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Deep within the sprawling Virgo Cluster, amidst a thousand distant galaxies, lies one of the most captivating sights in springtime night: Markarian's Chain. This isn't a single object, but a stunning, gently curving line of galaxies, seemingly strung together like pearls against intergalactic space. It's a remarkable visual alignment, a cosmic river flowing through the heart of a galactic metropolis, inviting observers and astrophotographers alike to explore its diverse members.
While the chain appears cohesive and obvious, its recognition came relatively late. The two brightest anchors, the giant elliptical/lenticular galaxies M84 (NGC 4374) and M86 (NGC 4406), were first catalogued by Charles Messier in 1781. Many of the other prominent galaxies weaving through the chain were subsequently discovered by William Herschel and later included in John Louis Emil Dreyer's seminal New General Catalogue (NGC), published in 1888.
However, the chain truly earned its name thanks to the work of Armenian astrophysicist Benjamin Markarian in the early 1960s. He meticulously studied the motions of galaxies in this region. He discovered that at least seven galaxies along this apparent line shared a common proper motion – they were physically moving together through space as part of the larger Virgo Cluster structure. This shared journey cemented their identity as "Markarian's Chain."
Markarian's studies of the proper motion within the Virgo Cluster indicate that the galaxies are generally drifting toward the southeast across our field of view.
Visually, this galactic stream is nestled in the constellation Virgo, roughly halfway between the star Denebola (marking the eastern point of Leo's triangle) and the star Vindemiatrix in Virgo. The chain is a rewarding target. Even small telescopes can reveal the bright core members like M84 and M86 under dark skies. Larger instruments begin to unveil the fainter NGC galaxies strung along the curve. Perhaps the most intriguing feature lies near the centre: the interacting pair NGC 4438 and NGC 4435, famously nicknamed "Markarian's Eyes". This pair, situated about 50 million light-years away, shows clear signs of gravitational disruption, offering a dramatic glimpse into the dynamic processes shaping galaxies within dense cluster environments. Other key members contributing to the chain's visual appeal include NGC 4477, NGC 4473, NGC 4461, and NGC 4458. While some galaxies along the line might be chance superpositions, the coherent movement of the core members makes this a truly fascinating structure to observe and image.
M84 (NGC 4374) is a giant elliptical or lenticular galaxy located in the dense core of the Virgo Cluster, discovered by Charles Messier in 1781. Classified as E1, it has a high luminosity and is surrounded by a significant dark matter halo. Observations reveal two jets shoot from its centre and a rapidly rotating disk of gas and stars, indicating a supermassive black hole estimated at 1.5 billion solar masses. M84 shows minimal ongoing star formation and possesses a relatively low number of globular clusters for its type.
M86 (NGC 4406) is a large elliptical or lenticular galaxy located in the heart of the Virgo Cluster, often grouped visually with M84. Discovered by Messier in 1781, it's notable for having the highest blueshift among Messier objects, indicating it's approaching the Milky Way at 244 km/s as it falls towards the Virgo Cluster's center. Evidence suggests M86 has interacted with nearby galaxies, potentially stripping gas from NGC 4438. (see below) and is currently undergoing ram-pressure stripping as it moves through the cluster's medium, leaving a long trail of hot X-ray emitting gas. The galaxy hosts a rich system of roughly 3,800 globular clusters and shows stellar streams in its halo, likely remnants of absorbed dwarf galaxies.
NGC 4435 is a barred lenticular galaxy interacting with NGC 4438. Its nucleus shows signs of a relatively young stellar population, possibly triggered by the recent interaction between the galaxies. While a tidal tail was suspected, it might be a foreground galactic cirrus.
Due to interactions, NGC 4438 is a highly distorted galaxy, classified as either lenticular or spiral. It shows signs of past starburst activity and has displaced its interstellar medium (gas and dust), likely due to tidal interaction with NGC 4435 and ram-pressure stripping as it rushes through the Virgo Cluster's medium.
While their interaction seems evident, recent findings also show filaments linking NGC 4438 to the giant elliptical galaxy M86, suggesting a complex history possibly involving interactions among all three galaxies (NGC 4435, NGC 4438, and M86) within the dense Virgo Cluster core. The exact energy source heating NGC 4438's nucleus (starburst or AGN) is still under investigation.
The remaining members of the chain MOVING THROUGH THE VIRGO CLUSTER showcase diverse characteristics:
NGC 4473, an elliptical/lenticular galaxy about 50 million light-years away, harbours a supermassive black hole of roughly 100 million solar masses and features two counter-rotating stellar disks in its inner regions, possibly formed from past gas accretion or mergers. It also possesses around 376 globular clusters, potentially accumulated through minor galactic mergers.
Nearby, NGC 4477, a barred lenticular galaxy classified as a Seyfert 2 type and located about 55 million light-years distant, displays a complex structure with a prominent bar within a large envelope. It features ring-like structures and diffuse arcs suggestive of an evolved double ring morphology.
Completing this trio, NGC 4458 is an elliptical galaxy around 54 million light-years away, known to be interacting with its neighbour NGC 4461. It features a distinct, edge-on nuclear disk estimated to be 6 billion years old, likely formed from a gas-rich merger, and also exhibits a counter-rotating core. NGC 4458 might host an even larger supermassive black hole (estimated ~200 million solar masses) and shows unusual metallicity, low in metals but rich in iron. William Herschel discovered all three galaxies in April 1784, key members of the Virgo Cluster.
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