Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Failed explosions explain most peculiar supernovae

20.11.2012
Supercomputer simulations have revealed that a type of oddly dim, exploding star is probably a class of duds—one that could nonetheless throw new light on the mysterious nature of dark energy.

Most of the thousands of exploding stars classified as type Ia supernovae look similar, which is why astrophysicists use them as accurate cosmic distance indicators. They have shown that the expansion of the universe is accelerating under the influence of an unknown force now called dark energy; yet approximately 20 type Ia supernovae look peculiar.

"They're all a little bit odd," said George Jordan, a research scientist at the University of Chicago's Flash Center for Computational Science. Comparing odd type Ia supernovae to normal ones may permit astrophysicists to more precisely define the nature of dark energy, he noted.

Jordan and three colleagues, including his chief collaborator on the project, Hagai Perets, assistant professor of physics at Technion – Israel Institute of Technology, have found that the peculiar type Ia supernovae are probably white dwarf stars that failed to detonate. "They ignite an ordinary flame and they burn, but that isn't followed by a triggering of a detonation wave that goes through the star," Jordan said. These findings were based on simulations that consumed approximately two million central processing unit hours on Intrepid, the Blue Gene/P supercomputer at Argonne National Laboratory. Full details of the simulations will appear in the Astrophysical Journal Letters.

The triggering of a detonation wave is exactly what happens in normal type Ia supernovae, which incinerate white dwarfs, stars that have shrunk to Earth size after having burned most or all of their nuclear fuel. Most or all white dwarfs occur in binary systems, those that consist of two stars orbiting one another.

Faint, hard to detect

Peculiar type Ia supernovae are anywhere from 10 to 100 times fainter than normal ones, which are brighter and therefore more easily detected. Astrophysicists have estimated that they may account for approximately 15 percent of all type Ia supernovae.

The first in this class of exceptionally dim supernovae was discovered in 2002, noted Robert Fisher, assistant professor of physics at the University of Massachusetts Dartmouth, a co-author of the paper. Called SN 2002cx, it is considered the most peculiar type Ia supernova ever observed.

The dimmest of the lot, however, was discovered in 2008. "If the brightness of a standard supernova could be thought of as a single 60-watt light bulb, the brightness of this 2008 supernova would be equivalent to a small fraction of a single candle or a few dozen fireflies," Fisher noted.

Flash Center scientists have been successfully simulating type Ia supernova explosions following the gravitationally confined detonation scenario for years. In this scenario, the white dwarf begins to burn near its center. This ignition point burns outward, floating toward the surface like a bubble. After it breaks the surface, a cascade of hot ash flows around the star and collides with itself on the opposite end, triggering a detonation.

"We took the normal GCD scenario and asked what would happen if we pushed this to the limits and see what happens when it breaks," Jordan said. In the failed detonation scenario, the white dwarf experiences more ignition points that are closer to the core, which fuels more burning than in the detonation scenario.

"The extra burning causes the star to expand more, preventing it from achieving temperatures and pressures high enough to trigger detonation," noted co-author Daniel van Rossum of UChicago's Flash Center.

No incinerated star

Instead of detonating, the white dwarf remains intact, though some of the star's mass burns up and gets ejected from its surface. This failed detonation scenario looks quite similar to the peculiar type Ia explosions. The simulations resulted in phenomena that astronomers now can look for or have already found in their telescopic observations.

These phenomena include white dwarfs that display unusual compositions, asymmetric surface characteristics and a kick that sends the stars flying off at speeds of hundreds of miles per second. "This was a completely new discovery," Perets said. "No one had ever suggested that white dwarfs could be kicked at such velocities."

Normal type Ia supernovae display a relatively uniform appearance, but the asymmetric characteristics of their peculiar cousins means that the latter will often look much different from one another, depending on their viewing angle from Earth.

The asymmetric explosion also produces the kick, which is possibly powerful enough to release the white dwarf from the gravitational hold of any binary companion it may have had. This can produce a peculiar type of hyper-velocity white dwarf, the fastest of which might even escape the galaxy.

Smaller kicks might leave the binary system intact, but also push the white dwarf into a tight and highly elliptical orbit around its companion. Most white dwarfs orbiting close to their companions display a more circular orbit.

Typical white dwarfs have compositions of carbon and oxygen, yet some of the simulated ones that failed to detonate displayed heavy elements such as calcium, titanium and iron. When the detonation fails to happen, much of the ejected mass falls back onto the surface of the white dwarf, where the heavy elements become synthesized.

"I had never heard of such strange white dwarfs," Perets said. But when he conducted a literature search, he found reports of white dwarfs with properties that an irregular composition could explain. "It is quite rare that a new model brings about so many novel predictions, and potentially solves several distinct, seemingly unrelated puzzles."

Citation: "Failed-detonation supernovae: sub-luminous low-velocity IA supernovae and their kicked remnant white dwarfs with iron-rich cores," by George C. Jordan IV, Hagai B. Perets, Robert T. Fisher, and Daniel R. van Rossum," Astrophysical Journal Letters.

Funding: U.S. Department of Energy, National Science Foundation, Harvard-Smithsonian Center for Astrophysics and the Israel Science Foundation.

Steve Koppes | EurekAlert!
Further information:
http://www.uchicago.edu

More articles from Physics and Astronomy:

nachricht Hope to discover sure signs of life on Mars? New research says look for the element vanadium
22.09.2017 | University of Kansas

nachricht Calculating quietness
22.09.2017 | Forschungszentrum MATHEON ECMath

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: The pyrenoid is a carbon-fixing liquid droplet

Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.

A warming planet

Im Focus: Highly precise wiring in the Cerebral Cortex

Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.

The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...

Im Focus: Tiny lasers from a gallery of whispers

New technique promises tunable laser devices

Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...

Im Focus: Ultrafast snapshots of relaxing electrons in solids

Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!

When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...

Im Focus: Quantum Sensors Decipher Magnetic Ordering in a New Semiconducting Material

For the first time, physicists have successfully imaged spiral magnetic ordering in a multiferroic material. These materials are considered highly promising candidates for future data storage media. The researchers were able to prove their findings using unique quantum sensors that were developed at Basel University and that can analyze electromagnetic fields on the nanometer scale. The results – obtained by scientists from the University of Basel’s Department of Physics, the Swiss Nanoscience Institute, the University of Montpellier and several laboratories from University Paris-Saclay – were recently published in the journal Nature.

Multiferroics are materials that simultaneously react to electric and magnetic fields. These two properties are rarely found together, and their combined...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

“Lasers in Composites Symposium” in Aachen – from Science to Application

19.09.2017 | Event News

I-ESA 2018 – Call for Papers

12.09.2017 | Event News

EMBO at Basel Life, a new conference on current and emerging life science research

06.09.2017 | Event News

 
Latest News

Rainbow colors reveal cell history: Uncovering β-cell heterogeneity

22.09.2017 | Life Sciences

Penn first in world to treat patient with new radiation technology

22.09.2017 | Medical Engineering

Calculating quietness

22.09.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>