Gaps in the star stream were discovered with the Gaia satellite. The LSST telescope must investigate them further.
Shortly after the Big Bang, 13.8 billion years ago, dark matter clumped together and attracted ordinary matter, which united into the first stars and galaxies.
That is the story of the birth of the Melkweg. Since then our galaxy has grown by attracting more matter and stars from the environment, such as from small clusters of stars.
The existence of dark matter has not been demonstrated because it does not emit light or other measurable radiation.
Dark matter holds stars together
But calculations show that the Milky Way must now contain six times as much dark matter as normal matter, otherwise it would have insufficient gravity to hold the stars together.
They would then fly in all directions.
By studying observations from the Gaia satellite, which has charted the position of more than a billion stars in the Milky Way and around it, Harvard and Princeton astronomers in the US discovered visible traces of dark matter.
Gaps in the star stream were discovered with the Gaia satellite. The LSST telescope must investigate them further.© Ken ikeda madsen & ESA & NASA
Far from the disk of the Milky Way, there are still remains of star clusters, which have been stretched into long star streams by the gravity of the Milky Way.
One of them, GD1, has holes, and measurements indicate that the current has passed through a particularly dense lump of dark matter.
This confirms the theory that in and around the Milky Way there are areas with a high density of dark matter.
Dark matter makes holes
Outside the Milky Way there are star clusters that are stretched into long streams by the gravity of the galaxy. Holes in those streams (red arrow) indicate that the stars have passed large 'clogs' of dark matter.
Before the meeting ...
... with the dark matter, the flow is smooth. The gravity of the Milky Way has pulled the stars out of the cluster.
During the meeting ...
... with a particularly dense lump of dark matter, the stream necessarily forms two tails around the meeting point.
After the meeting ...
... the tails come closer together again and two compacted areas of stars with a gap in between arise.