Galaxy NGC 4036 is on my list of galaxies to observe in search of a supernova. When it came up on my schedule on August 6, I immediatel knew a star had exploded into a supernova.
In the image below, you can see how the galaxy looked in February, 2007, the last time I'd taken an image of the object (although not the last time I'd observed it).
Compare this to the image below, which I took on August 6th. The supernova is VERY clear.
Unfortunately, I hadn't been paying attention to the Astronomy Alerts from CalSky. It seems Koichi Itagaki beat me to the punch!
Well, I can't complain too much -- take a look at Itagaki's observatory -
Koichi Itagaki (on the far right in the photo) is an amatuer astronomer who has discovered quite a number of supernovae. Previously this year he has discovered 2007af and 2007cd.
Below you can see Itagaki's discovery photo -- as you can see the supernova (designated as 2007gi) was much less prominent than when I saw it on August 6th. Itagaki had a sharp eye to see it so early. By the time I saw it, the supernova was very obvious.
http://www.supernovae.net/sn2007/sn2007gi.html lists me as one of the earliest astronomers to image Supernova 2007gi. I'm the 11th observer. I suppose that's like Great Britain saying they came in second in the American War for Independance. Oh well, the work goes on.
NGC 4036 is a galaxy in the constellation Ursa Major. To view it, go to RA 12h 01m 23.42s and DEC +61 degrees 53m 33.8s. It was discovered in 1790 by Friedrich Wilhelm Herschel .
200y gi is classified as a Type Ia supernova.
Type Ia supernovae result from the violent explosion of a white dwarf star. A white dwarf is a remnant of a star that has completed its normal life cycle and has ceased nuclear fusion.
If a white star has ceased nuclear fusion, where does the supernova explosion come from?
Simple. In a type Ia supernova, the white dwarf is in a binary star system with a main sequence star. Double stars often have a lot of distance between them, but with type Ia supernovae, the two need to be rather close. The main sequence star expands into a giant or supergiant and the white dwarf begins to capture some of the larger star's gas.
Eventually, the mass of the white dwarf is nudged up to the Chandrasekhar limit. One way to explain the definition of the Chandrasekhar limit is to say it is the maximum nonrotating mass which can be supported against gravitational collapse by electron degeneracy pressure.
But a simpler way to say it is that the star's outside pressure and inward pressure (gravity) struggling against each other. At a certain point, the balance between the outward and inward pressure is lost.
The white drawf's radius decreases.
That means the density increases.
And that means the temperature increases.
At the higher density and temperature, the fusion of carbon and oxygen into iron occurs in a runaway fsashion. The white dwarf is converted into a fusion bomb.
Result - the biggest type of explosion we see in the universe.
The energy that is released in the explosion is about what the Sun radiates away during its entire lifetime. You can see that the single star that has become a supernova outshines its home galaxy.
The last supernova in our galaxy was discovered on Oct. 9, 1604, making us about 300 years overdue for another one.
Supernovae are important to the ecology of the universe. Most people think that all matter was created at the so-called Big Bang. Not so. The Big Bang only created the lighter elements - Hydrogen, Helium and a little bit of Lithium. The rest of the elements were forged in the spectacular deaths of stars. The universe needs these supernovae to continue the creative process -- a fact that caused Carl Sagan to frequently proclaim, "We are the stuff of stars."