With Unusual Orbiting Clusters

Ever wonder what a galaxy would look like some millions of years after it collided with another one?  Hubble Space Telescope captured a view of the distant galaxy PGC 6240 and it’s a very unusual-looking site. There’s a bright core surrounded by petal-like shells of material. The petals of this elliptical galaxy appear to be tightly wound in some areas and much more open and spread out in others. The most distant petals of material look like they are detached wings, heading out to space.

The strange petal layers aren’t the only thing unusual about this galaxy. It also has a collection of globular clusters that range in age from very old to very young. This is odd because most galaxies (including the Milky Way) have collections of globulars that all formed at about the same time. This galaxy’s clusters are all over the map, age-wise.

So, how could such an amazing vision of galactic  loveliness be created?  The best suggestion for how the galaxy’s stacked shell structure came into being and the existence of unexpectedly young globulars alongside clusters with much older stars is a galactic collision.

At some point in the past, PGC 6240 merged with another galaxy. An interaction of two galaxies is a gravitati0nal dance that displaces stars and nebulae and warps the shape of the galaxies that are merging. It sends ripples through the galaxy and eventually it disrupt the galactic structure. In this case, the interaction formed concentric shells of material.

Another byproduct of galaxy merger is bursts of star formation in the galaxy. Massive numbers of new stars were created in this collision leading to the creation of new, younger globular clusters around PGC 6240. They would orbit the galaxy, along with older globular clusters that formed when the galaxy was first born.

Galaxy collisions create fascinating structures out of two or more galaxies. Interactions and collisions are how most galaxies grow and evolve, a process that began billions of years ago with the first galaxies and continues to this day.

In Fact, It’s Getting More Interesting All the Time

I’ve seen a quote floating around the Internet/WebThing that “comets and cats do as they please”. With respect to C/2012 ISON, that’s very true. This comet, much touted as “the comet of the year” may actually live up to its billing, despite the many folks of my acquaintance who have delighted in calling it a fizzle or worse just because it’s not blazing across the sky–yet.

Today there’s news that Comet ISON could be easily visible from Earth in early December, after its closest approach to the Sun (November 28). Since it’s not very bright now, how can this be?

Here it is straight from the scientist’s mouth (press release, actually):

 “We measured the rotational pole of the nucleus.  The pole indicates that only one side of the comet is being heated by the Sun on its way in until approximately one week before it reaches it closest point to the Sun,” said Planetary Science Institute Research Scientist Jian-Yang Li, who led a team that imaged the comet.

“Since the surface on the dark side of the comet should still retain a large fraction of very volatile materials, the sudden exposure to the strong sunlight when it gets closer to the Sun than Mercury could trigger huge outbursts of material,” Li said.

Dr. Li presented this information at a meeting of the American Astronomical Society’s Division for Planetary Scientists, being held in Denver, Colorado this week.

I think that’s pretty good news and reinforces that the comet is doing just what it wants. All we can do is hang on and wait to see how it survives perihelion in a few weeks.

A lot of other folks aren’t disappointed with ISON, including Adam Block, who used the Mount Lemmon Observatory  to take this great image on October 8, 2013.

If you’re new to the comet game, here’s a little background on Comet ISON.  It was discovered in September 2012. At that time, it was out past the orbit of Jupiter and was showing some activity already. After some observations, astronomers determined that Comet ISON is a sungrazer — that means it will pass very close to the Sun.  As it does, the comet will sublimate its ices as it is heated, and may also release a lot of silicate and metal-rich dust. It’s highly likely that this comet will become much brighter than any other sungrazer as it rounds the Sun.

The other interesting thing about Comet ISON is that it’s on its first trip around the Sun. That means its ices have never been heated (or “processed”). It’s a treasury of information about conditions in the outer solar system — and also about what it was like in the early solar nebula when the comet formed some 4.5 billion years ago.