Category Archives: galaxy interactions

evolution of galaxies, galaxies, galaxy interactions, Gemini Observatory

Exploring the Galaxies

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The past few months I’ve been working with the Gemini Observatory, doing a series of interesting and absorbing projects for their outreach team. These range from science reports and newsletters to press release edits and consultations. A couple of weeks ago they sent me this great image of members of Stephan’s Quintet, a troupe of five galaxies that lies about 300 million light-years away. What we see here tells an interesting tale of galactic intrigue.

Courtesy Gemini Observatory
Courtesy Gemini Observatory

Some members of the group are interacting with each other, tearing huge swaths of gas and stars away from each other in a sort of cosmic dance. One thing that really stands out in this image is a collection of brilliant red clumps in the spiral galaxy NGC 7320 (just above the center of the image). These are star-forming regions as seen with the help of a special filter.

This galaxy may or may not be part of the Quintet—its relation to the other galaxies in the cluster is the subject of some controversy. Most astronomers now think that NGC 7320 is quite some distance away from the others. Spectroscopic data show its apparent velocity away from us at around 800 kilometers per second. The rest of the group is moving away from us (through the expansion of the universe) at over 6,000 kilometers per second. This puts the the other galaxies in the cluster almost 8 times farther away from us than the brilliantly-lit spiral.

The interacting members of Stephan’s Quintet will continue their dance for millions of years, but eventually they will combine into a different, smaller set of objects than we see today.

astronomy news, galaxies, galaxy interactions

Cosmic Galaxy Ballet

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Courtesy the Very Large Telescope
Courtesy the Very Large Telescope

As astronomers gaze across the deeps of space and time, they run across scenes like this one — where two (or more) galaxies just get too close to each other for comfort. When this happens, sometimes galaxies end up colliding.

The European Southern Observatory’s Very Large Telescope caught a glimpse of a cosmic tango taking place 190 million light-years away in the direction of the southern hemisphere constellation Pavo, the Peacock. And, like Hubble’s spectacular image of a ring galaxy (created by yet another collision), this VLT image was taken to celebrate another telescopic anniversary — the VLT’s fifth birthday.

So what’s happening in this scene?

NGC 6769 (the one on the upper right) is a spiral galaxy with very tightly wound spiral arms. Its neighbor (NGC 6770) has two major spiral arms. One looks rather straight and points towards the outer disc of NGC 6769. NGC 6770 is also peculiar because it shows two comparatively straight dark lanes and a fainter arc that curves towards the third galaxy toward the bottom of the image, called NGC 6771 (below). Stars and gas have been stripped off of both NGC 6769 and NGC 6770, and they’re starting to form a common envelope around them. Some folks have suggested it looks like the shape of a Devil’s Mask. There might also be a tenuous bridge between NGC 6769 and NGC 6771. All of these features are there because there’s strong gravitational interaction between the three galaxies.

Well, you might think that such a collision would destroy the galaxies and any chances for the normal things that galaxies do (like host star-forming regions).

Not… quite…

There is a true baby-star boom going on in this scene. A cosmic catastrophe like this one normally results in the formation of many new stars, which you can see in the blueish clouds that highlight the spiral arms in NGC 6769 and NGC 6770. There are many sites of star-forming regions.

VLT, and other telescopes (including HST) are studying a great many cosmic collisions like this one to help scientists figure out how and why galaxies form, evolve, and change over time. There’ll no doubt be more cool pix like this one in the years to come!