"Day after day, day after day,
We stuck, nor breath nor motion;
As idle as a painted ship
Upon a painted ocean.
Water, water, every where,
And all the boards did shrink;
Water, water, every where,
Nor any drop to drink." -Samuel Taylor Coleridge, Rime of the Ancient Mariner Despite the discovery of dozens of worlds -- planets and moons -- in our own Solar System, as well as hundreds (soon to spill into the thousands) of confirmed planets orbiting other stars, our Earth is still unique.
(Image credit: The Suomi NPP Blue Marble, NASA / NOAA.)
At least, it's unique as far as we know.
A smaller, dense rocky world with not just continents, but also oceans and life, Earth is the only one of its kind. So far, that is. And yet given the huge variety of stars and worlds found to date, it makes you wonder just what sort of unusual places this Universe contains.
(Image credit: NASA, ESA and G. Bacon (STScI).)
The first exoplanets found were Hot Jupiters: gas giant planets orbiting very close to stars even hotter and brighter than our own. And this is no surprise: it's much easier to detect large, heavy planets that are close to their parent star. Conversely, it's much more difficult to detect planets when they're any combination of smaller, lighter, or farther away from their parent star.
In the last few years, our technology has improved enough that we've found a vast variety of stars, from the smallest, coolest, reddest stars up through big, bright hot blue stars (and even a few red giants and supergiants) that have planets orbiting them. In the image below, all 2,326 exoplanet candidates discovered by the Kepler Mission are shown.
(Image credit: NASA's Kepler Science Team / Jason Rowe.)
Based on the temperature and luminosity of the star that's central to each of these solar systems, each planetary system has a region of space where -- according to our current knowledge of biology and chemistry -- life may be likely to arise. We call this region the Habitable Zone, and planets found within it are excellent candidates for the one Earthlike condition we prize over any other: liquid water.
Planets too close to their star, like Mercury in our own Solar System, are going to be too hot for this. Rocky worlds that are too far distant, like those out beyond Mars, will be too cold. We have reached the point where we've discovered solar systems other than our own that have planets in all three zones!
(Image credit: wikimedia commons user Henrykus.)
Like the vast majority of stars in the galaxy, the parent star of the exoplanet system above, Gliese 581, is a red dwarf star with less than 40% the mass of the Sun. While their habitable zones are tiny compared to the one around our Sun, there are already many excellent rocky planetary candidates found interior to and within their habitable zones.
In fact, the Kepler team has put together a tremendously illustrative video of all the candidate planets found. Have a look for yourself!
Now, if we were to rescale these raw distances, we'd find that there are a great number of planetary candidates closer to their star than Mercury is to the Sun that would be too cold to support life, but that -- by far -- the most common type of exoplanet found so far is still the one too close to its star to support Earth-like life.
But one of the most interesting things to consider is that not every solar system is going to have the same chemical composition as ours. How's that?
(Image credit: La Silla Observatory / MPG / ESO.)
The way you form stars -- as the star forming region NGC 3324 illustrates -- is by collapsing molecular gas clouds down into regions with a central star and a protoplanetary disk. Over time, the atoms in the disk accrete into planets, with typically the densest elements closest to the parent star and the least dense elements the farthest away. It is no coincidence that Mercury, Venus, and the Earth (and Earth's Moon) have significantly higher densities than all other planets, moons, comets and asteroids in our Solar System.
But the reason we have as many heavy elements as we do is because the molecular cloud that formed us had enough enriched elements from deceased, previous generations of stars to form us. Stars that were formed much earlier in the Universe, as well as stars that formed later in less enriched regions, would have solar systems containing planets with much lower densities. Even the innermost planets.
(Image credit: David A. Aguilar (CfA).)
And by measuring not just the mass and radius of the planet, but the star's light filter through the planet's atmosphere, we can measure the infrared color of "sunset" on the world, and hence determine the elemental composition of the planet's atmosphere!
What did they find? A thick, dense, featureless atmosphere composed primarily of water vapor! As the Harvard-Smithsonian Center for Astrophysics reports:
"The Hubble measurements really tip the balance in favor of a steamy atmosphere," said [Zachory] Berta.
Since the planet's mass and size are known, astronomers can calculate the density, which works out to about 2 grams per cubic centimeter. Water has a density of 1 g/cm3, while Earth's average density is 5.5 g/cm3. This suggests that GJ1214b has much more water than Earth, and much less rock.
As a result, the internal structure of GJ1214b would be very different than our world.
"The high temperatures and high pressures would form exotic materials like 'hot ice' or 'superfluid water' - substances that are completely alien to our everyday experience," said Berta. That strong signal favoring an atmosphere composed 100% of water vapor is definitely there, as the signatures of models with significant other atmospheric components are clearly disfavored in Figure 10 (thanks, Michael Richmond) from the paper:
(Image credit: Z. K. Berta et al.)
The conclusion that the planet has this uniform, thick H2O atmosphere around it indicates a large, watery chemical composition. The sheer amount of water indicated by this data -- combined with the information about the overall density of the planet -- renders a solid, rocky surface is inconceivable!
This world most likely is a waterworld, with a 100% oceanic surface!
(Image credit: retrieved from Steven Andrew.)
This planet is likely to be at very different temperatures and pressures from Earth, and so will likely have unusual states of water. It should be constantly boiling (at an average temperature of 450 degrees Fahrenheit (230 Celsius), and there should be strange states of matter, like "hot ice" or "superfluid water" composing the surface/atmosphere.
There are stranger worlds out there than most of us have ever imagined, and this one orbiting this star -- GJ 1214 -- just 42 light years away, is the first super-Earth that's ever had its atmosphere detected.
I can't help but look on with awe, and enjoy wondering what else is out there!Read the comments on this post...
Both Phil Plait and Sean Carroll are tentatively reporting that they may have an explanation for the recent anomalous report of neutrinos traveling faster than light: it may have been a case of a faulty connection in a timing circuit. If that bears out, it may be a bit embarrassing.
But it does suggest an important possibility. When we get around to building the first starship, don't have those fussy, punctilious physicists wire it up. Gather a gang of sloppy slapdash biologists to stick it together with spit and chewing gum. We'll have it going a heck of a lot faster than light than those experts can even imagine.
(Also on FtB)Read the comments on this post...
I'm grading exam papers at the dining room table when Emmy trots in. "Hey, dude," she says. "Where do we keep the superconducting wire?"
I'm not really paying attention, so I start to answer before I understand the question. "Hmm? Wire is in the basement, next to the--wait, what?"
"The superconducting wire. Where do we keep it?"
"We don't have any superconducting wire. And you're a dog. What do you need superconducting wire for, anyway?"
"I'm building a particle collider! I need superconducting wire for the beam-steering magnets."
How to Teach Relativity to Your Dog goes on sale next Tuesday, wherever you buy books. The above video is a dramatic reading of the dog dialogue that opens Chapter 8: Looking for the Bacon Boson; E = mc2 and Particle Physics. If you enjoy that, there are 11 more such conversations in the book, along with longer, more detailed explanations of the relevant physics.Read the comments on this post...
... Well, everything is in space, but I mean outer space!Observations by NASA's Hubble Space Telescope have come up with a new class of planet, a waterworld enshrouded by a thick, steamy atmosphere. It's smaller than Uranus but larger than Earth.
Zachory Berta of the Harvard-Smithsonian Center for Astrophysics (CfA) and colleagues made the observations of the planet GJ1214b.
"GJ1214b is like no planet we know of," Berta said. "A huge fraction of its mass is made up of water."
The ground-based MEarth Project, led by CfA's David Charbonneau, discovered GJ1214b in 2009. This super-Earth is about 2.7 times Earth's diameter and weighs almost seven times as much. It orbits a red-dwarf star every 38 hours at a distance of 1.3 million miles, giving it an estimated temperature of 450 degrees Fahrenheit.Read the comments on this post...
"I have difficulty to believe it, because nothing in Italy arrives ahead of time."
-Sergio Bertolucci, research director at CERN, on faster-than-light neutrinos You know the story. Last year, the OPERA experiment at CERN announced, to the shock and surprise of practically everyone, that they had observed what appeared to be neutrinos moving faster than the speed of light.
How did the experiment conclude this? Let's refresh your memory.
(Image credit: OPERA collaboration; T. Adam et al.)
A beam of high-energy protons, moving very close to the speed of light (but not quite there thanks to Einstein's relativity) is smashed into a target, creating a whole bunch of debris. Some of that debris consists of neutrinos (and unstable particles that will decay into neutrinos), which are incredibly light -- millions of times lighter than a single electron -- but not quite massless.
Because neutrinos hardly interact at all, we can fire them through the Earth pretty much at will. While all the other particles will be blocked by the particles in the ground, the neutrinos continue to travel as if in free-fall, affected only by the gravity of the objects around them.
(Image credit: OPERA / INFN / CERN.)
From CERN, these neutrinos travel through around 732 kilometers of Earth, until they arrive at the OPERA detector, buried beneath the Italian mountain of Gran Sasso. The OPERA detector is huge, and that makes it good enough to detect about one out of every 1016 (that's ten quadrillion) neutrinos that pass through it.
(Image credit: OPERA / INFN / CERN.)
Over the course of more than a year, OPERA detected somewhere around 16,000 of these neutrinos, measuring a number of their properties, including their arrival times. What they found, when they took a look at their data, was absolutely shocking. Based on how energetic these neutrinos were and how far they had traveled, they were able to calculate exactly how long it should have taken for these neutrinos to travel the distance between where they were created at CERN to when they arrived in the OPERA detector.
And the result should have been a time corresponding to a speed indistinguishable from the speed of light in a vacuum.
(Image credit: retrieved from Amazon S3.)
At least, that's what it should have been in theory, if physics behaves as we expect it to. What they found, instead, is that the neutrinos arrived about 60 nanoseconds early, which is incredibly fishy. This doesn't appear to happen for either significantly lower-energy or higher-energy neutrinos, as other experiments (and Matt Strassler) showed.
But when an experiment claims to have been done well and gives you a surprising result, you have to investigate exactly what's going on here. Now, we thought we understood neutrinos, and if we did, they shouldn't be arriving early. Certainly nowhere near this early. We immediately wondered if we were fooling ourselves with the results, and while some errors have been ruled out, there are still many questions remaining. The big one, of course is why did these neutrinos arrive earlier than we expected?
The OPERA collaboration could have made an experimental error that they haven't accounted for. (Some plausible explanations are as mundane as faulty wiring in the experiment.) This is sort of the default position that many people -- including myself -- take: that there's some error in the experiment somewhere. But this could also be an indicator of some potentially revolutionary new physics. If we want to know what's going on, you know how science works: we test it again, in different ways!
And that's exactly what's going on at two different locations, unconnected to the OPERA experiment. In Japan, they're creating neutrinos at similarly high energies to the OPERA experiment, and sending them from Tokai to Kamioka, over a distance of 295 kilometers.
We're also, in the United States, sending a beam of neutrinos underground from Fermilab to Soudan Mine in Minnesota. The distance from Fermilab to Soudan Mine? An uncanny -- wait for it -- 732 kilometers.
(Image credit: Univ. of Minnesota / NASA / Google / TerraMetrics / Europa Technologies.)
At the terminal point in both experiments, giant neutrino detectors await. Now, what they see will teach us a tremendous amount -- assuming that everyone is a competent experimentalist -- about what's going on with these neutrinos. Let's run through some of the most likely possibilities of what these experiments may see, and what that will point to!
(Image credit: Renee L. of 3inq.com.)
Option 1: MINOS neutrinos arrive on time, T2K neutrinos arrive on time.
This is perhaps the most boring option, and also perhaps the most expected. If neutrinos really don't move faster-than-light, and the OPERA collaboration achieved their results because of a unique fault in their experiment, the other collaborations won't see it. (This will also be what we see if the recent faulty cable theory turns out to be true.)
If this happens, the OPERA collaboration will be left with a lot of egg on their faces, and many jokes like Bertolucci's, at top, will ensue.
(Image credit: OPERA collaboration; T. Adam et al.)
Option 2: MINOS neutrinos arrive ~60 ns early, T2K neutrinos arrive ~60 ns early.
This possibility -- that everyone sees their neutrinos arrive about 60 nanoseconds early -- is also really interesting, although it could be happening for two very different reasons.
On one boring hand, everyone doing these experiments could be making the same systematic error. We've never done timing at this precision over these distances before, and there could be some sort of universal error related to the type of equipment or the setup used that affects everyone equally.
There are also some exciting, theoretical possibilities that the neutrinos travel incredibly fast initially, resulting in a very fast traversal of maybe the first 18 meters or so, followed by normal, roughly light-speed travel over the remaining distance. This idea, currently considered to be extremely fringe, would suddenly be thrust into the spotlight.
(Image credit: Jennifer Ouellette.)
Option 3: MINOS neutrinos arrive 60 ns early, T2K neutrinos arrive 24 ns early.
If this happens, the idea that neutrinos move at some speed faster-than-light through the Earth, or that the Earth acts as a medium with an index of refraction slightly less than 1 for neutrinos, would gain a lot of traction. In other words, neutrinos in a vacuum would move at the speed of light, but neutrinos moving through the Earth somehow move faster than light in a vacuum by some small amount; maybe 0.0025% faster.
This would be incredibly interesting from a theoretical perspective, and is quite possibly the result that many of the OPERA experimentalists are hoping for; if this came to pass, theoretical physics would certainly be very busy trying to explain why this was happening.
(Image credit: Schuhlelewis.com.)
Option 4: MINOS neutrinos arrive some time other than on time or 60 ns early, T2K neutrinos arrive at some other time than on time, 24 or 60 ns early.
If this happens, we'll know that there are either experimental errors somewhere or some really bizarre theoretical things going on, but nothing that was reasonable to expect.
You can, of course, make your bets as to what you think is most likely, but there's a reason we do the experiments; don't state any definitive conclusions until the results come in! For my own part, the faulty cable theory is a pretty lame explanation that would be shocking at this point. We have to assume some base level of competence when experiments are performed, and it would be a tremendous blow to everyone involved if this turned out to be the culprit. But with the experiment at MINOS already running, we should have our first check, and hence the first information leading us towards a definitive answer in just a few months!
So if you want to know whether neutrinos are moving faster than light, whether there is there some new physics lurking in high-energy neutrinos, whether the Earth is a faster-than-light material to neutrinos, or whether this whole fiasco is just an experimental blunder, you have to stay tuned! Any guesses?Read the comments on this post...
From Science Insider, there is a possible explanation for the recently observed "faster than light" neutrinos. The Neutrinos were clocked at faster-than-light speeds on their way form CRN in Switzerland to a detectors site in Italy. I had originally proposed that the neutrinos were merely very hungry but unwilling to eat Swiss food, and since they were on their way to Italy, why not go FTL?
The research at first was assumed to most likely be some kind of mistake, but a Mulligan Redo Procedure clearly demonstrated that the most obvious errors could not explain the observation, which violates The Laws of Physics.
It turns out that the reason that the Neutrinos appeared to go faster than the speed of light is exactly the same reason most of these things happen:Read the rest of this post... | Read the comments on this post...
Formally named buckministerfullerene, buckyballs are named after their resemblance to the late architect Buckminster Fuller's geodesic domes. They are made up of 60 carbon molecules arranged into a hollow sphere, like a soccer ball. Their unusual structure makes them ideal candidates for electrical and chemical applications on Earth, including superconducting materials, medicines, water purification and armor.Read the comments on this post...
Our mission is to re-invigorate the interest of our nation's youth in science, technology, engineering and math (STEM) by producing and presenting the most compelling, exciting, educational and entertaining science festival in the United States. In addition to the celebration, throughout the year we work to sustain the Science Festival's impact through year-round programming and curriculum development and a content-rich, interactive website. We strive to establish ourselves as a resource for everyone in the STEM community and especially our future STEM leaders.
One of the ways that we hope to achieve this is through our website feature: STEM Advice Corner. The STEM Advice Corner highlights careers in science and engineering. We host a new career each month and offer an in depth analysis on what it takes to pursue the given career path including the skills required to succeed; the details of the work performed and related careers in the field. This is a great resource for students pursuing careers in STEM!
This month our focus is on How to Grow a Career in Plant Biology! Students will see that it is fun to discover the active, useful, beautiful, eco-friendly, and even bizarre things plants can do! They will learn the skills required to excel in plant biology including curiosity, success in science and math and the motivation to pursue college and beyond.
Please visit the STEM Advice Corner to read more about this month's career focus: How to Grow a Career in Plant Biology!Read the comments on this post...
A correspondent from the UK sends along this picture from the Waterstones outlet in Heathrow airport:
As you can see, How to Teach Quantum Physics to Your Dog is #55 on their bestseller rack, just ahead of Confessions of a London Call Girl. I'm not sure what this says about London call girls, but I'm pretty psyched that it's still selling well over there.
On this side of the Atlantic, I got a note from my editor at Scribner the other day that they've just printed another batch of the US paperback of How to Teach Physics to Your Dog, which is also good news. There's probably a blog post in the future about the sales numbers for that, because Amazon now makes BookScan numbers available, while Simon & Schuster make point-of-sale numbers available, giving me a nice way to test BookScan's claim to capture 75% of all sales.
And, of course, you might've heard somewhere that How to Teach Relativity to Your Dog will be released soon-- next Tuesday, to be precise (but who's obsessively counting days to that, anyway?). They were selling it at the AAAS meeting last week, and I heard that a very well-known physicist picked one up, which is cool. I know how many they shipped to stores, both here and in the UK, which is fairly substantial, so it should really be available "wherever books are sold," as the phrase goes. And there is an electronic edition, for those of you who snarkily disparage "legacy books," also on sale next Tuesday.
In terms of publicity, I've already linked most of the reviews. I'll be doing a signing at the Open Door in Schenectady on the 10th of March, and one at the B&N in Vestal, NY (closest big store to where I grew up) on the 24th. And one of the local papers, the Troy Record, just ran a five-question interview with me, though some of the responses got a little garbled (I don't have a thirteen-year-old, for example...).
And that's where things stand with the books. Which isn't a bad place to be standing, really.Read the comments on this post...
On Dynamics of Cats, Steinn Sigurðsson flags a few foreboding articles on the future of NASA. Sigurðsson says the orbiting telescope Galex, or Galaxy Evolution Explorer, will be shut down later this year despite continuing to function. NASA has withdrawn from the international research mission known as ExoMars, and many other "2011-12 programs appear effectively suspended pending the 2012-13 budget, to the point where an entire funding cycle will be lost for some lines." Meanwhile, Ethan Siegel conjures up an apt scenario on Starts With a Bang, writing "Let's pretend that, for all of our history on Earth, we had never once bothered to look up with any instruments beyond what our own eyes could offer. [...] What would we find, today, if we turned our attention upwards for the first time ever?" From neighboring planets to the stars to extended nebulae and distant galaxies, our existing technology would allow us to peer deeper and deeper into the universe and quickly arrive at a conclusion that historically took centuries: the Big Bang theory. Of course, we've employed every technological advance every step of the way. There's something innately human about keeping an eye on the stars. And although old habits die hard, they also run out of money.
- Ominous signs for NASA on Dynamics of Cats
- The Big Bang for Beginners on Starts With a Bang!
Posted to the homepage on February 10, 2012.
Brookesia micra sp. n. from Nosy Hara, northern Madagascar.
Imagine a supercomputer suitable for this cute little guy, the recently discovered Brookesia micra.Read the rest of this post... | Read the comments on this post...
Science Documentaries You Can Watch Online to Get in the Mood for the Festival [USA Science and Engineering Festival: The Blog]
We have a guest blogger this week. Documentary-log.com offers free online documentaries and wanted to reach out to the science community. Read more about their organization and the many science documentaries available to view below.
You're never too young to become obsessed with science. In fact, Einstein was barely into his twenties when he started working on some of the equations that still influence popular science to this day. However, even after a lifetime of brilliant deduction, Albert Einstein wasn't finished! Einstein was passionate about science right up until his death. On his deathbed, he was working on what he hoped would become his greatest contribution to science: unlocking the mind of God. You can watch a documentary about Einstein's Unfinished Symphony and see for yourself if you believe that Einstein was close to bridging the gap between science and religion.
On the topic of death, imagine that Einstein was still alive today. Imagine if any human had the power to live forever. This concept teeters on the brink of science fiction, but recent science has shown that humanity has the potential to live hundreds - if not thousands - of years longer than we currently live. This documentary on Living Forever discusses very real science. Rather than 'what ifs,' the documentary explores genome discoveries that have blown the door open on conceptualizing life and death. Scientists have even been able to regenerate parts of a live mouse's body. Could regeneration in humans be far behind?
With all of this talk about aging and death, let's go in the opposite direction for this next documentary. "Whatever! The Science of Teens" is a documentary series that examines how a teenage brain differs from a child and adult. The image of the moody, lazy, sex crazed teenager is blamed on societal pressures but scientific research can show how the teenage brain has physiological differences that explain many of these tendencies. So, the next time that you forget to do your homework you can say: "My brain is changing" instead of "the dog ate my homework."
We hope that you enjoyed these scientific documentaries. Visit documentary-log.com for more thought-provoking documentaries about science and engineering.Read the comments on this post...
"Not explaining science seems to me perverse. When you're in love, you want to tell the world." -Carl Sagan Nothing lasts forever in this Universe, not even the seemingly timeless stars in the sky. At any moment, any one of the brilliant, twinkling points of light from across the galaxy could run out of fuel, ending its life as we know it. It's happened a number of times before in recorded history, and will no doubt happen again. With a typical supernova rate of one per galaxy per century, we've got a number of nearby potential candidates for what the next supernova to occur in the Milky Way might be.
Today, I'd like to showcase a really special one, and to do that, I'm going to take you far into the southern skies, to the constellation of Carina, the Keel.
(Image credit: F. Espenak, http://astropixels.com/.)
In most constellations, astronomers name the brightest star "Alpha," the second brightest "Beta," and so on. So Canopus, the brightest star in Carina and second brightest star in the entire night sky, is also α Carinae, while the second brightest, Miaplacidus, is β Carinae, etc.
Well, almost etc.
For Carina, not only have modern astronomers broken the original constellation up into smaller ones, so that there is now no γ Carinae (it wound up in the constellation Vela, where it's known as γ Velorum), but something very, very unusual happened to what was, for thousands of years, the seventh brightest star in that region.
(Image credit: © 2003 Torsten Bronger, annotated by me.)
The star is still there, mind you, but it's not nearly as bright as it used to be. What happened? All was well with the world; there hadn't been an observed supernova in our galaxy since 1604, when, in 1837, this star underwent a great eruption, becoming much brighter than normal -- but not quite as bright as a supernova -- for a period of twenty-one years! At its peak brightness in 1843, it was called a supernova impostor, where it temporarily became the second brightest star in the night sky, outshining even Canopus.
(Image credit: Celestia, by author / user HeNRyKus.)
Since that eruption, η Carinae's brightness died down so severely that, by the 1860s, it was no longer visible to the naked eye. What exactly happened during that 21-year eruption, from 1837-1858, was a mystery for a very long time. The star wasn't destroyed; there's still a Luminous Blue Variable star there to this day. There was also another, minor eruption in 1887, lasting seven years, and it has slowly continued to brighten as time has progressed.
(Image credit: University of Minnesota.)
So what, exactly, is η Carinae, and what happened here?! One of the most massive stars, weighing it at somewhere around a hundred to 150 solar masses (and somewhere around four million times as luminous as our Sun), η Carinae very clearly underwent some type of eruption. The star itself can be found in a particularly dusty, beautiful region of space known as the Carina Nebula.
(Image credit: ESO / Very Large Telescope / T. Preibisch et al., in infrared light.)
That's η Carinae, down at the lower left, surrounded by swirling loops of gas and dust. Spectacular also in visible light, the Hubble Space Telescope got the best view of η Carinae ever back in 1995. Take a look, and see for yourself why, ever since this image, the area around the star has also been known as the Homunculus Nebula.
(Image credit: Nathan Smith (University of California, Berkeley), and NASA.)
But this was no supernova; the Homunculus Nebula is no supernova remnant and, most importantly, the original star is still intact! You can see it in there, peering out through those explosive clouds, if you zoom deep into the nebula in this very image!
What we think happened, of course, is that just as we get tremors before a massive earthquake, η Carinae had some sort of explosive "hiccup" that will lead up to an eventual supernova. It's estimated to have blown off about twenty Suns worth of material from its outer layers during this eruption, but the collapse of this star's core is inevitable. The supernova could come tomorrow or it could not come for another million years; we simply don't know as much about these ultra-massive stars as we'd like to.
If only we'd had the instruments we have today back in 1837, or even better, in 1843, when η Carinae became a supernova impostor! But we didn't even have the ability to take photographs back then; all we have are eyewitness accounts from 170 years ago.
But sometimes, the Universe helps us out in ways we could never have predicted.
Above is a video from our satellite galaxy, the Large Magellanic Cloud. From 160,000 light years away, there was a supernova (named SNR 0509-67.5) that occurred about 400 years ago. That is, the light from it reached Earth about 400 years ago; you can see the aftermath here. But, hundreds of light years away was a cloud of gas that reflected the light from the supernova back towards us, giving us a second viewing of that supernova explosion today, hundreds of years later!
This phenomenon is known as a light echo, and it allows us to do something remarkable.
(Image credit: Wikimedia user Arkyan.)
How is it that we can observe the supernova once again, hundreds of years later? It's because light can only travel at the speed of light, and the light that takes path B travels a longer distance than path A, while path C is even longer, giving us multiple viewings of the same object, so long as there are clouds of gas for the light to reflect off of. But, unlike hundreds of years ago, we not only have better telescopes, we have photometric filters and spectrographs!
In other words, we can figure out the temperature of the star, what elements are present and in what concentration, and, if we get a light echo, we can watch those things evolve over the course of the explosion!
But getting an echo from a supernova is one thing; getting it from a supernova impostor, because it's so much dimmer, would be a first.
(Image credit: NASA, NOAO, and Armin Rest (STScI) et al.)
Welcome to the first supernova impostor light echo ever seen!
In fact, we can learn a tremendous amount about the η Carinae eruption from observations of the echo. From the Hubble press release:
The observations mark the first time astronomers have used spectroscopy to analyze a light echo from a star undergoing powerful recurring eruptions, though they have measured this unique phenomenon around exploding stars called supernovae. Spectroscopy captures a star's "fingerprints," providing details about its behavior, including the temperature and speed of the ejected material.
The delayed broadcast is giving astronomers a unique look at the outburst and turning up some surprises. The turbulent star system does not behave like other stars of its class. Eta Carinae is a member of a stellar class called Luminous Blue Variables, large, extremely bright stars that are prone to periodic outbursts. The temperature of the outflow from Eta Carinae's central region, for example, is about 8,500 degrees Fahrenheit (5,000 Kelvin), which is much cooler than that of other erupting stars. "This star really seems to be an oddball," Rest said. "Now we have to go back to the models and see what has to change to actually produce what we are measuring." Combined with 2003 images from Nathan Smith (who took that picture of η Carinae's "Homunculus Nebula" above), you can really see the light echo evolve over time.
The full paper details some amazing things we've learned from spectroscopy on this light echo, including:
- The eruption/nebula appears to be expanding at speeds of 210 km/s (!),
- The star's eruption temperature is ~5,000 K, much cooler than was previously thought and cooler than the current theoretical models allow for,
- There are no emission lines, only absorption lines, ruling out the "opaque winds" model, and, in a direct quote from the article,
- "The cause that triggered such an explosion and the mass-loss without destroying the star is still unknown, but predictions from future radiative transfer simulations trying to explain η Car and its Great Eruption can now be matched to these spectral observations. Other alternative models that were proposed, e.g. the ones that use mass accretion from the companion star... as a trigger for the eruption, can be either veriﬁed or dismissed."
Regular reader Johan Larson sends in a good question about academic physics:
You have written about teaching various courses in modern physics, a subject that has a fearsome reputation among students for skull-busting difficulty. That suggests a broader question: what is the most difficult course at your university? Or even more broadly, how would one determine what course is the most difficult?
This is a good question, but hard to give a single answer to. The most difficult course at the college as a whole would be nearly impossible to determine, because different students find different things difficult. Lots of students who would cower in fear at the mathematics in our sophomore modern physics course will thrive in upper-level literature seminars on critical theory, the very idea of which gives some physics majors cold sweats. And, of course, any given student only takes a tiny fraction of the courses offered, thus most of them will avoid the courses that would be most difficult for them.
So, I don't think there's any useful way to define the "most difficult" course for the institution as a whole. The only sensible way to talk about "most difficult" courses is to look at what courses are most difficult for the subset of students who are required to take them. In other words, the question we can actually answer is "What is the most difficult course required for physics majors?"
In which case, there are two courses from the Physics major at Union that are generally regarded as the most difficult, for different reasons. At least as far as I know-- I know there are some Union physics grads reading this, who can correct me if I say anything wrong.Read the rest of this post... | Read the comments on this post...
At age 28, theoretical physicist Dr. Zohar Komargodski became head of a research group in the Institute's Particle Physics and Astrophysics Department. A recent paper, published with Prof. Adam Schwimmer of the Physics of Complex Systems Department, made some waves in the physics world with a proposed proof of a 23-year-old theorem. If the proof stands, it will have implications for many fields, including the analysis of LHC results and supersymmetry. Komargodski and Schwimmer claim they had been kicking around various ideas for a proof for several years before the solution came to them - while contemplating a sunset together on an Aegean beach.
We recently interviewed Komargodski:
WSW: You are fairly young to be head of a research group.
ZK: I completed a very significant fraction of my B.Sc. in high school (in an accelerated program through the Open University), and I completed my Ph.D. two years earlier than what's considered standard. I also did a pretty short postdoc (at the Institute for Advanced Study, Princeton) before coming back... I guess this accounts for 5-6 years in total?
WSW: What led you into theoretical physics in the first place?
ZK: I actually got really fascinated by physics after reading Hawking's A Brief History of Time.
This must have been around 1998, when I was 15 or so. Since then I have been totally immersed in grappling with the principles of theoretical physics (and mathematics... since our subject requires a lot of advanced mathematics).Read the rest of this post... | Read the comments on this post...
The standard solar model predicts a young Sun which was too faint to sustain liquid water on the Earth, unless there was an extreme greenhouse effect at the time, which seems to contradict the geochemical record. It seems to be almost impossible to get liquid water on Mars under the standard solar model with any plausible early Mars atmosphere.
Here is an interesting article on an old problem...Read the rest of this post... | Read the comments on this post...
"What's that star?
It's the Death Star.
What does it do?
It does Death. It does Death, buddy. Get out of my way!" -Eddie Izzard Like it was for many people, the original, very first Star Wars movie was one of my favorites as a child. And while there was a lot to be in awe of, the idea of jetting around the Universe in your own private, gargantuan structure, free from planets, Solar Systems, and even the rest of the galaxy was simply the most amazing idea to me.
(Image credit: Star Wars' Wookieepedia.)
That's what I wanted: a Death Star. Of course, you know what happens to the Death Star, don't you? At least in the version I remember, Darth Vader shoots down Keith Hernandez, Han Solo saves Luke, Luke blows up the Death Star, and then goes home and reunites with Leia, whom he calls Carrie. (Watch it!)
This image -- of the blown-up Death Star -- was the one that stuck with me. And it wasn't until I was in graduate school, learning about the structures that form in the Universe, that actual astrophysics made me think about the Death Star once again.
(Image credit: Jean-Charles Cuillandre, Hawaiian Starlight, CFHT.)
This object, Messier 22, is known as a globular cluster. A collection of somewhere around a hundred thousand stars in a sphere that's maybe 100 light years across, globular clusters exist in great abundance around -- but not in -- our galaxy.
Consider that the nearest single star to us is still over four light years away to get an appreciation of how tightly packed these stars are! The Hubble Space Telescope -- taking a deep look inside -- can show you better than I could ever describe on my own.
(Image credit: NASA, ESA, and the Hubble SM4 ERO Team.)
This 2009 Hubble image is of globular cluster Omega Centauri, which lives some 16,000 light years away from us. All the stars in this image belong to Omega Centauri's core, and the width of the image is 6.3 light years. For comparison, know how many star systems there are within 6.3 light years of us?
Three. The Alpha Centauri trinary star system at 4.3 light-years distant, Barnard's Star, barely making the cut at a distance of 6.0 light years, and... the Sun itself. That's what a globular cluster is. Isolated but full of riches all its own, traveling throughout the galaxy.
(Image credit: Larry McNish, data from W. E. Harris / McMaster U.)
Looking around the vicinity of our Milky Way galaxy, there are well over 100 globular clusters -- dense collections of hundreds of thousands of stars -- orbiting and plunging through our galactic plane. Over the entire history of the Universe, each globular cluster has had time to make a mere ten-to-twenty passes through the galaxy, and spend nearly all their time well outside the galaxy itself.
These objects -- globular clusters -- are what I think of as Death Stars. Isolated objects, And as far as we can tell, the Milky Way is awfully typical among galaxies for having a little over a hundred of these "Death Stars."
(Image credit: Valter Luna, Vegaquattro Astronomical Observatory.)
Andromeda, as a careful observer can find in a night, has over 100 globular clusters as well! These object range from old -- like, many billions of years old -- to the very old. In the case of Messier 22, the first globular cluster I showed you, it's almost as old as the Universe itself, with an estimated age of over 12 billion years! (Not bad, considering the Universe itself has only been around for 13.7 billion years.) Based on what we know about structure formation, we can understand their ages, their distributions in and around galaxies, and their masses. All of that makes sense within our picture of how the Universe works.
But there is a problem with globular clusters, one that has troubled theorists like me. You see, knowing what we know about the Universe -- a Universe that started with the Big Bang, and that contains the measured amounts of radiation, normal matter, dark matter, and dark energy -- there shouldn't just be a couple of hundred globular clusters for every large galaxy. When we do our simulations of structure formation, we get... well, let's just call it a different answer.
Instead of hundreds, our simulations of structure formation predict tens of thousands of globular clusters for each isolated galaxy. And you don't have to be Einstein to realize that that's wrong. But the question, of course, is why that's wrong.
In other words, who destroys all these Death Stars, and how?
Well, if you came by this site for Valentine's Day, you might recall something interesting.
(Image credit: Rosette Nebula by Adam Block and Tim Puckett.)
This is the Rosette Nebula, one of the largest star-forming regions in our galaxy, with a total mass of about 10,000 Suns. The central region has the hottest, brightest, youngest stars, and -- as you can also see -- the least amount of hot, pink, star-forming gas. Why is that?
Because these ultra-hot, young stars emit great stellar winds, blowing the gas and dust out of the region where these stars live! And this nebula is in our galaxy. Our quiet, boring, low-rate-of-star-formation galaxy. What would happen if we took two similarly-sized galaxies and -- as structure in the Universe is wont do to over billions of years -- allowed them to merge together?
Instead of star-forming regions containing the mass of thousands of Suns, colliding galaxies (like the Antennae Galaxies, above), have star forming regions containing the mass of billions of Suns! That's right: billions. We even have a special name for galaxies that are doing this right now: Starburst galaxies.
So you can imagine how powerful the stellar winds are in galaxies like this. And in the early Universe, where mergers between similar-sized objects were how galaxies like the Milky Way got so big in the first place, it is conceivable that -- during this intense period of star formation -- the vast majority of globular clusters were blown apart!
This is all just theory, of course. But if we can put this starbursting into our simulation, we should be able to see -- for the first time -- whether the globular clusters come out right! Let's go to the video.
What the simulation shows is that nearly all of the globular clusters get destroyed due to the merger-induced starburst! What you can't see so obviously is that it's the most isolated, largest globular clusters that survive intact. As the researchers from Germany and the Netherlands say themselves: It is ironic to see that starbursts may produce many young stellar clusters, but at the same time also destroy the majority of them. This occurs not only in galaxy collisions, but should be expected in any starburst environment. In the early Universe, starbursts were commonplace - it therefore makes perfect sense that all globular clusters have approximately the same number of stars. Their smaller brothers and sisters that didn't contain as many stars were doomed to be destroyed. So that's how the Universe does it! Create a large enough star forming region that the vast majority of your globular clusters are blasted apart; that's how the Universe destroys its Death Stars!
What the researchers don't say is that this may help explain another mystery of globular clusters: blue stragglers.
(Image credit: Francesco Ferraro (Bologna Observatory), ESA, NASA.)
Inside some globular clusters, there are stars that are hotter, bluer, more massive, and younger than all the other stars found in that cluster. Where did they come from? There are a few ideas, of course, but now there's actually some good evidence pointing towards the simplest idea: that passing through a star-forming region may help form these blue straggler stars, but your cluster needs to be large enough to hold together or be destroyed.
Here's a logic puzzle for you: Suppose I offer you a million dollars, in return for which you agree to answer a certain yes/no question. You can answer either truthfully or falsely as you desire. That's it. Should you accept that offer? Solution below the fold.
Those of you reading this who enjoy logic puzzles are probably familiar with Raymond Smullyan. I was pretty young, eight or nine I think, when I first discovered his writing. Somehow I noticed his book What is the Name of This Book? sitting in a bookstore, and I persuaded my parents to buy it for me. The book opened with some very elementary puzzles I was able to appreciate even as a young child. But pretty soon I came to one of his most famous creations, the island of knights and knaves.
On this island the knights always tell the truth and the knaves always lie. The inhabitants of this island are in the habit of gathering in small groups and making various statements, from which you are to determine who among them is a knight and who is a knave. Smullyan intended these puzzles as a device for teaching basic ideas in propositional logic, and I use them for that purpose in my discrete mathematics classes. Anyway, at some point little kid me came across the following problem:
Suppose you meet three people, who we shall call A, B and C. You ask A, “How many knights are among you?” A mumbles an answer, but you cannot understand what he said. So you ask B to tell you what A said. B says, “A said that there is one knight among us.” At this point C interrupts and says, “Don't listen to B! He's lying.” Can you determine anything about what type B and C are?Read the rest of this post... | Read the comments on this post...