Merging Galactic Spirals Becomes Red

Reasons why merging of spirals becomes red

by Ju Boo Lim - Sunday, 6 October 2019, 3:13 PM

Number of replies: 10

Forum Discussion

University of Oxford 

I think this is quite simple to explain

Since the spiral arms of galaxies are new with new blue and hot population 1 stars, over time they slowly burn up their fuel and became less hot and older. Their spectrum shifts from blue hot to the cooler red colour

At the same time their spiral arms whatever their various tunning fork classification, became to merge or coalesce, maybe I guess due to the gravitational pull of their elliptical or oval centers which are more massive due to the crowd of metal poor population 2 stars  within their galactic nuclei.

When two spirals merging to form an elliptical galaxy they began to contain older red stars.

These "centralized stars" are cooler, older and redder  than the metal rich population 1 blue and hotter stars

As the population 1 stars grow older and redder in the spirals, they may merge to become ellipticals

 Their centres too became redder because they now contain larger content of old red stars

Older population 2 stars in the galactic nuclei  are less rich in metal content than newer population 1 stars in their spiral arms due to the blast of some massive stars in supernovae spilling out their metal contents from nucleosynthesis outwards to contaminate the gas clouds and dusts in the surroundings even before they can  form new less  metal-rich  stars.

I think the shortest way to answer this question is, hot blue spiral galaxies after merging they become older over time, and became cooler and redder.

In reply to Ju Boo Lim

Re: Reasons why merging of spirals becomes red

by Dr. Grant Miller, University of Oxford

 - Thursday, 10 October 2019, 5:06 PM

This is basically the right answer! Good work! The key is in what you pointed out at the end. Red stars are cooler and older, so if merging takes some time then those are the stars that will be left at the end, whereas more of the younger, hotter blue stars from the original spiral galaxies will have died off.