An international team of astronomers using the NASA/ESA Hubble Space Telescope has discovered a ghostly ring of dark matter
formed long ago during a colossal collision between two galaxy clusters.
This is the first time that dark matter has been found with a distribution that differs radically from the distribution of ordinary matter.
This is the Hubblecast!
News and Images from the NASA/ESA Hubble Space Telescope. Travelling through time and space with our host Doctor J a.k.a. Dr Joe Liske.
Hello and welcome to the Hubblecast!
Scientists reckon that most of the matter in the Universe is something called “dark matter”, an unknown type of matter that neither emits nor reflects light.
But does dark matter really exist? Can scientists prove it? The NASA/ESA Hubble Space Telescope is helping to answer this question.
In 2004 an international team of astronomers pointed Hubble towards the constellation of Pisces, the Fish,
to observe the galaxy cluster that goes by the telephone number of CL0024+17
and which is located 5 billion light-years away from Earth.
Now Hubble’s Advanced Camera for Surveys produced a stunning image of this cluster.
The galaxies in the cluster are here seen in yellow.
Analysing the image over the last couple of years, the team discovered a ring of dark matter – seen here in blue -
and realised that the position of this ring did not match at all the position of the hot gas and the galaxies in the cluster.
The ring itself is 2.6 million light-years across.
Now this is the first time that dark matter’s been found with a distribution that is so radically different from the distribution of the ordinary matter.
This remarkable finding is attributed to the collision of the cluster with another cluster between 1 to 2 billion years ago.
The team's computer simulations show – here seen from the side - that when the two clusters smashed together,
the dark matter fell to the centre of the combined cluster and bounced back out.
In reality the collision occurred along our line of sight, so that we have a head-on view of it.
From this perspective, the dark-matter structure looks like a ring, just as the new analysis shows.
So how did astronomers spot the ring of dark matter?
Well, tracing dark matter is not an easy task.
The reason is of course that dark matter does not emit or reflect any light.
The most direct way of detecting its influence is to study the way its gravity deflects light.
Now to do this, astronomers study the faint light from galaxies that lie behind the cluster
and whose light gets distorted and smeared into arcs and streaks by the gravity of the dark matter in the foreground cluster.
Now this powerful trick is called gravitational lensing.
To illustrate this, imagine that I am the background object being lensed by a massive foreground cluster.
So by mapping the distorted light, astronomers can deduce the mass of the cluster, and they can trace the distribution of the dark matter within the cluster.
This amazing image shows us some spectacular examples of faint background galaxies that have had their light bent by the cluster’s strong gravitation
field. One of them, located about two times farther away than the yellow cluster galaxies in the foreground,
has been multiply imaged into five separate arc-shaped components.
Hubble’s high resolution can even show the details within this background galaxy.
The ring's discovery is among the strongest evidence that dark matter actually exists and it increases confidence in our current theory of gravity.
This is Dr J signing off for the Hubblecast.
Once again nature has surprised us beyond our wildest imagination …
Hubblecast is produced by ESA/Hubble at the European Southern Observatory in Germany.
The Hubble mission is a project of international cooperation between NASA and the European Space Agency.