Hubble Snaps Galaxy Pair Arp 116

Using NASA’s Hubble Space Telescope, astronomers have captured a new image of a peculiar galaxy pair called Arp 116.

Hubble snapped this image of the elliptical galaxy Messier 60, center, and the spiral galaxy NGC 4647 (NASA / ESA / the Hubble Heritage / STScI / AURA / Hubble Collaboration)

Arp 116 is composed of a giant elliptical galaxy known as Messier 60 and the spiral galaxy NGC 4647. The image shows the dramatic differences in size, structure and color between spiral and elliptical galaxies.

Messier 60 (M60 for short) is the third-brightest giant elliptical galaxy of the Virgo cluster of galaxies, a collection of more than 1300 galaxies. It is noticeably larger than its neighbor, and has a far higher mass of stars. M 60, like other elliptical galaxies, has a golden color because of the many old, cool and red stars in it. NGC 4647, on the other had, has many young and hot stars that glow blue, giving the galaxy a noticeably different hue.

M60 lies some 55 million light years away from Earth, NGC 4647 is about 63 million light-years away. Astronomers have long tried to determine whether these two galaxies are actually interacting. Although they overlap as seen from Earth, there is no clear evidence of vigorous new star formation.

In interacting pairs of galaxies, the mutual gravitational pull that the galaxies exert on each other typically disrupts gas clouds, much like tides on Earth are caused by the Moon’s gravity. This disruption can cause gas clouds to collapse, forming a sudden burst of new stars.

Although this does not appear to have happened in the pair, studies of very detailed images suggest the onset of some tidal interaction between the two. Regardless of whether they are actually close enough to be interacting, however, the two galaxies are certainly near neighbors.

Surprisingly M60 was discovered independently by three different astronomers in 1779. Johann Gottfried Koehler of Dresden first spotted it on 11 April that year while observing a comet, the Italian Barnabus Oriani noticed it a day later, and the French Charles Messier saw it on 15 April. Charles Messier then listed the galaxy in the Messier Catalogue.