Archive for: September, 2011

Off to VCON36

This weekend (Sep 30 - Oct 2) I'm heading off to VCON 36, a science fiction convention in Vancouver, BC. I'm going to be sitting on several panels (including one on digital art, one on podcasting, one on games, and one on "messy science"), and I'll be giving two talks:

  • "The Science Behind Larry Niven's Neutron Star". Larry Niven is the guest of honor, so I figured that this would be a good topic. I'll talk about what neutron stars are, and also about tidal forces (oops, I just spoiled the story for you... it's still worth reading!). This short story is one I discovered in a used bookstore back in the early years of grad school (early 1990's), and it started me on a kick of reading all of Niven's "Known Space" stories.
  • "Constructing a Space Combat Game Consistent with Newton's Laws". Last year I talked about Newton's Laws in science fiction movies and TV. This year, it's with a miniatures boardgame.

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Thermonuclear Supernova in M101!

Sep 26 2011 Published by under Astronomy & Physics, What's Up?

On August 23 of this year, a supernova exploded in galaxy M101.

Discovery images from the Palomar Transient Factory

M101 is a grand design spiral a mere 22 million light years or thereabouts away (here's a summary of literature distance measurements from NED). Cosmologically speaking, that's in our back yard. The closest galaxies to our own are our satellite galaxies, including the Magellanic Clouds. However, the closest big galaxy to our own is the Andromeda Galaxy, which is about 2 million light-years away. The closest actual cluster of galaxies is the Virgo Cluster, at a distance of 65 million light-years.

Why This Is Cool

SN 2001fe is a thermonuclear supernova. These are the types of supernovae that were used to discover the acceleration of the Universe, so they're cosmologically important. As such, some have pointed out the importance of this supernova as a calibrator for that observation. However, that's of secondary importance. Yes, you really want to understand the standard candle you're using cosmologically, but the repeatability of the peak luminosity of these supernovae has already been empirically demonstrated, and that's what the cosmological result really resets on. What's more important for this supernova, however, is understanding the supernovae themselves. Supernovae are where we get the vast majority of the atoms heavier than Helium in our Universe; thermonuclear supernovae in particular are primarily responsible for the heavier elements, such as iron. Thus, these are important events not only for measuring the expansion history of the Universe, but for understanding other aspects of our history.

Beyond it being close, it is very awesome how early this supernova was discovered. It was discovered less than a day after the explosion. (Aside: well, really, 22 million years later. But I will be talking about times relative to when the light reach earth. So, when I say "the date of the explosion was August 23", what I really mean is that the first photons from the star at the moment it was exploding reached Earth on August 23.) The discovery was announced, and a wide variety of follow-up observations started within just a day or two of the explosion. Not only is this the closest thermonuclear supernova to go off during the era of ubiquitous digital imaging on telescopes, but we have also been observing it from the very beginning.

Citizen Science

Below is a lightcurve of SN2011fe, that is, a plot of its brightness versus time:

This lightcurve comes from the American Association of Variable Star Observers. It represents the work of amateur astronomers around the world. They each make observations, and submit them to the AAVSO. Historically, many of the AAVSO observations were made using the Mark 1 Eyeball. People would look at a star, and compare its brightness to other stars of known magnitude in the same field in order to figure out the target star's magnitude. Nowadays, with many amateur astronomers having digital imaging equipment, they can use that (with other stars in the field for calibration) to measure star magnitudes. The data points on the lightcurve above show the blue (B) and yellow-green (V) magnitudes of the supernova. We can see that people started submitting magnitudes within two days of the explosion of the supernova. It peaked around September 11 or 12. Today, it's still brighter than 11th magnitude, so if you've got clear skies and something like an 8-inch telescope, and if you're in the Northern hemisphere, head into your backyard after sunset and see if you can see the supernova in M101! (You'll need to use a finding chart to be able to tell what is the supernova versus what is a foreground star. Here is one from the Society for Popular Astronomy.

Supernova Progenitors

What science has come from this supernova? We're still in early days; the supernova is only a couple of weeks past maximum light, so many observations remain to be made, never mind the processing of the data. However, already a couple of papers have shown up about this supernova.

One of the outstanding questions about thermonuclear supernovae is where they come from. Most people agree that they come from a white dwarf star— a dead (no longer performing fusion) star made out of Carbon and Oxygen that is supported by "electron degeneracy pressure", which is typically half the mass of the Sun but only the size of the Earth. If one of these stars reaches a critical mass of 1.4 Solar Masses, it starts to collapse, triggering runaway fusion that completely blows it away in a thermonuclear supernova. The question, then, is how to get the white dwarf star up to this critical mass.

Most scenarios are divided into two broad classes. The "Single Degenerate" scenario is where the white dwarf has a companion star, such as a normal "main-sequence" star (like the Sun), or a red giant star. If you'd asked me ten years ago, I would have told you that the red giant companion was most likely. The "Double Degenerate" scenario starts with two smaller white dwarf stars, which merge, yielding a merger that is above the critical mass and that therefore explodes. Until the last few years, I believe that most astronomers preferred the single degenerate scenario. However, some observations in recent years have started to indicate that the double degenerate scenario may be more common.

Two papers have shown up on that address this. The first, Horesh et al., arXiv:1109:2912, reports on radio and X-ray observations of the supernova starting just a day after the explosion. The result: they didn't see anything. While that may sound uninteresting, in fact it is significant. A supernova has an expanding "photosphere", that is, the bright thick ball that is glowing. As time goes by, the photosphere expands at a rate slower than the gasses that make it up, because the outer layers become thin enough to see through. Outside the expanding photosphere is the blast wave, which propagates through the interstellar gas. The shock wave does two things. First, it compresses magnetic fields; electrons caught in that magnetic field will spiral around it, emitting "synchrotron radiation" in radio wavelengths. Second, it heats up the post-shock gas, which should glow in X-rays. If the supernova happened in a single-degenerate system, and if the non-degenerate companion was undergoing substantial mass loss, then the interstellar material should be thicker, which would lead to both enhanced radio and X-ray emission.

Because they didn't see any, it means that if SN2011fe came from a single-degenerate system, the companion can not have been a red giant, for no plausible model of a white dwarf/red giant binary system would have a mass loss rate low enough that the X-rays and radio waves would be undetectable. While this might suggest that SN2011fe came from a double-degenerate system, in fact the observations are still consistent with a single-degenerate system where the companion is a less evolved star: a main sequence star or a subgiant.

The other paper, Li et al., arXiv:1109.1593v1, used the adaptive optics system with an infrared camera on the Keck 10m telescope to obtain an extremely precise position for the supernova. They then went into the archives of the Hubble Space Telescope, and pulled out all pre-explosion images of M101 that were available. They used the very precise position to look to see if they could identify a progenitor star. The result:

Archival HST images of the SN2011fe location from Li et al., arXiv:1109.1593v1.

Nothing! Or, rather, nothing to the detection limits of the HST. Note that the circle on the image to the right is an error circle. That is, it's an extremely conservative error circle; "Star 1" and "Star 2" at the edge of the circle are too far away to have any reasonable chance of being the progenitor system of SN2011fe. The fact that the HST couldn't see anything also rules out a single-degenerate system consisting of a red giant star, or indeed of a single-degenerate system with a companion star more than about 4 times the mass of the Sun. Again, this might seem to favor a double-degenerate progenitor system, but it's still possible that a dimmer main-sequence star no more massive than (say) 3 or 4 times the mass of the Sun was present as the mass donor for a white dwarf.

And Onwards

This supernova is still hot. As I mentioned above, with a modest telescope, you may still be able to see it for another week or so. I predict that a lot of supernova science comes out of this event, and that we see a plethora of papers on it. It will probably become a "classic" event much in the same way that SN1987A has.

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The true tragedy of 9/11

The true tragedy of 9/11 is not just that thousands of people died in an evil and criminal attack. (Aside: I don't use the word "cowardly" like everybody else, because I have a hard time seeing how sacrificing your life in an attack on your perceived enemies is cowardly. Misguided, deluded, even evil, yes, but cowardly? Why can't we call these things what they are? Why is, somehow, "cowardly" a more stinging condemnation than evil?)

No, the true tragedy is how wildly successful those attacks were. What's more, they were successful not because of the death and destruction of the attacks themselves, but rather because of our reaction as a society to those attacks. The way the USA, in particular, has behaved in the last 10 years has served not to remember and honor those who lost their lives on 9/11. Rather, not only were they meaningless deaths, but the tragedy of their deaths have been magnified many times by our reaction and response to them.

What is the goal of a terrorist attack? I can't be sure, of course. However, the 9/11 attacks were targeted at the symbols of American power around the world: the World Trade Center, probably the largest single symbol of American financial might (our true imperialistic power at the moment); the Pentagon, the center of the American military; and the White House, the head of the American seat of government. When ideologues on our side talk about what it's for, it's because they "hate us for our freedom" and "want to destroy our way of life". I suspect on their side the more ambitious thought that these attacks would cripple the USA, undermining our imperialistic power, showing the world that we're not everything we say we are, and forcing us to further cripple ourselves by changing the way we live because we're living in fear.

Most of these goals, whether you take the ones that were perceived by the attackers or that come out of the rhetoric of those who think the attackers hate us for our freedom, were in fact achieved. Not directly as a result of the 9/11 attacks, but rather because of our response to them.

Showing the World the "True" USA

Immediately after the 9/11 attacks, there was an outpouring of goodwill worldwide towards the USA. Yes, it was not universal; there were places where people were dancing in the streets celebrating that the USA had been attacked. And, doubtless, there was some snark from our allies in the form of "now you have on your soil what we've been dealing with all along". But, the world recognized this as one of the most major terrorist attacks, and recognized it as an attack on the modern civilized world, not just on the USA.

With a different presidential administration, I suspect that this goodwill could have been fostered, and used to help bring about changes in the world that made it a better place. Instead, what did we do? We completely squandered it. A few years later, it became embarrassing to travel abroad as an American. The USA became not known as the world leader of the great democracies who suffered a terrible attack, but rather as the jingoistic unilateral bully that was going to do whatever the hell it wanted militarily, regardless of what its allies thought. The 9/11 attacks were used as a pretext for an invasion of Iraq, even though Iraq had nothing to do with them.

The outpouring of the "good" form of patriotism that happened right after 9/11 very quickly morphed into the ugly form of patriotism. The kind of patriotism that asserts you're completely for the USA and what it's doing, or you're effective aiding and abetting the enemy. The kind of ugly patriotism that makes people in other countries see Americans not as a proud people, but as an arrogant and ignorant people. Americans have always suffered this to some extent; and, to some extent, it's earned. But it's become much worse in the years since 9/11, as a direct result of our nasty reaction to 9/11. I'm talking about the invasion of Iraq, our open defense of torture, the Guantanamo Bay prisons, our doctrine of unilateral military adventurism and ignoring the protests of the other great world democracies... but also just the general behavior and rhetoric of so many individual Americans.

Losing our freedoms

On the evening of 9/11, George W. Bush gave a rather nice speech that was broadcast worldwide on television. Notably, he didn't refer to the terrorist acts as "cowardly"; that came later. Rather, they were "evil and despicable", much more apt descriptions. Most inspirationally, he said:

These acts of mass murder were intended to frighten our nation into chaos and retreat. But they have failed. Our country is strong. A great people has been moved to defend a great nation.

Terrorist attacks can shake the foundations of our biggest buildings, but they cannot touch the foundation of America. These acts shatter steel, but they cannot dent the steel of American resolve.

America was targeted for attack because we're the brightest beacon for freedom and opportunity in the world. And no one will keep that light from shining.

In an administration that was filled with a lot of misdirection, dissembly, and obfuscation of the truth, I believe that this, right here, was W's most egregious untruth. I do not call it a lie, because I think he believed it when he said it. But the years that followed showed that this was completely wrong. American resolve was in fact undermined, and changed from resolve into an ugly sort of aggression. The brightest beacon for freedom and opportunity in the world turned into a bully that disgusted the world. And, freedom in the USA, while still greater than many (if not most) societies that have existed throughout the history of Western civilization, has been seriously curtailed.

Obviously, freedom of speech still exists, or I could not write this blog post. And, indeed, most of us effectively have no fewer freedoms than we had ten years ago. But those freedoms are much less secure now, and there are some who have less effective freedom than they did ten year ago. What am I talking about?

  • Airport "security". The fourth amendment of the Constitution ("The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures,...") has been trampled upon and treated as toilet paper if you're anywhere near an airport. In many airports, you must agree to be photographed effectively naked, or, if you "opt-out", you are subject to official sexual assault (including groping of children that would lead to the kid being immediately taken away by child protective services if the parent were observed doing it). This would be inexcusable even if these measures were effective, but they're not. Indeed, as that Schneier piece points out, if our security is going to be insistent on identifying each and every potential weapon that goes on to an airplane, the only recourse is an escalation of intrusiveness that will completely destroy personal dignity (if there is, indeed, any left now), and/or make flying effectively impossible. (At which point, of course, terrorists will blow up trains, or buses! Indeed, right now, if they're going after air travel, the lines at security are probably the most juicy target.)
  • The PATRIOT act. This was a gigantic piece of legislation that was passed, with the legislators that passed it not having read it, or, in many cases, not even fully realizing what was inside it. Yet, it was passed overwhelmingly, because the politics of fear, and the fear that our country was feeling at the time, meant that they all had to be seen "doing something". Our legislative process was completely undermined. Supposedly, our congressmen talk about, debate, and argue about the laws being passed. The process fails a lot, I admit, but this failure was truly egregious. Measures were passed overwhelming that would have garnered tremendous controversy (both inside and outside Congress) at any other time. The act granted a huge expansion of the discretionary powers of law enforcement. Again, most of us haven't experienced the loss of freedom due to this, but it is always the people on the margins for whom the defense of freedom is most precarious, and most necessary. (If you're not worried about them, remember that the margins can move in over time, after all.) Among many, many other things, the PATRIOT act includes National Security Letters, that allow them to get private information about you from institutions such as libraries... and not only are these not subject to review, but the libraries (or whatever) are not allowed to even admit that they've received this request. This sounds to me like a very key tool of somebody building a police state!
  • Our general response to what is seen to be reasonable in a free society:
    • Many people have gotten in trouble for photographing public buildings. And, the rhetoric is such that that we now think, hey, wait, those people might be planning attacks! We need to be safe!
    • Many of us argued in favor of torture. Never mind that it doesn't work. Never mind that it's evil and we as a society shouldn't want to be doing this. It's effectiveness on the TV series 24 has lead us to think it's patriotic to want to torture those we suspect of being our enemies.
    • Warrantless wiretapping, something that would have been anathema on September 10, 2001, is always being pushed and expanded.
    • Because we're all so afraid of terrorists, we're happily allowing our state to turn into a surveillance state where we can expect that law enforcement is watching us and recording us wherever we go, whatever we do.
    • At the same time, people are getting in trouble for photographing or videotaping the police. Put "the state surveils you" and "you are not allowed to surveil the state to hold it accountable" together, and you've got the technological underpinnings of the state described in Orwell's 1984. Accuse me of hyperbole— I'm using it, after all— but seriously folks: do we want to keep this a free society or not?
    • The current administration, elected on promises of being different from the last one, of trying to undo the expansion of the power of the executive branch, is, in contrast to those promises, quietly pushing forward all of these measures.

9/11 was a tragedy. Many people lost their lives due to the evil and despicable acts of some religious fanatics. But the true horrors of 9/11 are how amazingly successful those attacks were, because of our response. We've handed the terrorists their objectives on a golden platter.

Let's go back to standing firm, to resolve, to freedom not being deterred. If we're to make changes in our way of life, let's not fall in upon ourselves, become ever more jingoistic and ever more afraid, and sacrifice our freedoms in the name of that fear. Instead, let's examine what it is, really, that makes people hate us so much, and ask if there are things we're doing wrong. Let's make changes in how we interact with the rest of the world that build goodwill. In the long run, having more goodwill around the world is going to make us safer than any security walls we build around ourselves. And, by maintaining and upholding freedom and dignity, we might begin to truly honor those who died on 9/11, instead of claiming to honor them while pissing on their graves by allowing fear to turn us into what we're becoming.

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Online Talk, 10AM Pacific Time : SpaceTime Diagrams

As a part of MICA, the Meta-Institute of Computational Astrophysics, I will be giving a public talk tomorrow morning entitled "Understanding Relativity with SpaceTime Diagrams".

Einstein's theory of Relativity completely changed our notions of reality in the early 20th century. Time, it turns out, is not absolute, but rather mixes with space in a particular way that depends on how fast a clock (or other time measuring device) is moving relative to whoever is asking questions about it. Spacetime diagrams are a great tool for understanding Special Relativity. In this talk I'll introduce a few of the startling results of Special Relativity, and show how they can be described using spacetime diagrams. In next week's talk (September 17), we'll use SpaceTime diagrams as a tool to help us describe the geometry near black holes.

The talk will be at the MICA Large Ampitheater in Second Life. Remember that Second Life accounts are free, so register today!

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