"The thing's hollow—it goes on forever—and—oh my God—it's full of stars!" -Dave Bowman, 2001: A Space Odyssey
Back in October, we began a new, weekly series here called Messier Monday. Each Monday, we've taken a look at one of the 110 deep-sky objects that make up the Messier Catalogue, nebulous objects that might potentially be confused with comets by unaware comet-hunters.
These objects include stellar remnants, star-forming nebulae, young star clusters, ancient globular clusters, and distant galaxies far beyond the Milky Way. Today, we're going to take an in-depth look at the sixtieth object in this catalog, the great elliptical galaxy Messier 60. To find it, head outside sometime between midnight and sunrise at this time of year and look towards the east/southeast to locate the two bright stars, Arcturus and Spica.
Just a little bit to the west of the imaginary line connecting these two bright stars, you'll see three prominent but dimmer stars in a row: Vindemiatrix, Auva (δ-Vir), and Porrima. Head on over to Vindemiatrix, and aim your binoculars/telescope maybe three-to-four extra degrees away from the imaginary line connecting Arcturus-to-Spica.
Out in that sea of stars lies a faint, elliptical fuzzball that's been known since the late 1770s: M60. What wasn't known until less than 100 years ago was that this is actually a galaxy all unto itself: a giant elliptical galaxy more than 50 million light-years distant!
We've looked at spiral galaxies in the Messier Catalogue before, but this is our first elliptical galaxy, and for good reason.
This is the first galaxy we've looked at from this portion of the sky. You probably notice a smaller companion galaxy that is a spiral just a small distance away from the elliptical M60. But what you may not notice -- not unless you're viewing M60 with a very wide-field imager -- is that if you continued to look away from the direction that Vindemiatrix was in, you'd find that M60 wasn't alone.
On the contrary, other galaxies -- mostly ellipticals but a few, smaller spirals -- abound as we continue onwards through the sky. In fact, if we continued onwards in that same direction, looking at an even wider field of view, we'd find that this compact group of galaxies is just the edge of an even more impressive structure.
Messier 60 is a large elliptical galaxy on the outskirts of the largest cluster of galaxies in our neighborhood! While our local group -- the group that the Milky Way is apart of -- contains just two large galaxies (us and Andromeda) and a total of 54 known members if you include dwarf galaxies, the Virgo cluster of galaxies contains anywhere between 1,300 and 2,000 galaxies, and spans more than ten million light-years from end-to-end.
This amazing, huge collection of galaxies is completely in line with the typical size of large systems that's predicted by our current best model of the Universe, and if we were able to fast-forward into the far future, the thousands of galaxies in this cluster will all eventually merge together into one superstructure: an elliptical behemoth that rivals the largest known galaxy in the entire Universe. In fact, it's only on account of dark energy that we won't wind up as a part of it; our local group is actually an outlying member of the Virgo Supercluster!
Messier 60 is an impressive member of this great cluster of galaxies: it's the third brightest galaxy in the entire Virgo Cluster, and that means something when you consider that the Virgo cluster is so prominent that sixteen of its galaxies are members of the Messier Catalogue!
But whereas most of the galaxies that aren't found in clusters are spiral-shaped, Messier 60, like all the largest, brightest galaxies in the Virgo cluster, is a giant elliptical. Why is that?
While it's true that a galaxy that forms (mostly) in isolation will almost always end up in a spiral shape, remember we have literally over a thousand galaxies in a relatively small region of space, clustered together. What do you suppose happens over the billions of years that these galaxies have been in close proximity to one another?
If you said, "they're going to interact and occasionally merge," you've hit the nail on the head. And -- according to the best of our understanding -- what happens when two comparably-sized spiral galaxies merge together? (The footage that illustrates this is about one minute long, starting at the 0:32 position, below.)
And this one in particular -- Messier 60 -- has an interesting story in its own right.
As this visible / UV / X-ray composite shows, the smaller spiral galaxy near Messier 60 -- which is actually about 10 million light years farther away -- is beginning to merge with the large elliptical. The ultraviolet light in the second panel -- which indicates hot, young blue stars -- is evidence of that gravitational interaction that triggers star formation.
But it's that last panel -- the X-rays -- that's the most fantastic. That giant X-ray source coming from the center of M60 tells us that there's a supermassive black hole in there. When we do the math, we find that this one is over 1,000 times larger than the one at the center of the Milky Way. At an estimated 4.5 billion solar masses, this supermassive black hole alone outweighs over 90% of the galaxies in our local group!
We were also fortunate enough -- just 9 years ago -- to observe a supernova go off in M60!
But -- as always, where applicable -- the best image of this supermassive elliptical galaxy comes courtesy of the Hubble Space Telescope. Click the image below for a full-resolution behemoth.
To give you an example of just what's there, remember that this "fuzzball" is lit up by individual stars; it's estimated that there are over a trillion in this galaxy alone, making it more massive than our entire local group, combined.
The individual "stars" you can see are from our own foreground galaxy; individual stars are not resolvable at this distance.
But through the galaxy, you may be able to find background, even-more-distant galaxies! Here's just a small strip -- presented at high-resolution -- that tears through the center of this behemoth.
And that's Messier 60, a giant elliptical galaxy that's your gateway into the amazing Virgo Cluster! Including today's entry, we’ve taken a look at the following Messier objects:
- M1, The Crab Nebula: October 22, 2012
- M8, The Lagoon Nebula: November 5, 2012
- M13, The Great Globular Cluster in Hercules: December 31, 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
- M41, The Dog Star’s Secret Neighbor: January 7, 2013
- M44, The Beehive Cluster / Praesepe: December 24, 2012
- M45, The Pleiades: October 29, 2012
- M60, The Gateway Galaxy to Virgo: February 4, 2013
- M67, Messier’s Oldest Open Cluster: January 14, 2013
- M78, A Reflection Nebula: December 10, 2012
- M81, Bode’s Galaxy: November 19, 2012
- M83, The Southern Pinwheel Galaxy, January 21, 2013
- M97, The Owl Nebula, January 28, 2013
- M102, A Great Galactic Controversy: December 17, 2012
Come back next week for another Messier Monday, where we'll continue to look deep into the night sky at the wonders therein!
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Ellipticals arise from merging of spirals.
The center of M60 is so massive that it would be a reasonable guess that it might have been born of the fusion of 2 or more black holes at the center of spirals merging.
If that had happened, there would have been a massive outpouring of xrays. (is this correct?)
If that happened, could there be evidence of the earth being bathed in these xrays at some time in the distant past.
There are many fail points in this chain, but just fun to think about.
Mmm, that is fun.
It's hypothetically possible to detect the effect of such events on the earth if they occurred. Recently there was a paper suggesting that a spike in Beryllium-10 found in ice cores and carbon-14 found in tree rings was the result of a Gamma Ray Burst.
The big questions would probably be -- how big was the event, and could it have left a measurable impact on the earth at this extreme distance? The GRB would have had to be pretty close -- 3000 to 12000 ly away. The merger of two SMBHs would presumably be vastly more powerful, but it's seriously far away and that inverse-square law is a killer (for earth life not being killed, so, I guess, an anti-killer) at these distances.
Then there's how long ago it occurred. M60's merger is clearly long in the past. It very well might pre-date any of the things (like ice sheets) that we use to find ancient isotope ratios. How long does it take for two galaxies to go from colliding to a well-mixed elliptical?