A Beautiful Star Cluster for Dark Times

As many readers switch from Daylight Savings Time to find darker evenings awaiting them, here is a beautiful new image from the Hubble Space Telescope. We see a "globular cluster" with the catalog name M5 -- an ancient collection of stars, with about 100,000 of them visible on this remarkable photo.

The image combines views taken with visible light and infra-red cameras, and highlights some of the younger bluer stars sprinkled among the older yellower stars that make up the majority of the cluster. This grouping is about 25,000 light years away and was born 12-13 billion years ago.

It was about 100 years ago that Harlow Shapley, one of the greatest astronomers of the 20th century, used such bright globular clusters to map the extent and shape of our Milky Way Galaxy and to demonstrate conclusively that the Sun and the Earth were not in its center.

Such a beautiful picture can help remind us that there is a larger perspective out there, and help us put aside thoughts of the crazy things we seem to be doing to each other and to our fragile planet on almost a daily basis. Click on the pictures to see them bigger.  The diagram below shows how the globular clusters, distributed above and below the plane of our Galaxy, help outline its shape and extent.

A Sparkling Cluster of Stars from the Hubble

Here is a beautiful new image from the Hubble Space Telescope, showing a young cluster of stars called Trumpler 14.

Located about 8,000 light years away in the constellation of Carina, this grouping of hot bright stars formed only recently from a great cloud of cosmic raw material, called the Carina Nebula. It is one of the great ideas that we now know about how stars live that the more massive a star, the brighter it shines, and the shorter its life-span will be before it "burns out." Superstars die first, is the general rule.

Because Trumpler 14 formed only about 500,000 years ago (which is a very short time on the cosmic scale), this group still includes a lot of bright superstars, which dominate our image.

Robert Trumpler (1886-1956) was a Berkeley astronomer, who compiled a very useful list of star clusters (places where dozens to thousands of stars are born together.) An annual award at the Astronomical Society of the Pacific, honoring the best PhD thesis in astronomy in North America, is named in his honor.

In our picture, you can see a jewel-like display of bright stars in front of the glowing gas and dust of the nebula. The stars in this cluster are one ten thousandth the age of our Sun. Mere babies, really!

Click on the photo to enlarge it and see it even better.  

A Possible Sister Star that Formed with Our Sun

Astronomers now know that stars, like people, tend to be sociable. Stars are often born and hang out in groups -- double stars, triple stars, star associations, and star clusters.  Yet our Sun is a single star, surrounded only by its family of planets and moons, but no sibling star to keep it company.  Was it always this way?

In recent years, it's become clearer that our Sun could well have formed in a loose group of thousands of stars, when it first "clumped" out of the gas and dust (raw material) of the Galaxy some 5 billion years ago.  If our mother cluster was indeed just loosely held together by the mutual gravity of the stars, in all that time, the stars could have drifted apart -- as many families do in the busy course of life. 

So we have been on the lookout for the Sun's now far-away sisters. This past week, a team of astronomers, headed by Ivan Ramirez of the University of Texas, announced that they might have found our first long-lost sibling. 

There are perhaps as many as 400 billion stars in our Milky Way Galaxy.  How can we possibly find our sisters in that huge and anonymous crowd?  After all, there are no star birth certificates on file at county offices and no little tags that hang around a star's neck.  The search involved two factors: First they looked for stars that have the same chemical make-up as the Sun (they consist of the same proportion of elements) -- which you'd expect from stars born in the same"womb."  And then they searched for stars whose motion could be calculated backwards in time and would have placed them close to us 5 billion years ago. 

Sorting through 30 possible candidates identified by other groups of astronomers after painstaking work, Ramirez' group came up with exactly one star that fit all the criteria.  Called by its catalog number, HD 162826, it's 110 light years away now, in the constellation box called Hercules.  (See the map.)  It has 15 % more mass than the Sun, and so it is a little brighter and a little hotter than our star. (In astronomy jargon, it's a Type F star, while our Sun is Type G.)

It turns out that HD 162826 has been searched for planets for the last 15 years, and so far, no planets have turned up.  But the kind of search it has been subjected to can't find small (Earth-like) planets. So the we have a long way to go before we can decide it the star has a planetary system around it or not.

Future surveys, allowing us to analyze the make-up of fainter stars, could well turn up other family members out there.  For now, astronomers will keep a far closer eye on this one possible sister star and follow it as it goes about its life.  Who knows, one day, someone from there may just respond to the equivalent of a cosmic blog post.

A Cluster of Stars Thrown Out of Its Galaxy at 2 Million MPH

A team of astronomers has discovered the first cluster of stars that has been thrown out of another galaxy. Whatever threw this rich grouping of stars out of the galaxy known by its catalog number as M87, was able to accelerate it to a speed of some 2 million miles per hour. Kids, don't try this at home without adult supervision!

It just so happens that the star cluster is being thrown roughly in our direction, but since M87 is 54 million light years away, no one is worried. The cluster will just wind up in the space between galaxies, wandering like the lost ships of legend, never finding its home port again.

M87 is a huge galaxy of stars and clusters, almost a million light years in diameter (our Milky Way Galaxy is about 100,000 light years across, by comparison.) In addition to thousands of billions of stars, M87 contains an estimated 12,000 "globular clusters" -- tightly bound groups of roughly 100,000 stars each. Our home galaxy only has about 150 of these globular clusters, and we are a pretty good-sized galaxy as far as cosmic requirements are concerned. So M87 makes us look like a 90-lb weakling in comparison.

So how did a cluster with many thousands of stars get loose from the considerable gravity of a giant galaxy like M87? No one knows for sure, but here is the clever idea that discoverers of the high-speed cluster are suggesting. Giant galaxies like M87 get bigger by eating smaller neighbor galaxies for lunch. Occasionally, they even merge with a big galaxy, gently pulling in the other galaxy's stars and other "inhabitants." What if M87, in the distant past, swallowed a big galaxy with a giant black hole at the center?

Astronomer have recently found that all big galaxies have big black holes in their crowded cores. The bigger the galaxy, the bigger the central black hole, in general. So M87 probably had a big black hole and the other galaxy would have had a big black hole too. As the two galaxies merged, their two black holes, like boxers circling each other in the ring, could have begun to orbit around each other. (We have seen pairs of big black holes in other such systems, so this is not a wild idea at all.)

Now, along comes our victim globular cluster, which had some orbit around the center of M87 that might well have brought it a bit too close to the pair of black holes. When the black holes interacted with the cluster, their gravity might have played a "game of pool" with it. In pool (or billiards, for some of you), you often see one ball interacting with another and then causing a third ball to go shooting off into a distant pocket. When the two black holes and the cluster had their moment of gravitational interaction, the cluster could have been thrown out of the galaxy by the tremendous gravitational energy of the giant black holes.

Astronomers have seen superfast stars thrown out of galaxies, but this is our first instance of seeing a whole cluster of stars shooting out from its home galaxy. M87 is one of my favorite galaxies anyway, with many other signs of violence and inner turmoil. This makes it even more interesting. The accompanying image is an artist's attempt to show the cluster coming out of M87, which is correctly shown as a fuzzy rounded blob.

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On a personal note, I would like to dedicate today's post to the memory of my good friend and colleague, Alan Friedman, the former director of the New York Hall of Science, who passed away this weekend.  Alan and I taught weekend courses on Einstein together, wrote papers on interdisciplinary approaches to teaching astronomy and physics, and bemoaned the state of science education in the U.S. over many dinners.  Alan also helped chart the course of the Lawrence Hall of Science in Berkeley, the Parc de la Villette science museum outside of Paris, and dozens of other museums and science centers where his advice was frequently sought.  He leaves an emptiness in the universe that will be impossible to fill.

Stunning Wide-Field Image of a Star Nursery

Every once in a while, I see a new astronomical picture that leaves me with my mouth open, saying "Wow!" The above image, assembled by a talented amateur astronomer, from information taken by a number of different telescopes, is one of those.

This wide-angle view is centered on a cluster of recently-born stars that is known by its catalog number of NGC 2264. Surrounding the adolescent stars is a whole region of cosmic gas and dust -- the raw material from which stars are born. The nearby gas glows with the characteristic red color of its most common constituent -- hydrogen.

At left center is the Cone Nebula, a region of gas and dust in the shape of a sideways dark cone; the energy of bright stars to the right of the cone is eating away at the sides of this thick dusty region, leaving only a cone of thicker material behind.

To the right of the Cone Nebula, you can see an opposite (larger) cone pattern of bright stars stretching rightward. Some people see the lights of a sideways holiday tree in the pattern of bright stars.

At the bottom center of the image, pointing upward into the bluish emptier region (where the energy of freshly made stars is clearing things out), you can see an odd region of gas and dust that is sometimes called "The Fox Fur Nebula." Click on the picture and take a good look -- can you see the head of a furry red fox pointing upward into the bluish region?

The entire complex of stars and gas and dust is about 2,600 lightyears away, which means the light we see tonight left this region about 2,600 years ago -- a time when humans on Earth lived a much more challenging existence and lifespans were less than half of what we enjoy today.

This remarkable picture was assembled by Dr. Robert Gendler, a physician and amateur astronomer, who is a master at working with photographic information using his computer. The image was constructed from information provided by the Subaru Telescope in Japan and the Digitized Sky Survey, put together by astronomers at the Space Telescope Science Institute from a number of earlier surveys of the sky. To see more information about the photo, see:
http://www.robgendlerastropics.com/Cone-Subaru-DSS.html

You can go to Dr. Gendler's home page at that site and then browse his many other wonderful images. But take a minute and just enjoy a full-screen version of the picture -- you are seeing the same process of star birth that gave rise to our Sun some five billion years ago.

A Magnificent Cluster of Stars Captured

I wanted to share a remarkable new Hubble Space Telescope image with you. In the accompanying picture, you see a magnificent cluster of over 250,000 stars, a grouping whose catalog number is M9. (This designation comes from a list Charles Messier made long ago of fuzzy objects of interest in the sky.)  The colorful cluster is in the direction of the center of our Milky Way galaxy, some 25,000 light years away. (This means that, traveling at the speed of light, it would take you 25,000 years to travel there!) What's fascinating about this Hubble image -- taken with the Advanced Camera for Surveys -- is how clearly we can see individual stars in this crowded, distant group. (The cluster is so far away and so small that it takes up about as much of the sky as the head of pin, held at arms' length.)

The stars in this cluster are typically older than the Sun and contain fewer of the heavier elements that make life and technology on Earth possible. Such clusters, called globular clusters, are thought to be among the oldest objects in our Milky Way Galaxy.  We study the globular clusters like M9 to learn more about the archaeology of our home galaxy and how things were in our neighborhood long before the Sun and the Earth ever existed.