Galactic Heartbeats

When giant red stars approach the end of their life an epic tug-of-war becomes evident. The outward force from pressure begins to overcome the inward force from gravity. After expanding to a certain volume,  activity decreases in the star and the outward force from pressure decreases. That is, gravity begins to overcome. This oscillatory phenomenon effectively changes the star's luminosity thus causing it to pulsate in brightness.

This cycle was thought to be imperceivable in other galaxies due to luminosity averaging from the light of other, steady, stars. But astronomers at Yale and Harvard have successfully detected such pulsating in a galaxy known as M87. They found that 25 percent of the pixels in the Hubble image increased in brightness periodically. The "heartbeat" of the galaxy is, on average, every 270 days.

One could imagine that this period varies due to millions of old red stars oscillating with different phases. It does seem curious that these pulses are not averaged out to a constant flux. This suggests that a large number of the old red stars must somehow have similar phases. Astronomer Jieun Choi says that their model predicts more dramatic pulsating in younger galaxies and that they hope to discover more examples of this in the future.


Sources:
http://www.scienceworldreport.com/articles/33072/20151116/galaxy-heartbeat-astronomers-find-pulse-distant.htm
https://en.wikipedia.org/wiki/Red_giant