Earlier this year, I captured one of my favourite deep-sky objects from the observatory here on the Stoer Peninsula: M104, better known as the Sombrero Galaxy. This edge-on galaxy of yet unclear classification, sometimes called peculiar, never fails to impress, and after processing 50 exposures of 120 seconds each (that’s 100 minutes of total integration time), the results revealed far more than I expected.
What Is the Sombrero Galaxy?
M104 sits roughly 31 million light-years away in the constellation Virgo. We view it nearly edge-on from our perspective, which gives it that distinctive appearance: a bright central bulge bisected by a dark dust lane. The resemblance to a Mexican hat is pretty uncanny—hence the name.
What makes this galaxy particularly striking through a telescope is its unusually large central bulge and prominent dust lane. At approximately 100,000 light-years across, it’s comparable to our own Milky Way, but it packs around 800 billion stars—that’s more than twice what our galaxy contains.
Discovery and Historical Significance
The Sombrero Galaxy was discovered by Pierre Méchain in May 1781, though it was independently rediscovered by William Herschel in 1784. Charles Messier added it to his famous catalogue as the 104th entry, though interestingly, it wasn’t included in the original publication—it was added later based on Méchain’s notes.
By the early 20th century, M104 became scientifically important when astronomers measured its redshift and discovered it was moving away from us at roughly 1,000 kilometres per second. This was early evidence for the expansion of the universe, work that contributed to our modern understanding of cosmology.
Modern Scientific Interest
Today, the Sombrero Galaxy continues to fascinate astronomers. It harbours a supermassive black hole at its centre—weighing in at about one billion solar masses—making it one of the most massive black holes in our cosmic neighbourhood. The galaxy also hosts around 2,000 globular clusters, roughly ten times more than orbit the Milky Way.
Recent studies have revealed that M104 might actually be a large lenticular galaxy, challenging earlier classifications. Its unusual structure continues to provide insights into galaxy formation and evolution.
The Imaging Session
For this capture, I used my William Optics FLT132 refractor paired with the ZWO ASI2600MC camera. The FLT132’s 132mm aperture and 925mm focal length makes it excellent for larger deep-sky objects like M104, providing enough resolution to capture the dust lane detail while maintaining a wide enough field of view to include surrounding galaxies.
After gathering 50 frames at 120 seconds each, I stacked and processed the data in PixInsight before final adjustments in Lightroom. The total exposure time of 100 minutes allowed me to pull out significant detail in both the bright central bulge and the darker dust lane.
Hidden Galaxies in the Background
Here’s where things got really interesting: when I created a starless version of the image using PixInsight’s StarXTerminator tool, dozens of background galaxies suddenly became visible. These faint, distant objects are completely overwhelmed by foreground stars in the normal image, but removing the stars revealed an entirely different view.
Using astronomical software, I was able to identify most of these background galaxies. Each one represents another island universe, potentially billions of light-years beyond M104 itself. It’s a humbling reminder that nearly every patch of sky, when observed deeply enough, reveals countless distant galaxies receding into the cosmic distance.
This technique of creating starless images has revolutionised how we can share astrophotography with the public. It lets us reveal structures and objects that would otherwise remain hidden in the visual noise of foreground stars.
Observing M104 from Scotland
From our latitude here in the northwest Highlands, M104 doesn’t climb particularly high in the sky—it reaches a maximum altitude of only about 20 degrees above the southern horizon. This makes it a challenging target, requiring clear conditions toward the south and careful timing during spring months when Virgo is best placed after dark.
The excellent dark skies we enjoy on the Stoer Peninsula make all the difference for objects like this. Light pollution would easily wash out the faint background galaxies and reduce contrast in the dust lane.
Want to Explore the Night Sky Yourself?
If you’re interested in learning more about observing and photographing galaxies like M104, I run bespoke astronomy events here at the observatory. Whether you’re a complete beginner or an experienced observer, I can tailor sessions to your interests and experience level.
I also coordinate the Assynt Astronomy Club, where local residents and visitors can connect with others who share an interest in the night sky. We meet regularly to observe, share techniques, and discuss what’s visible in the current season.
Key Facts: M104 Sombrero Galaxy
- Distance: Approximately 31 million light-years
- Diameter: ~100,000 light-years
- Stellar population: ~800 billion stars
- Discovery: Pierre Méchain, May 1781
- Central black hole mass: ~1 billion solar masses
- Globular clusters: ~2,000
- Apparent magnitude: +8.0 (visible in small telescopes)
I’m already planning my next imaging run on M104 when conditions allow. With more integration time and optimal seeing, there’s always more detail to reveal in this remarkable galaxy, and more beyond.
Watch this space…
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