SYDNEY: The Milky Way is encircled by streams of stars in shapes resembling a “jumble of pasta” according to scientists examining data from the biggest survey ever made of our galaxy.

The sky was mapped by the Sloan Extension for Galactic Understanding and Exploration (SEGUE) survey, which will ultimately create a detailed 3-dimensional map of the galaxy, featuring 240,000 stars.

Ripped apart

The survey has revealed new details of streams of stars that wrap around our galaxy. Astronomers found 14 distinct stream structures, 11 of them previously unknown. Many are believed to be dwarf galaxies on the margins of the Milky Way that were ripped apart by the gravity of their larger companion.

Kevin Schlaufman, lead astrophysicist behind the work at the University of California, Santa Cruz, said the new discoveries were just a small fraction of the mysterious structures waiting to be found within the Milky Way’s more than 100 billion stars.

"Even with SEGUE, we are still only mapping a small fraction of the Galaxy, so 14 streams in our data implies a huge number when we extrapolate to the rest of the Milky Way," he said.

The SEGUE project is part of the ambitious Sloan Digital Sky Survey (SDSS), being conducted by the 2.5-metre telescope at the Apache Point Observatory in New Mexico, USA. Schlaufman presented the results of the project earlier this month at the SDSS symposium in Chicago, Illinois.

Stretched like spaghetti

In another presentation at the symposium, astronomer Kathryn Johnston of Columbia University in New York City, described her theoretical models of the Milky Way's stellar halo as "a jumble of pasta".

She said that the stellar streams represent dwarf galaxies stretched out like spaghetti by the gravitational tides of the Milky Way.

"In the centre of the galaxy, these stellar strands crowd together and you just see a smooth mix of stars. But as you look further away you can start to pick out individual strands, as well as features more akin to pasta shells that come from dwarfs that were on more elongated orbits,” said Johnston.

Related research, led by Jelte de Jong from the Max Planck Institute for Astronomy in Heidelberg, Germany, was presented at an International Astronomical Union Symposium, in Copenhagen, Denmark in June.

His team used the SEGUE data to examine a stream of stars called the Low Latitude Stream (also known as the Monoceros Ring), which circles the Milky Way just outside the plane of the galactic disk. The stream is thought to be trailing from a dense lump of stars near the constellation Canis Major, which was once a dwarf galaxy.

Crucial constraints

The scientists plotted the relationship between stars’ absolute magnitude, luminosity, classification, and effective temperature. These plots can be used to distinguish between different models of the Low Latitude Stream, and help to shed light on the nature of the system, they say.

The results – also published on the Arxiv physics website – provide “crucial constraints” for theoretical models of the evolution of these star streams, the experts said.

Geraint Lewis an astrophysicist from the University of Sydney in Australia, who was not involved in the survey, said the research represents the “first step in what’s going to come out of the SEGUE survey”.

“It seems a bit weird that we’ve been looking at the Milky Way for 100 years and we still don’t know how the stars are distributed,” he added. “What’s been shown now is that it is not a smooth galaxy; there are lots of lumps and bumps hanging around.”