Supernova SN2017 eaw

SN 2017eaw in  NGC6946 - Graphic prepared by Pip Stakkert based on images taken with the Bradford Robotic Telescope in 2015 and the Autonomous Robotic Telescope- PIRATE Telescope (Open University)  in August 2017

"Supernova are separated into two categories: those without hydrogen - Type 1 and those with - Type 11. Type 1a supernova are thermo-nuclear explosions which result when gas captured by a white dwarf in a binary pair exceeds a critical limit. All other sub-types of Supernova whether Types 1 or 2 are believed to be result of core collapse in massive stars. Whilst a star has nuclear fuel to fuse, primarily hydrogen and helium, it manages a balancing act between gravity -trying to make the star collapse and radiative pressure from the fusion process trying to make it expand. When a massive star runs out of fuel gravity overwhelms radiative pressure and the star's core collapses releasing enormous amounts of energy as a supernova.

Supernova SN2017 eaw was discovered  on 14 May 2017 by the Utah based amateur astronomer Patrick Wiggins. SN2017 is located in the intermediate spiral "Fireworks Galaxy" NGC 6946 some 22 million light years away on the border between the constellations Cepheus and Cygnus. The galaxy is no stranger to supernovae with 10 confirmed - hence the name 'Fireworks Galaxy'.

SN2017 eaw has been identified from its spectrum as a Type11P supernova which is believed to have arisen from the core collapse of a super giant star with an initial mass somewhere between 8 and 10 solar masses and a retained  hydrogen envelope.
On the 21st of August the brightness of the SN2017eaw was reported as Mag 13.5"  

I should like to take this opportunity to introduce and welcome a new member of the Jodrell Plank Observatory Team.  Ronald Clump has been appointed by the JPO Trust to be the Jodrell Plank Observatory's first CEO.  Mr. Clump joins our organisation after a successful career in business and the media.  We all wish Ronald every success in bringing his unique blend of skills and experience to bear in leading the JPO where no other Observatory has been before".

Kurt Thrust current Director of the Jodrell Plank Observatory 

Inverted image of NGC6946 showing location of SN2017eaw - (North is up) - image taken with the Autonomous Robotic Telescope (Open University)    PIRATE Telescope - 25 August 2017 (00:53:21 UTC) - Pip Stakkert

"How is it possible to see a Supernova in a Galaxy 22 million light years distant?  The simple answer to this question is because it is so very very bright.  In classical times the Greeks classified the visible (to the naked eye) stars into five groups. Group 1 stars were the brightest and Group 6 were the dimmest that could be seen. Unfortunately the human eye does not assess brightness on a linear scale and it was eventually discovered that a change from one group to the next represented a decrease in brightness by a factor of 2.512.  Today astronomers use the term 'Apparent Magnitude' to decribe the 'Groups' eg. a Mag 6 star is the dimmest star you can see with your naked eye from a dark location.  

The sun, if it were at a distance of 10 parsecs ( where one parsec = 3.26 light years)  from the earth would have a magnitude of 4.83 (this measure is known as Absolute Magnitude) As we are much closer to the sun at 93 million miles or 8.3 light minutes its apparent magnitude is much brighter at Mag -26.74

SN2017eaw was reported as Mag 13.5  - so many times dimmer than could be seen without the optical aid of a telescope.

To give some idea how intense and luminous the Supernova is we can use some mathematics to compare the supernova with our Sun. Luminosity is the rate at which an object produces radiation energy in watts and brightness or intensity (I) is given by the equation:   
  
         Intensity I = Luminosity  watts   per metre^2 
                                   4πd^2


Where d = distance from the source

If you want to compare the luminosity of a star or a supernova with the luminosity of the Sun you can write:

equation  A            Luminosity (SN2017eaw)  = (d SN)lyrs ) ^2 x Intensity (SN)
                                Luminosity (Sun)                  (d Sun )lyrs)       Intensity (Sun)


The Sun has a luminosity of approximately 3.86 x 10^26 watts


 So :       Intensity I(Sun) = 3.86 x 10^26 watts                 =  3.24 x 10^-11 w/m^2
                                           4π(3.08x 10^17) metres^2



 As: 
              I(SN2017aew) = I(Sun)x(2.512)^(MagSun - MagSN2017aew)

Then     I (SN2017aew) = (3.24 x 10^-11 w/m^2)(2.512)^(4.823 - 13.5)

 or         Intensity (SN) =(3.24 x 10^ -11)  = 1.095 x 10^ -14
                                        (2.512)^ 8.677

And from the intensity it is possible to calculate the Luminosity using equation A above

              L(SN2017aew) = L(Sun) x    (distance to SN lyrs)^2    x I (SN)
                                                                    (32.6 lyrs )                  I (Sun)
So
              L (SN2017 eaw) = (3.86 x 10^26) x (22 x 10^6)^2  x  1.095 x 10^ -14
                                                                            (32.6)             3.24 x 10^-11

or       Approximately    Luminosity (SN2017 eaw)  =    5.94 x 10^34 Watts

or       Approximately  the Supernova was, at the time that its magnitude was determined, 150 million times more luminous  than our Sun. - Thats why at the vast distance of 22million light years this 'enormous bang' could be seen from Earth with relatively small telescopes. The other mind boggling fact is that this Supernova actually occured some 22 million years ago towards the end of the geological Oligocene epoch. At that time our ancestral apes were still in Africa. The photons of light we captured from SN 2017 eaw have been travelling for all that time to reach us.

Clearly, if you were anywhere near this cataclysmic event, Rayburns and Factor 40 Sunscreen would not do the business."

Archie Mendes  - visiting Astrophysicist and Mathematician at the Jodrell Plank Observatory.
                                                        
 Please note the calculations are only approximate and account for visible light only.