Milky Way ties with neighbor in galactic arms race

The Milky Way and Andromeda prior to the merger. Credit:

Astronomers have discovered that our nearest large neighbour,
the Andromeda galaxy, is roughly the same size as the Milky
Way. It had been thought that Andromeda was two to three
times the size of the Milky Way, and that our own galaxy
would ultimately be engulfed by our supposedly bigger
neighbour. But the latest research, published today, evens
the score between the two galaxies.

The study found the weight of the Andromeda is 800 billion
times heavier than the sun, on par with the Milky Way.
Astrophysicist Dr Prajwal Kafle, from the University of Western
Australia node of the International Centre for Radio Astronomy
Research, said the study used a new technique to measure the
speed required to escape a galaxy. “When a rocket is launched
into space, it is thrown out with a speed of 11 km/s to
overcome the Earth’s ,” he said. “Our home galaxy,
the Milky Way, is over a trillion times heavier than our tiny
planet Earth so to escape its gravitational pull we have to
launch with a speed of 550 km/s. We used this technique to tie
down the mass of Andromeda.”

Dr Kafle said the research suggests scientists previously
overestimated the amount of dark matter in the Andromeda
galaxy. “By examining the orbits of high stars, we discovered that this galaxy has
far less than previously thought, and
only a third of that uncovered in previous observations,” he
said. The Milky Way and Andromeda are two giant spiral galaxies
in our local Universe, and light takes a cosmologically tiny
two million years to get between them.

With Andromeda no longer considered the Milky Way’s big
brother, new simulations are needed to find out what will
happen when the two eventually collide. Dr
Kafle used a similar technique to revise down the weight of the
Milky Way in 2014, and said the latest finding had big
implications for our understanding of our nearest galactic
neighbours. “It completely transforms our understanding of the
local group,” he said.

The Milky Way and Andromeda during the merger. Credit: ICRAR

“We had thought there was one biggest galaxy and our own Milky
Way was slightly smaller but that scenario has now completely
changed. It’s really exciting that we’ve been able to come up
with a new method and suddenly 50 years of collective
understanding of the local group has been turned on its head.”

University of Sydney astrophysicist Professor Geraint Lewis
said it was exciting to be at a time when the data was getting
so good. “We can put this gravitational arms race to rest,” he

In about 5 billion years time, nearby massive galaxy
Andromeda will merge with our own galaxy, the Milky Way.
There haven’t been any large mergers with our galaxy
recently, but we can see the remnants of galaxies that have
previously been snacked on by the Milky Way. We’re also going
to eat two nearby dwarf galaxies, the Large and Small
Magellanic Clouds sometime in the future.

This simulation shows what will happen when the Milky Way
and Andromeda get closer together and then collide, and
then finally come together once more to merge into an even
bigger galaxy. Credit: Simulation Credit: Prof Chris power
(ICRAR-UWA), Dr Alex Hobbs (ETH Zurich), Prof Justin Reid
(University of Surrey), Dr Dave Cole (University of Central
Lancashire) and the Theoretical Astrophysics Group at the
University of Leicester. Video Production Credit: Pete
Wheeler, ICRAR.

Explore further:

Distant galaxy group contradicts common cosmological models,

Provided by: International Centre for Radio
Astronomy Research