Galactic cannibals devour hapless neighbors, don’t pick up after themselves

NGC 5907, also known as the Splinter Galaxy, is surrounded by loop de loops of stars and dust either ripped from a companion galaxy in an act of galactic cannibalism or spewed when two galaxies merged. Click to supersize. Credit: Jay Gabany,  Blackbird Observatory

Four billion years ago and 40 million light years away, an act of galactic cannibalism was committed. No human eyes saw the smaller galaxy shredded and ripped apart by the gravitational might of the larger. No tears were shed when its remains were finally devoured, but clues of the catastrophe remain to this day.

The Splinter Galaxy, an 11th magnitude edge-on spiral, is located high in the June sky in the constellation Draco. You can star-hop to it with your telescope using the Big and Little Dippers and the detailed map below. Edasich is also known as Iota Draconis. Maps made with Stellarium

High in the northern sky in the constellation Draco the Dragon ghostly ribbons of stars and dust swirling about the edge-on spiral galaxy NGC 5907 are all that remains of its one-time companion. Don’t expect to see those ethereal streams in a typical telescope; only long time-exposures reveal the remaining clots of dust and streams of stars torn from the companion galaxy during the close encounter and likely merger. The gigantic loops extend for more than 150,000 light years from NGC 5907, nicknamed the Knife-Edge or Splinter Galaxy.

In this closeup view, NGC 5907 is just a short star-hop from Edasich. Field of view is about 3 degrees.

Astronomers call these rivers of stars tidal streams. They’re created by disruptive gravitational tides induced when two galaxies pass near or through one another. As the companion orbited through the Splinter’s disk, repeated encounters stripped it of most of its goodies – stars, dust clouds and even dark matter – and flung the material into multiple tidal streams. When nothing but the compact stellar core was left it presumably merged (was eaten) by NGC 5907 and lost its individuality forever.

This illustration shows a stage in the predicted merger between our galaxy and the neighboring Andromeda galaxy, as it will unfold over the next several billion years. The image represents Earth’s night sky in 3.75 billion years. Andromeda (left) fills the field of view and begins to distort the Milky Way with tidal pull. After some 6 billion years the two will merge into a single elliptical galaxy. Click for more details. Credit: NASA; ESA; Z. Levay and R. van der Marel, STScI; T. Hallas; and A. Mellinger

Or … it could have happened a different way when two equally mighty galaxies on a collision course yanked swirls of stellar debris from each other before their eventual merger into one serene spiral we see today. Here neither was the winner – two came together much as the Milky Way and Andromeda Galaxy will several billion years from now to meld into something altogether new.

Tidal streams of stars torn by gravitational tides exerted by the Milky Way on one of its small satellite galaxies the Sagittarius Dwarf. The dwarf’s core is shown to the right of  our galaxy’s disk. Credit: David R. Law, UCLA

As far as galactic cannibalism goes, we needn’t look any farther than our own Milky Way, which has been munching on the Sagittarius Dwarf Galaxy for at least the past billion years. Four separate whirls of stars peeling off above and below the plane of the Milky Way attest to our galaxy’s systematic preying on what was once a bright companion. Now half its contents are gone, dumped along the winding highway by an unrepentant galactic litter bug. Over time the dwarf and its contents will be fully absorbed by our galaxy with little left of its presence save a few stray globular clusters that once called it home.

2 Responses

  1. Aloha Astro Bob!

    GREAT article. This is exactly what I try to convey when I say how reading articles such as these, just how very small our solar system (let alone us humans, individually) really are in the “grand scheme of things”.

    All I can do is sit back and think, “WHOA MAN!” Most folks cannot grasp the concept of just how “small” we on Earth really are in “big picture”. I love reading things that blow my mind and this article was one of them. Great writing Bob!

    Aloha For Now!

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