Colliding Galaxies

THE UNIVERSE IS FILLED WITH YOUNG GALAXIES AND OLD, SMALL
GALAXIES AND BIG, FLAT GALAXIES AND ROUND.  ONE OF THE CURRENT
THEORIES ASTROPHYSICISTS HAVE IS THAT THE BIGGER GALAXIES ARE
OLDER ONES MADE UP AS SMALLER ONES MERGED TOGETHER. FOR
EXAMPLE, SPIRAL GALAXIES LIKE OUR OWN WHICH HAVE HUBS AT THE
CENTER WITH A BUNCH OF WHEEL SPOKES STICKING OUT, MAY HAVE
JOINED TOGETHER TO FORM ELLIPTICAL GALAXIES WHICH ARE MORE
EVENLY DISTRIBUTED INTO A BALL SHAPE.  BUT IT'S DIFFICULT TO COME
UP WITH WAYS TO PROVE THIS THEORY SAYS BRAD WHITMORE, AN
ASTRONOMER WITH THE SPACE TELESCOPE SCIENCE INSTITUTE. 

Whitmore: "The problem with a lot of astronomy is things happenon very long time
scales, millions of years, hundreds of millions of years, billions of years, so it's not like the
lab where you can just set up the experimenta nd watch it happen in real time."

ONE WAY AROUND THE PROBLEM IS TO TAKE MANY PICTURES OF A
NUMBER OF GALAXIES AT DIFFERENT STAGES IN THEIR EVOLUTION, SAYS
CHRIS MIHOS AT CASE WESTERN.  

Mihos: "It would be sort of like trying to go out with a camera nd taking pictures of every
person that walked by and then reconstructing the life history of a human being.  You'd
have pictures of young people, pictures of old people, pictures of men, pictures of
women, pictures of tourists, pictures of worker people and you'd have to sort that
together."

THE TRICK IS TO PUT THESE PICTURES ALL IN THE RIGHT ORDER, WHICH
THEY CAN DO BY LOOKING AT STAR CLUSTERS.  YOUNGER STARS BURN
VERY HOT, MAKING THEM BRIGHT BLUE, WHILE OLDER STARS GET
REDDER AND FAINTER OVER TIME. 

Whitmore: "So all we have to do is look at the star clusters see how bright and how blue
they are and watch as they evolve. . . and that allows us to put this set of snapshots
together in chronological order. . . the upshot of that is . . . it looks quite good that you
can . . .put together this sequence from merging spirals all the way to ellipticals."