Galaxies, Galaxies And More Galaxies – 225 Billion And Counting!

The mysterious old spiral galaxy NGC 524 that has evolved into what astronomers call a lenticular galaxy. Credit: NASA/ESA/Hubble
The mysterious old spiral galaxy NGC 524 that has evolved into what astronomers call a lenticular galaxy. Credit: ESA/Hubble & NASA/Judy Schmidt

Like a spinning hypnotic disk, who can’t resist the spiral swirls of dust that draw your gaze to the core of galaxy NGC 524? It’s one of billions of galaxies that populate the observable universe. Located 90 million light away in the constellation Pisces, this mysterious-looking object is known as a lenticular galaxy.

The lenticular galaxy 4866 seen close to edge-on. Lenticulars have a bright disk of old stars with weak or absent spiral features and a central core or bulge rich in ancient stars. Credit: NASA/ESA/Hubble
The lenticular galaxy NGC 4866 in Virgo seen close to edge-on. Lenticulars have a bright disk of old stars with weak or absent spiral features and a central core or bulge rich in ancient stars. Astronomers classify lenticulars. Credit: NASA/ESA/Hubble

It used to be a spiral galaxy resembling other spirals like our own Milky Way or the Andromeda Galaxy with their vast, pinwheeling arms. Spirals are dotted with hot pink clouds of gas and dust that are the sites of new star formation. Within their folds, gravity hammers dust into new generations of stars. All we have to do to see that our galaxy is actively forming stars is to look to the Orion Nebula below Orion’s Belt. Thousands of newborn stars have recently lit up within this massive interstellar cloud.

At left is the elliptical galaxy M87 in Virgo. The wisp of light near the core is a jet of material powered by a black hole in the galaxy's center. At right is a classic spiral galaxy, M74. Credit: NASA/ESA/Hubble
At left is the elliptical galaxy M87 in Virgo. The wisp of light near the core is a jet of matter ejected by a black hole in the galaxy’s center. At right is a classic spiral galaxy, M74, also located in Pisces. Credit: NASA/ESA/Hubble

Not so in lenticulars. Over time, they either use up or lose to space much of their interstellar dust — the material used to make stars — leaving a nearly featureless disk filled with old red stars and a bright bulge of even older stars in the middle. They’re intermediate in form between spirals and that other major class of galaxies, the ellipticals. Elliptical galaxies are disk-free and comprised almost purely of stars gathered into spheres and ovoids. You can think of them as naked bulges.

Astronomer Edwin Hubble created this diagram in his quest to classify galaxies' diverse forms. The ellipticals (letter "E") are at left, while lenticulars (S0) lie at the juncture of two different branches of spirals, ones without bars (top) and ones with. The Milky Way is a barred spiral galaxy. Credit: Wikipedia
Astronomer Edwin Hubble created this diagram in his quest to classify and understand galaxies’ diverse forms. The ellipticals (letter “E”) are at left. The higher the number, the more flattened their appearance. Lenticulars (S0) lie at the juncture of two different branches of spirals, ones without bars (top) and ones with. The Milky Way is an SBc barred spiral galaxy. Credit: Wikipedia

American astronomer Edwin Hubble wasn’t the first to observe that galaxies have a variety of shapes, but in trying to understand their evolution, he was the first to classify their forms in his famous “tuning fork” diagram in 1926. Although a simplification of the full scheme of galaxies, it’s still the most popular classification system used to this day.

NGC 2787 is an example of a lenticular galaxy with visible dust absorption. While this galaxy has been classified as an S0 galaxy, one can see the difficulty in differentiating between spirals, ellipticals, and lenticulars. Credit: HST
NGC 2787 is an lovely example of a lenticular or S0 galaxy with visible dust absorption. It lies 25 million light years from Earth in Ursa Major. Credit: HST

Hubble thought that galaxies evolved from ellipticals through lenticulars and into spirals. He called ellipticals “early galaxies” and spirals “late galaxies”. While these terms are still used by astronomers, we now know that ellipticals can’t evolve into spirals. Ellipticals appear to arise from mergers of two or more galaxies, and they’re slow rotators. Spirals form from the collapse of massive clouds of dust and gas that rotate rapidly as they flatten into disks.

Spirals, ellipticals, irregulars - 170 billion in all. Credit: NASA/ESA/Hubble
Spirals, ellipticals, irregulars – 225 billion and counting! Credit: NASA/ESA/Hubble

Whatever their classification, galaxies possess a delightful array of shapes that show what nature can do when handed a parcel containing little more than interstellar dust and dark matter. It’s estimated that the observable universe contains some 225 billion galaxies. Click the image above for close-ups of a small sample.

6 Responses

  1. David

    225 Billion galaxies, each having millions or billions of stars. Around most of those stars are any number of planets….it must be an almost mathamatical certainty that there is other life out there somewhere.

  2. Jeannette

    Love David’s thought about life. But a question:
    Those images are fantastic. Do you know if they are available as posters anywhere?
    I’d love to give them as gifts to friends/family.
    Thanks–
    Jeannette

  3. Edward M. Boll

    Quite a cosmos. I like hunting Lovejoy in the evenings. Binoculars work best, but with the Moon getting so bright, a small telescope maybe best.

  4. David

    Edward, I too have been following Lovejoy. Took many images of it from Dec18,2014 right up to last week. It has gone right across the sky, from Lepus the hare, through Taurus where it is now in Cassiopeia. I think its heading just over Polaris.

    Got it naked eye once in January. My images brought out a green fuzzball, but through binoculars it showed up as a huge gray fuzzball. Amazingly it has maintained almost the same brightness since I first observed it. It also looks like the tail has fanned out and got larger, in my images…

    It has been a wonderful, easy to find target this past winter.

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