14, 2000 -- The gigantic clouds of gas and matter that pelted the Milky Way
in its infancy are mere fenderbenders compared to the catastrophic
collision set to occur with the Andromeda galaxy in several billion
years – and one U of T astrophysicist has mapped the fallout.
“We're on a collision course right now,” says John Dubinski, professor
of astronomy at U of T and the Canadian Institute for Theoretical
Astrophysics, who led the project with co-author Lars Hernquist
of the Harvard-Smithsonian Center for Astrophysics. “Within three
billion years, the Milky Way will be swallowed up and merged with
the Andromeda galaxy.”
The 2.2-million-light-year gap between the Milky Way and Andromeda
is closing at about 500,000 kilometres an hour, he explains. That
pace will quicken as the two galaxies near each other.
According to Dubinski, merging galaxies are not uncommon. In fact,
this type of interaction plays a key role in helping build larger
galaxies and structures in the universe. While mergers of galaxies
are less frequent now than in the early days of the universe, it
is still an ongoing process, and one in which our own Milky Way
and its big sister, the Andromeda galaxy, are active participants,
Dubinski simulated this Milky
by following the motion
of more than 100 million stars and dark matter particles as the
gravitational forces of the two galaxies force them to collide.
The simulation was a feat of parallel computing that took four
to complete on the San Diego Supercomputing Center’s 1152-processor
IBM SP3 “Blue Horizon” – one of a new class of supercomputers that
can perform more than one trillion arithmetic operations per second.
In the end, the simulation required the equivalent of three years
of continuous operation on a single workstation. The result is
high-resolution computer animation of the collision and merger
of the two galaxies from start to finish and some very detailed
of the structure and dynamics of a galaxy merger.
“We just used the Milky Way and Andromeda galaxies as a test case,”
says Dubinski. “It’s the first time we’ve been able to develop
a full picture of tens of millions of stars in two separate galaxies
merging and interacting. The power of these new machines will allow
us to improve the dynamic range and reliability of our simulations
of galaxies and large-scale structures in the universe.”
Perhaps even more intriguing is the fact that life on Earth – whatever
it may be – will probably live through and witness the entire merger
over the billion-year dance of the two galaxies, he says. The reason
is that the expected lifetime of our sun is projected to last another
five billion years. Plus, the likelihood of stars and planets slamming
into each other is very low because the distance between them is
so vast. The interaction will be “collision-less,” with the most
significant effect involving huge gravitational distortions of
systems as they coalesce.
At some point three billion years hence, the night sky will be
completely filled by the approaching Andromeda galaxy and when
the two galaxies
intersect there will be two bands of light arching overhead – looking
like two Milky Ways, says Dubinski. With the merger, two possible
fates await the sun and Earth – we could be flung into the depths
of intergalactic space and escape the galaxy forever or hurled
the centre of the merging pair where new stars will be formed.
And for those on Earth, it will be a spectacular display of galactic
fireworks, he says. Massive stars near the sun will be exploding
as supernovae at such a rate that the night sky will be bright enough
to read a newspaper.