Super Novas Super Novas
Web site compiled by Lauren Mosler
What is a Supper Nova?
Wayne P. Johnson (also known as Mr. Galaxy) explains on his web site at http://www.chapman.edu/oca/benet/intro_sn.htm Supernovae are massive exploding giant stars. When the explosion occurs, the resulting illumination can be as bright as an entire galaxy! Sherri Calvo at NASA/GSFC Supernova Home Page describes a supernova as follows "One of the most energetic explosive events known is a supernova. These occur at the end of a star's lifetime, when its nuclear fuel is exhausted and it is no longer supported by the release of nuclear energy. If the star is particularly massive, then its core will collapse and in so doing will release a huge amount of energy. This will cause a blast wave that ejects the star's envelope into interstellar space. The result of the collapse may be, in some cases, a rapidly rotating neutron star that can be observed many years later as a radio pulsar."
What causes these stars to explode?
Wayne P. Johnson also reviles that "As a result of gravitational forces acting against the nuclear structure of the core of a fuel depleted star, tremendous shock waves are generated which cause the outside layers of the star to be blown away from the core. This can happen in one of two ways depending on the type of supernova.
The types of supernovae are characterized by their spectral lines which indicate their chemical composition. Dr. Mike Richmond at the Astrophysics Department of Princeton University categorized the various types of supernovae and their characteristics in his informative
SN Taxonomy chart.Type I Supernovae.
These type of supernovae involve two stars, one of them being a white dwarf whose gravitational attraction is so intense that it is capable of siphoning off material from its companion. Unfortunately for the star (but fortunately for us at a long distance!), the white dwarf exceeds its Chandrasekhar limit of stability causing it to go into thermonuclear instability and produces one of the largest explosions known in the Universe, the Type I SN. There are currently three types of Type I SNe accepted by the astronomical community in general. The subclass types (Ia, Ib, and Ic) are basically determined by the state of the white dwarf's companion star, though to qualify as a Type I SN the companion should have expelled its hydrogen layer. Mike Richmond's SN Taxonomy table gives a good schematic idea about the (more or less) current thinking on the topic.Type II (Core Collapse) Supernovae.
Gravitational forces condensing hydrogen gas raises the temperature at the center of the star to the point where nuclear fusion is initiated. According to the Onion Skin Model (illustrated above), the following sequence occurs. Hydrogen is fused into helium and energy is given off in the process. As more helium accumulates at the center, the temperature rises due to compression until another nuclear fusion is initiated. This time helium is converted to carbon and oxygen and additional energy is given off during the nuclear fusion. A similar process continues with carbon and oxygen fusing to neon, magnesium, and oxygen. These elements then undergo another fusion process as the temperature and pressure increase to produce silicon and sulfur. The latter two elements then fuse into iron. During each nuclear fusion, energy is given off. This takes two orders of magnitude less time to happen than on the previous fusion. However, nuclear fusion stops at iron because energy is no longer produced by fusion. The iron core collapses very quickly (within hours or less). Since the iron core can collapse only so far and can no longer undergo fusion, it becomes extremely hot and now begins to expand rapidly. This occurs while the star's outer shells are rushing in to fill the void left by the collapsed iron core. The expanding iron and the collapsing outer gases collide with each other producing tremendous shock waves which blow the outer layers away from the core, thus causing the supernova's gigantic explosion."
What happens after the explosion?
Wayne P. Johnson also says that "what happens after the explosion depends on the type and mass of the progenitor stars. Mostly they produce a gas cloud called a supernova remnant which initially expands at a rate of about 10,000 km/s. Gradually the expansion rate slows down while dissipating into the interstellar medium, seeding the neighborhood with heavy elements and providing the necessary shock waves for new stellar formation. The Crab Nebula, M1
(image) http://www.chapman.edu/oca/benet/m1.gif , is a remnant of the supernova of 1054 (which occurred within our Milky Way Galaxy)."
Did Super Nova’s Create Most Elements?
Super novae’s are responsible for the creation of all elements besides hydrogen and helium explains a professor of Astronomy at University of California Los Angles, Mirek Plavac at
http://www.smmirror.com/Volume1/issue22/starry_skies.html. He says: "Today we know that supernovae are much more than just "cosmic fireworks." We may say that we exist also thanks to many supernovae that exploded billions of years ago. And our wives and daughters and girlfriends should be especially thankful to supernovae! In the very early stages of our universe, only hydrogen and helium atoms formed. Heavier elements have been synthesized deep in the interiors of massive stars, but that production ends with iron. Elements heavier than iron, for example gold, platinum, lead, or mercury, are synthesized (as far as we know) only during the tremendous outburst of a supernova. This means that even some atoms now inside our bodies once participated in the fantastic explosions of supernovae. Naturally not in those that have been observed. In the distant past, many more massive stars were formed, shone brightly, then exploded, and scattered their atoms into space. Eventually, some of them accumulated in our part of the Galaxy, and after some billions of years, here we come!"
Who First Discovered Supper Novas?
The history of how supper novas were discoved explained Mirek Plavac
"While the Moon obliterates the fainter stars, the conspicuous W of Cassiopea can still be recognized high above the north-east. Astronomers have been familiar with it for many centuries. However, when the famous astronomer Tycho Brahe walked home on the evening of November 11, 1572, he was shocked to see a conspicuous change in its appearance: there was a brand new star there, much brighter than the rest, actually brighter than any other star in the sky! Tycho began to measure its position among the stars, hoping to detect its motion (he believed first that it might be a comet) and/or finding out how far away the strange object was. That latter task can be accomplished by two distant observers using a method developed by land surveyors, but only for nearby objects. Tadeas Hajek in Prague cooperated with Tycho, and their conclusion was: the mysterious star was definitely farther away than the Moon. Such an announcement sounds, to a contemporary astronomer, as equivalent to the "discovery" that New York is farther away from us (us in Santa Monica, California) than San Bernardino (in California). However, in the 16th century, the Aristotelian model of the universe still dominated, and, according to it, no change can ever occur in the universe beyond the orbit of the Moon. Thus Tychoís star played an important role in the destruction of the obsolete geocentric model of the universe.
The "new star" shone, for some weeks, so bright that it was visible even during the day in full sunshine, but then gradually faded and became invisible to the naked eye (there were no telescopes then) after 17 months.
As astronomy advanced, it gradually dawned on the scientists that the universe is not static, and that there is evolution in it. Towards the end of the 18th century, Immanuel Kant and Pierre S. Laplace proposed that the Sun and the planets of the solar system originally formed from a rotating flattened gaseous disk. On August 20, 1885, astronomer Hartwig at the Dorpat Observatory (now Tartu, in Estonia) entertained some friends and talked about the Kant-Laplace hypothesis. Then he pointed a telescope at the famous Andromeda nebula (M 31), which he considered to be a good example for a precursor to a planetary system. To his great surprise, there was a fairly bright new star close to the center of the nebulosity! It is indeed a rare event when nature seems to collaborate to support a scientist's story! However, the "newly formed star" eventually disappointed him. For a short time, it was visible even to the naked eye, but by 1886 February, it faded into invisibility.
At that time, most astronomers believed that the "Andromeda nebula" is rather a small object inside our Galaxy, i.e. astronomically speaking not very far away, and then the new star of 1885 could be classified as a typical "nova." (As we know today, a nova is an outburst on the surface of a white dwarf, nothing terribly energetic). However, by 1919, the astronomers at the better telescopes on the Mt. Wilson Observatory above Pasadena began to discover numerous novae in the Andromeda nebula, and these were much, much fainter than the one seen in 1885. And then came, in 1924, the discovery by Edwin Hubble that the Andromeda nebula is actually a distant huge stellar system, at a distance of at least 1 million light years (today we know that it is about 2.5 million light years).
With this discovery, it became obvious that the "new star" of 1885 must have been something much more powerful than an ordinary nova explosion. In 1933, Walter Baade and Fritz Zwicky, at Mt Wilson, made one of the most astonishingly correct and broad prediction in the history of astronomy. They wrote:
"There exist in the universe explosions much bigger than novae, so let's call them super-novae [the hyphen disappeared in 1938]. They represent an essential annihilation of a massive star, the remnant of which becomes a neutron star." This bold idea explained the bright temporary object seen in the Andromeda galaxy in 1885, as well as Tycho Brahe's "new star" seen in Cassiopeia in 1572. Not long after Tycho's discovery of the 1572 supernova, another one erupted in 1604, before the eyes of another famous astronomer, Johannes Kepler. And historical search showed that, in 1054, the Chinese observed a "guest star" in the constellation Taurus (the Bull). And that is all -- four conspicuous supernovae in our region of the Galaxy over a period of 1,000 years! It seems that another is badly overdue by now -- so better look at the sky as often as you can! "
This is an image of the newly discovered super nova.
Links to Interesting Web Sites
News on supper novas and other space phenomenon: http://www.xs4all.nl/~carlkop/news.html
Uranium was formed in super novae. A link about uranium: http://www.uic.com.au/uran.htm
Sites of interest on astronomy: http://www.ngcic.com/websites.htm
Links to the up and coming comic book character named Supper nova: http://www.patric.net/morpheus/cast/legend/supernova.html
List of current super novas:
http://www.ggw.org/freenet/a/asras/supernova.htmlList of Historical super novas:
http://merlino.pd.astro.it/~supern/snean.txtA space calendar: http://www.jpl.nasa.gov/calendar/history.html
References
Mr. Galaxy’s Supernova.
http://www.chapman.edu/oca/benet/intro_sn.htmStarry Skies Above Santa Monica November 17-23.
http://www.smmirror.com/Volume1/issue22/starry_skies.htmlPictures of super nova at the top of the page from Mr. Galaxy’s Supernova.
http://www.chapman.edu/oca/benet/intro_sn.htmPicture of super nova at the bottom of the page from A Guide to the Deepsky Astronomy Resources at SEDS. http://www.seds.org/pub/images/supernova/nova-st7.gif