Page 96 - How It Works - Book Of Amazing Answers To Curious Questions, Volume 05-15

This is an artist’s
impression of the
asteroid collision
around the star NGC
2547-ID8, which
released a huge
cloud of dust

Asteroid collisions

Space rock smash-ups happen once per year in the asteroid belt

Forget the asteroid chase scene in The Empire 4.6 metres (15 feet) across, which struck it at a meteorites, are believed to come from this family
Strikes Back – the asteroid belt is really quite velocity of 17,700 kilometres (11,000 miles) per as well. Sometimes collisions can send asteroids
empty – you could be standing on one asteroid hour. Astronomers suspect impacts like this could larger than these small meteorites our way too,
and not be able to see another! Even so, that happen between minor asteroidal bodies in the and when that happens they can endanger life
doesn’t stop them from bumping into each other. asteroid belt about once per year on average. on Earth.
And when they do, it can be dramatic. Some asteroids come in groups or families. The Asteroid collisions happen around other stars,
In 2010 the Hubble Space Telescope spotted families are believed to be chunks of the largest too. In 2012 a star called NGC 2547-ID8 suddenly
something mysterious in the asteroid belt: a member of the family, smashed off in an impact. found itself having much more dust around it
strange, X-shaped object with a long tail like a For example, Vesta – one of the largest asteroids in than it used to have, released by a giant asteroid
comet. The tail was asteroid dust, believed to be the Solar System – has a family of smaller impact. Spitzer saw the infrared emission from
released when a 122-metre (400-foot) wide asteroids, while a rare type of meteorite found on this dust, which contains sand-sized grains that
asteroid collided with a smaller asteroid, about Earth, called HED (howardite-eucrite-diogenite) are grinding themselves down even smaller.

Galaxy 1. Collision course
Galaxies are usually millions of
light years apart, but their huge
gravity can cause an attraction,
collisions making them move inexorably
towards one another.

What happens when these 2. First contact

swirling systems of stars meet? At first, the momentum of each
galaxy may take them past one
another, but their gravity will tear
streams of stars and gas out of
3. Tidal tails each other, called tidal tails.
These can stretch hundreds of
thousands of light years and the gas
within them can form many new stars,
far away from their home galaxy.

4. Caught by gravity
Although the two galaxies pass each
other, their mutual gravity prevents 6. Elliptical galaxy
them from escaping and pulls them If two spiral galaxies
back. This could happen several times, collide, their characteristic
yo-yoing to and fro, until they are arms become distorted.
moving slowly enough to begin merging. The galaxies merge into a
combined blob-shaped
galaxy called an elliptical,
and their supermassive
5. Stars black holes also merge.
During the merger, huge gas
clouds collide, causing them to
form new stars. However, amid
a galaxy collision, stars rarely
collide because the distances
between them are so vast.

96 How It Works