Category Archives: galaxies

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The Dance of the Galaxies

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Hubble Sees It

Hubble Space Telescope has been peering out at galaxies (and all kinds of other objects in the cosmos) since 1990. Over the years it has captured many views of galaxies interacting. By interacting, I mean that they come together, they collide, they mingle stars and clouds of gas and dust, and then in the aftermath, new stars are formed. The view from a distance is breathtaking. Like this one. The combined galaxy interaction is named NGC 5331, and they lie about 450 million light-years away from us in the direction of the constellation Virgo.

The collision of a pair (or more) of galaxies begins long before they look like they’re actually touching. The gravitational influence of both galaxies begins to pull shreds of galaxy parts (gas, dust, stars). It also starts to distort the shape of the galaxies doing the interacting. If you look closely at this pair you’ll see some part of the lower galaxy is being pulled toward the “upper” galaxy. There are also little blue clouds out to either side of the galaxy. Most likely those are star-forming regions, so-called “starburst” knots that are ignited during galaxy interactions. (There are also other galaxies in the picture — see if you can spot them all.)  As things proceed, you start to see definite “shredding” effects as the shockwaves of collision distort the galaxies.

To celebrate the 18th anniversary of Hubble’s launch (gad, has it been 18 years already?), the Space Telescope Science Institute and the Hubble ESA folks have released an image collection of 59 galaxy interactions. Here’s another one — the interacting galaxy pair that makes up Arp 148. This one shows the pair well after the collision (interaction) began. The blue “ring-shaped” object is a collection of matter ejected by the shockwave generated during the collision. It’s blue because the shock also touched off a burst of star formation. Those are hot, young blue stars there, just beginning their lives in the chaos of a galaxy collision.

You can see the other 57 galaxy interactions here. Be prepared for quite a fascinating tour! It’s amazing what can happen when some of the biggest structures in the universe do a little cosmic dance with each other!

astrophysics, galaxies, HII regions, starbirth, stars

Exploring Galaxy Evolution

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Galaxies Change the Universe

We live in a stellar city called the Milky Way Galaxy. It’s a collection of hundreds of billions of stars. Some of those stars (the really old ones) were formed in the infancy of the universe in the first clouds of hydrogen to coalesce after the Big Bang. The younger ones are being born in clouds of gas and dust interspersed through the Milky Way, but mostly in the spiral arms.

There are other galaxies out there, and astronomers want to know if they “tick” the same way ours does. So, they launched the Galaxy Evolution Explorer to study all kinds of galaxies and track how they change over time.

Now, you don’t just look at galaxies in visible light. To make a good survey of a galaxy’s stars and starforming (and star death) regions, you need to survey it in different wavelengths.

So, GALEX looked at the Southern Pinwheel galaxy (M83) in ultraviolet wavelengths. UV light is given off by energetic regions, such as starbirth clouds. This composite image shows ultraviolet light emissions from the central disk and assorted starbirth regions coded in blue and green, and an extended set of arms as seen in radio wavelengths (coded in red) by the Very Large Array radio telescope in New Mexico. It shows where the star-forming action IS in the galaxy. It also shows that the hydrogen clouds that feed starbirth are extending far out into space. Now, if you look closely, you can make out bright blue and green dots in the extended arms of the galaxy. These are star-forming regions full of baby stars, which is a stunning and completely unexpected thing to find 140,000 light-years away from the center of the galaxy. Just for reference, we are about 26,000 light-years away from the center of our own galaxy, and we’re more or less out in the galactic sticks. So, these stellar nurseries are in the equivalent of a galactic outback. What’s fascinating about these baby stars is that they’re forming in more-or-less pristine hydrogen clouds, not the kind of clouds our solar system formed in, contaminated with heavy elements from older, long-dead stars. The newborns in the Pinwheel are being born under conditions that are a LOT like the conditions in the early universe, when the first stars were being born. So, astronomers are excited about this find because it’s giving them a second chance to check out what it was like when stars first started forming more than 13 billion years ago.