Category Archives: astronomy

astronomy, Astronomy outreach, galaxies, galaxy clusters, galaxy evolution

Peeking into Galaxy Clusters

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Gravitationally Bound Galaxy Collections Have Much to Reveal

Galaxies at the heart of the Virgo Cluster. This formation is called Markarian’s Chain. Courtesy Samuel Oschin Telescope/CalTech.

Some years ago, I had the privilege of being the science writer for the Griffith Observatory exhibit project. Griffith, in case you don’t know, is located in the Hollywood Hills of Los Angeles, and is one of the best-known observatories and landmarks in the U.S. It was a rare honor, and in the years since then, I’ve found out how unusual it is for ONE person to be responsible for undertaking such a project. I didn’t know how rare it was. I was just thrilled to be on the project!

Standing by one part of the Big Picture exhibit at Griffith Observatory.

One of the exhibits that really caught my imagination (and offered me incredible writing challenges) was a giant wall containing an image taken by the Samuel Oschin telescope called The Big Picture. It features a look at the Virgo Cluster of galaxies, a collection of that lies some 53 million light-years away from us, and contains somewhere between 1,000 and 2,000 galaxies. If you visit Griffith, you can sit in front of the picture for as long as you like admiring the galaxies, quasars, stars, and other objects captured in an area of sky that you can cover with your finger, held out at arm’s length. It’s an incredible experience, and it was my great pleasure to study that image for many weeks as I wrote the descriptive text (and a video script) to go with it. In the end, it was all about what we can SEE in that image, and there’s a lot to study.

Checking Into the Coma Cluster

There are many galaxy clusters in the universe, and as astronomers get more sophisticated instruments and telescopes online, they’re digging into these galactic families to understand what makes them tick. And, it turns out that in at least one cluster (and probably many more), understanding them hinges not just on what we see, but what we don’t see.  Dark matter likely plays a huge role in what we detect going on in these galaxies and clusters. Take the Coma Cluster, for example. It is about 321 million light-years away from us and contains at least a thousand galaxies. Probably more, but many of them are very difficult to see. Why would that be?

Some of the more than 800 “dark galaxies” detected by Subaru Telescope in the Coma Cluster. Courtesy Subaru Telescope/NAOJ.

The Subaru Telescope, located on the Big Island of Hawai’i, has been studying this cluster. Recently astronomers took a look at all the archival data and found something rather interesting: it contains mysterious “dark” galaxies. More than 800 of these faint, diffuse galaxies exist, situated in the heart of a busy galactic city. Many are similar in size to our home galaxy, so imagine our immense Milky Way, but darker and dimmer. Yet, there are still stars in these galaxies. In fact, there are scads of old stellar systems, which is interesting since gravitational interactions between members of the cluster can really disrupt star systems. By all rights, those older systems should be flung around by tidal forces.

So, what’s protecting them? The best answer is: dark matter. In these galaxies, dark matter outnumbers the amount of visible matter by 99 to 1.

However, the protection of dark matter haloes isn’t the only thing going on here. Astronomers saw few “new” stars in these galaxies, which means that they lost the gas needed to form new generations of stars. This occurred fairly early in these galaxies’ lives, not long after they formed. So, the evolutionary story of these galaxies is a mystery needing further insight. And the detection of dark matter raises a LOT of questions.

Why is there so much dark matter in them? What role did it play early in the galaxies’ history? And, when did the galaxies lose the ability to form new stars? Does the dark matter than plays a role in protecting the older stellar populations have anything to do with mass loss in their home galaxies? Lots of questions, and the answers will come from additional observations of these distant galaxies.

I love looking at pictures of galaxy clusters. I’ve seen many images of the Coma Cluster, and of course, revelled in the study of the Virgo Cluster. Are all the things happening in those galaxies also happening in the many other clusters astronomers study? What’s the REALLY big picture? Stay tuned!

astronomy, charon, New Horizons mission, Pluto

Announcing Charon’s Dark Pole

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What’s Causing THAT?

These recent images show the discovery of significant surface details on Pluto’s largest moon, Charon. They were taken by the New Horizons Long Range Reconnaissance Imager (LORRI) on June 18, 2015. The image on the left is the original image, displayed at four times the native LORRI image size. After applying a technique that sharpens an image (called “deconvolution”), details become visible on Charon, including a distinct dark pole. Deconvolution can occasionally introduce “false” details, so the finest details in these pictures will need to be confirmed by images taken from closer range in the next few weeks. Credits: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

As the New Horizons spacecraft gets closer to Pluto, we are seeing more detailed images of this world and its companion, Charon. The latest ones, taken with the LORRI instrument onboard the spacecraft, show what looks like a darkened pole on Charon, a somewhat lighter region below it, and some bright regions along the limb. “Fascinating” as Mr. Spock would say. But, what is happening at Charon to make it look like that? The final answer is a couple of weeks away, so let’s talk about how we figure out what’s happening at a world (planet, dwarf planet, moon, asteroid, or comet) from images of it.

An artist’s conception of Charon (with Pluto in the background). The plumes and brighter spots depicted on Charon’s “left side” are thought to be created as water (with some ammonia hydrate mixed in) “erupts” from deep beneath the surface. The material sprays out through cracks in the icy crust, immediately freezes and snows crystalline ice down onto the surface, creating a water-ammonia hydrate ice field. Such fields were detected and studied using the near-infrared imager on Gemini North. (This composite image includes Pluto and Charon models (enhanced), courtesy of Software Bisque. www.seeker3d.com, with plumes and ice fields added by Mark C. Petersen, Loch Ness Productions. Star field from DigitalSky 2, courtesy Sky-Skan, Inc.)

As in all other aspects of planetary science, you have to look for processes on the world you’re studying to understand how they affect the surface of that place. For example, if you were approaching Earth and were still quite a ways away as you came in to assume a standard orbit (Mr. Sulu), you’d likely notice the poles, the bluish color, and the darker areas that indicate land masses. The existence of ice at the poles tells you something about the climate and temperature in those regions. The bluish water in a liquid state tells you that conditions are good enough to permit liquid water. And, the land masses have many messages of their own, from the signatures of volcanoes to the ongoing (and long-term) deformation of the surface due to plate tectonics. What you see on Earth, even at the most cursory level — and at Pluto and Charon — are all caused by complex interactions comprising chemical reactions, atmospheric mixing, and actions going on below the surface.

So, with that in mind, what’s going on at Charon? I wish I could tell you for sure. But, it looks really, really interesting! Now that we’re seeing a great variety of surface features (or, as the scientists call it, “terrain types”) it’s a hint that Charon is not just a frozen dead world. A dark terrain could indicate some sort of chemical interaction as sunlight hits specific ices on the surface. That normally happens with methane-rich ice, which Charon doesn’t appear to have much (if any) of. Instead, it has been measured to be mostly water and nitrogen ice.

However, I suspect there’s more going on at Charon than meets the eye.

A few years ago, we created a graphic “approximation” of Charon for a project with Gemini Observatory. We had to guess at what the surface looked like. You can see that, even in 2007, we had an idea that there’d be darker areas on an already darkish object. The real interesting bit was that astronomers using Gemini telescope had spotted what looked like evidence for geyser-like activity on Charon. I will be really interested to see if New Horizons finds that same evidence and confirms such activity. If it does, then we’re looking at a dynamic world with an interior that is forcing mixtures of ammonia hydrates (ammonia mixed with water) and water crystals onto the surface.  And, THAT’s cool.

I don’t know why Charon has a dark pole, yet. I suspect that the New Horizons mission team members don’t YET know for sure. They’re likely going through all the ideas en masse, and once they have more data, we’ll all know what’s ticking inside this little world.