In about a third of spiral galaxies, the arms
spiral out, not from the center, but from a straight bar of stars, gas, and dust that
extends from both sides of the bright nucleus. Hubble classified these barred spirals into
sub-groups "a" to "c" in order of increasing openness of the arms, but
with a "B" for barred
inserted: "SBa", "SBb",
"SBc". Here are examples of these three sub-groups of
barred spiral galaxies.
A new image from the Hubble telescope first posted on "Astronomy Picture of the Day" reveals a barred spiral galaxy with a starburst ring near its center, where new stars are being formed.
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