Date: April 3, 2011

Title: Exótico Cielo Profundo: Through Markarian’s Chain

Podcaster: Julieta De Simone Shecre

Organization: Sur Astronómico – www.surastronomico.com

Description: An observational proposal in which we will be moving through a chain of galaxies, by Virgo and the border of Coma Berenices, studying visual characteristics, astropphysic data and some history of selected objects. Different instruments will offer us different perspectives and details. We will notice different aspects and even be able to recognize a Face galaxterism.

Bio: Sur Astronómico is a website in Spanish managed by Enzo De Bernardini. The Exótico Cielo Profundo (Exotic Deep Sky) section was created by Rodolfo Ferraiuolo and Enzo De Bernardini and it is devoted to the visual observation of select objects from the deep sky. Having started in January 2008 and having received great approval from the amateur public, getting a lot of comments in the forum of the group, the periodic articles of the section were shaped to be written on a book.

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Transcript:

Hello, and welcome to the Sur Astronómico edition of the 365 days of astronomy podcast. I am Julieta De Simone Shecre and this is “Through Markarian’s Chain”.
In December 1961, the Armenian astronomer Benjamin Markarian published a paper entitled Physical Chain of Galaxies in the Virgo Cluster and its Dynamic Instability in The Astronomical Journal. He introduced there a study of the region occupied by 8 galaxies situated in the central area of the gigantic Virgo Cluster, joined in a curved chain of 1.5 degrees of stretch and with apparent physical connection. Markarian noticed that the chain was part of a circle centered very closely to a couple of galaxies of 11th magnitude, recorded in the catalogue as NGC 4298 and NGC 4302 and that it was quite improbable for it to be a formation made by chance. This idea has always been argued and it is nowadays believed that the whole of this system is only created by the effect of projection, without real gravitational connection.

As time went by, this group was named Markarian’s chain and became an attractive target for many amateur astronomers, and this is the reason why we chose it. Two of these galaxies are part of the well-known Charles Messier’s catalogue, with numbers 84 and 86, and the other 6 are part of the New General Catalogue of Nebulae and Clusters of Stars, or NGC, by J. L. Dreyer, with numbers 4435, 4438, 4458, 4461, 4473 and 4477.

These eight galaxies, spiral or elliptical, have a brightness of between 9th and 12th magnitude; two of them, NGC 4473 and NGC 4477, are situated within the boundaries of the constellation Coma Berenices, and the other six in Virgo. By observing them with a 4-inch refracting telescope and low magnification all of them will appear within the same field of view, contrasting with stars of varying brightness and offering a gratifying display.

Now we will only focus upon the two Messier galaxies, the most well-known galaxies of the group.

We will begin with the elliptical galaxy M84, situated to the west of the chain. In order to spot it, we will put ourselves halfway between the stars beta Leonis (Denebola) and epsilon Virginis (Vindemiatrix). Then, with 10 x 15 binoculars, we will find in Coma Berenices the white star of 5.1 magnitude, 6 Comae Berenices, to the north-east of the field. This star is 6.5 degrees to the east of Denebola.

From 6 Comae Berenices, we will look for the orange star of 7th magnitude, BU 27, 1.4 degrees to the south-east. Finally, from this star, we repeat the same distance, following the line to the south-east, and we will find the galaxy at 1.5 degrees.

M84 was discovered by Charles Messier in the fruitful night of 18th March 1781, when he also discovered M86 and many other galaxies of the area. It is a bright galaxy brimful of questions, such as its doubtful morphology which could be a massive giant elliptic E1, or a large lenticular of class S0. It shows a magnitude of 9.4 and surface brightness of 12.5. Its angular size is of 6.5 minutes x 5.6 minutes and Heliocentric Radial Velocity estimated in 1060 km/s, which might get us closer to the datum of its distance to the sun, of about 52 million light years. Its real diameter is of 110000 light years and it is presented with a position angle of 135 degrees.

It is a radiogalaxy with an active fast-rotation nucleus. This fact confirms the studies carried out by the end of the 1990’s with the Hubble Space Telescope, which yielded more data that provided evidence of the presence of a supermassive black hole in its center. Reasserting this, two jets of hot gas emerging from the nucleus were also found. Apart from that, strange and large dark stripes crossing the halo of the galaxy have been found. In this case, it could be residual material of disturbances produced by a close passing with massive galaxy M87, about one thousand million years ago.

This particular galaxy is made up by numerous evolved stars which give it a general yellowish hue, and about 1800 globular clusters have been identified around it.

Three supernovae of 13th and 14th magnitudes, one of them controversial, have been found in this galaxy.

In a 3-inch refracting as well as in a 4.5 inch reflector, its appearance will be interesting, provided that we are away from luminous pollution of cities. We will observe it quite circular and bright with those telescopes, as an evident nebular object, with a 1-minute diameter. With an 8-inch telescope, it will be oval-rounded, directed from north-west to south-east. With a halo of 2 minutes x 1.6 minutes, blur borders, increasing the brightness towards the bright and condensed center, where a core with a stellar aspect appears. By using medium magnification, the disk increases its size and the core expands itself, but the borders do not improve their definition, and it smoothly integrates into the field. With an 11-inch, it will be seen of 3.5 minutes x 2.8 minutes, very dense and with strong gradient. Its core is not stellar anymore, and a faint star of 14th magnitude appears, overlapped with the halo, very close to the west-south-west border. This star is the variable NSV 5605.

Outstandingly, near M84, there are many quasars approachable at large apertures, such as the one catalogued by the Large Bright Quasar Survey, LBQS 1222+130, which is 4 minutes to the west, and of magnitude 18.7.

Highly close to M84, only 17 minutes to the east, there is M86, another massive galaxy which also has a controversial classification, between lenticular and elliptical, class S0 (3)/e3. I could possibly be a giant elliptical galaxy, physically interacting with M84.

Recent studies, trying to find an explanation to the extremely high velocity, of about 1300 km/s. with which it moves towards our direction, as if it were escaping from the center of the dynamic cluster, testify that it could be because of a gravitational tug given by the giant galaxy M87, with which it will have a close encounter in the future. This fast movement produces a lot of pressure, induced by the intergalactic medium, altering the structure of the galaxy and enlarging it to the north-west, towards the opposite side of M87. The effect is easily spotted in photographs taken by large telescopes.

Some dwarf galaxies have been detected close to M86, one of 17th magnitude, 1.2 minutes to the east, catalogued as PGC 40659 (which might be seen with a 14-inch reflecting telescope as its surface brightness increases to 14.1). In addition, almost 400 globular clusters have been found in its halo. The said exciting galaxy has a position angle of 130 degrees, magnitude of 9.28, surface brightness of 13.2 and apparent size of 8.9 minutes x 5.8 minutes.

It is also visible with 10 x 50 binoculars from a rural sky, seen with M84 as two small faint tailless comets. Interesting with small apertures, in a 5-inch Schmidt-Cassegrain telescope it appears as oval and bright towards the center, with a stellar core of 11th magnitude and a halo of 2 minutes x 1.5 minutes, stretched from south-east to north-west. With an 8-inch, its halo will increase its size up to 3 minutes x 2.5 minutes. Its borders will be dim, as translucent, integrating with the field, and its core will be small and intense, appearing as stellar. With an 11-inch, the shape will lengthen more and it will be clearly bigger than M84, but with lower surface brightness. Its size will be of 4.2 minutes x 3.2 minutes and its brightness will increase towards the center, where we will find a small almost-stellar bright nucleus. It is actually one of the most beautiful galaxies in the chain.

These two first galaxies, together with three others, make up a face-shaped asterism, with a diameter of about 30 minutes, which we have lovingly named the Face galaxterism; being M84 and M86 its big eyes, NGC 4387 the small nose, NGC 4388 the mouth and NGC 4402 an eyebrow over M86.

This concludes our Sur Astronómico episode. Sur Astronómico is a website in Spanish managed by Enzo De Bernardini. The Exótico Cielo Profundo (Exotic Deep Sky) section was created by Rodolfo Ferraiuolo and Enzo De Bernardini and it is devoted to the visual observation of select objects from the deep sky. For a further selection of interesting deep sky objects by Enzo De Bernardini and Rodolfo Ferraiuolo please visit the Exotic Deep Sky section at www.surastronomico.com.

End of podcast:

365 Days of Astronomy
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