Young stars push dark matter
ASTRONOMY We know almost nothing about the dark matter of the universe — where it comes from, what it consists of, the qualities it has. We only know that it exists because we can see that gravity from dark matter influences visible matter. But now at last we are learning something new.
Astronomers have wondered why the dark matter of a galaxy is not distributed in the way that computer models predict. Dark matter should unite into dense, ball-shaped structures at the centre of a galaxy, and in looser clouds further out. But that is not the case. In many galaxies, the dark matter is more common on the outskirts than in the interior regions. A team of astrophysicists has found an explanation: a galaxy’s age determines the distribution of dark matter. The scientists studied the distribution of dark matter in 16 dwarf galaxies, which they divided into two categories. The first contained old galaxies, in which star formation stopped billions of years ago. The other involved younger galaxies in which star formation stopped recently or is still going on.
The scientists discovered that there was a marked difference between the distribution of dark matter in the two categories. When a galaxy is young, many new stars are formed, particularly in the inner regions. The intense radiation and solar wind of particles from the young stars blow dark matter away from the centre. Once the galaxy has grown older and star formation stops, the dark matter collects in the interior of the galaxy again, just as the computer models predict. If this explanation proves to be correct, we will know at least that dark matter is influenced by star radiation and solar wind.