Messier 3...

Object: Messier 3 (NGC 5272)
Type: Globular cluster
Constellation: Coma Bereneces
Distance: 34,000 light years

Date: April 25th 2020
Equipment: ATIK 460EX with EFW2, Skywatcher f5.5 Esprit 100 ED refractor, Avalon Linear mount, guiding with Lodestar X2/PHD

Subframes: 20 x 150s (2x2 binned) each for RGB, flats for each channel, bias as darks (hot pixel removal in Astroart).

Globular clusters are some of the oldest objects in the universe. They consist of vast, spherical agglomerations of stars, typically hundreds of thousands in number, and exist in galactic halos in orbit around larger galaxies.  The Milky Way galaxy has around 150 globular clusters in attendance, with more massive galaxies having proportionally larger numbers.

M3 was discovered on May 3, 1764, and was the first object in the Messier catalogue to be discovered by Charles Messier himself. Messier originally mistook the object for a “nebula without stars”. With a larger and better quality telescope, the object was resolved into stars by William Herschel around 1784, who first coined the term “globular cluster”.

Stellarium map showing location of image field

From the UK, M3 can be found high above the southern horizon at around midnight in late April, between the bright stars Arcturus and Cor Caroli. The cluster has a bright core with a diameter of about 6 arcminutes and spans a total of 12 arcminutes (or just under the half the diameter of a full moon). This cluster is one of the largest and brightest of its type, and is made up of around 500,000 stars. It is estimated to be 11.4 billion years old.

I had originally planned to gather both luminance and colour data for this object, but the seeing was very poor and I struggled to get the auto-guiding to run below 1.3” RMS, so I restricted myself to collecting 2x2 binned sub-frames, where the guiding requirements aren’t as demanding.

However, I was quite pleased with the way the RGB image scrubbing up without any additional luminance data, so I’ve decided to let well enough be. 

If you look closely, the image shows up the strange straight lines of stars that appear to run from the edges of the cluster, which Stephen O'Meara illustrated for M3 in his book "Deep-Sky Companions - The Messier Objects".  It also shows up the 16th magnitude spiral galaxy NGC 5263, visible at the centre right of the main image as small fuzzy dash of light and lying some 196 million light years away...

M106 and friends...

M106 and adjacent galaxies

Object: Messier 106 (NGC 4258)
Type: Spiral Galaxy (morphological classification SABbc)
Constellation: Canes Venatici
Distance: 24 million light years

Date: April 22nd 2020
Equipment: ATIK 460EX with EFW2, Skywatcher f5.5 Esprit 100 ED refractor, Avalon Linear mount, guiding with Lodestar X2/PHD

Subframes: 12 x 600s luminance, 12 x 300s (2x2 binned) each for RGB, flats for each channel, bias as darks (hot pixel removal in Astroart).

High overhead in on April evenings, the galactic north pole looks out beyond the arms of our own Milky Way galaxy and into the chilling depths of intergalactic space. 

Stellarium map showing location of image field

Mid-way between Beta Canum Venaticorum (a 4^th magnitude star called Chara, second brightest star in the rather obscure constellation of Canes Venatici – the Hunting Dogs – which is tucked beneath the handle of the Plough) and gamma Ursae Majoris (Phecda, also called Phad, the left-hand star in the bowl of the Plough), lies the distant spiral galaxy Messier 106.

It was discovered by the French astronomer Pierre Méchain in July of 1781. Méchain mentioned the discovery in a letter to fellow astronomer Johann Bernoulli dated May 6, 1783:

The galaxy, however, was not included in the Messier Catalogue until 1947, when Canadian astronomer Helen Sawyer Hogg added it (along with galaxies M105 and M107) based on Méchain’s letter.

William Herschel independently discovered M106 on March 9, 1788

M106 - crop from above image

Located a little over 20 million light-years away, practically a neighbour by cosmic standards, Messier 106 is one of the brightest and nearest spiral galaxies to our own. NGC 4248, a small galaxy which can be seen next to M106 in the cropped image opposite and which lies at a similar distance, is thought to be a satellite of M106.

M106 occupies an area of 18.6 by 7.2 arc minutes of apparent sky, corresponding to a spatial diameter of 135,000 light years. It has a high surface brightness (an apparent magnitude of 9.1) and can be glimpsed in binoculars, which reveal a faint patch of light.

  

Messier 106 is classified as a SABbc type galaxy, which means that it is an intermediate between a normal and barred spiral galaxy. It is home to at least 400 billion stars, being similar in size and luminosity to the Andromeda Galaxy (M31) and making it one of the brightest, largest nearby galaxies.

It is also classified as a Seyfert II galaxy, having an active nucleus. It has a considerably larger extent in radio than in visible light and exhibits emission line spectra from the nucleus. M106 shows unusual emission lines and X-rays, indicating that a portion of the galaxy is falling into an active central super-massive black hole.

Luminance frame, showing galaxies in the field of M106

Several other NGC galaxies occupy the same field of view shown in the main image. The edge-on spiral NGC 4217 is thought to be approximately 60 million light years away, whilst the galaxy pair NGC 4231 and 4232 are thought to be 350 million light years away. Other un-named tiny galaxies, rendered as mere smudges of light by their unimaginable distances, can be seen scattered across the luminance frame shown opposite. Even given the vast distance of M106, it is a mere foreground object compared to the remoteness offered up by intergalactic space.

The evening of April 22^nd was very clear, but the seeing was initially somewhat shaky. I therefore set out to gather blue binned data, but the seeing improved and as the guiding accuracy dropped to 0.6” RMS, I switched to collecting full frame luminance, finishing off with some red and green binned data before the sky began to brighten. The green frames were plagued by a bit of a gradient, partly because a haze had set in, and partly because the dawn light was making itself apparent

The final luminance image was a bit noisy, and probably requires more than the 2 hours of data that I collected. 

One bonus of seeing the dawn come in was the sight of Jupiter and Saturn, a mere 5 degrees apart, rising above my south-eastern horizon.

The Owl and the Surfboard...

M97 and M108

Objects: M97 (NGC 3587), M108 (NGC 3556)
Type: Planetary nebula (M97) and Spiral Galaxy (M108, morphological classification SBbc)
Constellation: Ursa Major
Distance: 2000 light years (M97), 46 million light years (M108)

Date: April 15th and 19th. 2020
Equipment: ATIK 460EX with EFW2, Skywatcher f5.5 Esprit 100 ED refractor, Avalon Linear mount, guiding with Lodestar X2/PHD

Subframes: 12 x 600s H-alpha, 12 x 600s OIII, 12 x 600s luminance, 10 x 300s (2x2 binned) each for RGB, flats for all channels, bias as darks (hot pixel removal in Astroart). 

These two objects from the Messier catalogue are pictured above in the same one-degree field of view, located overhead in late Spring evenings adjacent to the star Merak (beta Ursae Majoris) in the bowl of the "Big Dipper". Though they may seem close to each other, the bluish disc of the planetary nebula M97 is a foreground object that lies a "mere" 2000 light years away within our own Milky Way galaxy, whilst M108 is a giant galaxy in its own right, 110,000 light years in diameter and nearly 46 million light years distant.

Stellarium map showing image field

The Owl Nebula is a planetary nebula named after its distinctive appearance, resembling a pair of owl-like eyes, which can be seen in larger telescopes. 

Its apparent dimensions in the sky are 3′.4 x 3′.3, or about a tenth of the diameter of the full moon. 

It was discovered by the French astronomer Pierre Méchain, Charles Messier’s friend and colleague, on February 16, 1781. Messier included the object in his catalogue on March 24, 1781.

Upon discovery, Méchain reported that the nebula was a difficult object to see.

 

Messier noted: “Nebula in the Great Bear, near Beta: It is difficult to see, reports M. Méchain, especially when one illuminates the micrometer wires: its light is faint, without a star. M. Méchain saw it the first time on Feb 16, 1781, & the position is that given by him.  Near this nebula he has seen another one which has not yet been determined, and also a third which is near Gamma of the Great Bear.”

The two “nebulae” Messier mentioned in his description of M97 are barred spiral galaxies later named Messier 108 (in the field of view above) and Messier 109 by the American astronomer Owen Gingerich, and added to Messier’s catalogue in 1960

The estimated age of the Owl Nebula is about 8,000 years. The Owl Nebula was formed when its parent star expelled its outer gaseous layers about 8,000 years ago. As the outer layers were gradually blown off over thousands of years, what was left of the original star contracted to form a hot white dwarf. The 16th magnitude central star has 55 to 60 percent of the Sun’s mass, only 4 percent of the Sun’s radius, and an estimated surface temperature of 123,000 K. The star can be seen between the Owl’s eyes. Its radiation is responsible for the nebula’s glow (see my notes on M27 for information about planetary nebulae).

Most stars that expel material to form planetary nebulae – about 80 percent of them – expel a large amount of it in two opposing directions. The jets blown off by the progenitor star of the Owl Nebula are almost aligned with our line of sight. The dust within the jets blocks enough light from the expanding nebula to create the appearance of owl-like eyes.

One of the nebula’s eyes appears darker than the other. This is the jet that is emitted in our direction,

while the fainter eye marks the jet expelled in the opposite direction, away from us.

Line of sight galaxies adjacent to M97

The nebula will gradually disperse over the next several thousand years, while the central white dwarf will cool and fade away. In about 5 billion years, our Sun will end its life in similar fashion.. 

There are several remote galaxies lying in the same line of sight as the Owl Nebula. These distant galaxies are shown in a crop of the above wide field view (see opposite).

Admiral William H. Smyth was the first to classify the object as a planetary nebula in 1844. 

M97 has about 0.13 solar masses and stretches across 0.91 light years in radius. It is expanding at an approximate speed of 27 to 39 km/s into the surrounding space.

As noted above, M108 was discovered by Pierre Méchain in 1781 three days after he discovered M97. 

Close-up of M108 from wide-field image above

M108 (known by some as the "Surfboard Galaxy") is classified as a barred spiral galaxy with loosely wound spiral arms, but visually there is little evidence of a well-defined spiral pattern in the galaxy as the spiral is inclined towards us only 15 degrees from edge-on. It is one of the larger members of the Ursa Major galactic cluster, being approximately 100,000 year years across. 

Observations show young star clusters exposed against dark dust lanes and bright emission regions. M108 also contains "super-shells", which are shells of gas driven by bursts of star formation and resulting supernova explosions. The super-shells could also be driven by stellar jets or an in-fall of gas from outside the galaxy.

At the centre of M108 is a supermassive black hole estimated to be 24 million times as massive as the Sun. The Chandra X-ray Observatory discovered multiple X-ray sources in M108, with the brightest X-ray source suspected to be an intermediately sized black hole that is actively accreting material.

I took the LRGB data on the cold, frosty evening of the 15th. There was a bit of a haze and the stars were a bit bloated. Once I had acquired the Ha and OIII data I wanted for M97, I made an RGB frame to add the star colours (in "Lighten" mode) to an HOO image, and then used the luminance data just to brighten up and add detail to M108.  Although the image scale is small, the Ha regions in both objects can definitely be seen.