* Astronomy

Members Login
Username 
 
Password 
    Remember Me  
Home -> Astronomy News -> Astronomy News -> Type Ia supernovae
Post Info
TOPIC: Type Ia supernovae
Blobrana


L

Posts: 131433
Date:
RE: Type Ia supernovae
Permalink  
 

Title: Novae and accreting white dwarfs as progenitors of Type Ia supernovae
Authors: Mariko Kato

I review various phenomena associated with mass-accreting white dwarfs (WDs) in relation to progenitors of type Ia supernovae (SNe Ia). The WD mass can be estimated from light curve analysis in multiwavelength bands based on the optically thick wind theory. In the single degenerate scenario of SNe Ia, two main channels are known, i.e., WD + main sequence (MS) channel and WD + red giant (RG) channel. In each channel, a typical binary undergoes three evolutional stages before explosion, i.e., the wind phase, supersoft X-ray source (SSS) phase, and recurrent nova phase in order of time because the accretion rate decreases with time as the companion mass decreases. We can specify some accreting WDs as the corresponding stage of evolution. Intermittent supersoft X-ray source like RX J0513.9-6951 and V Sge are corresponding to the wind phase objects. For the SSS phase Cal 87-type objects correspond to the WD+MS channel. For the WD + RG channel, soft X-ray observations of early type galaxies gave a statistical evidence of SSS phase binaries. Recurrent novae of U Sco-type and RS Oph-type correspond to the WD + MS channel and WD + RG channel, respectively. Majority of recurrent novae host a very massive WD (~> 1.35 Mo) and often show a plateau phase in optical light curve correspondingly to the long lasted supersoft X-ray phase: These properties are indications of increasing WD masses.

Read more  (101kb, PDF)



__________________
Blobrana


L

Posts: 131433
Date:
Permalink  
 

Our Galaxy Might Hold Thousands of Ticking "Time Bombs"

New research shows that some old stars might be held up by their rapid spins, and when they slow down, they explode as supernovae. Thousands of these "time bombs" could be scattered throughout our Galaxy.
The specific type of stellar explosion Di Stefano and her colleagues studied is called a Type Ia supernova. It occurs when an old, compact star known as a white dwarf destabilises.
A white dwarf is a stellar remnant that has ceased nuclear fusion. It typically can weigh up to 1.4 times as much as our Sun - a figure called the Chandrasekhar mass after the astronomer who first calculated it. Any heavier, and gravity overwhelms the forces supporting the white dwarf, compacting it and igniting runaway nuclear fusion that blows the star apart.
There are two possible ways for a white dwarf to exceed the Chandrasekhar mass and explode as a Type Ia supernova. It can accrete gas from a donor star, or two white dwarfs can collide. Most astronomers favour the first scenario as the more likely explanation. But we would expect to see certain signs if the theory is correct, and we don't for most Type Ia supernovae.
Read more



__________________
Blobrana


L

Posts: 131433
Date:
Zombie Stars
Permalink  
 

'Zombie' Stars Key to Measuring Dark Energy

"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.
Andy Howell, adjunct professor of physics at UCSB and staff scientist at Las Cumbres Observatory Global Telescope (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.
Read more



__________________
Blobrana


L

Posts: 131433
Date:
RE: Type Ia supernovae
Permalink  
 

Waiting for the next supernova

One of these days we might see a supernova. It might seem more correct to say "one of these nights," but a star exploding in our galaxy as a supernova would easily be so bright it would be seen in a blue daytime sky, outshining any star or planet in the night sky.
We are long overdue. Supernovae are very rare, although astronomers say they should occur on the average every few hundred years. The last one seen in the Milky Way Galaxy was in 1680.
Read more 



__________________
Blobrana


L

Posts: 131433
Date:
Permalink  
 

The Best Way to Measure Dark Energy Just Got Better

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 Type Ia supernovae 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 colour.
Read more

__________________
Blobrana


L

Posts: 131433
Date:
Permalink  
 

University of Toronto physicists create supernova in a jar

A team of physicists from the University of Toronto and Rutgers University have mimicked the explosion of a supernova in miniature.
A supernova is an exploding star. In a certain type of supernova, the detonation starts with a flame ball buried deep inside a white dwarf. The flame ball is much lighter than its surroundings, so it rises rapidly making a plume topped with an accelerating smoke ring.
Read more

__________________
Blobrana


L

Posts: 131433
Date:
Permalink  
 

Origin of Key Cosmic Explosions Still a Mystery

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 that astronomers use them to measure the universe's expansion. The resulting discovery of dark energy and the accelerating universe rewrote our understanding of the cosmos. Yet the origin of these supernovae, which have proved so useful, remains unknown.
Read more

__________________
Blobrana


L

Posts: 131433
Date:
Permalink  
 

Supernovae don't make the biggest atoms

They are the brightest of stars, but supernovae may not forge the heaviest elements. That's the suggestion arising from analysis of a new model of the particle winds that rush from the cores of supernovae.
The only two elements formed in abundance shortly after the big bang were hydrogen and helium. All the heavier ones must have been forged by fusing these smaller nuclei together. The high pressures and temperatures inside ordinary stars can account for elements up to a certain size, but making elements bigger than iron, which has a nucleus containing 26 protons, requires some other mechanism.
Read more

__________________
Blobrana


L

Posts: 131433
Date:
Permalink  
 

Realistic computational models of supernovae might soon solve a long-standing mystery.

In a paper published in the 10 May issue of the Astrophysical Journal1, Janka and his colleagues from the Max Planck Institute for Astrophysics in Garching, Germany, used their model to address a long-standing puzzle: how do heavier elements, synthesised in the core of the massive, dying star, get out of the explosion before the lighter stuff that sits in the star's outer shells?
Read more

__________________
Blobrana


L

Posts: 131433
Date:
Smoothed Particle Hydrodynamics
Permalink  
 

The cosmic burp of dying stars

Stellar explosions provide the key to understanding the fate of the Universe

The mysteries of the Universe and how we came to be are set to be unlocked by a technique for modelling fluids, similar to one which is becoming increasingly popular within the film industry to improve the realism of special effects.
Theoretical Astrophysics student, Fergus Wilson from the University of Leicester, is currently utilising a fluid modelling technique within his doctoral research to enable investigation of the mass transfer from one star to another in a binary star system.
Smoothed Particle Hydrodynamics (SPH) is a computational method for modelling fluid as a set of moving particles and can be used to solve the equations of motion between two or more particles. A similar technique has been used to enhance the special effects in blockbuster Hollywood movies such as Tomb Raider and The Matrix Reloaded.
Mr Wilson uses the SPH method to model the explosive eruptions of dying stars to provide vital clues to the current accelerated expansion of the Universe. Preliminary results from the study will be showcased at the University of Leicester's Festival of Postgraduate Research on 24 June. Mr Wilson's research focuses on Type Ia supernovae, which occur when White Dwarf stars explode upon reaching a critical mass. His simulations model the formation of discs around accreting stars within a binary star system.
Read more

__________________
«First  <  1 2 3 4 5 … 8  >  Last»  | Page of 8  sorted by
Quick Reply

Please log in to post quick replies.
Home -> Astronomy News -> Astronomy News -> Type Ia supernovae


Create your own FREE Forum
Report Abuse 		Powered by ActiveBoard