OUT THERE
72 DISCOVERMAGAZINE.COMCLOCKWISE FROM TOP LEFT: GEMINI OBSERVATORY/AURA; NASA/ESA/Z. LEVAY AND R. VAN DER MAREL (STScI)/A. MELLINGER; ESO/C. MALINsuch as the Crater 2 dwarf galaxy found
earlier this year. The Large and Small
Magellanic Clouds, the Milky Way’s
two largest remaining companions, also
could end up as meals someday, and
features like the ribbon of gas called
the Magellanic Stream connecting the
two clouds might be evidence of our
galaxy starting to nibble. But recent
evidence suggests the clouds are moving
fast enough to escape the Milky Way’s
gravitational clutches — for now.COSMIC KARMA
Gravity, like death, is a great equalizer.
The Milky Way, having victimized
countless galaxies over its lifetime,is destined to become prey itself in
4 billion or 5 billion years.
The Andromeda Galaxy, the
largest member of our Local Group of
galaxies, is heading our way. Although
currently separated by 2.5 million
light-years, the Milky Way and
Andromeda are hurtling toward each
other at 250,000 mph (112,000 meters
per second), almost 10 times faster
than the speed of New Horizons,
the fastest spacecraft launch to date.
A few billion years from now, our
descendants — whoever or whatever
they may be — will have a spectacular
view as Andromeda looms ever larger
in the night sky before engulfing
the Milky Way.
Outweighed 2 to 1,
the Milky Way doesn’t
stand much of a
chance. After a flurry
of encounters that will
batter and bruise both
of them, the two galaxies
will slowly come together
like tired boxers in a
clinch until eventually
Andromeda absorbs
the Milky Way. From
this chaos, a new, larger
galaxy will emergethat has already been nicknamed
Milkomeda. The sun, with its planets in
tow, will be one of more than a trillion
stars that call this new galaxy home.
But there’s no reason to think the
cannibalism will end there. With dozens
of other small galaxies in the Local
Group, there’s plenty for Milkomeda to
munch on in the future.
In 2000, Swinburne University
astronomer Duncan Forbes
and colleagues wondered what
complete cannibalism of the Local
Group might look like. Using
computers, they digitally assembled
a Frankensteinian mix of all known
Local Group galaxies. The final result
— the last galaxy standing — turns
out to be indistinguishable from large
elliptical galaxies found throughout
the universe, a placid collection
of stars and star clusters with few
obvious signs of past trauma. Forbes
and his colleagues christened it “the
elliptical galaxy formerly known as
the Local Group.”MESSY EATERS
In 1951, pioneering Swiss astronomer
Fritz Zwicky noticed “large luminous
patches” of material in the space
between galaxies. He realized thatNGC 660 bears the scars of a violent encounter that probably occurred about a billion years ago.
The ring of gas, stars, and dust that encircles NGC 660 may be the twisted remains of a smaller
galaxy that strayed too close.The Milky Way might someday make a meal of the Large
Magellanic Cloud, seen here as a whitish smudge of light
above the Atacama Large Millimeter/submillimeter Array
(ALMA) in Chile.