Category Archives: galaxies

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.

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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

A Distant Starry City

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The Lion’s Treasure

The spiral galaxy NGC 3512, as seen by the European Southern Observatory's Very Large Telescope in Chile. The galaxy is about 35 million light-years away and spans an area of space 50,000 light-years across. Courtesy ESO.

I like to look at pictures of galaxies. They always trigger in my mind questions about what kind of life must exist on planets around their stars. Since we’ll likely never know (at least in our lifetimes) about beings in other galaxies, it’s a great way to think about starry empires and the civilizations that support them. As a science person, I look at galaxies and immediately start cataloguing in my mind their structures, which gives me some idea of their evolutionary history— that is, what they went through to get to the shape we see them in—and also how much star-forming activity is occurring in the arms. Galaxies are treasure houses of star formation, star death, and the materials for new stars, planets, and life.

This galaxy, NGC 3521, is what astronomers call a “flocculent” spiral galaxy. That means its spiral arms are fluffy with clouds of gas and they are dotted with star-forming regions.  The areas where new stars are being born are mostly blue in color because of the hot young ultraviolet-bright stars they contain. The reddish areas contain older stars, and the dark lanes are those clouds of gas and dust. There could be stars forming inside those clouds and in a few tens of thousands of years, bright blue splotches will light up more regions of the dust lanes.

The core of this galaxy is really quite compact—meaning tightly bound together. There are likely millions of stars in that little region, and possibly a black hole.  All in all, this is a busy galaxy—bustling with star formation, and with the creation of many stars, very likely it has a population of planets in orbit around some of those stars.  If so, I expect that this treasure of a galaxy in Leo also has some life forms in it—maybe some of them are looking at pictures of our galaxy and wondering the same things about the Milky Way.