He was a plasma physicist.
Hannes Olof Gosta Alfven won The Nobel Prize in Physics in 1970.
The Nobel Prize in Physics 1970 was divided equally between Hannes Olof Gosta Alfven for fundamental work and discoveries in magnetohydro- dynamics with fruitful applications in different parts of plasma physics and Louis Eugene Felix Neel for fundamental work and discoveries concerning antiferromagnetism and ferrimagnetism which have led to important applications in solid state physics.
The Nobel Prize in Physics in 1970 was awarded to Hannes Alfvén and Louis Néel. Hannes Alfvén received half of the prize for his work in magnetohydrodynamics and theories on plasma physics, while Louis Néel was awarded the other half for his discoveries regarding antiferromagnetism.
A broader answer would still be no. There is no consensus on what the so-called "dark matter" is.
A biologist is a specific type of scientist specializing in Biology. A scientist can be any type of scientist but their specialty is not specified.
Hannes Steinert has written: 'Hannes Stainert'
Hannes Schwarz has written: 'Hannes Schwarz'
The name for this type of scientist is a teuthologist
Hannes Kallio's birth name is Hannes Kalervo Backman.
Hannes Kuokkanen's birth name is Hannes August Kuokkanen.
A space scientist
Alfven wave