Astronomers find hundreds of massive gas clouds streaming away from the Milky Way’s center

Using new 21 cm radio observations made with NSF’s Green Bank Telescope, astronomers have discovered that more than 250 clouds of neutral gas are blasting out into interstellar space from the center of the Milky Way. These clouds are likely the product of the same phenomenon that created the Fermi bubble.

It has long been known that energetic processes at the center of the Milky Way generate high-velocity hot winds that spread through intergalactic space with temperatures of millions of degrees and speeds of thousands of kilometers per second. Most large galaxies have winds like this.

The serendipitous discovery that some of this hot gas is trapped in cold hydrogen clouds was made by Australia’s ATCA telescope, which measured 21cm radio emissions from interstellar hydrogen atoms.

This suggests that there may be an undiscovered population of clouds transporting material away from the Milky Way’s core.

Hydrogen clouds are important in their own right, but they also act as probes for hot air.

Conditions in very hot winds are difficult to measure, but just as a few leaves thrown up on Earth indicate the direction and speed of the wind in the area, cold clouds can You can track its status.

The sensitivity of the Green Bank Telescope (GBT) makes it an ideal instrument for detecting faint signals from interstellar hydrogen, but mapping these clouds and understanding their true extent is essential. It wasn’t easy.

Dr Felix James ‘Jay’ Rockman, senior astronomer at Green Bank Observatory, said: ‘It took many years to systematically map hundreds of square degrees using GBT in search of weak hydrogen emissions. ” he said.

“Once we identify a few promising candidates, we can follow up with targeted observations with other telescopes to show us even more.”

“This cloud must have been ripped off from a region near the center of the Milky Way galaxy and flung outward by a burst of star formation or black hole activity.”

Some of these clouds have the fastest outflow velocities of any cloud ever observed in the Milky Way, and may even escape from the Milky Way.

In an unexpected development, new data from the APEX telescope reveals that some hydrogen clouds contain molecules and dense cold gas.

“No one would have expected that the clouds violently ejected from the Milky Way would harbor relatively fragile molecular material, but that’s what happened,” Rockman said.

Astronomers using the MeerKAT array recently mapped hydrogen in several clouds with high angular resolution, showing that it evolves and gets shredded as it flows into interstellar space.

“These new results open the door to further discoveries,” Dr. Rockman said.

“How clouds that are accelerated to speeds of more than 400 kilometers per second remain stable is a mystery.”

“The chemical processes inside these clouds are very unusual and unexplored.”

Dr. Rockman and his colleague Dr. Enrico Di Teodoro of the University of Florence, findings in AAS243243rd Meeting of the American Astronomical Society, New Orleans, Louisiana, USA.

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Felix Rockman and Enrico di Teodoro. 2024. New investigation of neutral clouds in the Milky Way’s core wind. AAS243Abstract #2851