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Messier Monday: The Black Eye Galaxy, M64

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A uniquely-darkened spiral galaxy is one of the most unusual sights in the night sky. But what gives it its one-of-a-kind appearance?

“Some day I hope to meet you. When that happens you’ll need a new nose, a lot of beefsteak for black eyes, and perhaps a supporter below!” –Harry Truman, to a music critic who panned his daughter’s singing

It’s time for one of my favorite Messier objects tonight, visible in the early part of the night. There are 110 deep-sky objects in the Messier catalogue, and in many ways, the most spectacular are the galaxies located far beyond our own Milky Way. There are a whopping 40 galaxies represented in the Messier Catalogue, more than any other class of object.

Image credit: Mike Keith’s delightful (a)periodic table of Messier objects, via http://cadaeic.net/astro/PeriodicMessier.htm!

The combination of the Moon not rising until much later in the evening along with the end of February heralding the rising of a number of galactic targets in the northeast makes this an ideal time — if you can withstand the cold — to look for some of the most distant objects visible from Earth.

For today’s Messier Monday, let’s take a look at one of the most unique spiral galaxies not just in the Messier Catalogue, but in the entire night sky: Messier 64, the Black Eye Galaxy. Here’s how to find it.

Image credit: me, using the free software Stellarium, available at http://stellarium.org/.

From the northern hemisphere, after sunset, look for the Big Dipper rising high in the northeast skies, with the prominent constellation Leo farther to the east. If you move perpendicularly towards Leo from the tip of the Big Dipper’s handle, you’ll come to the prominent star Cor Caroli, while if you continue the line formed from Leo’s two brightest stars — Regulus and Denebola — you’ll arrive at Vindemiatrix.

It’s these two stars — Cor Caroli and Vindemiatrix — that will help you locate Messier 64. Draw an imaginary line between them, and start at Vindemiatrix, backtracking towards Cor Caroli.

Image credit: me, using the free software Stellarium, available at http://stellarium.org/.

There are two naked-eye stars that roughly head towards Cor Caroli: Diadem (also known as α Comae Berenices) and the slightly fainter (and slightly more in line) 36 Comae Berenices. If you continue to follow the line from Vindemiatrix to 36 Comae Berenices and beyond, you’ll arrive at the yellow giant 35 Comae Berenices, and that’s your guide to Messier 64, which lies less than a degree away.

Image credit: me, using the free software Stellarium, available at http://stellarium.org/.

Although it was independently discovered by Messier, he was actually the third to find it, as reported by seds.org, where they say:

M64 was discovered by Edward Pigott on March 23, 1779, just 12 days before Johann Elert Bode found it independently on April 4, 1779. Roughly a year later, Charles Messier independently rediscovered it on March 1, 1780 and cataloged it as M64. However, Pigott’s discovery got published only when read before the Royal Society in London on January 11, 1781, while Bode’s was published during 1779 and Messier’s in late summer, 1780. Pigott’s discovery was more or less ignored and recovered only by Bryn Jones in April 2002!

But this is certainly a wonderful target for anyone with a telescope, regardless of its power.

Image credit: Martin S. Ferlito, via http://www.martin-ferlito-astrovideo.com/galaxies.php.

Even small telescopes can capture the bright central nucleus, the fading surface luminance as you move off to the edges, and the unique feature of this galaxy: its darkened appearance on one side only.

But through a more powerful telescope, we can really get a handle on what’s at play here.

Image credit: Isaac Newton Group of Telescopes, La Palma; Nik Szymanek, via http://www.ing.iac.es/PR/science/galaxies.html.

The bright central nucleus appears to spiral outwards in a large number of arms in the inner portion, yet there appear to only be one very large, sweeping one that encircles the galaxy over and over on the outer parts. The “black eye” appearance — also called the evil eye or the sleeping beauty by some — is due to a prominent partial dust lane, likely evidence of a recent merger.

This is also a highly unusual galaxy for a number of other reasons: despite being so bright, its distance is poorly measured (estimated at 24 million light years), as there are no known cepheids inside, highly unusual for a galaxy this close. Despite the recent merger evidence, there hasn’t been a single supernovae observed in it, ever.

Image credit: Andrea Tamanti, via http://www.tamanti.it/astronomy.htm.

As you can see from long-exposure images like Andrea Tamanti’s, above, the outer arms extend for a very large distance, about 65,000 light-years in diameter at a distance of 24 million light-years, whereas the inner dust lane extends for only about a quarter of that.

And — despite recent Hubble observations — there’s still an intense debate as to just what’s causing this unique dust feature.

Image credit: Torsten Boeker, Space Telescope Science Institute (STScI), and NASA.

As revealed in the infrared (above), there is an intense, bright population of new stars, and the dust in the very inner region rotates in the same direction. However, in the outer dusty region (out of frame of this image), the interstellar dust rotates in the opposite direction from all the stars. Yet it’s the co-rotating inner region where a population of new, young stars have recently formed.

Image credit: Martin Pugh of http://www.martinpughastrophotography.id.au/, via http://apod.nasa.gov/apod/ap130404.html.

So that’s a clue, and it provides us with two reasonable possibilities for this galaxy’s appearance:

  1. A satellite galaxy collided with M64 maybe a billion years ago, and the dust from that is responsible for what we’re seeing.
  2. The dust feature is due to infalling matter in the galaxy’s halo, accruing asymmetrically onto the galaxy’s core.

The best view — and the most suggestive answer between these possibilities — comes from Hubble’s WFPC2 in the visible, shown below.

Image credit: NASA and The Hubble Heritage Team (AURA/STScI); acknowledgment: S. Smartt (Institute of Astronomy) and D. Richstone (U. Michigan).

Although, to be frank, we could really use a quality N-body simulation to learn more, what does the image above show you about the position of the dust lanes? Does it appear to you — like it does to me — that on the right side of the image, there’s a tremendous amount of foreground dust between the plane of the galaxy and our eyes? Whereas on the left, it looks like there are more stars between the dust lanes and our eyes, yet it still appears to be there?

Based on this, I would assume that there was a satellite that merged with M64, and that it did so not only with its rotation in the opposite direction, but that it merged asymetrically. I’d be willing to bet that if we could view this galaxy from the opposite side, we’d find a matching prominent dusty feature where the plane of our galaxy obscures our view today. And I’d be willing to admit the possibility that the central, “black eye” region and the dusty outer arms have different origins from one another. Whatever the case, this galactic wonder will surely keep us busy for years to come as we try and uncover the root of its mysterious appearance! I’ll leave you with one final true color image…

Image credit: S. Reilly at Dogwood Ridge Observatory, via http://www.astral-imaging.com/M64-Redo-Full.htm.

…as we wrap up today’s Messier Monday! Including today’s object, we’ve profiled the following deep-sky wonders:

Come back next week for another deep-sky wonder and another fantastic story that the Universe tells us about itself, only here on Messier Monday!

Have something to say? Head on over to the Starts With A Bang forum at Scienceblogs and join the discussion!

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