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All posts for the month April, 2004

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!

If you’ve always wanted to spot a comet with your very own eyes, there are a couple of them inbound that you should be able to see in the next few weeks. They’re called Comet LINEAR and Comet NEAT. Right now, Comet LINEAR is hard find to in the bright glow of dawn just above the eastern horizon before sunrise, and Comet NEAT is visible only from the Southern Hemisphere. But that will soon change.

For now, in the final week of April and the first few days of May, North American and European skywatchers do have a shot at spotting Comet LINEAR before dawn on clear mornings. Look with binoculars just above the horizon due east about 60 minutes before your local time of sunrise.

Later on in the month, both LINEAR and NEAT will come into in the evening sky. Starting around May 5th or 6th, scan for Comet NEAT just above the southwest horizon as evening twilight fades. Look for a small, fuzzy “star” with a small tail pointing to the upper left. (The much brighter star Sirius will also be low in the southwest; on May 5th the comet will be not far to its left, and on May 6th the comet will be to Sirius’s upper left.) In the next two weeks Comet NEAT will get much higher in the southwest at nightfall, though it will also fade. Binocular users may be able to follow it through the end of May.

Around May 26th or 28th, Comet LINEAR could steal the show when it too enters the evening sky. Look for it just above the west-southwest horizon as twilight fades. It will get only a little higher in the following week or two, while fading rapidly.

Full details, including charts showing when and where to look for both comets (from the Southern Hemisphere too!) appear in the May 2004 issue of SKY & TELESCOPE and in the article “The Double Comet Show of 2004,” online at SkyandTelescope.com.

Thanks to Alan MacRobert at Sky & Telescope for this information!