Milky Way seen to be a galactic cannibal

April 7, 2008

A stream of debris across the sky is the result of intergalactic cannibalism, researchers from The Australian National University conclude, and it is the not the first time our galaxy has had one of its neighbours for breakfast.

Astronomers from the Research School of Astronomy and Astrophysics at ANU have identified a huge swathe of debris that has been wrenched from a neighbouring galaxy to our Milky Way. Their findings are published in the April issue of the Astrophysical Journal.

“The stars we have found have been stripped from the Sagittarius dwarf galaxy,” said lead author Dr Stefan Keller. “The Sagittarius dwarf is a cosmic lightweight weighing 10,000 times less than our Milky Way. It has ventured too close to our galaxy and is now getting stretched out and torn apart.”

The pieces of debris from the Sagittarius dwarf sweep across the entire sky but are buried among the countless foreground Milky Way stars. In order to trace the stream, Dr Keller and his colleagues – Professor Gary Da Costa, Professor Brian Schmidt and PhD students Simon Murphy and Sayuri Prior – sifted through over 15,000 images of the sky looking for a very rare type of pulsating star called an RR Lyrae variable.

These stars change their brightness as they get bigger and smaller. “The great thing about RR Lyraes is that they all have the same intrinsic brightness so each time we found one we were able to derive an accurate distance to the star,” Dr Keller said.

The team was able to trace the extent of the debris to over 150,000 light years, further than previous studies. “The new debris patches are particularly exciting as they offer us the best chance to measure the mass and shape of the Milky Way,” Dr Keller said. “We know that the Milky Way contains roughly ten times more mass than we can see, suggesting the presence of mysterious dark matter. We can’t see the dark matter itself but our study can see the effects of its gravitational pull on the Sagittarius dwarf.”

It’s currently thought that the Milky Way has had a steady diet of smaller galaxies during its lifetime. “Early in the life of the Milky Way galaxy mergers such as this occurred on a much more frequent basis, contributing substantially to the mass of the Milky Way,” Dr Keller said. “The devouring of the Sagittarius dwarf is like the after dinner mint on top of what has been an extensive banquet for the Milky Way.”

The research is based on data taken with the Great Melbourne Telescope at the ANU Mt Stromlo Observatory.

Source: Australian National University

Explore further: Globular clusters on a plane

Related Stories

Globular clusters on a plane

September 23, 2011

Globular clusters are generally some of the oldest structures in our galaxy. Many of the most famous ones formed around the same time as our galaxy, some 13 billion years ago. However, some are distinctly younger. While many ...

Recommended for you

Where is the universe's missing matter?

April 19, 2018

Astronomers using ESA's XMM-Newton space observatory have probed the gas-filled haloes around galaxies in a quest to find 'missing' matter thought to reside there, but have come up empty-handed – so where is it?

New research seeks to optimize space travel efficiency

April 18, 2018

Sending a human into space and doing it efficiently presents a galaxy of challenges. Koki Ho, University of Illinois assistant professor in the Department of Aerospace Engineering, and his graduate students, Hao Chen and ...

2 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

nilbud
not rated yet Apr 07, 2008
AARS at ANU, really, wow.
brant
not rated yet Apr 08, 2008
Gives their speculations more credibility......

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.