Merging Galaxies

They make me think of two chambered nautiluses fighting in a dark sea, these space oddities. Actually, they are galaxies NGC 5426 and NGC 5427 in the Virgo constellation, which gravity has drawn so close together that they are interacting. Instead of nautilus tentacles, they are connected by a bridge of stars and gas, material pulled out from both.
I photographed them on the night of May 4-5 at the site called Lakeside, about 50 miles west of Salt Lake City and a few miles north of Delle, Tooele County. They may be a preview of what will happen as our Milky Way Galaxy and M-31, the great galaxy in Andromeda, begin to collide in 5 billion years.

[The colliding galaxies NGC 5426 and NGC 5427, a view I took in Tooele County the night of May 4-5, 2011. For a larger view, click HERE.]
Here’s an amusing error in the popular Starry Night Pro 6 software, which is a computerized planetarium and telescope-control program: “NGC 5426 + 27 is a planetary nebula, the last breath of a dying star.” No, the pair is not the remnant of a dying star.
But in another place the program correctly identifies NGC 5426 as a galaxy and notes, “Galaxies are vast stellar cities, containing anywhere from several million to several trillion stars.” It says the same about its twin sister, NGC 5427.
According to NASA’s Astronomy Picture of the Day for July 21, 2008, the galaxies, also dubbed Arp 271, stretch across about 130,000 light-years and are around 90 million light-years from Earth.
The galaxies are about equal size and are rotating in a clockwise direction as seen from here, reports a paper published in February 2004 in the journal Astronomy & Astrophysics. In my view, north is up; the galaxy NGC 5427 is toward the top and NGC 5426 is toward the south, or bottom of the picture. Based on motion studies, the paper says the lower left of NGC 5427 is turned slightly in our direction while the right side of NGC 5426 is tilted toward us.
From our perspective, adds the article, titled “The isolated interacting galaxy pair NGC 5426/27 (Arp 271)”, the southernmost galaxy is “in front” of the other. The article is copyright European Southern Observatory. The journal is part of Edition Diffusion Presse Sciences (EDP Sciences). Its authors — I. Fuentes-Carrera, M. Rosado, P. Amram, D. Dultzin-Hacyan, Cruz-Gonzlez, H. Salo, E. Laurikainen, A. Bernal, P. Ambrocio-Cruz and E. Le Coarer — are with institutions in Mexico, France and Finland.
Observing the pair in May 1997 with a telescope in San Pedro Mrtir, Mexico, that is nearly 83 inches in diameter, they found that the galaxies’ gas has some “non-circular motions,” the abstract notes. “We found a small bar-like structure in NGC 5426, a distorted velocity field for NGC 5427 and a bridge-like feature between both galaxies which seems to be associated with NGC 5426.”
The central bar structure was detected in NGC 5427, while an “incipient bar” — also called a “small, bar-like feature” was detected in NGC 5426. A bridge of stars connects both galaxies because of their interaction; one section seems to be an extension of an arm of NGC 5426, they add. Another section may be associated with a spiral arm of NGC 5427.
The star bridge is the set of tentacles stretching from the chambered nautiluses in my astrophoto.
When galaxies collide, new star-forming regions are created. Among other such sites, the tip of a spiral arm of NGC 5427 has a large area where “important star formation is going on,” says the report. This is the bright clump that stacks out farthest to the right of the upper galaxy in my image.
Even though rapid star formation is happening and will accelerate as the collision continues, the stars are so far apart in each galaxy that probably none will collide.
As the NASA caption for the Astronomy Picture of the Day explains, when galaxies of vastly different sizes collide, usually “a large galaxy eats a much smaller galaxy.”
However, in the case of NGC 5426/27, “the two galaxies are quite similar …. As the galaxies advance over the next tens of millions of years, their component stars are unlikely to collide, although new stars will form in the bunching of gas caused by gravitational tides.”
The distant pair has just begun its merging dance. Before it is finished, gigantic star trails will be flung about and parts of the galaxies will slam through one another. Eventually they will settle down as a single mash-up.
A simulation of galaxy collision by the Harvard-Smithsonian Center for Astrophysics shows how it happens. Click HERE to watch it.

Our Milky Way Galaxy has devoured smaller galaxies in the past and is gobbling one presently. Such absorption just adds to the Milky Way’s bulk and doesn’t change it fundamentally. But when the Milky Way merges with Andromeda, the outcome probably will be the creation of a new super-galaxy.
The Andromeda Way will be a celestial bully, maybe a tremendous elliptical galaxy with a blazing jet, like M-87.

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