快猫短视频

ASTRONOMERS in the US have mapped a cluster of invisible galaxies for the
first time. They spotted the cluster by analysing the effect its gravity had on
the light from more distant galaxies. The discovery opens a new window on the
Universe, because a large part of its mass may be 鈥渄ark matter鈥�.

Last year, a team of European astronomers caught a glimpse of a dark galaxy
as it distorted light from the more distant bright ones they were imaging. But
astronomers have never been able to confirm such sightings or work out what the
galaxies were like. 鈥淚t was a true mass detection but difficult to confirm,鈥�
admits Peter Schneider of the University of Bonn, a member of the team.

Now Tony Tyson, David Wittman and colleagues at Lucent Technologies鈥� Bell
Labs in New Jersey have made a similar discovery, which they later confirmed by
picking up very faint light from the cluster.

They looked at 31,000 distant galaxies within a square patch of sky half a
degree across using the Blanco 4-metre telescope at the Cerro Tololo
Inter-American Observatory in Chile. They then entered data on the apparent
shapes of the galaxies into a computer and combined them to produce an average
shape.

They reasoned that because most galaxies are elliptical, the average of many
galaxies with different orientations should be circular. In fact the average was
an ellipse, indicating that dark matter in front of the galaxies was distorting
the images. Analysing what sort of bodies would produce such distortion, the
team was able to construct a three-dimensional map of the positions of 26 dark
galaxies in a cluster.

Because the Universe is expanding, light from distant objects gets stretched,
shifting it to redder wavelengths. By comparing the 鈥渞ed shifts鈥濃�攚hich are
proportional to distance鈥攐f the background galaxies to the amount the dark
cluster distorts their light, Wittman says he was able to estimate the distance
to the dark cluster. At the moment his claim is controversial. 鈥淚 don鈥檛 think
you can get the red shift using [such] data,鈥� says Schneider.

But if the team is right, astronomers may soon be able to produce 3D maps of
truly dark galaxies that cannot be seen any other way. Tyson believes the only
way to test current theories about dark matter is to study such galaxies.
鈥淎stronomers need no longer be biased towards what glows in the dark,鈥� he says.