Collision of interstellar bubbles helps star formation

Brno, 24 November 2016

Astrophysicists from Masaryk University and the Academy of Science found colliding interstellar bubbles inside our galaxy. It turned out that due to the collision of these giant objects with a diameter of 200 light years new star formation is held at the point of collision. These newly formed stars then create another substantially younger bubble and therefore, in comparison with colliding bubbles much smaller. Work contributes to understanding the star formation in the universe as it proposes a way how thanks to the collision of two bubbles new stars can form.

Lenka Zychová from the Departement of Theoretical Physics and Astrophysics, Masaryk University, together with Soňa Ehlerová from the Astronomical Institute of the Czech Academy of Science published work dealing with the collision of interstellar bubbles in the prestigious journal Astronomy and Astrophysics. Their research of interstellar medium in a particular area of the sky revealed two pairs of interstellar bubbles, which age is several million years and an average diameter of 200 light years. These bubbles collide and produce new star formation at the point of the collision. These newborn stars blow other gas bubbles, whose age is only a few hundred thousand years (vs. several million years of the larger bubbles).

Interstellar bubbles are formed around very massive and luminous stars. These stars can ionize the surrounding gas, consisting mostly of hydrogen, which as a result of warming expands into its surroundings. Gradually during its development bubble of hot gas collects surrounding cooler gas and creates a dense gas envelope that encloses the inner warmer parts of a bubble. Most of previous works dealing with interstellar bubbles were done in the infrared observations, which emit dust granules, often located in the walls of bubbles, or observing dense and cold molecular clouds around these bubbles. Research and innovation of Zychová and Ehlerová is studying bubbles in the 21 cm line, which is emitted by atomic hydrogen. They managed to identify individual bubbles, calculate their distance and thus discover their collision.

The envelopes of interstellar bubbles may form stars. The first reason is that bubbles by their expansion gain vast amounts of interstellar material, with masses up to several tens of thousands of solar masses, which then gravitationally collapse, creating protostars (mechanism so-called "Collect and collapse"). The second reason is the pre-existence of clumps in a gas cloud, in which the bubble expands. Ehlerová and Zychová propose, based on the discovery of star formation at the site of the collision of two interstellar bubbles, another possible way of star formation, which is basically a more intense form of the already mentioned "collect and collapse" scenario. Due to the collision of bubbles the collected interstellar medium was compresses from two directions and significantly support the possibility of star formation.

You can find more information in the published paper: Colliding interstellar bubbles.

Contacts: Mgr. Lenka Zychová: zychova@physics.muni.cz, RNDr. Soňa Ehlerová, Ph.D.: sona@ig.cas.cz

Mgr. Lenka Zychová, zychova@physics.muni.cz