Extreme Universe: New Class of Supernovae: SN 2007bi December 2, 2009
Posted by jcconwell in Astronomy, Extreme Universe, supernova.Tags: pair instability supernova, SN 2007bi, supernova
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First confirmed pair instability supernova
Berkeley, CA – An extraordinarily bright, extraordinarily long-lasting supernova named SN 2007bi, snagged in a search by a robotic telescope, turns out to be the first example of the kind of stars that first populated the Universe. The superbright supernova occurred in a nearby dwarf galaxy, a kind of galaxy that’s common but has been little studied until now, and the unusual supernova could be the first of many such events soon to be discovered.
from SN factory team
The analysis indicated that the supernova’s precursor star could only have been a giant weighing at least 200 times the mass of our Sun and initially containing few elements besides hydrogen and helium – a star like the very first stars in the early Universe.
“Because the core alone was some 100 solar masses, the long-hypothesized phenomenon called pair instability must have occurred,” says astrophysicist Peter Nugent. A member of the SNfactory, Nugent is the co-leader of the Computational Cosmology Center (C3), a collaboration between Berkeley Lab’s Physics Division and Computational Research Division (CRD), where Nugent is a staff scientist. “In the extreme heat of the star’s interior, energetic gamma rays created pairs of electrons and positrons, which bled off the pressure that sustained the core against collapse.”
“SN 2007bi was the explosion of an exceedingly massive star,” says Alex Filippenko, a professor in the Astronomy Department at UC Berkeley whose team helped obtain, analyze, and interpret the data. “But instead of turning into a black hole like many other heavyweight stars, its core went through a nuclear runaway that blew it to shreds. This type of behavior was predicted several decades ago by theorists, but never convincingly observed until now.”
SN 2007bi is the first confirmed observation of a pair-instability supernova. The researchers describe their results in the 3 December 2009 issue of Nature.
3D Supernova Simulation! September 27, 2009
Posted by jcconwell in Astronomy, supernova.Tags: Astronomy, EIU, supernova
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What’s a simulation? It’s a computer model, usually of a complicated system, that can’t be solved using pencil and paper. You tell the computer what the physical laws are, usually in the form of differential equations, and let the computer try to solve them. They are also used in design and prototypes of airplanes, buildings and complicated systems. Simulations are also used in cases where doing lab measurement might not be possible, think nuclear detonations, and their big brother, type Ia Supernova.
Type Ia supernova are thought to be caused by a white dwarf stealing mass from a companion star. If it exceeds Chandrasakar’s limit of 1.4 Solar Masses, it will start to compress and detonate. They have found a new importance in astronomy as standard candles to measure distance. It is thought that since they detonate at the same mass they will have the same brightness. They’ve been used to measure Hubble’s constant in the distance past and are the foundation for the existence of the accelerated universe and the existence of dark energy. BUT it not KNOWN if all behave the same. Maybe small variations of chemical abundance or rotation change the energy given off by the supernova. That’s were the simulations are important.
3D simulations take a big computer. The computational requirements can go up like the 4th power of the grid size (how finely divided do chop up a linear dimension in the star). So up until this point most simulations have been 2D or 1D. When simulations went from 1D to 2D new physics appeared. Asymmetric explosions and other effects not seen in simpler simulations. It is expected that going to 3D we’ll be able to see new effects. If you are interested in Computational Physics, Eastern has a an option in its physics major. Contact either me ( Dr. Conwell) or Dr. Zou for more information.
“WHEN STARS ATTACK” September 16, 2009
Posted by jcconwell in IYA 2009, supernova.Tags: EIU, International Year of Astronomy, IYA 2009, supernova
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THURSDAY, Sept 17 in the Phipps Lecture Hall at 7:00 P.M
Crab Supernova.
“When Stars Attack! In Search of Near-Earth Supernova Explosions,” a presentation by a University of Illinois faculty member, will continue Eastern Illinois University’s yearlong celebration of the International Year of Astronomy.
Brian Fields, associate professor of astronomy and physics at the U of I, is to speak at 7 p.m. Thursday, Sept. 17, in the EIU Physical Science Building’s Phipps Lecture Hall. The event is free and open to the public.
In a supernova, a massive star is destroyed in an extremely powerful explosion, leaving behind a neutron star or a black hole. A shock wave carries the star’s ashes — newly created heavy elements — through space, stirring interstellar gas and, at times, spurring the formation of new stars. Fields will discuss how recent evidence suggests that radioactive iron atoms found deep in the Earth’s ocean are debris from a star exploding near Earth about 3 million years ago.
In addition to giving scientists a clue of what powers supernovae, the findings suggest that the explosion’s proximity to Earth might have had major results on the planet, Fields wrote. “An explosion so close to Earth was probably a ‘near-miss,’ which emitted intense and possibly harmful radiation,” Fields wrote on his Web site. “The resulting environmental damage may even have led to extinction of species which were the most vulnerable to this radiation.”
Fields’ presentation will be the first event of the fall semester in EIU’s yearlong celebration of the International Year of Astronomy. IYA is a worldwide commemoration of many historic astronomical achievements, including the 400th anniversary of Galileo’s first look through a telescope and the 40th anniversary of man’s first steps on the moon.
EIU’s IYA events are sponsored by the EIU College of Sciences and the EIU Department of Physics.
Formation of the Elements July 20, 2009
Posted by jmegenhardt in Astronomy, stars, supernova.Tags: Astronomy, stars, supernova
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James Megenhard has his blog at: http://eastrichlandchemistry.wordpress.com/
Stardust, the Building Block of Everything?
At the birth of our universe the only elements formed in any substantial amount was helium and hydrogen. There were some heavier elements like lithium and beryllium, but these were so minor that they are not even considered. So where did the carbon that all life is made of, the oxygen that all animals need to breathe, or the iron that makes up some of our strongest buildings come from? Hydrogen and helium were formed during the Big Bang, while all of the other elements come from small bangs; the death of stars.
At this time, there are 118 known elements. The simplest element is hydrogen which has only 1 proton and 1 electron.
In order to make hydrogen into another element, protons need to be added; which in turn requires the addition of electrons and neutrons. For example, add a proton, an electron, and two neutrons, and hydrogen has become helium.
Adding a proton, electron, and two neutrons creates lithium. Adding yet another proton, electron, and neutron gives beryllium. By simply adding more protons, electrons, and neutrons, heavier and heavier elements can be formed. It seems reasonable for helium to form, after all, what else is to be done with the neutrons that hydrogen did not use from the Big Bang? The question is, why would more protons, neutron, and electrons come together to make any elements past helium?
The Big Bang roughly states that everything that would one day form the physical universe began as a super hot, super condensed mass. This mass reached a critical point which resulted in the mass exploding. As the material from this mass cooled hydrogen and helium were formed. The hydrogen and helium started pooling together into various gas clouds. These gas clouds were pulled in towards their center, resulting in an increase of mass at center, which created more gravity, which resulted in more hydrogen and helium being pulled in.
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In the Center of Star More mass in center → More gravity in center ↑ ↓ More gravity in center ← More mass in center
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The increasing density of that material resulted in more gas atoms colliding. Each time there was a collision, some of that energy was converted to heat. As more gas was pulled in, there were more collisions resulting in heat increasing, until the temperature reaches around 10 million degrees Kelvin at which point nuclear fusion of hydrogen begins; a star is born. To sum it up…
More gravity in center → More density in center → More collisions in center → More heat in center until nuclear fusion is reached.
Nuclear fusion is the process by which two atoms are combined to form a new atom. When two hydrogen atoms fuse they produces helium and energy. Click here to see how hydrogen becomes helium. It is the energy produced by nuclear fusion that runs a star. Since hydrogen is the simplest element with only a proton and electron, the star begins the process of fusion with it, but as hydrogen is used up and temperature increases, the helium produced can undergo nuclear fusion of its own to produce carbon, oxygen, or neon. Carbon can further fuse to form metals like sodium or magnesium, until nuclear fusion produces iron.
Layers of Fusion in a Star
But why did these elements not form during the Big Bang? The answer is repulsion. Hydrogen is a proton and electron, so its formation is easy since opposites attract. Helium, on the other hand, was a little tougherto form since it needs two positive protons in its center; but like charges repel. The only reason the two protons in helium did not repel away from each other was the pressure within the expanding material from the Big Bang was higher than the repulsive force. But this force was not great enough for more than two protons to come together. The only place in our universe where the force is so great that multiple protons cannot repel from each other is in the heart of a star.
The first 26 elements on the periodic table are formed by stars as they produce energy. The remaining elements are formed from a star dying. When a star dies, the gravitational pull upon that star causes the iron center to collapse. As the center collapses, it reaches a point where the energy build-up causes the collapse to stop and reverse just like a rubber ball will collapse so far before it rebounds. In other words, the center implodes and then explodes out. As the center is blown back outwards, it collides with the outer material surrounding the star; which was also being pulled in to the center. Just like in the birth of a star, this increase of collisions results in even more heat and pressure, which means even more nuclear fusion. The net result being that as the star is being blown apart, further nuclear fusion is occurring resulting in elements even heavier then iron. Not only does the stars death form these heavy elements, but it also causes those elements to be blasted out into space, where they can collect and form other astronomical bodies like planets and asteroids.
External resources:
3D View of a Supernova Remnant January 6, 2009
Posted by jcconwell in Astronomy, supernova.Tags: supernova
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Cassiopeia A is remnant of an supernova about 11000 light year (3400 parsecs) away. The original supernova was thought to have been visible around 300 years ago, but except for a possible identification by Flamsteed in 1620, no record of its sighting is recorded. While faint in the visible spectrum its the brightest radio object in the sky, outside the solar system.
Observations using the Hubble telescope have shown that, despite the original belief that the remnants were expanding in a uniform manner, there are 2 opposing jets that are traveling at 14000 kilometers per second. This speed is estimated to be 8800 km per second faster than the rest of the debris. Viewing the expanding star using colors to differentiate chemical composition, it shows that similar materials often remain gathered together.
Cass A in Radio, IR, Visible & X-ray (Chandra Space Telescope)
Thanks to Tracey Delaney of the Massachusetts Institute of Technology and her collaborators, by using Doppler data from the spectrum, she was able to do a 3D map of the elements in the explosion. “Now we can see for ourselves with this ‘hologram’ of supernova debris.” And you can see it in the movie below:
Click to see
