Try out drawing on these streams with the Experiment platform - click here and select the Stellar Streams workflow. Experiment is external to Zooniverse. See this blog post for details.
Also, this project recently migrated onto Zooniverse’s new architecture. For details, see here.
FAQ
What are Stellar Streams?
Stellar streams are long, thin "streams" of stars orbiting a galaxy. They form when a much smaller galaxy passes too close to the larger galaxy and gets pulled apart by the larger galaxy’s gravity. The stars spill out of the smaller galaxy and end of flowing away from it. The flow looks somewhat like a stream, hence the name!
How do Streams Relate to Dark Matter?
The short answer: the shape of a stream is determined by the gravity of the galaxy and the dark matter. If you understand the stream's shape and the galaxy's mass then the missing piece is the dark matter!
The slightly longer answer is... Even if we couldn't see the Sun, from the orbit of the Earth we would still be able to tell the mass of the Sun. Add in measurements of the other planets and asteroids and we could even measure the sun's size and shape. We can do all of this by understanding how an objects orbit is determined by the sun's gravity. Similarly, by measuring the orbits of objects around galaxies we can measure gravity from the galaxy. Since we understand the normal matter in a galaxy, the rest of the gravity comes from the dark matter.
That doesn't sound too bad... Unfortunately the timescales necessary to observe the orbit of a star around a galaxy is longer than all of recorded history!
If we don't want to wait, what can we do? Instead of sitting around to measure an orbit of a single star, we can instead find many-star systems which together tell us about a single orbit. This is what makes stellar streams so useful. When the stars spill out of the small galaxy they end up basically following the orbit of that small galaxy around the larger one. So by measuring along a stream we get snapshots, millions of years apart, of the single orbit of the smaller galaxy.
From the orbit we can map the gravity. From there we can map the dark matter.
So the science connection between stellar streams and dark matter is: stream -> orbit -> gravity -> dark matter.
What Can We Learn About the Dark Matter?
So much! We're starting by learning about how it's distributed on large scales, aka it's "shape". Is it spherically symmetric like a football (aka soccer ball) or squashed like a rugby or American football? In what direction is it squashed? Does that point in the same direction as the galaxy? Is the dark matter aligned with the galaxy or off-centred? And so many more unanswered questions. Our theory of cosmology makes predictions for all questions.
Help us find the answers to better test our theories.
Tell us more about the data!
Images are taken from the Euclid Q1 data release. ESA's Euclid mission is designed to explore the composition and evolution of the dark Universe. The space telescope will create a great map of the large-scale structure of the Universe across space and time by observing billions of galaxies out to 10 billion light-years, across more than a third of the sky. Euclid will explore how the Universe has expanded and how structure has formed over cosmic history, revealing more about the role of gravity and the nature of dark energy and dark matter.
Find out more at https://www.esa.int/Science_Exploration/Space_Science/Euclid