6 January 2009

Milky Way faster and heavier than thought

Agence France-Presse
The Milky Way is spinning much faster and has 50 per cent more mass than previously believed, increasing the chance of a collision with another galaxy, say astronomers.
Milky Way

Spinning top: An artist's impression of the Milky Way showing the approximate position of our Solar System. Credit: NASA/JPL-Caltech/R. Hurt

WASHINGTON DC: The Milky Way is spinning much faster and has 50 per cent more mass than previously believed, increasing the chance of a collision with another galaxy, say astronomers.

An international team of researchers have used ten telescopes spread out between Hawaii, the Caribbean and the northeastern United States to determine that the Milky Way is rotating at a speed of 161,000 km/h faster than previously thought.

Gravitational pull

That increase in speed boosts the Milky Way’s mass by 50 per cent, said Mark Reid, of the Harvard-Smithsonian Centre for Astrophysics, in research presented at the American Astronomical Society meeting this week in Long Beach, California.

“No longer will we think of the Milky Way as the little sister of the Andromeda Galaxy,” he said.

The larger mass, however, also means that the galaxy has a greater gravitational pull, which heightens the likelihood of collisions with the Andromeda galaxy or smaller nearby galaxies, Reid said.

The Earth’s Solar System is located some 28,000 light years from the centre of the Milky Way. At that distance, the new measurements show that the galaxy is rotating at a speed of 965,600 km/h, compared to previous estimates of 804,672 km/h, the astronomers report.

The new observations from the network of radio telescopes is “producing highly-accurate direct measurements of distances and motions,” said Karl Menten of the Max Planck Institute for Radio Astronomy in Germany, a member of the team.

Difficult to determine

“These measurements use the traditional surveyor’s method of triangulation and do not depend on any assumptions based on other properties, such as brightness,” Menten said. The direct measurements “are revising our understanding of the structure and motions of our Galaxy.”

It is difficult to determine the structure of the Milky Way because the Earth is inside it.

“For other galaxies, we can simply look at them and see their structure, but we can’t do this to get an overall image of the Milky Way,” added Menten. “We have to deduce its structure by measuring and mapping.”

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