
science & techESA/Hubble
A spiral galaxy 500,000 light-years across is distorted by a passing neighbour
NGC 6872 is a spiral galaxy about 300 million light-years away, and at over 500,000 light-years from tip to tip it is one of the largest spirals known. Its unusual shape comes from gravitational interaction with the smaller galaxy IC 4970, which sits just above it. The upper left spiral arm is distorted and filled with bright star-forming regions, probably because IC 4970 passed through it around 130 million years ago. Astronomers note the galaxy is relatively short of free hydrogen, the raw material for new stars. Without the interaction, it might not have been able to produce these bursts of star formation at all.
Gravity from a nearby galaxy pulls on gas and stars, stretching spiral arms and compressing gas clouds. Compressed hydrogen gas collapses into new stars, so interactions can trigger bursts of star formation.
Galaxy collisions and close passes can trigger new star formation, reshaping galaxies over time. The effect shows that galaxies grow and change through encounters, not only in isolation.
ESA/Hubble · CC BY 4.0
Image: Image credit: ESA/Hubble & NASA Acknowledgement: Judy Schmidt (geckzilla.com)
