Every once in a while, I am mistakenly introduced as an astrologer instead of an astronomer. There's a big difference, as I am quick to point out. Astrology is an ancient superstition, left over from thousands of years ago, when most people saw celestial objects as gods or symbols of the gods, and not as physical bodies whose characteristics our instruments can now explore.
When, in the 1980's, it was revealed that President Reagan's White House schedule was for years vetted by a San Francisco astrologer, I was interviewed by the media as a critic of astrology. I tried to come up with an analogy that would make sense to the news media and the public for why scientists had a hard time believing in the idea that your personality or destiny would be governed by the location of the Sun, Moon, and planets in the sky at the moment of your birth. I suggested a new form of "cosmic wisdom" called JETOLOGY, where your personality or fate could be explained by the position of all the jumbo jets at the time you were born. When people sniggered at the notion of jetology, I could then ask why astrology sounds any better.
I am reminded of this because, for those of you who are in the San Francisco Bay Area, I am preparing to be one of the featured speakers at SkeptiCAL, a one-day conference Saturday, May 31 in Oakland, on how to confront claims of the paranormal or the "too good to be true" by using common sense skeptical thinking. See: http://www.skepticalcon.com/
Years ago, I wrote a short "Astrology Defense Kit" for science-oriented people who meet astrology believers. You can read it at: https://www.researchgate.net/publication/253783518_Your_Astrology_Defense_Kit?ev=prf_pub
If you want to see a wonderful short video on how it can be that the vague pronouncements that make up most astrological readings are taken seriously, I recommend the following episode of "Trick of the Mind" by British magician and skeptic, Derren Brown: https://www.youtube.com/watch?v=haP7Ys9ocTk
Ah, skeptical thinking -- if we had more of it during our years of education, during political campaigns, or when we view advertisements, our country would be so much better off.
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 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.
