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Astrophysicists describe new way that stars form

Czech scientists document how a collision of giant interstellar bubbles in the Milky Way gives rise to new suns.

The Milky Way as seen from earth.

Two astrophysicists from Masaryk University and the Czech Academy of Sciences have discovered a new way in which stars can form in space. Their work involves observing “interstellar bubbles” that form close to massive and highly luminous stars and they have recently noticed a collision of two such bubbles that gave rise to new stars at the site of the collision. Their work has been published in the prestigious journal Astronomy & Astrophysics.

The proportions of the two pairs of interstellar bubbles observed by the two women are astounding, reaching up to 200 light years across.

“A collision of such giant bodies leads to the formation of new stars at the site of the collision. These, in turn, cause the formation of a new bubble, which is much younger and consequently much smaller than the original colliding bubbles,” explains Lenka Zychová from the Department of Theoretical Physics and Astrophysics at the MU Faculty of Science.

Massive and highly luminous stars ionize the surrounding air, which consists mostly of hydrogen. The hydrogen expands due to the increase in temperature, giving rise to interstellar bubbles. As Zychová describes, “The hot gas bubble then gradually picks up the surrounding cooler gas, creating a shell of dense gas around the inner, warmer part of the bubble.”

One of the observed pairs of colliding bubbles. At the site of the collision, you can see a bright area: this is where the new star formation takes place. The picture was taken in a radio continuum, showing the luminous ionized hydrogen.

One of the observed pairs of colliding bubbles. At the site of the collision, you can see a bright area: this is where the new star formation takes place. The picture was taken in a radio continuum, showing the luminous ionized hydrogen.

Together with her colleague Soňa Ehlerová from the Czech Academy of Sciences, Zychová observes bubbles using electromagnetic radiation emitted by neutral hydrogen. In this way, they were able to identify individual bubbles in our Milky Way galaxy, calculate the distances, and thus discover the collision.

The reason why new stars can form in the shells of interstellar bubbles is that as they expand, these bubbles pick up enormous amounts of interstellar material, several tens of thousands times the mass of our Sun. This leads to a gravitational collapse, creating star seeds. Another reason is that star seeds are present in the gas cloud where the bubble expands. As Zychová adds, “Moreover, their collision means there is pressure on the collected interstellar matter from two directions, which significantly increases the likelihood of star formation.”