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Messier 106 (NGC 4258)
Harshit Chauhan

Messier 106

About 22 to 25 million light years from earth lies a magnificent creation of the universe, Messier 106 (M106). Located in the constellation Canes Venatici or "the Hunting Dogs" lies M106 as a spiral galaxy, almost similar in size and luminosity to our closest neighbor, Andromeda Galaxy. It was discovered by Pierre Méchain in 1781. Also designated as NGC 4258 in the New General Catalogue, M106 spreads out in the diameter of 135,000 light years (In comparison to Milky way diameter which is nearly 100,000 light years) and a home to over 400 billion stars.

What's fascinating about M106 is that unlike most spiral galaxies who have super massive black hole at their centers, M106 actually have have an active one. Unlike the black hole at the center of our galaxy which pulls matter and gas occasionally, the black hole at the center of M106 is actively engulfing up matter. M106 also have a very bright nucleus and distinctive S-shape, formed by its spiral arms.

NASA/ESA HUBBLE M106

The above image was taken by NASA/ESA Hubble Space Telescope (http://hubblesite.org/image/3143/news/91-astronomical)

The above high quality image taken by Hubble Space Telescope shows more clear s-shape of the galaxy, with various other distinctive characteristics. Messier 106 spiral arms shows a wide variations in its overall composition. The blue part in the galaxy's spiral arms show young stars which will only live for a few hundred million years, while tiny red dots shows comparatively older stars with a potential of living over 10 billion years. The well-spread out red material represents interstellar gas and cloud, and highly luminous center represents an active black hole.

The tale of uniqueness for M106 galaxy does not seems to end. Another distinctive feature of M106 is that the galaxy seems to have, not two, but four spiral arms, when observed under non-optical imagery. This observation of M106 galaxy has shocked astronomers all around the world because It is highly unlikely that an active galactic nucleus could have more than one pair of jets.

M106 Composite

M106 Infrared M106 X-ray M106 Radio

The above four images were taken by "The Chandra X-ray Observatory" as spectrum of composite, infrared, X-ray and radio, respectively.

A set of non-optical images can reveal a lot about a galaxy. In infrared spectrum (red image), Light corresponds with much longer wavelengths that human eyes can't see, and infrared light can pierce through the obstruction produced by interstellar dust; hence, infrared portion of electromagnetic spectrum shows the light the dust emits and what may be concealed inside it, helping us study various features that can't be studied and observed under visible light.

On the other hand, X-ray (blue image) have wavelengths ranging from 0.01 to 10nm and, in the above image, indicates huge concentration of hot gas above and below the plane of the galaxy. In other words, the two jets visible in the X-ray image indicates that the gas, which was originally in the disk of the galaxy, was heated to millions of degrees by the black hole at the center and released into the outer region of M106 galaxy.

The purple image above was captured when observed in the radio spectrum. Radio waves are longer than 1mm, and being the longest waves, they have low energy and corresponds with the lowest temperatures. The above radio image shows that the SBH (Super-massive black hole) at the center of M106 is producing robust jets of high-energy particles (supported by observation in X-ray spectrum). It is also believed that when jets strike the disk of the galaxy, shock waves are generated. These shock waves heat up some gas, mainly hydrogen, to thousands of degrees.

In conclusion, the above set of images reveals two extra spiral arms when specially observed under X-ray and radio spectrum. The composite image clearly shows four spiral arms as the part of incredibly unique, Messier 106 Galaxy.

References:

Usher, Oli. "A spiral galaxy with a secret". <https://www.spacetelescope.org/news/heic1302/>.

NGC 4258 (M106): Galactic Pyrotechnics On Display <http://chandra.harvard.edu/photo/2014/m106/>

Wikipedia, "Messier 106".

Hubblesite Galaxy M106, "http://hubblesite.org/image/3143/news_release/2013-06"

Jet-Shocked H2 and CO in the Anomalous Arms of Molecular Hydrogen Emission Galaxy NGC 4258, "https://arxiv.org/abs/1405.2040"

NASA Extragalactic Database (NED), "http://ned.ipac.caltech.edu/"

Right Ascension (J2000) 12:18:58
Declination (J2000) +47:18:14
Filters used B (Blue), C (Clear), R (Red), V (Green)
Exposure time per filter B (300s x 15), V (300s x 3), and R (150s x 4); C (90s x 13)
Image dimension 1092x736 pixels; 19 x 7.5 arc minutes
Date/time observed March 4, 2017, 5:58 UT

Data Reduction Process:

In order to get the above colored image, the data received from Rehobeth NM telescope was needed to be analyzed and improved to a great extent. To get clear and crisp image of the galaxy, various reduction and calibration steps were taken. After receiving multiple bias, dark and flat frames, the first step was combining/stacking multiple frames as one. Initially, multiple bias frames were stacked together to form one master bias. This master bias is later subtracted from other calibrated frames. The bias reduction process get rid of any intrinsic camera chip noise.

The same procedure is followed for multiple dark frames with a very minor change, that is, the bias frame is subtracted from the dark frame, then all dark frames are stacked as one single master dark. The reduction of dark frames clears any thermal noise impression captured.

Finally, the bias and dark frames were subtracted from every flat frame, and later on stacked according to the filters with which those flat images were taken. This will result in final flat frames, one of each filter.

These flat frames are later subtracted from color frames based on the filter. These flat frames, when reduced, get rid of any variations due to dust in telescope reception. After all the calibration and reduction is completed, all color images were combined to form one final color image, visible above.

The multipliers used for color combination are as follows:

Filters:

Red (R) : 2.25

Green (G) : 1.5

Blue (B) : 7.35

Other Calculations :

Distance to M106 (in Mpc) : 8.97

Major axis pixel value : ( 553, 348 )-( 627, 214 )

Minor axis pixel value : ( 552, 347 )-( 616, 390 )

Angular size :19 x 7.5 arc minutes

Diameter of object (in light years) (l) : 135,000

 

 

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