Astronomers Observe Galaxy In Act Of Dying

Lee Rannals for — Your Universe Online

Astronomers announced at the 222nd American Astronomical Society meeting in Indianapolis that they have observed the first clear example of a galaxy in the act of dying.

The team says they saw a bright dwarf galaxy relatively close to Earth’s Milky Way that was “trailing fireballs.” They said until now, there has been no clear example of this transformation happening.

“We think we´re witnessing a critical stage in the transformation of a gas-rich dwarf irregular galaxy into a gas-poor dwarf elliptical galaxy — the depletion of its lifeblood,” Jeffrey D. P. Kenney of Yale University, the principal investigator, said in a statement.

Star formation is the drive behind a galaxy’s vitality, and many of the universe’s known galaxies are active star factories. However, due to gas depletion, many galaxies have stopped making stars. The researchers said galaxy IC 3418 inside the Virgo Cluster is now all but totally out of gas.

The astronomers believe IC 3418’s distinctive fireball-dotted tail shows evidence of recent star formation that took place within the last few million years or less. However, the depletion of the core and the generation of the fireballs are probably the result of the process that is killing the galaxy, which is known as “ram pressure stripping.”

During this process, the interaction of gases in the space between galaxies generates an enormous pressure that can force out an individual galaxy’s interior gas while leaving existing stars untouched. Ram pressure pushes gas away from the galaxy, forming stars that do not feel the ram pressure and remain behind. The fireballs are a signature of active ram pressure.

“If you hold popcorn and unpopped kernels of corn in your hand and stick it out the car window as you drive, the wind caused by the car´s motion through the air will blow away the popcorn but leave the denser unpopped kernels in your hand,” Kenney said in the statement. “This is like the gas clouds in galaxies being blown out of the galaxy by the wind of cluster gas, while the denser stars remain behind.”

Kenney said IC 3418 would no longer be fertile because stars, planets and life can form only if a galaxy has gas to make them.

“It´s gratifying to find a clear example of an important process in galaxy evolution,” Kenney explained. “I enjoy digging through evidence to assemble a story about what happens to galaxies. I´ve come to think of myself as an intergalactic forensic pathologist — someone who studies the bodies of galaxies seeking evidence of traumatic events responsible for the present state of the galaxy.”

The astronomers plan to submit their paper titled “Transformation of a Virgo Cluster Dwarf Irregular Galaxy by Ram Pressure Stripping: IC 3418 and Its Fireballs” to the Astrophysical Journal.



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