Page 97 - How It Works - Book Of Amazing Answers To Curious Questions, Volume 05-15

Space

Menage à trois Collision
The Triangulum galaxy, In four billion years’ ‘Milkomeda’
lurking about three million light time the Andromeda
years away, will also eventually galaxy will merge
merge with the new elliptical with the Milky Way Our Milky Way galaxy is stuck on a
‘Milkomeda’. and form a giant
elliptical galaxy. collision course with another galaxy
Like lovers in a last embrace, our Milky Way and the Andromeda
galaxy are caught in a mutual pull of gravity and are hurtling towards
each other at 112 kilometres (69 miles) per second. In about four billion
years’ time they will come into contact with each other, and we can
expect to see the same interactions between our galaxy and
Andromeda as we have witnessed in galaxy collisions elsewhere in
the universe. It is unlikely that individual stars will collide (so if the
The Andromeda Sun is still around, it will be safe) but the galaxy’s spiral arms will be
galaxy
Currently 2.5 million twisted and pulled apart, and stars and gas will be flung out in tidal
light years away, the streams. The black hole at the heart of our galaxy will then merge with
Andromeda galaxy is the black hole inside Andromeda, possibly becoming active for a time
hurtling towards us as huge amounts of gas are pushed down its throat by the gravitational
at 400,000km/h
(250,000mph). forces of the collision. The end result will be a giant elliptical galaxy
that some astronomers have nicknamed ‘Milkomeda’. Some also
suspect that another nearby spiral galaxy, the Triangulum galaxy,
will also play a part in the merger as it comes close.

Survival of the Sun
During such collisions it is rare for
stars to collide, but the Sun may
well be ejected to the outskirts of
the new elliptical.

What will we see? Earth’s night sky will change dramatically over the next four billion years

Present day The encounter begins Collision!
We can see the Milky Way and the Andromeda galaxy As the Andromeda galaxy gets nearer it will grow larger As the spiral arms of the two galaxies collide their
spanning three degrees in the sky. However, Andromeda in our sky. Its invisible gravitational force will begin to structures are completely disrupted. From Earth we will
has a blueshift meaning it’s moving towards us. distort the shape of the Milky Way. see the Milky Way become misshapen and tangled.

© Science Photo Library; NASA/ESA/A. Feild/R. van der Marel

Starburst Black holes The end result
During the merger huge gas clouds collide, creating the The black holes in each galaxy edge their way towards Eventually the star formation ends, the black holes
conditions for a burst of star formation. In the night sky each other. From Earth, we will see two galactic cores, merge, the spiral arms are destroyed, and the two
we will see more nebulae and bright star clusters light up. getting closer until they merge. galaxies form a blob of stars called an elliptical galaxy.

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