Andrew Hearin ’03

Like most academics, I obsessively keep track of who’s citing my work.  As a result, this paper caught my eye today.  (If that link doesn’t work, try this one.)  The lead author is a UR alumnus and winner of both of the physics departments main awards in his senior year.  During my first year here, I taught him in an independent study course on relativity.  He went off to graduate school in mathematics, but he later saw the light and came back to physics.

I haven’t read the paper in detail yet, but from the abstract it looks like a very nice piece of work (in addition to having the good taste to cite me). Congratulations, Andrew!

Good luck to Kepler!

NASA successfully launched the Kepler satellite, which will spend 3-4 years surveying nearby stars to look for Earthlike planets.  We’ve discovered lots of giant planets so far, but we know relatively little about how common smaller planets like ours are.  Assuming that life elsewhere is most likely to have evolved in environments similar to our own (a reasonable guess, although it’s important to bear in mind that we don’t really know it’s right), this is obviously a really important piece of information to acquire.

Congratulations to Alicia Soderberg

Alicia Soderberg is the winner of the 2009 Annie Jump Cannon award.  This very prestigious award is given by the American Astronomical Society to a female astronomer, at most 5 years post-Ph.D., for “outstanding research and promise for future research.”

I taught Alicia when she was an undergraduate at Bates College.  In fact, I think I was nominally the advisor for her senior thesis or something.  I say “nominally,” because I really had little or nothing to do with it: her thesis work was with a group at Harvard, and she  really worked with them, not me.   (Even so, I’m a bit embarrassed that I can’t remember for sure whether I was her advisor: I don’t think that there are any other students about whom I’m unsure whether I was  their research advisor!)

By the way, if you don’t know who Annie Jump Cannon was, you should read about her.  She did very important work in astronomy, figuring out the classification of stars that is still used today, at a time when women were largely excluded from science. Despite the importance of hr work, she was denied full recognition, only receiving a proper academic appointment very late in her career.

McCain tweets about astronomy

This news is a few days old, but in case you haven’t heard, John McCain has apparently been making fun of various earmarks in the current spending  bill on his Twitter feed.  One recent tweet:

$2 million "for the promotion of astronomy" in Hawaii – because nothing says new jobs for average Americans like investing in astronomy.

I agree that that earmarks are a lousy way to allocate funding.  But it really bothers me that complaints about earmarks so often take the form of contemptuous mocking of science.  For the record, astronomy jobs are jobs, and astronomy is a significant industry in Hawaii.  Yes, the average American doesn’t work in the astronomy industry, but the average American doesn’t work in, say, road construction either. 

This post from the Cosmic Variance blog (a very good science blog, by the way) says it all much better than I can.

Planck preparing for launch

The Planck Surveyor, the European Space Agency’s satellite-borne microwave background telescope, is preparing for launch on April 16.  Andrew Jaffe has some pictures of the preparations.

Planck will map the microwave background with finer resolution than NASA’s WMAP satellite.  It’ll also cover a considerably broader range of frequencies.  This is helpful in separating the microwave background from other, more local sources of radiation.

I think I’m still officially a member of the Planck team in some sense, although I haven’t done any real work on it.

Collision course?

Recent observations apparently suggest that our home Galaxy, the Milky Way, is considerably more massive than had been thought.  The actual measurements are of the orbital speeds of objects in the Galaxy, but the speed gives an estimate of the mass, and mass is more interesting than speed, so that’s what people seem to talk about.

It’s interesting that we’re still relatively ignorant about our own Galaxy: orbital speeds of objects in other galaxies  are measured much more accurately than those in our own. I guess it’s all a matter of perspective: it’s harder to tell what’s going on from our vantage point in the middle of our Galaxy.

Some news stories have  drawn attention to the fact that this means that our Galaxy will collide with the nearby Andromeda galaxy (M31 to its friends) sooner than had been previously estimated.  Supposedly, that collision is going to happen in a mere5-10 billion years.  I’ve never understood why some people say with confidence that a collision is going to happen, though.  It’s true that the two galaxies are getting closer, but as far as I know there’s no way to measure their transverse velocity, so we don’t know if they’re heading straight at each other or will move sideways past each other.  It seems quite likely to me that the galaxies are actually orbiting, not plunging straight at each other.  If anyone knows whether there’s any evidence one way or the other on this, I’d be interested.

One technical note: The new rotation speed measurements are about 15% larger than the previously accepted values.  Science News says that that results in a 50% increase in the estimated mass.  That would make sense if the mass scales as the cube of the speed, but naively it just scales as the square.  If the revised speed measurements go along with a revised length scale for the Galaxy, then that might explain it.  I suppose if I dig up the actual scientific paper rather than the news accounts, I could find out the answer, but that sounds like work.


You’ve probably seen these pictures of planets orbiting other stars.  They’re obviously amazingly cool, but they raise a number of questions:

1. Why does one of them look like the Eye of Sauron?

2. Are these just cool pictures, or do they represent a significant advance in science.

(Full disclosure: I stole #1 from a student.)

Part of the answer to #1 is that the people who made this picture had to choose a more-or-less arbitrary color scheme to show the image, and they happened to choose a red one.  This image is apparently taken using visible wavelengths of light, but the colors shown are”false colors.”  (Extra-geeky aside: I’m not sure, but I think they might have gone with IDL’s “red temperature” color scheme, which happens to be one I’m partial to.)

The black region in the center is where they blocked out the light from the star by putting something in front of the telescope.  If they hadn’t done this, the light from the star would have overwhelmed the faint signal from the planet.  The reddish stuff is mostly radiation from the dust surrounding the star.

What about question #2: how important is this?  This is far from my area of expertise, but I’ll give my impressions anyway.  I think it’s mostly important as a milestone on the way to future discoveries.  Even with these images, the amount that we now know about these particular systems is not all that much greater than what we already knew about the few hundred other star systems where we’ve discovered planets.  In those other systems, even though we don’t see the planets, we can often figure out quite a bit about their locations, masses, orbits, etc., by observing the planets’ effects on their host stars.

But this is still a really big deal, because it’s a step on the way to eventually learning a lot more about these planets.  If you can learn to isolate the light from the planet, as distinct from the starlight, then you can study properties of the planet that can’t be gotten by the earlier kinds of observations.  In particular, if you can take that light and pass it through a spectrometer, you can do chemistry.  You can figure out what the planet is made of, what’s in its atmosphere, etc.

Ultimately, of course, doing chemistry on planetary atmospheres might give us evidence of life out there, which would be the just about the most important bit of science I can imagine.  But even if that doesn’t happen, just being able to study the composition of planets at all will be pretty amazing.

I don’t know how big a step it is to go from the sorts of images we’ve seen this week to spectroscopy, but this is definitely a lot closer than we’ve been before.

Black holes

The section of my Black Hole FAQ on the observational evidence for black holes is sadly out of date, although the rest of it is still reasonably current. I don’t have any plans to update it, because that sounds altogether too much like work. I’d have to read a lot about things I don’t know much about in order to get up to speed on the subject, and if I’m going to do that, I think it’d be more fun to do it on some new subject rather than revisiting this one.

If I were going to write about this subject, though, I’d certainly want to talk about some recent results published in Nature concerning observations of the black hole at the center of our Galaxy. I think you need to be a subscriber to see the article or Nature’s newsy description of it, but there’s a Science News article that I think is publicly available. (Thanks to my brother Andy for pointing this out to me.)

There’s no way to see past the horizon of a black hole, so the name of the game in this business is to try to see as close as you can to the horizon. If you can resolve details near the horizon, you can look for distorting effects due to gravity, which provide pretty definite evidence that what you’re looking at really is a black hole. If all you can see is stuff that’s 1000 times bigger than the horizon, then it’s hard to tell the difference between a black hole and any other object of the same mass. The authors of this paper have managed to resolve structures that are just about the same size as the horizon.

By the way, one of the authors was a friend of mine in graduate school. Among his lesser-known accomplishments is writing a brochure describing the Berkeley astronomy department to incoming graduate students, in the form of Allen Ginsberg’s “Howl”. I don’t know if copies of it survive, unfortunately.

Down with the rubber sheet

People like to visualize the expanding Universe as a sort of a stretching rubber sheet. Textbooks and popular cosmology books play up this analogy in a big way. Like most analogies, it’s useful in some ways, but taken too far it can lead to misconceptions. David Hogg and I have written an article in which we try to fight back against some of these mistakes.

The article is about how we should interpret the redshifts of distant objects. Most of the time, redshifts are Doppler shifts, indicating that something is moving away from you. In the cosmological context, though, a lot of people think that you’re not allowed to interpret the redshift in this way. The idea is that galaxies are “really” at rest with respect to the stretching rubber sheet. Since they’re not “really” moving, what we see is something different from a Doppler shift. The point of our article is to rehabilitate the Doppler shift interpretation.

The real reason I care about this is not that I think it matters much what we call the redshift, but because I think that this is a good example of the muddled thinking that the rubber sheet analogy causes. In particular, the analogy provides precisely the wrong intuitions about the nature of space and time in the theory of relativity. If you want to know more specifically what we mean by this, you’ll have to read the article!

To understand the guts of the article, you really need to have studied relativity a fair bit. (Students who took my Physics 479 course should be able to handle it.) Even if you don’t know enough relativity to understand all the technical details, the beginning and end might be interesting and accessible. (Certainly, this paper should be more accessible to non-specialists than the last one I wrote about, which is pretty technical.)