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A plain little sister of Andromeda

Our glamorous next-door galaxy, Andromeda, gets all the attention. That leaves a lot for the other members of her family to live up to; unfortunately for viewers at home, they don’t. But the largest of them has intriguing aspects.

NGC 205 teems with stars in this partial view of the galaxy, released by NASA on Sept. 20, 2019.
ESA/Hubble & NASA, L.Ferrarese e

Editor’s note: This has been previously published on the author’s website.

Our glamorous next-door galaxy, Andromeda, gets all the attention.

She’s a spiral about as large as our own Milky Way. Less than a century ago, a Cepheid variable star in the galaxy gave astronomers their first reasonably accurate notion of the size of the visible universe. Her swirls of gas clouds are dramatic in astrophotos. Andromeda is so close — 2.5 million light-years — that she can be seen without optical assistance on clear, fairly dark, fall and winter nights. In moderate-size telescopes, she overwhelms the viewer, a glimpse of her extent requiring moving the instrument from side to side. And she is coming; gravity draws Andromeda and the Milky Way toward each other at 250,000 miles an hour — they are destined, in about 4 billion years, to merge.

That leaves a lot for the other members of her family to live up to; unfortunately for viewers at home, they don’t. But the largest of them has intriguing aspects.

The Great Galaxy in the Andromeda constellation, M31, is shown with her smaller satellite galaxies NGC 205, above at right, and M32, the fuzz-ball just below Andromeda. The photograph was taken at Kitt Peak National Observatory, 56 miles southwest of Tucson, in 1979.
Bill Schoening and Vanessa Harvey, REU program/NOAO/AURA/NSF

The Great Galaxy in Andromeda — often called just Andromeda and also identified as Messier 31 — is part of our Local Group of galaxies. Others in the group include the beautiful Messier 33, the Milky Way, Messier 32, NGC 205, the Large and Small Magellanic clouds, and several more, according to NASA. Closer to Andromeda, its immediate family consists of at least 13 dwarf satellites; the status of some remains to be proved, but the recent deep survey that uncovered three just swept through a southerly patch on Andromeda’s outskirts, and more must be lurking in other sectors.

The only satellites of Andromeda visible to moderate-sized telescopes are Messier 32 (M32) and NGC 205. Both seem insignificant compared to their behemoth sibling, but it’s preposterous to call an island universe of billions of stars “insignificant.”

Andromeda, the closest large galaxy to the Milky Way, is an estimated 260,000 light-years across. NGC 205, also called M110 (more on that soon), is farther than M31, at nearly 2.7 million light-years distant, and measures 15,000 light-years across. The smallest of the major satellites, M32, is around the same distance as M31, 2.5 million light-years; it is 2,400 light-years in diameter.

Many references use the name M110 for the galaxy NGC 205. It’s true that the little galaxy was discovered by Charles Messier in the late 18th century when he was compiling his invaluable list of dim blurry objects in the night sky that are not comets (so that he could better detect comets). We know this because he drew it while sketching M31 and M42. But he didn’t place it on his list. It was added as the last Messier object, tacked on in 1966. This blog sides with those who reject the “Messier designation” not made by Messier, and use the New General Catalogue number.

While Andromeda is a spiral, M32 is a dwarf elliptical galaxy. NASA explains that ellipticals are smooth and nearly featureless. “Elliptical galaxies do not have arms or regions of star formation. They are oftentimes considered ‘dead’ compared to spiral galaxies, and the stars in elliptical galaxies are often older than those in other galaxies.” NGC 205 is called a small elliptical by NASA and “a dwarf spheroidal rather than a normal elliptical” by the National Optical Astronomy Observatory at Kitt Peak, Arizona.

The small galaxy NGC 205, also called M110, is shaped like a flying saucer. This photo was taken in Tooele County, Utah, the morning of Sept. 25, 2019. Note the gas clouds above and to either side of the central region. Stars in the picture are in the foreground, part of our Milky Way Galaxy.
Joe Bauman

NGC 205 has “has approximately 10 billion stars, as well as at least eight globular clusters (the brightest of which can be seen with large telescopes),” says the Goddard Space Flight Center in Greenbelt, Maryland.

NGC 205 doesn’t fit the definition of an inactive galaxy. On Sept. 20, NASA released a new photograph of it taken by the Hubble Space Telescope. The text, provided by the European Space Agency, notes:

”Messier 110 may not look like much, but it is a fascinating near neighbor of our home galaxy, and an unusual example of its type. … (A)stronomers have spotted signs of a population of young, blue stars at the center of Messier 110 — hinting that it may not be so ‘dead’ after all.”

Another way NGC 205 differs from a featureless elliptical is that it hosts at least two prominent dust clouds. They are big enough to show up in a view I took of the galaxy a few days ago.

Why do young stars show up where none are expected? Why dust clouds? Although outshone by Andromeda, NGC 205 has unusual features that deserve more study.

Joe Bauman, a former Deseret News science reporter, writes an astronomy blog at the-nightly-news.com and is an avid amateur astronomer. His email is joe@the-nightly-news.com.