ABOUT THIS IMAGE:

Summary:

One doesn't need a Ph.D. in astrophysics to recognize there is something odd-looking about this otherwise beautiful galaxy, NCG 4485. Like the Batman character Two-Face, one side looks normal, but the other side looks contorted with a firestorm of star formation going on. Why the colorful asymmetry in an island star city many thousands of light-years across? The clue is off the edge of the photo. It's another galaxy, NGC 4490, that swept by NGC 4485 millions of years ago. The gravitational taffy pull between the two galaxies compressed interstellar gas to trigger a flurry of new star birth as seen in the abundance of young blue stars and pinkish nebulas. So, out of a near-collision between two galaxies comes stellar renewal and birth. It's a trademark of our compulsive universe where even things as big as galaxies can go bump in the night.

The Full Story:

The irregular galaxy NGC 4485 shows all the signs of having been involved in a hit-and-run accident with a bypassing galaxy. Rather than destroying the galaxy, the chance encounter is spawning a new generation of stars, and presumably planets.

The right side of the galaxy is ablaze with star formation, shown in the plethora of young blue stars and star-incubating pinkish nebulas. The left side, however, looks intact. It contains hints of the galaxy's previous spiral structure, which, at one time, was undergoing normal galactic evolution.

The larger culprit galaxy, NGC 4490, is off the bottom of the frame. The two galaxies sideswiped each other millions of years ago and are now 24,000 light-years apart. The gravitational tug-of-war between them created rippling patches of higher-density gas and dust within both galaxies. This activity triggered a flurry of star formation.

This galaxy is a nearby example of the kind of cosmic bumper-car activity that was more common billions of years ago when the universe was smaller and galaxies were closer together. NGC 4485 lies 25 million light-years away in the northern constellation Canes Venatici (the Hunting Dogs).

This image is a composite of separate exposures acquired by the WFC3/UVIS and ACS/WFC instruments on the Hubble Space Telescope. Several filters were used to sample narrow wavelength ranges. The color results from assigning different hues (colors) to each monochromatic (grayscale) image associated with an individual filter. In this case, the assigned colors are:

Blue: F275W + F336W     Cyan: F435W     Green: F606W     Red: F657N + F814W

From ESA:

This image shows galaxy NGC 4485 in the constellation of Canes Venatici (The Hunting Dogs). The galaxy is irregular in shape, but it hasn't always been so. Part of NGC 4485 has been dragged towards a second galaxy, named NGC 4490 - which lies out of frame to the bottom right of this image.

Between them, these two galaxies make up a galaxy pair called Arp 269. Their interactions have warped them both, turning them from spiral galaxies into irregular ones. NGC 4485 is the smaller galaxy in this pair, which provides a fantastic real-world example for astronomers to compare to their computer models of galactic collisions. The most intense interaction between these two galaxies is all but over; they have made their closest approach and are now separating. The trail of bright stars and knotty orange clumps that we see here extending out from NGC 4485 is all that connects them - a trail that spans some 24,000 light-years.

Many of the stars in this connecting trail could never have existed without the galaxies' fleeting romance. When galaxies interact hydrogen gas is shared between them, triggering intense bursts of star formation. The orange knots of light in this image are examples of such regions, clouded with gas and dust