Spiral Galaxy NGC 1512: The
Inner Ring
From
NASA’s Astronomy Picture of the Day
Most
galaxies don't have any rings -- why does this galaxy have two?
To
begin, the bright band near NGC 1512's center is a nuclear ring, a ring that
surrounds the galaxy center and glows brightly with recently formed stars.
Most
stars and accompanying gas and dust, however, orbit the
galactic center in a ring much further out -- here seen near the image edge.
This
ring is called, counter-intuitively,
the inner ring. If you look closely, you will see this the inner ring
connects ends of a diffuse central bar that runs
horizontally across the galaxy.
These
ring structures are thought to be caused by NGC 1512's own
asymmetries in a drawn-out process called secular evolution.
The gravity of these
galaxy asymmetries, including the bar of stars, cause gas and dust to fall from
the inner ring to the nuclear ring, enhancing this ring's rate of star formation.
Some spiral galaxies also
have a third ring -- an outer ring that circles the
galaxy even further out.
Image
Credit: NASA, ESA, Hubble Space
Telescope
