Galaxies stop neighbors from growing by stealing gas from their hearts
Massive galaxies may be siphoning off star-forming material from the very hearts of smaller satellite galaxies, according to the results of a newly published study. The interaction causes the smaller cosmic structures to stagnate and essentially cease evolving, as their larger cousins continue to grow.
In every ecosystem on Earth there is a food chain, which generally involves larger creatures preying on smaller, more helpless animals. In a way, the larger cosmos has a food chain of its own.
The universe plays host to a dizzying array of galaxies of many different shapes and sizes. Interactions between these massive structures are surprisingly common. In these scenarios, large, fully formed galaxies, such as our own Milky Way, have been known to completely consume, or more accurately absorb smaller galaxies.
However there are also many interactions wherein both galaxies survive, and the smaller structures become what are known as satellite galaxies, which orbit the larger galaxy.
In these scenarios, the smaller galaxies are not taken in whole, but instead are consumed piecemeal. Astronomers have been aware for some time that monster galaxies habitually feed off the atomic gas that occupies the space between stars located near the outskirts of satellite galaxies.
However, fresh research has revealed that the damage being wrought on these smaller galaxies may be more devastating than first thought. According to the new study, huge galaxies are stealing reserves of molecular gas that exists in great clouds around the cores of the smaller cosmic structures.
These reserves are needed to create new generations of stars, which the more diminutive galaxies need to continually produce in order to grow and mature.
Led by the International Centre for Radio Astronomy Research, the team behind the new study first used an advanced cosmological computer simulation and made predictions as to the amount of gas that should exist at galaxies’ outskirts (atomic gas) and in their cores (molecular gas) based on their theory. Predictions made by the team were then compared to observations of molecular and atomic gas reserves from over 500 galaxies as captured by the Arecibo telescope in Puerto Rico and the IRAM 30-meter telescope in Spain.
It was discovered that the predictions matched closely with the telescopic observations, and with earlier evidence that highlighted low rates of star formation in small satellite galaxies.
According to the authors of the study, the molecular gas drawn out from the satellite galaxies initially enters an orbit of the larger galaxy. It is possible that the material could remain there, or proceed to rain down on the larger galaxy over time, slowly feeding it new star-forming material.
This allows the more mature galaxy to continue to grow and evolve at the expense of its neighbors. Ultimately, in most scenarios, satellite galaxies only survive for a couple of billion years past the point they are fed on. Eventually, the powerful gravitational influence of the central galaxy causes the smaller structures to be drawn inwards, where they are cannibalized by their larger cousin.
However, this inevitability does not render the research less valuable, as the quantity and rate at which new material is added plays a significant factor in how the central galaxy continues to evolve.
The paper has been published in the Monthly Notices of the Royal Astronomical Society.