A South African astronomer has made a startling discovery about one of the world’s most closely studied galaxies. A team of scientists led by David Block from the University of the Witwatersrand has found new evidence that the Andromeda galaxy was involved in a violent head-on collision with its neighbouring dwarf galaxy, Messier 32, more than 200-million years ago.
Scientists have generally believed that the Andromeda galaxy, which is 2,5-million light years from Earth, was a tranquil galaxy drifting in space, and its turbulent past remained undetected. But Block’s discovery has changed the way the galaxy will be viewed in future.
“We’ve unlocked the holy grail of galaxies,” he said, smiling, while discussing his discovery in Johannesburg this week.
Messier 32 hit Andromeda when the Atlantic Ocean was still forming on Earth, the only witnesses a few dinosaurs that could not begin to interpret the light in the sky.
“These collisions are the diamonds of the universe because they are so rare,” Block said. “We knew of some others, such as the famous Cartwheel collision 500-million light years away, but this one was so close and so recent. It happened right on Earth’s doorstep.”
Block and his team made the discovery while looking through images taken by the Infrared Array Camera on Nasa’s Spitzer telescope, designed by renowned space pioneer and Harvard scientist Giovanni Fazio. The results of his discovery were revealed this week in the prestigious scientific journal Nature.
Block was intrigued by two glowing rings of fire in Andromeda that did not seem to fit with a normal spiral galaxy. Then, six months ago, the penny dropped.
“These dust rings are like ripples in a pond,” Block explained, pointing at the ripples of Andromeda taken by Fazio’s camera. “Plop a stone into water and you get an expanding series of rings or waves. Let a small galaxy collide nearly head-on with a larger one and you will see waves of gas and dust which propagate outward.”
“We never would have detected this if David had not come in,” Fazio said. “My eye was simply not trained.”
Ken Freeman, a Royal Society fellow and famous astronomer, described the Andromeda collision as “one of the most important discoveries yet made concerning that galaxy’s history, ever since Charles Messier catalogued the galaxy in 1764”.
Andromeda itself is again on collision course with another galaxy — our very own Milky Way. “It is approaching the Milky Way at 300kph. The two galaxies will collide in say a couple of billion years,” Block chuckled.