The Milky Way, the galaxy in which we live,
has only half the mass it was previously thought to have, scientists said
Tuesday in Germany after calculating the orbit speeds of 2,400 stars.
The galaxy turns out to be a comparative lightweight in the universe,
with a mass of only about 1,000 billion times the mass of our sun.
The finding was disclosed by the Max Planck Astronomy Institute in Heidelberg,
Germany and has been posted on the internet.
The calculations were led by Xiang-Xiang Xue, who is a a PhD student in
Heidelberg. She studied how much gravitational pull the galaxy and its dark
matter must have to stop outer stars of the Milky Way whirling off into space.
"The galaxy turns out to have less mass than we expected," she said.
"There's a lot less dark matter than supposed."
The same day, other astronomers in Germany who devised a way to hook up two
powerful telescopes in stereo said they had observed for the first time the
details of a star outside our Milky Way.
They trained the two telescopes on a red supergiant named WOH G64 in the Large
Magellanic Cloud, a neighbouring galaxy. WOH is about 2,000 times larger than
the sun and is 163,000 light years away.
Keiichi Ohnaka of the Max Planck Radio-Astronomy Institute in Bonn led the
research.
He and his team worked with the European Southern Observatory (ESO) in
Garching, a suburb of Munich, remotely using the ESO telescope complex, which
is built on a desert mountain in Chile.
They used two 8-metre-reflector scopes to create a virtual 60- metre telescope.
Normally a distant star only appears as a point of light. But the observations
made visible how the ageing star was blowing much of its substance into space. It
has lost 40 per cent of its original mass already, developing a shroud of dust
around it.
An explosion as a supernova is inevitable.
The article about WOH appears in Astronomy & Astrophysics.
Xue's article is set to be published this autumn in the
Astrophysical Journal, dpa
reported.