The stars in galaxies are just the tip of the iceberg. We know galaxies contain extended gaseous envelopes surrounding their stars, which are commonly referred to as the circuingalactic medium.
Recent studies reveal that the extension of the circumgalactic medium of a galaxy from its center is 10 to 20 times that of its stellar component, which itself extends to a few tens of thousands of light-years from the center.
Although astronomers believe the circumgalactic medium is extensive, it has eluded detection due to its low emissivity. One way to locate such faint gas is via absorption against a bright background source.
The circumgalactic medium absorbs specific frequencies of the background light passing through it. The specific amount of absorption of various frequencies depends on the elemental makeup and ionization state of the circumgalactic medium. This allows us to infer the presence of the faint gaseous envelope and its elemental abundances, temperature, and other physical conditions.
Using data from the Hubble Space Telescope, astronomers have now discovered not only that such a medium exists but also that it can have as much mass as the stars in the galaxies.
The physical conditions of the circumgalactic medium also reveal how galaxies exchange matter and energy with their surroundings. For example, in a recent study we found that galaxies undergoing intense star formation produce winds that quickly ionize their circumgalactic medium. This, in turn, can break the supply of cold gas required for future star formation.
This is the first evidence that a central burst of star formation affects an entire galaxy, including its circumgalactic medium. Also, this influences how a galaxy gets gas, which in turn dictates the future of that galaxy.
Did you Know ?
Moon rocks might not be all Moon rock
The projectiles that formed the Moon’s craters left more than their mark on the planet — they also left parts of themselves. Scientists previ-ously thought these space rocks vaporized or melted when they collided with our satellite, leaving a depression as the only evidence of their existence. However, some of the meteoroids merely broke into pieces — and these pieces congregated in the centers of craters — according to an arti-cle that appeared May 26 in Nature Geoscience. This frag-mentation makes astronomers’