The distance to Messier 51

It is a simple question: Would we see our sun in a distant galaxy like Messier 51 (shown below)?

The answer is: No! It is impossible to find a star similar to our sun with the largest telescopes currently available. This is very surprising, as Messier 51 belongs to those neighboring galaxies with distances of only "a few" Million light years distance from our planet earth.

Are the bright knots at noise level single stars? 

The galaxy pair shown in my image contains NGC 5194, also known as Messier 51, and NGC 5195. Certain objects seem to appear like bright single stars. A few of them are foreground stars found in our own Milky Way. The brighter knots in the galaxy are the brightest gaseous nebulae and star clusters containing a few hundreds to thousands of stars. Certain stars in these clusters are very luminous, young and massive stars. The apparent magnitude (brightness) of such luminous single stars is about 10.000 times larger than the brightness of our sun. This is the reason, why we seem to find bright "stars" in a distant galaxy, which in fact are clusters of many stars. A close look on the image will give evidence of some of these clusters and H-II regions resolved at a limiting magnitude of Vmag~20 at about 2" seeing. They appear close to noise level with my image. Not much light detected from such luminous stars. The brightest stars are detectable only with large exposure time and because of their typical variation with time (variable stars). With the given distance modulus of Messier 51 our sun would have an apparent magnitude of Vmag~31 at this distance. Given the limiting magnitude of the Hubble space telescope, which of course is better than that of my own telescope, our sun would appear 5 magnitudes fainter than the faintest objects detectable with the Hubble space telescope. We would need a very huge telescope to confirm detection of a star similar to our sun. It is nearly impossible to imagine such a large distance. And we shall assume, that our distance estimate still is wrong.

The image shown has been taken with a Canon EOS 40D DSLR camera, which is modified having only a clear glass in front of the CMOS sensor. This camera now is able to record light from the near ultra-violet to the near infrared wavelength. The Astronomik UV/IR block filter cuts the colors to provide an appearance which is close to natural colors. The sensitivity in the red light is much better and a few H-II regions appear in my image. The typical noise of these cameras has been removed by a newly developed algorithm. Such an image is able to compete with those taken with a dedicated cooled CCD camera. The advantage of a DSLR: It takes these images of three colors (RGB) with one single observation. No filter to change means a lowered risk to loose important amount of images, e.g. in one or more color planes, due to a bad weather condition. 

Telescope:Vixen VC200L, focal reducer f/6.4, Sphinx SXD
Camera:Canon EOS 40D, 400 ASA, UV/IR block filter (Astronomik)
Exposure:24 x 240s
Calibration:Dark (100 images), Sky flatfields (100 images)
Image Processing:Shift & add with correction of subpixel movement, improved noise reduction
Date of exposure:23. April 2010, 22:11 h MEZ
Software:ArgusPro SE
Remark:Limiting magnitude around 20mag, image cropped
 
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