Hubble: You Decided Arp 274

BY DR EMILY BALDWIN

ASTRONOMY NOW

Posted: 06 April, 2009

The Hubble Space Telescope imaged the winning target in the “You Decide” competition last week, revealing a triplet of galaxies called Arp 274 in unprecedented detail.

Arp 274, also known as NGC 5679, attracted 67,021 votes of the 140,000 that were cast towards six different galactic objects.

Hubble’s Wide Field Planetary Camera 2 was used to image Arp 274. Blue, visible, and infrared filters were combined with a filter that isolates hydrogen emission. The colours reflect the intrinsic colour of the different stellar populations. Image: NASA, ESA, M. Livio and the Hubble Heritage Team (STScI/AURA).

The first close-up view of the system revealed the galactic trio in striking detail. Previously thought to be a set of interacting galaxies, this may have been an optical illusion since there is no evidence for the galaxies becoming distorted due to gravitational forces.

The entire system resides at about 400 million light years away from Earth in the constellation Virgo, but the galaxies themselves may be separated by some distance.

Although they appear to be partially overlapping, the spiral shapes of the two largest galaxies appear mostly intact. The smallest galaxy, located on the far left, is the most compact, but shows evidence of star formation, betrayed by the bright blue knots of stars illuminating the galaxy.

Arp 274 in relation to nearby constellations. Image: NASA, ESA, and Z. Levay (STScI), A. Fujii for STScI.

The right hand galaxy also displays much evidence of star formation, with blue beads of star formation strung across the spiral arms along with pinkish nebulae that are illuminated by young stars. Interstellar dust is silhouetted against the starry population. Older, yellow stars form the main population of the galaxies’ central bulges, especially in the middle galaxy, which may have a central bar.

The release of this new image was part of the International Year of Astronomy's 100 Hours of Astronomy initiative, a global project aimed at encouraging as many people as possible to look at the night sky.

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