Which description best characterizes an irregular galaxy?

Which description best characterizes an irregular galaxy?

• A. It has a very regular, smooth shape.
• B. It is always the brightest type of galaxy.
• C. It has mostly old stars and little gas.
• D. It has an undefined shape with many young stars and lots of gas and dust.

Answer: (D)

Irregular galaxies lack a defined, smooth shape and typically contain lots of gas and dust that fuel ongoing star formation. This combination leads to many young stars and a patchy, uneven appearance, which matches the description about an undefined shape with young stars and abundant gas and dust. The other descriptions don’t fit: a very regular, smooth shape describes galaxies like spirals or ellipticals; saying irregulars are always the brightest type isn’t a defining trait; and being mostly old stars with little gas aligns with elliptical galaxies rather than irregular ones.

Irregular galaxies lack a defined, smooth shape and typically contain lots of gas and dust that fuel ongoing star formation. This combination leads to many young stars and a patchy, uneven appearance, which matches the description about an undefined shape with young stars and abundant gas and dust. The other descriptions don’t fit: a very regular, smooth shape describes galaxies like spirals or ellipticals; saying irregulars are always the brightest type isn’t a defining trait; and being mostly old stars with little gas aligns with elliptical galaxies rather than irregular ones.