Category Archives: galactic history

astronomy, astronomy news, galactic history, galaxies, galaxy interactions

Disturbed Galaxies

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I Blame Gravity

The galaxies in this cosmic pairing, captured by the Wide Field Imager on the MPG/ESO 2.2-metre telescope at the La Silla Observatory in Chile, display some curious features, demonstrating that each member of the duo is close enough to feel the distorting gravitational influence of the other. Courtesy ESO. Click to enlarge.

Take a look at the galaxies in this image. The one on the left, called NGC 3169, looks a little unsettled, not quite perfectly formed. The one on the right (NGC 3166) seems more blobby and its spiral arms aren’t quite as well-defined as, say, our Milky Way’s.

The reason they look this way?

Gravity. Both galaxies each have an extremely strong gravitational pull, and that plays a part in the cosmic dance they are undergoing.

As each galaxy feels the gravitational influence of the other, a push-pull tug-of-war is warping the spiral shape of one galaxy while fragmenting dust lanes in the other.

Spiral galaxies like NGC 3169 and NGC 3166 usually have arms of stars and dust that are arranged in a swirl around their central regions.  They stay in such configurations for quite a long time, until they have close encounters with other galaxies.

When galactic interactions happen, the combined gravity of the objects jumbles things up.  The classic spiral shape is stretched and pulled and sometimes torn apart, particularly when the galaxies merge. That’s what gravity does when massive systems of stars get close to each other during their mutual, lengthy cosmic dances.

The Advanced Camera for Surveys (ACS), the newest camera on NASA/ESA Hubble Space Telescope, has captured a spectacular pair of galaxies engaged in a celestial dance of cat and mouse or, in this case, mouse and mouse. Located 300 million light-years away in the constellation Coma Berenices, the colliding galaxies have been nicknamed "The Mice" because of the long tails of stars and gas emanating from each galaxy. Otherwise known as NGC 4676, the pair will eventually merge into a single giant galaxy. Courtesy Hubble Space Telescope.

Unlike the two galaxies shown in the Hubble image above, NGC 3169 and NGC 3166 aren’t yet in a full-out merger. Their close passage toward each other has only begun the transformation they may ultimately undergo. NGC 3169’s arms, shining bright with big, young, blue stars, have been teased apart, and lots of luminous gas has been drawn out from its disc. In NGC 3166’s case, the dust lanes that also usually outline spiral arms are in disarray. Unlike its bluer counterpart, NGC 3166 is not forming many new stars. In a few million years, these two galaxies could look very, very different — and, when their merger (if they have one) is complete, there’ll be an elliptical galaxy left where two majestic spirals once existed.  That’s what gravity will do to large-scale stellar systems!  For more information on this gorgeous image, visit the ESO web site writeup. There’s way more to these galaxies than meets the casual glance.

extinctions, galactic history, planetary history

Riding on the Winds of Time

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What Were YOU Doing A Galactic Year Ago?

Think about what you were doing a year ago. For me, it was summertime, and I was probably working on a script for a fulldome video show. That was one EARTH year ago. One Mars year ago (687 Earth days), I was still working on exhibits for the Griffith Observatory and they were about to reopen. One Jupiter year ago (11.9 Earth years ago) I was just finishing graduate school. One Saturn year ago (29.5 years ago) I had just gotten married and was working for a school district. One Uranus year ago… well, my grandparents were just getting married. One Neptune year ago (165 years ago), their grandparents were probably just meeting. And, one Pluto year ago (248 years ago)… well, you get the idea.

So, what was going on one galactic year ago? That’s roughly the time it takes for Earth to make a trip once around the center of the galaxy (from our viewpoint out here in the spiral arms). It’s an incredibly long time — roughly 250 million Earth years ago (give or take a couple of dozen million years).

Fortunately, we weren’t around a galactic year ago. Why do I say that? Because if we were around then, we’d either be puzzling out one of the largest mass extinctions of life in Earth’s history.  There WAS life on our planet at that time, but some 250 million years ago, it was already declining in the oceans, and was about to be nearly wiped out on land. This was an event called “The Great Dying” and it began around a galactic year ago. The formal name of the event is the Permian-Triassic Extinction, and to give you an idea of how extensive it was, about 9 in 10 marine species died out, and 7 in 10 land species suffered the same fate. This wasn’t the first or the last time that life has been threatened with extinction during our planet’s history.

255.jpg (119462 bytes)The best explanation for this mass extinction, backed up by data from studies of marine life forms and rocks that date back to that time, is that ocean life had been struggling along due to some toxic upwelling from ocean depths. It was gasping for breath, in essence.

On the land, extensive volcanic activity was pumping grunge into the air and resurfacing the planet, which affected land life. And, at that time, the continents didn’t look anything like they do today, as you can see in Chris Scotese’s rendering of Pangaea

Anyway, to make matters worse, along came a huge impactor, perhaps 6 to 12 kilometers across. When it crashed into Earth’s surface, it did severe damage, and may have hastened the Great Dying that was already in progress. In any case, it was a major mass extinction event. And it happened about a galactic year ago.

Life did thrive again, as we see in the fossil records from the next few eras and epochs as the new galactic year wore on. It makes me wonder what the next one will bring. A lot can happen in a year!