Milky way sidelined in galactic tug of war

Sep 29, 2010
This plot shows the simulated gas distribution of the Magellanic System resulting from the tidal encounter between the Large Magellanic Cloud and Small Magellanic Cloud as they orbit our home Milky Way Galaxy. The entire sky is plotted in galactocentric coordinates of longitude and latitude. The Magellanic Stream is the pronounced tail of material that stretches 150 degrees across the southern sky. The solid line shows the calculated path of the LMC and the dotted line is the path of the SMC. The color range from dark to light shows the density (lower to higher) of the hydrogen gas making up the Magellanic Stream and the Bridge that connects the two dwarf galaxies. Credit: Plot by G. Besla, Milky Way background image by Axel Mellinger (used with permission)

(PhysOrg.com) -- The Magellanic Stream is an arc of hydrogen gas spanning more than 100 degrees of the sky as it trails behind the Milky Way's neighbor galaxies, the Large and Small Magellanic Clouds. Our home galaxy, the Milky Way, has long been thought to be the dominant gravitational force in forming the Stream by pulling gas from the Clouds. A new computer simulation by Gurtina Besla (Harvard-Smithsonian Center for Astrophysics) and her colleagues now shows, however, that the Magellanic Stream resulted from a past close encounter between these dwarf galaxies rather than effects of the Milky Way.

"The traditional models required the Magellanic Clouds to complete an orbit about the Milky Way in less than 2 billion years in order for the Stream to form," says Besla. Other work by Besla and her colleagues, and measurements from the by colleague Nitya Kallivaylil, rule out such an orbit, however, suggesting the Magellanic Clouds are new arrivals and not long-time satellites of the Milky Way.

This creates a problem: How can the Stream have formed without a complete orbit about the Milky Way?

To address this, Besla and her team set up a simulation assuming the Clouds were a stable on their first passage about the Milky Way in order to show how the Stream could form without relying on a close encounter with the Milky Way.

The team postulated that the Magellanic Stream and Bridge are similar to bridge and tail structures seen in other interacting galaxies and, importantly, formed before the Clouds were captured by the Milky Way.

"While the Clouds didn't actually collide," says Besla, "they came close enough that the Large Cloud pulled large amounts of away from the Small Cloud. This tidal interaction gave rise to the Bridge we see between the Clouds, as well as the Stream."

"We believe our model illustrates that dwarf-dwarf galaxy tidal interactions are a powerful mechanism to change the shape of without the need for repeated interactions with a massive host galaxy like the Milky Way."

While the may not have drawn the Stream material out of the Clouds, the Milky Way's gravity now shapes the orbit of the Clouds and thereby controls the appearance of the tail.

"We can tell this from the line-of-sight velocities and spatial location of the tail observed in the Stream today," says team member Lars Hernquist of the Center.

Explore further: Can astronomy explain the biblical Star of Bethlehem?

More information: The paper describing this work has been accepted for publication in the October 1 issue of the Astrophysical Journal Letters and is available online at arxiv.org/abs/1008.2210v1

Related Stories

Giant intergalactic gas stream longer than thought

Jan 04, 2010

A giant stream of gas flowing from neighbor galaxies around our own Milky Way is much longer and older than previously thought, astronomers have discovered. The new revelations provide a fresh insight on what started the ...

Cosmic Dance Helps Galaxies Lose Weight

Jul 29, 2009

(PhysOrg.com) -- A study published this week in the journal Nature offers an explanation for the origin of dwarf spheroidal galaxies. The research may settle an outstanding puzzle in unders ...

No stars in the clouds

Jan 10, 2006

A team of astronomers from the University of Pittsburgh and the Universit√§ts-Sternwarte M√ľnchen in Munich, Germany, announced today in a paper presented at the meeting of the American Astronomical Society in Washington, ...

Origins of the Milky Way

Mar 19, 2010

(PhysOrg.com) -- According to current astronomical models, the Milky Way and other large galaxies formed over billions of years in a process that involved interactions between smaller galaxies, and in particular ...

New Hydrogen Clouds in the M81 Group of Galaxies

Jan 10, 2008

A composite radio-optical image shows five new clouds of hydrogen gas discovered using the National Science Foundation's Robert C. Byrd Green Bank Telescope (GBT). The spiral galaxy M81 and its satellite, ...

Chandra Peers at Cosmic Super Bubbles

Aug 31, 2007

Using the Chandra X-ray Observatory, astronomers explored a particular region of clouds and gas where stars are forming in one of the Milky Way's closest galactic neighbors.

Recommended for you

Can astronomy explain the biblical Star of Bethlehem?

Dec 24, 2014

Bright stars top Christmas trees in Christian homes around much of the world. The faithful sing about the Star of Wonder that guided the wise men to a manger in the little town of Bethlehem, where Jesus was ...

Hubbles spies the beautiful galaxy IC 335

Dec 24, 2014

This new NASA/ESA Hubble Space Telescope image shows the galaxy IC 335 in front of a backdrop of distant galaxies. IC 335 is part of a galaxy group containing three other galaxies, and located in the Fornax ...

Image: Multicoloured view of supernova remnant

Dec 22, 2014

Most celestial events unfold over thousands of years or more, making it impossible to follow their evolution on human timescales. Supernovas are notable exceptions, the powerful stellar explosions that make ...

Ultra-luminous X-ray sources in starburst galaxies

Dec 22, 2014

Ultra-luminous X-ray sources (ULXs) are point sources in the sky that are so bright in X-rays that each emits more radiation than a million suns emit at all wavelengths. ULXs are rare. Most galaxies (including ...

When a bright light fades

Dec 22, 2014

Astronomer Charles Telesco is primarily interested in the creation of planets and stars. So, when the University of Florida's giant telescope was pointed at a star undergoing a magnificent and explosive death, ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.