Credit: ESA/Hubble & NASA
This image from Hubble’s Wide Field Camera 3 (WFC3)
shows a spiral galaxy NGC 5917, perhaps best known for its intriguing
interactions with its neighbouring galaxy MCG-01-39-003 (not visible
here, but located off the bottom right of the frame — as seen here).
Mass is often confused with weight,
but they are very different things. Mass is the very substance of an
object and is something one always has, no matter the location. If you
fly to the Moon and experience low-gravity conditions, your mass has not
changed at all. What has actually changed is your weight, because
weight is a force caused by the gravitational attraction of another
massive body. Gravity is how objects with mass “talk” to one another.
People do weigh less on the Moon, but not because they have lost any
body mass — the mass of the Moon is less than that of the Earth, so it
exerts a smaller gravitational pull on them.
Understanding mass is
vital when it comes to understanding why objects behave the way they do
in space. Without mass “talking” via gravity, the planets would not
orbit the Sun, and galaxies would not interact as NGC 5917 does with its
neighbour. Galaxy interactions
can lead to very interesting effects; the galaxies can steal mass — in
form of stars, dust and gas — from one another, distort and warp one
another’s shape, or trigger immense waves of new star formation.
Sometimes, a galactic duo interact so strongly that they end up
colliding and merging completely. Unfortunately, if NGC 5917 is destined
to merge with its celestial neighbour, it will happen much too far into
the future for us to enjoy the spectacle.
Source: ESA/Hubble/Potw
