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.
Life on Other Worlds Could Well Look VERY Different
Black plants on a world with two Suns. Courtesy Jack O' Malley, University of St. Andrews.
Imagine if Earth had two Suns in its sky, similar to the otherworldly scenes we recall from movies like Star Wars. What would our gardens look like as we whirled around in a binary star system?
According to Jack O’Malley, a scientist at the University of St. Andrews in Scotland, it’s very possible that our gardens would NOT be the colorful delights we know today. They might very well be teeming with plants that are distinctly black or grey. He presented his ideas to the National Astronomy meeting of the Royal Astronomical Society this week.
How could strange darkened plants happen? To understand the idea behind these science-fiction type blackish-grey plants that could flourish under the light of binary stars, we have to look at the process that makes green plants here on Earth: photosynthesis. It provides the main energy source for plants, and of course for the animals that eat them. Photosynthesis is what a plant does to convert sunlight into energy. On Earth, our plants are attuned to sunlight for their photosynthetic activities — and in particular, the color of the light streaming from our nearest star.
However, if those plants had evolved on an Earth with TWO Suns, they’d have twice as many light sources to choose from. It’s entirely possible that they could use the light from both stars, or, perhaps some plants might evolve with a preference for the light from only one of the stars, particularly if they are exposed mostly to one of the stars for longer periods of time.
Think about this: the temperature of a star determines its color, which is the color that photosynthesis relies on to do its job. The star colors could then also affect the colors of the plants that are using photosythesis for their energy sources. So, star color, availability of light, and the chance to utilize multiple star sources are big factors in the colors of the plants that could evolve on worlds blessed with more than one star.
This is an interesting thought experiment — and one that O’Malley and his PhD supervisors — are doing to figure out the potential for finding photosynthetic life on planets around other stars. In particular, they are looking at the factors for such life in multi-star systems with different combinations of Sun-like stars and red dwarfs. Sun-like stars are known to host exoplanets and red dwarfs are the most common type of star in the Milky Way Galaxy. They are often found in multi-star systems, and are old and stable enough for life to have evolved.
In M star radiation habitats, vegetation may have more photosynthetic pigments in order to make use of a fuller range of wavelengths, giving them a ‘black’ appearance. These are terrestrial examples of a dark plants (and flowers).
O’Malley and his team are running simulations that consider Earth-like planets orbiting two stars close together or maybe are in orbit around one of two widely separated stars. Their simulations seem to show that planets in multi-star systems may host exotic forms of the more familiar plants we see on Earth. If this is true, then they would look much different from what we grow here.
For example, explorers collecting plants growing in the light of dim red dwarf suns would find black-looking leaves and strange-colored flowers. Those plants would be absorbing light from across the entire visible wavelength range. They’d have to use as much of the available light as possible in order to keep the photosynthesis process going.
It’s also possible that they could use infrared or ultraviolet radiation to drive photosynthesis. For planets orbiting two stars that are like our own, harmful radiation from intense stellar flares could lead to plants that develop their own ultraviolet-blocking sun-screens, or photosynthesizing microorganisms that could move in response to a sudden flare.
Someday, astronomers will find the chemical signatures of plants in the atmospheres of distant planets. From the light output of their stars and the chemistry lesson we get from those worlds, perhaps we’ll finally be able to “see” what gardens on the surfaces of faraway worlds will be like. Maybe we’ll find out that the worlds we imagine in our science fiction movies are not even half as “weird” and different as the real worlds that lie out there around nearby stars.
