Messier Monday: The Galaxy at the Head-of-the-Chain, M84

The core of the nearest great galaxy cluster holds a glorious sight unlike any other.


“Man must rise above the Earth, to the top of the atmosphere and beyond, for only thus will he fully understand the world in which he lives.” -Socrates

Each week on Messier Monday, we take an in-depth look at one of the 110 deep-sky wonders that make up the Messier Catalogue. Compiled by Charles Messier during the 18th Century, these fixtures in the night sky were catalogued to avoid confusion with potential new comets, but are now representative of the brightest, most easily (and spectacularly) viewed nebulae, star and globular clusters, and galaxies from our vantage point here on Earth.

Image credit: The Messier Objects by Alistair Symon, from 2005-2009, via http://www.woodlandsobservatory.com/messier_map.htm.

As both the June solstice and a new Moon approach, our nearest galaxy cluster — the Virgo Cluster — consisting of around 2,000 galaxies and an unequaled fifteen Messier objects, makes a perfect observing target for motivated skywatchers. And if you can find the gravitational center of this cluster, a treasure trove of galactic riches awaits you, with Messier 84 leading the way. Here’s how to find it.

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

In the Northern Hemisphere, the Big Dipper is the most recognizable pattern of stars, with the prominent constellation of Leo not only lying “below” the dipper (about 40° to the South), but easily visible to observers on all continents except Antarctica. If you can find the two brightest stars in Leo — Regulus and the somewhat fainter Denebola — the imaginary line connecting them will lead you, if you extend it, towards the prominent (although slightly dimmer) Vindemiatrix.

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

A large number of galaxies can be found in this region of space, as the Virgo Cluster is close enough — about 55-to-60 million light-years away — that its galaxies extend out for many degrees in all directions. But if you’re looking for the very core of the Virgo Cluster, you’ll want to head about halfway between Denebola and Vindemiatrix right along that imaginary line connecting them.

If you want a little help finding Messier 84, the naked-eye stars 6 Comae Berenices and ρ Virginis lie on either side of that imaginary line, and where that imaginary line and the Denebola-Vindemiatrix line intersect is where you should point your telescope.

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

Because just a little over 2° away from ρ Virginis lies not only Messier 84, but a whole slew of galaxies, including a number of very prominent ones that branch off in a chain. In fact, this chain has a name — Markarian’s chain — and is one of the most targeted astrophotography sights in all the night skies. And to those with exceptional equipment, many more galaxies will be revealed than just the obvious ones in the chain!

Image credit: © 2006 — 2012 by Siegfried Kohlert, via http://www.astroimages.de/en/gallery/M84.html.

Although galaxies often line up just by coincidence, at least seven of these galaxies appear to move coherently, with Messier 84 — the big lenticular galaxy on the end (at the right, above) — being the lone exception! This galaxy wasn’t the first roughly spherical, giant elliptical that Messier encountered, describing it as such:

Nebula without star, in Virgo; the center it is a bit brilliant, surrounded with a slight nebulosity: its brightness & its appearance resemble that of those in this Catalog, No.s 59 & 60.

But this island Universe tells a unique story all on its own.

Image credit: Palomar Observatory courtesy of Caltech, via Universe Today at http://www.universetoday.com/47133/messier-84/.

While the giant elliptical next to it — Messier 86 — is the most blueshifted of all Messier objects, moving towards Earth at around 400 km/s, Messier 84 is redshifted at 1000 km/s, moving in step with the majority of the Virgo Cluster. And while many of the galaxies nearest to it are highly ellipsoidal, this is a very spherical one, classified as an E1 galaxy. (Only the class E0 is more perfectly symmetrical.)

And yet, there’s a rich, fascinating story in here that isn’t normal for ellipticals at all!

Image credit: Courtney Seligman of Messier 84 (NGC 4374), via http://cseligman.com/text/atlas/ngc43a.htm#4374.

In standard, visible light, you might not be able to see anything out of the ordinary. But if you know what specific filters to look in, it turns out that there are some actually prominent dust features that block the light from the inner region of this galaxy. And these dust lanes look suspiciously like the ones we’re used to seeing in spiral and lenticular galaxies. Take a look at what the old WFPC2 instrument aboard Hubble was able to uncover!

Image credit: Gary Bower, Richard Green (NOAO), B. Woodgate, the STIS Instrument Definition Team, and NASA/ESA; Left image via the Hubble Legacy Archive, Right image via APOD at http://apod.nasa.gov/apod/ap970516.html.

That disk actually rotates very rapidly, something that Hubble was able to spectroscopically observe (at right), telling us something critical just from the Keplerian orbits inside: there must be an extremely concentrated mass source at the center that weighs in at 1.5 billion Suns; such a thing could only be a supermassive black hole!

But there’s more! We can look in the radio, as supermassive black holes, when they accelerate gas, tend to produce bipolar radio lobes. If that’s what we’ve really got here, we should see some huge ones.

Image credit: NRAO / Robert A. Laing (ESO) and Alan H. Bridle (NRAO), via http://www.cv.nrao.edu/~abridle/3c2721.htm.

No problem there. In addition to that, there are huge X-ray emissions coming from this galaxy as well. Not only from the center, but from point sources that are most consistent with accreting black hole binaries in this halo of the galaxy.

Check out the composite below, using data from the SDSS (visible; in yellow), the VLA (radio; in red) and the hot gas from Chandra X-ray Observatory (X-ray; in blue).

Image credit: NASA / Chandra, via NOAO/AURA/NSF; VLA and SDSS teams.

There are so many great images I could present you with to end this post, but truly the most spectacular shot out there is from a team of amateurs at Capella Observatory, showing the full glory of Markarian’s Chain, with M84 on prominent display at the bottom, with close to 100 galaxies visible to keen observers.

Take a look for yourself!

Image credit: Makis Palaiologou, Stefan Binnewies, Josef Pöpsel of Capella Observatory, via http://www.capella-observatory.com/ImageHTMLs/Galaxies/MarkariansChain.htm.

And with that grand tour, we come to the end of another Messier Monday! If you can’t get your fill of the deep sky wonders at your disposal, check out all our previous Messier Mondays below:

And come back next week for another star-filled delight of the night sky, only here on Messier Monday!


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