Category Archives: galaxy interactions

galaxies, galaxy interactions, starbirth

Galaxies Going Whump in the Night

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Create Realms of Starbirth Light

Galaxy collisions fascinate me. And, they intrigue a growing number of astronomers who look at them with an eye toward understanding the processes at work when two or more of these cosmic behemoths interact with each other. One of my favorite galactic traffic-jam sites is Stephan’s Quintet, a visual grouping of five galaxies. Four of them are an actual compact group of galaxies in a sort of gravitational grouping. The additional galaxy appears in images of the group but it really lies much closer to us than the others and is not actually part of the group.  Here’s a recent image of it, and below that is a schematic diagram naming the pieces and parts of this galactic mingling.

https://i0.wp.com/www.naoj.org/Pressrelease/2011/08/18/fig1.jpg?resize=474%2C228
Composite tricolor images of Stephan's Quintet. Courtesy Subaru Observatory, NAOJ.
A diagram of the member galaxies of Stephan's Quintet. NGC7320 is a closer galaxy and has a recession velocity of 0. The remaining four are a group of more distant galaxies 300 million light years away. The researchers believe that the merging of NGC7318A/B and NGC7319's crashing into them are responsible for the active star formation regions in the H? emitting region around NGC7318A/B.

Among the processes that get kick-started into motion when galaxies collide is star formation. The gravitational interactions create shock waves and compress the gases in the various galaxies together, and that in turn starts a wave of star formation. Astronomers often refer to this activity as “starburst activity”.

Take a look at any given galaxy interaction with starburst activity, and the bluish-colored blobs of light you see are more than likely the sites of starburst clumps.

The folks at Subaru Telescope in Hawai’i have released a three-dimensional view of Stephan’s Quintet. The observers used special narrowband filters on the telescope’s Suprime-Cam instrument that let very specific wavelengths of light emitted by ionized hydrogen (what they call hydrogen-alpha or H?). Think of H? as light that is emitted by hydrogen that is being heated by some process—like starbirth. Its presence traces the existence of star formation.

In addition to star-forming activity, the images created using the Subaru data help astronomers pinpoint more accurate distances to the galaxies. The contrasting images show that NGC7320 (the galaxy at the lower left) is closer than the other four  galaxies. It is about 50 million light-years away while the other four galaxies are about 300 million light-years away. This explains the intriguing arrangement of the galaxies in Stephan’s Quintet. And, it helps astronomers track the process of star formation during the collisions, and can also give them a clue of what to look for in other galaxy interactions where hot young stars will eventually be one of the by-products of the galactic traffic jam.

astronomy, astronomy news, galaxies, galaxy interactions, galaxy shapes, hst news, Hubble Space Telecope

It Was 21 Years Ago…

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That Hubble Went out to Play

To celebrate the 21st anniversary of the Hubble Space Telescope's deployment into space, astronomers at the Space Telescope Science Institute in Baltimore, Md., pointed Hubble's eye at an especially photogenic pair of interacting galaxies called Arp 273. This image is a composite of Hubble Wide Field Camera 3 data taken on December 17, 2010, with three separate filters that allow a broad range of wavelengths covering the ultraviolet, blue, and red portions of the spectrum. Hubble was launched April 24, 1990, aboard Discovery's STS-31 mission. Click to enlarge (and you WANT to see this one bigger).

And what a time it’s been!  As you can see by this image, the most famous of the Great Observatories is still crankin’ out some stunning visions of the cosmos.  Take this image, for example. It’s a pair of interacting galaxies, slightly farther along in their gravitational dance than the two I wrote about in my last entry. They are an interesting looking grouping called Arp 273.

The larger of the spiral galaxies in the group, known as UGC 1810, has a disk that is distorted into a rose-like shape by the gravitational tidal pull of the companion galaxy below it, known as UGC 1813. Not only are these two cosmic behemoths changing each other’s shapes, but in the process, they’re spurring huge swaths of star-forming factories in the process. Those are the blublogs at the top of UGC 1810, and the bluish clouds of light at the tip of the lower galaxy.  The image (embiggenate to see it better) shows a tenuous tidal bridge of material between the two galaxies that are separated by tens of thousands of light-years from each other.

Even more unusual are the off-center spiral patterns of each galaxy.  Even if you didn’t know anything else about these galaxies, just one look at the off-kilter spirals would tell you that something has happened. In this case, one galaxy has dived through the center of the other. The smaller one probably sliced right through its larger companion above it in this image.

Notice how the spiral arms of UGC 1810 (the upper one) are warped off-kilter with respect to each other.  The inner set is offset out of the plane of the galaxy.  This must have been a titanic interaction!

As if this wasn’t weird enough, there’s also a possible mini-spiral in the upper right arms of UGC 1810.

Astronomers have seen many interacting galaxies — enough to be able to understand something of how and why they form. In this case, the larger galaxy of the pair is about five times more massive than its smaller companion.   In unequal pairs such as this, the relatively rapid passage of a companion galaxy produces the lopsided or asymmetric structure in the main spiral. Also in such encounters, the starburst activity typically begins in the minor galaxy earlier than it does in the major galaxie. These effects could be due to the fact that the smaller galaxies have consumed less of the gas present in their nucleus — and that gas is what you need for stars to form. The gravitational shock waves spur “bursts” of star formation as the gas is compressed and heated during the interaction.

Arp 273 lies in the constellation Andromeda and is roughly 300 million light-years away from Earth. This image is just one of a stream of cosmic visions sent back by Hubble during its 21 years on orbit.  Currently, the telescope is in great shape and should continue its work for some time to come.