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Messier Monday: A Great Galactic Controversy, M102 [Starts With A Bang]


“Men… have had the vanity to pretend that the world creation was made for them, whilst in reality the whole creation does not suspect their existence.” -Camille Flammarion

Welcome to the latest — and most controversial – Messier Monday, where each week, I’ll take a look at one of the 110 deep-sky objects that make up the Messier catalogue. These objects were identified so as not to be confused with potential comets, and make up the brightest and best-known observational sights beyond our own Solar System. But there is one object that, if you go to the wikipedia list, that has not been conclusively identified.

Image credit: SEDS Messier Catalogue, from http://messier.seds.org/; Box by me.

You will notice that there are two candidates — that are two very different objects — for what this galaxy is.

Image credit: SEDS Messier Catalogue, from http://messier.seds.org/.

A little background first: you must realize that Charles Messier was not the first person to create a catalog of deep-sky objects. What was special about Messier’s catalogue is twofold: it was both the first one to be almost 100% correct, whereas the other catalogues of the time had many errors as far as locations (or even existences) of the objects therein, and Messier’s catalogue had a purpose, in that these objects were easily visible to an amateur with even a small telescope. It was smaller (at a total of 110 objects in its final form) than other contemporary catalogues (like William Herschel’s), but it was so uniquely useful that it remains in use even today, hundreds of years after its completion.

The problem is, Messier’s coworker (and co-compiler of the Messier Catalogue), Pierre Méchain, disavowed its existence, and claimed it was a duplicate of Messier 101, the well-known Pinwheel Galaxy. (Longtime readers may remember M101 from its spectacular supernova just a year ago, the closest supernova to us since 1987.)

Image credit: Reuters / BJ Fulton (Las Cumbres) and the Palomar Transient Factor.

But I think Méchain is wrong, and that Messier 102 is actually this spectacular object, also known as NGC 5866.

Image credit: NASA, ESA, and The Hubble Heritage Team (STScI/AURA); W. Keel.

The controversy has existed for hundreds of years. Here’s the problem. In his notes, this is what Messier wrote back in 1781:

102. Nebula between the stars Omicron Boötis and Iota Draconis: it is very faint, near it is a star of 6th magnitude.

Now, the constellations Boötes and Draco do, in fact, border each other. And the star Iota Draconis is, in fact, very close to the constellation Boötes, which is what you’d expect.

Image credit: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg).

The problem comes when we look for the star Omicron Boötis, which is over forty degrees away from Iota Draconis! This would make no sense to write down in a catalogue, and led Méchain to conclude that, in fact, this was just a duplicate observation of M101.

But there was another school of thought, and it wasn’t put forth until 1917 by Camille Flammarion, that perhaps the greek Omicron that Messier wrote down (ο, below in red) was actually a lowercase greek Theta (θ), which would be located below in blue.

Image credit: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg).

If this were the case, then what you’d find was that, just above the edge of the handle of the Big Dipper would correspond to the location of a certain deep-sky object that sounds an awful lot like the M102 object that Charles Messier described.

Image credit: Me, created with the free software Stellarium, http://stellarium.org/.

At sufficiently north latitudes (this is from my location, Portland, OR about an hour after sunset), you can find this object even in tonight’s wintery skies. To illustrate exactly where this is (and where the well-known M101 is relative to it), I’ve zoomed in just a little and labeled some of the key stars.

Image credit: Me, created with the free software Stellarium, http://stellarium.org/.

I think, based on this new information (which is still controversial), it’s pretty incontrovertible that Messier 102 is, in fact, the same as NGC 5866, which means that you can find these spectacular views for yourself!

Image credit: Bob Austin of http://www.astronomy-pictures.com/.

This faint, edge on spiral galaxy has a spectacular dust lane running through its center; it’s quite conceivable that this galaxy is somewhat similar to our own Milky Way as it would be viewed by a galactic outsider at just the right angle.

A nice, wide-field view of this galaxy is shown below.

Image credit: Paul and Liz Downing; http://paulandliz.org/Galaxies/Galaxies_Messier.htm

It looks very much like it’s an edge-on spiral galaxy through a small, amateur telescope. But what would a professional telescope be able to see?

This galaxy has been imaged by the Sloan Digital Sky Survey, which shows not only the galactic disk, bulge, and central dust lane, but also the extended “halo” of stars that live well outside of the planar disk that dominates in smaller telescopes.

Image credit: Sloan Digital Sky Survey.

In other words, this isn’t a spiral, but a Lenticular galaxy, or a galaxy that has both properties of a spiral and an elliptical.

Finally — as is the case wherever it’s available — the most spectacular view of this galaxy is revealed by Hubble. Even background galaxies are visible through the glow of this mammoth, located “only” 45 million light-years away.

Image credit: NASA, ESA, and The Hubble Heritage Team (STScI/AURA).

And that’s the story of Messier 102, perhaps the most controversial object in all of the Messier Catalogue!

Now that the mystery’s been solved, and we know it’s a giant lenticular galaxy (known as the Spindle Galaxy), feel free to take a look back at all our previous Messier Mondays:

M1, The Crab Nebula: October 22, 2012
M8, The Lagoon Nebula: November 5, 2012
M15, An Ancient Globular Cluster: November 12, 2012
M30, A Straggling Globular Cluster: November 26, 2012
M37, A Rich Open Star Cluster: December 3, 2012
M45, The Pleiades: October 29, 2012
M78, A Reflection Nebula: December 10, 2012
M81, Bode’s Galaxy: November 19, 2012
M102, A Great Galactic Controversy: December 17, 2012

Which Messier object will be highlighted next? Let’s hear which one you want, and I’ll make it happen. Happy Messier Monday!


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