this topic, published recently in Nature Communications. LCOGT, a privately funded global network of telescopes, works closely with UCSB.

Supernovae are stars that have been observed since 1054 A.D., when an exploding star formed the crab nebula, a supernova remnant.

More recently, the discovery of dark energy is one of the most profound findings of the last half-century, according to Howell. Invisible dark energy makes up about three-fourths of the universe. "We only discovered this about 20 years ago by using Type Ia supernovae, thermonuclear supernovae, as standard or 'calibrated' candles," said Howell. "These stars are tools for measuring dark energy. They're all about the same brightness, so we can use them to figure out distances in the universe."

These supernovae are so bright that they shine with the approximate power of a billion suns, noted Howell.

He calls Type Ia supernovae "zombie" stars because they're dead, with a core of ash, but they come back to life by sucking matter from a companion star. Over the past 50 years, astrophysicists have discovered that Type Ia supernovae are part of binary systems –– two stars orbiting each other. The one that explodes is a white dwarf star. "That's what our sun will be at the end of its life," he said. "It will have the mass of the sun crammed into the size of the Earth."

The white dwarf stars that tend to explode as Type Ia supernovae have approximately the same mass. This was considered a fundamental limit of physics, according to Howell. However, in an article in Nature about five years ago, Howell reported his discovery of stars that go beyond this limit. These previously unknown Type Ia supernovae have more than typical mass before they explode –– a fact that confounds scientists.

Howell presented a hypothesis to understand this new class of objects. "One idea is that two white dwarfs could have merged together; the binary system could be two white dwarf stars," he said. "Then, over time, they spiral into each other and merge. When they merge, they blow up. This may be one way to explain what is going on."

Astrophysicists are using Type Ia supernovae to build a map of the history of the universe's expansion. "What we've found is that the universe hasn't been expanding at the same rate," said Howell. "And it hasn't been slowing down as everyone thought it would be, due to gravity. Instead, it has been speeding up. There's a force that counteracts gravity and we don't know what it is. We call it dark energy."

The new findings relate to Einstein's concept of the cosmological constant. This is a term he added into his equations to make them valid. However, Einstein did it because he thought the universe was static; he didn't know the universe was expanding. When it was revealed that the universe is expanding, Einstein believed this concept was his biggest blunder. "It turns out that this cosmological constant was actually one of his greatest successes," said Howell. "This is because it's what we need now to explain the data."

He said that dark energy is probably a property of space. "Space itself has some energy associated with it," said Howell. "That's what the results seem to indicate, that dark energy is distributed everywhere in space. It looks like it's a property of the vacuum, but we're not completely sure. We're trying to figure out how sure are we of that –– and if we can improve Type Ia supernovae as standard candles we can make our measurements better."

Throughout history, people have noticed a few supernovae so bright they could be seen with the naked eye. With telescopes, astronomers have discovered supernovae farther away. "Now we have huge digital cameras on our telescopes, and really big telescopes," said Howell, "We've been able to survey large parts of the sky, regularly. We find supernovae daily." Astronomers have discovered thousands of supernovae in recent years.

During his career, Howell has used these powerful telescopes to study supernovae. Currently, besides teaching at UCSB, he is involved in LCOGT's detailed study of supernovae that is aimed at helping to understand dark energy. With this extensive network of observatories, it will be possible to study the night sky continuously.

"The next decade holds real promise of making serious progress in the understanding of nearly every aspect of supernovae Ia, from their explosion physics, to their progenitors, to their use as standard candles," writes Howell in Nature Communications. "And with this knowledge may come the key to unlocking the darkest secrets of dark energy."

Gail Gallessich | EurekAlert!
Further information:
http://www.ucsb.edu

More articles from Physics and Astronomy:

nachricht Shape matters when light meets atom
05.12.2016 | Centre for Quantum Technologies at the National University of Singapore

nachricht Climate cycles may explain how running water carved Mars' surface features
02.12.2016 | Penn State

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Shape matters when light meets atom

Mapping the interaction of a single atom with a single photon may inform design of quantum devices

Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

Im Focus: Molecules change shape when wet

Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water

In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

High-precision magnetic field sensing

05.12.2016 | Power and Electrical Engineering

Construction of practical quantum computers radically simplified

05.12.2016 | Information Technology

NASA's AIM observes early noctilucent ice clouds over Antarctica

05.12.2016 | Earth Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>