January 30, 2005 at 14:23 pm | 5 Comments
Back when I used to lecture in the planetarium I would solicit questions from the audience at the end of each presentation. Every once in a while somebody would ask me what it’s like inside a black hole.
Trick question, right?
Well, probably for some of the more smart-aleck audience members it was. But, I always had an answer. I’d go into a little discussion about how we don’t know exactly, and based on a number of factors (including the laws of physics, some Einsteinian laws, etc.), we’ll probably never have a chance to explore the inside of one (and, if the gravity is so strong that light can’t even escape, is the inside of a black hole REALLY a place we want to be?). Following that there’d be a silence as people digested the idea of “being there”. Then we’d get into a discussion about what it be like to be right next to a black hole, which is a lot easier to describe, even if it IS a shrieking maestrom of radiation and searing temperatures.
At the time I was first in school, back in the dark ages of the early 60s, black holes were sort of a mathematical curiosity, a physics problem for which we didn’t have any good examples. That all changed with the advent of telescopes and detectors able to “see” the effects of black holes, including the jets that spray out from the vicinity of one as matter (stars, gas, dust) spiral into the hole. Moreover, black holes have gravitational effects on nearby stars and gas and dust that we CAN track with spectroscopic observations of the light emanating from the nearby region.
Which brings us to the center of our own galaxy, where a supermassive black hole about a million times the mass of our Sun lies hidden by gas and dust clouds and star clusters. This SMBH (for short), also known as Sagittarius A* (or SgrA*), radiates tremendous amounts of energy which we can detect in gamma rays. As luck would have it, we have a spacecraft called INTEGRAL that “sees” that radiation. In the image above, INTEGRAL shows us a gamma-ray view of the region near the center of the Milky Way.
Now, SgrA* is a pretty quiet and harmless black hole, and isn’t quite the powerhouse of radiation that others are—like, say, the black hole at the center of galaxy M87, which sports a very active jet. Yet, in the past, the Milky Way’s resident black hole has been restless, and whenever it acts up, the surrounding clouds light up with the evidence.
Right near SgrA* is a cloud of gas called SgrB2, and the two are about approximately 350 light-years apart. Sgr B2 is being exposed to a blast of gamma rays emitted by Sgr A* that went off about 350 years ago. The cloud absorbed the radiation and has been emitting it. Interestingly enough, the astronomers studying the data think that the whole outburst took at least ten years, possibly longer. And they’re using their studies to figure out how often and how strongly “our” black hole turns on, radiates, and then turns off again.
I have to admit, it’s pretty heady growing up knowing that these weird things that scientists once thought were probably rare are now found all over the place (in many galaxies and at the death scenes of supermassive stars). And, I find it very cool indeed that we can study the near-black-hole environment and learn so much about them.
January 27, 2005 at 22:15 pm | Leave a Comment
The passage of Comet Machholz near the Pleiades a couple of weeks ago reminded me of a project I spent a number of years working on in the late 1980s and early 1990s—the International Halley Watch Atlas of Large-Scale Phenomena— a compendium of Comet Halley images. The whole thing began when applied for a job as a research assistant on an IHW team at the university. I spent the next several years measuring and studying many, many images of Comet Halley, teasing out details about its plasma tail structures. Our interest was to chart the changes in the plasma tail as the comet sampled various “regimes” of the solar wind, and use those changes to understand how the solar wind affected the charged particles in the plasma tail. It got to the point that I could look at an image of Comet Halley and tell you exactly when it was taken (date and time) and tell you something about whether or not its plasma tail was about to disconnect or was rebuilding itself after a disconnection event (when the plasma tail would break off and then re-form in response to changes in polarity in the solar wind stream).
So, it was with a great sense of memory and history that I looked at this image (and many others) of Machholz as it passed near the Pleiades star cluster in the January sky. For one thing, it was clear that the comet had just undergone a disconnection event. The new tail was sprouting out from the coma and the remnants of the old tail were streaming out in a clump highlighted against the Pleiades. (The dust tail, by contrast, is the yellowish streak that seems to point roughly downward in this image.)
Even cooler, I ran across this image from Gerald Rhemann, one of Austria’s best-known comet chasers and astrophotographers. I became quite familiar with Gerald’s work (along with his collaborator Michael Jaeger) during my Halley years, and in my subsequent role as coordinator for observations for the Ulysses Comet Watch network in the early 90s. It’s a double blast from the past—comet plasma tails and the fantastic work of a photographer whose work I’ve long admired. The scene is stunning, combining my old research interest with one of my favorite star clusters in the winter sky. Sometimes astronomy doesn’t get any better than this!
January 26, 2005 at 14:34 pm | Leave a Comment
Observatories are our windows to the universe. Through their gates, we can move out to distant realms and explore the lives and deaths of stars, the evolution of galaxies, and the origins of the cosmos. Astronomers used to travel to observatories quite regularly to do their work, which made them appreciative of the distant, lovely places where these facilities are built.
Now you don’t have to go to an observatory to get your data as much as in the olden days (or nights, actually), because many facilities are automated and can deliver your data across the Internet (or in digital format on tape or disk) very quickly. We are in the age of remote observing, and it seems to me to be a natural evolutionary step for astronomers to take. Yet, something is lost, something described in Patrick McCray’s book Giant Telescopes as a romantic link to a past time of astronomical discovery when lonely men (they were almost always men) wrestled with great astronomical beasts atop cold mountaintops. Many important discoveries were made by those men and their machines, and their hard work has led directly from the ways of the “old days” to the methods of today’s astronomers.
Still, that shouldn’t stop us from appreciating the beauty of the mountaintops, even as we revel in the rest of the cosmos that is revealed from their observatories. I think every astronomer should go up a mountain at least once in his or her career, and not just for the heady experience of trying to take data at high altitude (although that’s a hoot, too). You gain a new perspective on the world when you go up the mountain. You get to feel as if you could fall up to the stars when you step outside from the control room during an observing run. And, then there’s the rush you get from knowing that the night you’re up there, you’re one of a handful of human beings across the world who are doing what you’re doing.
In that sense, then, observatories are truly gateways to discovery. It’s just that what you discover isn’t always up in the sky!
January 23, 2005 at 11:51 am | Leave a Comment
I suppose it’s fitting that during the week of major discoveries on cold, methane/ethane-slushy Titan that a snowstorm would arrive to remind us of winter cold here on Earth. However, what some of us are experiencing in the snowstorm currently enveloping the New England area of the U.S. would be a balmy day on Mars and a downright searing heat wave on Titan! Imagine the report from The Weather Channel(tm) if we lived on Titan:
Folks out near Dragon’s Head are well advised to stay inside for the rest of the day, as a strong cold front is bringing methane flurries. Temperatures could plunge to -183 Celsius, with wind chills making it feel like -190. Watch out for lake-effect accumulations around the shores of Snowy Sea. And people, if you don’t have to be out, we advise you stay in and stay warm!
It’s kinda fun to think about “extreme” weather on other planets and how we’d deal with it if we lived there. Of course, life on Titan (for humans) would be a challenge of major proportions. Just how would we build habitats? Out of what? And why would anybody want to live there? There’s another good science fiction story there, just waiting to be written!
January 19, 2005 at 11:21 am | Leave a Comment
Remember a year or so back when the largest Kuiper Belt Object to date, named Sedna, was discovered? It shifted planetary scientists’ attention to the origin and evolution (and existence!) of large, planetoid-sized objects out beyond Pluto. They’ve been working out the fine details of Sedna’s orbit for a while now, using sophisticated models of the early solar system formation. One of the outcomes of this work is the idea that this nearly-Pluto-sized “worldlet” actually formed in place in the frigid deep-freeze of the outermost solar system. Originally scientists thought it was assembled farther in toward the Sun during the early days of the system’s formation, and was somehow ejected out to its current position.
Why does where Sedna formed matter? Astronomers have longed assumed that planetary formation took place in a rather smaller region of the original solar nebula. If Sedna was created from the collisions of smaller bodies out in the “sticks” of the solar system, then the planetary factory is bigger than everybody suspected. It also means that the Kuiper Belt, which hosts countless bodies at what used to be called “the edge of the solar system” is really part of a larger region called the Kuiper disk and played a much more prominent role in the formation of planets and moons.
The modeling that led to these conclusions was done at the Southwest Research Institute in Boulder, Colorado. In the press release they sent out announcing this work, the institute’s Executive Director for Space Studies, Alan Stern (a former colleague of mine from the University of Colorado), talked about some of the assumptions they made in constructing their model: “”The Sedna formation simulations assumed that the primordial solar nebula was a disk about the size of those observed around many nearby middle-aged stars — like the well-known example of the 1,500-AU-wide disk around the star Beta Pictoris.”
It’s interesting work because it gives us a whole lot MORE insight into the infancy of our own solar system, in particular the formation of planets from smaller planetesimals. And, chances are if Sedna formed where the astronomers think it did, then there could well be more large planetoids circling around out there with it — and that what we used to think of as the “emptiness of the outer solar system” isn’t so empty anymore. As astronomers learn more about the Sun’s outermost retinue of planetesimals, they are finding more clues to what conditions were like early in the history of solar system.
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Image of Horsehead Nebula: T.A.Rector (NOAO/AURA/NSF) and Hubble Heritage Team (STScI/AURA/NASA)
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