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One of my last astronomy projects was a study of a star surrounded by the debris of two planets that suffered a catastrophic collision.

Two planets colliding around the binary suns of BD +20 307.


When asteroids or planets collide, the debris that results ends up orbiting the star. Our own solar system contains a small amount of this sort of dust, which is produced by collisions between small asteroids and by comets evaporating as they approach the Sun. This dust is known as the Zodiacal light. It shines by reflecting sunlight. producing a glow that can sometimes be seen in the morning sky.

Very rarely, collisions between larger asteroids, or even planets, occur around other stars. This creates immense amounts of dust that can absorb light from its star, and re-radiate it at longer wavelengths. Therefore, astronomers identify stars around which collisions have occurred by looking for stars that are unexpectedly bright at infrared wavelengths.

We don’t really know how often big collisions occur between asteroids and planets around the Sun. Until recently, we only had indirect information from our own Solar System to work with. For instance, we think that when the Earth was less than 50 million years old, a Mars-sized planet collided with it, breaking off a material from our planet to form the Moon. The dust kicked up by this collision would definitely have been visible to extraterrestrial astronomers.

I am not sure whether later impacts would have produced much dust. Between an age of about 400 and 700 million years, there is some geological evidence that the Moon was bombarded by a large number of asteroids, during a period referred to as the late heavy bombardment. Presumably, other inner planets would have been bombarded as well, although erosion and volcanism would have erased the signs. This could have produced dust that was visible to astronomers near distant stars.

At its current age, asteroids are believed to hit Earth every few hundred million years. These isolated events might (or might not) wreak havoc on Earth, but they are minor on cosmic scales. In the past 20 years, we have also seen Jupiter hit by comets not once, but twice. However, Jupiter is so massive that it attracts those sorts of collisions, and in any case, the asteroid simply gets absorbed into the planet, without polluting the surroundings with dust.

So, to get a better handle on how often collisions occur around stars of different ages, astronomers get a large catalog of stars (such as the Henry Draper catalog and its extensions, which contain the 359,083 brightest stars), and see whether any are unexpectedly bright in the infrared. We find that most stars around which collisions have occurred are young (10 to 100 million years old), because the orbits of their planets and asteroids haven’t settled yet. Old stars surrounded by the debris of annihilated planets are reassuringly rare.

Nonetheless, we have some good evidence that big collisions do sometimes happen, even around older stars. Over the summer I noticed a couple papers. Lisse et al., recently described the composition of dust around a 12 million year old star HD 172555. They infer that a large asteroid recently collided with a rocky planet around that star. Moor et al. report the discovery of four stars surrounded by dust. Three of them are less than 200 million years old (phew), and one of which is probably about 2 billion years old (HD 169666, uh-oh). Moor et al. do not elaborate much on the origin of the dust in their paper (frankly, in the preprint version, they didn’t do a particularly good job of presenting their conclusions).

My collaborators and I, however, do not suffer from similar restraint. I joined a project led by Ben Zuckerman, to study the dustiest Solar-type star known, BD +20 307. The amount of dust around the star led us to believe that two planets had collided recently, in an event of a magnitude similar to that which formed the Moon. We expected to discover the star was young, but we were in for a surprise. . .

I have written a piece about the result, and placed it here. You can also see our press release, if you want the quick version.

A link on BoingBoing to a page describing how to make a poster for a conference made me realize that my own talks and posters were no longer easily available on-line. I know that other people’s presentations have influenced my own, and have always been glad when people shared their work. So, I have remedied that with a page of talks and posters.

It also got me thinking again about what goes into a good presentation. Reading the advice on posters, I found a lot of good ideas. However, I think that their recommendation of putting at most 800 words on a poster makes a poster that is still too wordy. In the biggest conferences, people will have hundreds of posters to look at per day, and only an hour or so to do so. I realized that I ended up standing next to my poster most of the time, and the people who were interested in it would ask me to explain it. Very few people would stand and read all the text, and when they did, it was awkward to be standing there.

So, I started to reduce the amount of words on my poster, and just keep the points advertising my conclusions. I made this poster to look a bit like a tabloid, and I think it worked well. My favorite, though, is an attempt to summarize several papers on X-ray emission from the Galactic Center with haiku.

My best talks were given when I followed some of the advice of Patrick Winston on How to Speak. His big four are: reminding the audience several times about what points you are trying to convey by referring back to an outline; using verbal punctuation (such as enumeration) to provide boundaries between points and allow the listener to get on board; teaching difficult concepts by talking about things that are close, but not quite, what you are trying to describe; and asking answerable questions to engage the audience.
If I even follow two of the four, I tend to get positive responses from the audience.

I’ve also incorporated advice from other researchers, including using the titles of slides to summarize my points, putting lists of collaborators at the ends of talks where they don’t derail the introduction, and, most importantly, making sure that only one or two thoughts are placed on each slide (never, ever split a slide into four quarters containing separate things to discuss).

I am particularly proud of a few talks. One of my first PowerPoint talks summarized my thesis, and I received a number of complements on it. I made the talk shortly after watching The Shining, so while the talk was mostly black text on a white background (the only image I had to work with was a simulation I made), the transitions were white text on a black background. The dramatic transitions helped people follow a talk that otherwise had a lot of rather dull graphs.

I also enjoyed giving my most recent talks on the Galactic center, because I had a lot of new images to work with that lent themselves to an attractive visual format. I also got to tour the Netherlands giving my talks.

Although I have improved my presentations through trial-and-error, there is still a lot I need to work on. In my new position, the group really emphasizes giving clear, concise, well-rehearsed presentations. I worked harder on the one 15 minute talk I’ve given so far than on any of my astronomy talks. The group’s work pays off when you compare our talks to the disorganized presentations that are usually churned out by the aerospace industry.

Which brings me around to the books I’ve been reading by Edward Tufte. Among other things, he’s picked apart the ways in which bad presentation contributed to both Space Shuttle disasters (see also Visual Explanations). I like them so far, and I’m going to try to put some of his advice into practice as I develop this site.

Starting Anew

I am starting a new blog, because I am going through a withdrawal, of sorts.

I was an astronomer for 11 years, until last September. I am counting in that time 5 years of graduate school at MIT to get a PhD, and a year as a postdoc at MIT, 3 years as a Hubble Fellow at UCLA, and 2 years funding myself with grants at Caltech. Last October (2008), I took a new position at MIT Lincoln Lab. The details aren’t particularly important to this post, but, in essence I am now working as a consultant.

I had several reasons for leaving astronomy. The biggest one is that I was not having any luck finding a permanent position someplace my wife and I wanted to live. Although my record as a researcher was good, I was having trouble for several reasons.

First, I was limiting my search to areas around large cities, so that my wife would be able to pursue her career. This limited my search to about a third of the available positions at research labs and universities.

Second, my research relied heavily on X-ray astronomy, which is not currently viewed as a hot topic in the US. A large fraction of astronomers work on cosmology and galaxy evolution, and so they naturally try to build their field by hiring colleagues working on similar topics. Searching for planets also has become an enormous growth field, for good reason. Both fields will be supported by the next major (billion-dollar plus) observatories, the James Webb Space Telescope (in some ways the successor to Hubble), and planned thirty-meter class ground based telescopes. In contrast, X-ray astronomy in the US has one small explorer mission ($150 million) planned for 2011 (NuSTAR, which I did some planning for), and nothing definite planned until past 2018, when there might be funding for the billion-dollar satellite X-ray astronomy needs in order to make serious progress. Although I was doing a lot of ground-based infrared astronomy as part of my research, I was still put into the X-ray astronomy box by hiring committees (fair enough; that’s what I was best at), and I think that they wondered how I would spend the next 10 years of my career.

Third, astronomy is saturated with excellent young researchers. I might have been able to boast that I wrote 26 first-author papers, produced multiple results that were picked up in the popular scientific press, and brought in several hundred thousand dollars in research funds. However, there are probably 20 or 30 other young astronomers applying for jobs each year who could say the same thing. At the same time, there are only about 20 or 30 positions at solid research institutions in the US each year. Given my constraints on location, and the lack of certainty in my sub-field (many of my competition was working on hotter topics), I wasn’t too surprised that I wasn’t getting offers.

Finally, I didn’t have any teaching experience, which probably kept my application from being considered by universities where teaching was a major emphasis. Having been educated at research universities, I had been told that this wouldn’t hinder me, but now I have my doubts.

In any case, for the past 6 years, I had been promising myself and my wife that I would have someplace permanent by now. Postdoctoral positions in astronomy tend to last 3 years. Although I was in the process of arranging a research scientist position that could have lasted until 2012 or so, I couldn’t provide any sense of certainty for us beyond that. As a result, my wife felt that she couldn’t become too committed to her work if we were just going to move in a few years, and buying a house seemed out of the question. The research position would also have put off our long-term goal of moving back to the East Coast.

So, after interviewing for faculty positions last year and receiving no offers, I did receive an offer from Lincoln Lab. It wouldn’t be an academic position. I’d have to work on the projects that our sponsors requested, so I would have less freedom during work hours. I also wouldn’t be publishing, or presenting my work to the public. I knew both things would be hard for me, and they have been. I went into astronomy in large part because I liked it, and it would give me a chance to be a natural philosopher. I enjoyed sharing the stories that came out of my work, about what happens when a star dies, and the fates of stars that get too close to black holes.

At the same time, though, research has a way of creeping into weekends and evenings, and tends to crowd out other interests. I liked what I was doing in general, but the specifics of my research were getting tedious. I didn’t want to be doing the same things 10 years from now, and if I had started on the path toward being a research scientist, that probably would have happened.

My new job has three great advantages: it will expose me to new opportunities, it pays a lot more, and it only needs to be done at work.

So that brings me to the point of this blog. With the time I have outside of work, I can work on my own projects. I don’t have to get funding, or the next job, so I can even dabble in things that I’m not really qualified for. That said, though, I think that with my background, I do have a lot to contribute to discussions about science, technology, and even philosophy. This blog, and the other elements of the site that I am building, will be the public outlet for my interests.

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