As a young child I remember going outside in my pajamas on a cool evening to see a lunar eclipse. Interesting I thought that the moon disappears regularly, yet this event was clearly special. I have since always wished I could have lived thousands of years ago and been able to predict lunar eclipses.
The moon appears to phase in and out of darkness to an Earth bound observer on a monthly cycle, but in reality the Sun's rays are always falling upon the moon. The arced and crescent moon shapes are due to our perspective on Earth of the spherical moon being illuminated from a single direction. The rotation of the moon and the revolution of the moon are synchronously locked in a period of 27 days, 7 hours, and 43 minutes such that only one lunar hemisphere is ever visible from Earth and the other side is apparently locked in darkness. In reality the dark side of the moon sees just as much Sun as the near side on a lunar day cycle almost matching the revolution period. Despite the moon's serene appearance it is a place of extremes because without an atmosphere the Sun heats the moon to 250 Fahrenheit (123 Celsius) during its day and the moon cools to -390 Fahrenheit (-233 Celsius) during its night.
There is of course one time in which the Sun's rays are not falling upon the moon. During a total lunar eclipse the Earth blocks the light from the Sun and the Earth's shadow casts the moon into a dark red copper shadow. A total lunar eclipse will be viewable tonight in the Northern Hemisphere at U.T. 7:41 (or E.S.T. 2:41 am or P.S.T. 11:41 pm). NASA has some further information about the lunar eclipse here. Unfortunately, clouds may block your view so check the weather, indeed here in Seattle the weather may completely block this rare winter solstice lunar eclipse. That is right, this lunar eclipse occurs on the winter solstice. This really is a rare event!
As solace I have looked up several times recently in Seattle to see a moon dog or a moon ring. A moon dog and moon ring is a halo (the ring) and bright spots (the dog) to the left and right of the moon created by the moon's light refracting through ice crystals or high clouds in the atmosphere. Even if you can't see the Eclipse tonight look up this winter to perhaps see the Moon's winter halo.
A black hole is a massive object with such powerful gravity that not even light may escape from it. Black holes only have three unique properties which are mass, charge, and spin. At one time black holes were a speculative phenomena, but astronomers now understand that black holes are a relatively common and important occurrence in our Universe, unfortunately the public and science fiction still seems to be in dark. There are a lot of misconceptions about black holes:
If the Sun was replaced by an equal mass black hole then the Earth would fall into it. In reality we would continue to orbit about the center of mass of the new black hole object and about eight minutes later after the Sun was removed it would be dark on Earth (that is how long it takes light from the sun to get to us).
Supermassive black holes distort the space time around them in a very extreme way. Actually, the larger the black hole the smaller the distortion and tidal forces around it such that a very massive black hole hardly distorts the space time outside its event horizon, of course, every black holes does very strange things with space time inside the event horizon.
Tiny black holes created by particle accelerators like the LHC may destroy Earth. The truth is that these tiny black holes would evaporate extremely rapidly via Hawking Radiation and they have such a small gravitational interaction they would not pull in any other matter.
Black holes lead to extra dimensions. Why don't you jump into one and tell astrophysicists what you find?
Black holes are strange objects. Massive black holes shape the evolution of galaxies, charged black holes are thought not to exist, and spinning black holes pull space itself around at close to the speed of light. According to Einstein mass tells space time how to curve and space time tells mass how to curve. So all mass distorts space in a small manner, but black holes create what are known as singularities where the mathematics which describes the curvature of space time breaks down.
You can solve the equations of general relativity and see how black holes arise, but they also arise in the context of standard Newtonian physics. Consider a rocket launching from earth into space. In order for the rocket to free itself from the gravitational pull of Earth it must be moving at the escape velocity (the actual situation is much more complicated than this, but suffice to say it's... complicated). We can find the escape velocity for any object of mass, m, away from a more massive object of mass M by setting the object's kinetic energy, 1/2 m v 2, equal to the potential energy of the object in the massive object's gravitational field, GMm/r, where G is Newton's gravitational constant. A terrible thing happens when you consider what happens if the object had a velocity equivalent to the speed of light, c. Suddenly you find there in a mass and radius combination which creates and object so dense from which not even light can escape. The radius to which an object must be compressed to form a black hole is known as the Shwarzchild radius or the event horizon.
Karl Schwarzchild was a German mathematician who was working as an artillery lieutenant during World War I when he was the first person to solve the Einstein field equations. He found a solution corresponding to a physical object with strange properties: apparently matter and energy could enter, but not exit ( again it is actually more complicated as Hawking has taught us, but I digress ). His solution known as the Schwarzschild metric is a rather succinct description of the spacetime around a non-spinning black hole:
The details of this equation aren't important here. I have shown it for two reasons. First, it really is a thing of beauty that some of you will hopefully appreciate. Second, is the realization that as the radius of the object r approaches the Schwarzchild radius rs the denominator becomes zero and dividing by zero is next to impossible. This is the singularity. The singularity is unavoidable as no mathematical trick or coordinate transformation can rid the Schwarzchild metric of all singularities.
The astronomy of supermassive black holes
Observations of other galaxies, particularly nearby galaxies, reveal compelling evidence that nearly all galaxies have a super massive black hole at their center. The Milky Way has a supermassive black hole at its center known as Sgr A*. How these black holes form is not well understood, but it must have been long ago when the universe was very young such that the black holes had time to grow. They may form from the collapse of some of the first stars created in the Universe known as Pop III stars or they may form from the monolithic collapse of a cold could of gas in the early Universe. Many galaxies emit very high energy radiation from their centers (ultraviolet, X-ray or gamma ray) that is easily explained by a super massive black hole at their center. These galaxies are said to have Active Galactic Nuclei (AGN), but our Milky Way does not emit such high energy radiation. This an interesting and lucky fact that astronomers have explained by noting that if gas is actively falling onto a black hole it forms and accretion disk which heats up to very high temperatures. Thus matter falling into a black hole emits massive amounts of powerful radiation just before it falls into the black hole. Active galactic nuclei are especially correlated with galaxies which have just undergone mergers with other galaxies which are gas rich; the theory, which is backed up by simulations and observations, says that when gas rich galaxies merge gas funnels into the central super massive black holes and induces a period of high luminosity. The black hole at the center of our Milky Way also undergoes periods of gas accretion or luminosity spikes in the X-ray to radio bands. One such event in May of 2003 was a powerful flare seen located just a few milli-arcseconds from the position of Sgr A* which corresponds to less than ten Schwarzschild radii from the black hole position.
Observing supermassive black holes
How do we know that we have really observed black holes not something else? This is a hard question and astronomers may often talk about compact massive objects instead of black holes if they are not certain about a particular object in the sky. In the case of the supermassive black hole at the center or our Milky Way more direct observations are possible. Astronomers have been watching Sgr A* for decades, but only with modern instruments has powerful evidence come to light. Observations of flare events close to the Schwarzschild radius of a suspected black hole like the event described above are one way. Also watching the gravitational influence of the dark object is another:
The movie above was made with high resolution near-infrared observations over many years (in the bottom left corner is the year of the observations) on the 10 meter Keck telescope in Mauna Kea by a group at UCLA led by Andrea Gehez. These stars are right at the center of the Milky Way in the immediate vicinity of Sgr A* and they are moving in a Keplerian orbit around a central mass which is unseen in optical light. The stars are moving at speeds up to 1400 km/s (or 3 million mph) and so using Kepler's laws of motion the central object is estimated to be four million solar masses. The object is also very minute. Given this great mass and small size astrophysicists only have one explanation for the object. In the near future radio astronomers plan to use interferometry to directly image the event horizon of Sgr A*.
An unexpected relationship between black holes and galaxies
We have good reason to believe that nearly all galaxies contain a central supermassive black hole. Furthermore, the mass of the central black hole strongly correlates with the mass, velocity dispersion, and momentum parameter of the corresponding host galaxy. The most interesting relation is that of the central black hole mass with the velocity dispersion of stars in the host galaxy bulge. This is known as the m-σ relation which has a very simple basic scaling:
Thus the mass of the central black hole and the velocity of nearby stars is highly correlated. This is an empirical relation and so the value of 5 here is approximate (for example in the plot below the value is 5.8 and in some previous work was as low as 4). This relation was discovered and reported in the literature in 2000 by two independent groups (Gebhardt et al. and Ferrarese et al.), but astronomers are still seeking a theoretical model able to elucidate the origin for the correlation.
What is so amazing is how strong the correlation is over a range of galaxy and black hole sizes as seen in the log-log plot above from a very recent paper on the archive by Feoli and Mancini which complied data from Hu 2009. Even a hundred million solar mass black hole will not have a significant gravitational effect on the stars in the bulge of a galaxy (the black hole is big, but there are billions of stars and they are far away from the black hole's gravitational force which of course drops as distance-2) so the m-σ relation is somewhat of a mystery. Likely the current relation is dependent upon the galaxy and black hole co-evolution (as evidenced by the fact that the empirical scaling is only measured for cosmologically very close galaxies). Theorists and rock bands continue to search for a coherent explanation.
Look up and find your local black hole
Lets try and bring black holes back down to Earth by stargazing. The nearest (super massive) black hole is at the center of our Milky Way Galaxy in the constellation Sagittarius. Sagittarius according to Greek mythology is a centaur archer who was shot with a poisoned arrow and in honor he was given a place in the sky in the constellation Sagittarius. The arrow of Sagittarius points towards the bright star Antares in Scorpius, but it also points to the galactic center and the super massive black hole that lies there. A modern interpretation of the constellation is as a teapot which is as I have outlined it here, but I think the image of a centaur shooting an arrow in the heart of our galaxy is much more dramatic.
Sagittarius is best viewed during summer nights (this paragraph has been kind of western history and northern hemisphere centric, sorry) and can be found between the constellations Ophiuchus and Capricornus near the galactic plane. The actual object that is identified as the super massive black hole at the center of our galaxy is the luminous compact radio object Sagittarius A* (or Sgr A*) which is not visible in the optical spectrum. Another way to identify Sgr A* is that Scorpius almost wraps his tail around it. Look for Saggitarius's arrow and Scorpius's tail and you will have found a super massive black hole; happy sky hunting.
Gebhardt, K., Bender, R., Bower, G., Dressler, A., Faber, S., Filippenko, A., Green, R., Grillmair, C., Ho, L., Kormendy, J., Lauer, T., Magorrian, J., Pinkney, J., Richstone, D., & Tremaine, S. (2000). A Relationship between Nuclear Black Hole Mass and Galaxy Velocity Dispersion The Astrophysical Journal, 539 (1) DOI: 10.1086/312840
Genzel, R., Schödel, R., Ott, T., Eckart, A., Alexander, T., Lacombe, F., Rouan, D., & Aschenbach, B. (2003). Near-infrared flares from accreting gas around the supermassive black hole at the Galactic Centre Nature, 425 (6961), 934-937 DOI: 10.1038/nature02065
Ghez, A., Salim, S., Weinberg, N., Lu, J., Do, T., Dunn, J., Matthews, K., Morris, M., Yelda, S., Becklin, E., Kremenek, T., Milosavljevic, M., & Naiman, J. (2008). Measuring Distance and Properties of the Milky Way’s Central Supermassive Black Hole with Stellar Orbits The Astrophysical Journal, 689 (2), 1044-1062 DOI: 10.1086/592738
Science doesn't stop, but blogging occasionally does. Some good posts are on the way, but for today I have something fun: QR codes. You may recognize them as those little matrix barcodes that carry text, numbers, binary, or URLs that are starting to crop up in the real world in augmented reality or hardlink applications where objects in the physical world get linked to the digital world. If you didn't know already you can use your phone or camera to read these things no matter where you see them. They can carry quite a bit of information and because of fault tolerance and error handling in some cases portions of the QR code can be lost and the data still read. I made a few artistic renditions of a QR code that link to The Astronomist. I removed some of the bits from the center and replaced it with an A and I found I was still able to read them handily with the code scanner on my iPhone so I assume they aren't corrupt. Now I just need to make some stickers out of them or something so the digital and physical world will meet at The Astronomist.
A Nature letter recently reported on trapping antihydrogen. Researchers at CERN snagged 38 antihydrogen atoms in magnetic trap in what promises to the begining of fruitful research on deep symmetries in nature like charge, parity and time. I wrote up an article discussing the research for Ars Technia (where I am now an occasional contributor in case you hadn't heard) and I figure I should shamelessly self promote. From the article:
Researchers at CERN have created and trapped antihydrogen in an attempt to study the underpinnings of the standard model of physics. Antihydrogen is made of antiparticles, specifically an antiproton and a positron, instead of the proton and an electron that are present in natural hydrogen. It has the same mass but opposite charge of its normal matter counterparts.
Antimatter has a bad reputation for being dangerous because it annihilates on contact with regular matter, releasing prodigious amounts of energy. However, the clever reader will note that they have not been annihilated by the antimatter produced at CERN. The reality is that if you gathered all of the antimatter CERN has ever created, you wouldn't garner enough energy to power your laptop through reading this article.
The Universe seems to be made of mostly regular matter, so any antimatter encounters matter and is annihilated immediately after it has been created. Production and detection of cold antihydrogen atoms also happened at CERN in 2002, but those were short-lived. The new Nature letter describes how to overcome the difficulty of containing antihydrogen so that it isn't immediately destroyed.
Thirty years ago a supernova exploded 50 million light years away (right, so it actually exploded 50 million plus thirty years ago if you take into account the space and time like separation from this event) in the grand spiral design galaxy M100. A year ago a paper titled Evidence for a Black Hole Remnant in the Type IIL Supernova 1979C appeared on the astrophysics preprint archive claiming that the continued X-ray emission from the object was consistent with a 5-10 solar mass black hole. Five days ago NASA announced it was going to make an an announcement. Today NASA made a press release claiming that NASA's Chandra satellite had found the youngest black hole ever. It is a beautiful discovery.
Or is it? Lets peer inside to see the inner beauty of this discovery. The original version of the paper was submitted to Astrophysical Journal Letters , but was not accepted and only after a revision was it submitted again this time to Monthly Notices of the Royal Astronomical Society Letters. Today along with the press release a third revision of the paper went up. The excitement really just boils down to the fact that SN1979c has been a remarkably consistent and bright X-ray source for its 30 year lifetime.
The object seems to have been an approximately 20 solar mass star before it collapsed, but the core which really counts when a star collapse was around 3 solar masses. A core that is much larger than 3 solar masses would collapse into a black hole, a core a little less than 3 solar masses would form a neutron star, but there is no way to know the exact size of the progenitor star's core. Previous theories suspected the object was a magnetar or pulsar wherein the super hot dense objected emitted vast amounts of energy as it cooled and hence this induced the X-ray brightness. The new theory posits that the object is an accreting black hole remnant.
But seriously, an announcement of an accoutrement? It is a little sad how this paper hiding in plane sight was overlooked by bloggers and science writers alike. Even blogs, like Bad Astronomy, that normally expose flimsy stories like this have taken it easy. I think all press releases should come with a warning, science in progress.
The Milky Way has some nerve (or after you see the picture you may think, excuse my language, big cojones) for hiding a massive structure that about equals the size of the visible Milky Way. The Fermi gamma ray satellite observed the structure mired in a fog of gamma rays which are pervasive through our sky. Fermi has been making a survey of the complete sky for some time, but only through careful data analysis and removal of diffuse sources were the lobes readily apparent.
Spotting the lobes inside the Milky Way was difficult because from our view within we can't see the forest for the trees, but astrophysics expect that some galaxies have gamma ray lobes and Fermi has spotted such lobe structures like this in other galaxies such as Centarus A. So this result isn't that unexpected, except that it is. These gamma ray lobes are comparable to the entire size of our galaxy and they are just now being seen for the first time.
The structures are orthogonal to the plane of the Milky Way and have distinct edges; they are surprisingly geometrically perfect. They span about 7.5 kiloparsecs (or 25,000 light years). The lobes are composed of gamma rays which are super high energy photons; the photons obtain such high energies by interacting with particles, like free electrons, which are themselves moving close to the speed of light which then interact with the lower energy photons in their vicinity to boost the photons up to gamma ray energies.
The distinct edges of the lobes are indicative of a large and rapid formation event. The structures may have been formed by a massive burst of star formation followed by stellar explosions which seeded the lobes with gas, dust, and hot electrons over millions of years. There is a supper massive black hole at the center of many galaxies, including the Milky Way, which may create high energy lobes, but those lobes would only form when the black hole is actively undergoing accretion of matter. So this may be evidence that the 4 million solar mass black hole at the center of our galaxy underwent an active period where it accreted a large amount of matter and simultaneously released massive jets of energetic particles just a few million years ago.
It is an exciting discovery, but I don't have anything other than a press release to go on as of yet though a paper is accepted for publication in ApJ so more to come.
A neutron star is made of neutrons, right? Astrophysicists ponder this question and forge theory after theory, but the only thing they conclude with certainty is that a neutron star by any other name would still be made of the densest form of matter know to exist in our Universe. Under certain conditions a star which has exhausted all of its fuel and is sufficiently massive will not be able to support its own weight with pressure support (as in a regular star) or with electron degeneracy support (as in a white dwarf) such that electrons and protons merge to form neutrons because it is a more energetically favorable arrangement of the matter. A neutron star is a sort of massive atomic nucleus, but without charge. The actual composition and detailed properties of neutron star are still theoretically uncertain. New measurements of the pulsating neutron star and helium-oxygen-carbon white dwarf binary system J1614-2230 reported in a Nature letter are the highest precision determinations of a neutron star's mass to date. The data comes from the massive Green Bank Telescope using the new Green Bank Ultimate Pulsar Processing instrument which accurately records the time of arrival of each radio pulse sent out by the rapidly rotating neutron star (which is a pulsar). The quality of this instrument, having over a tera op of computing power, and the size of the telescope, 100 meters, made this measurement possible. For a quick rundown of this result you can watch these quick movies on the scientific implications and the technology behind the discovery which were created by the NRAO.
The analysis uses a general relativistic effect involving the time delay of light known as the Shapiro delay effect. When a light ray passes a massive object it follows a curved path. General relativity says that curvature of light rays can only take place when the velocity of the propagation of the light rays also varies with position. The Shapiro delay increases the light travel time through the curved space-time near a massive body. The equation to determine the time delay effect is delightfully simple.
The delay depends on the mass, M, of the time delaying body between the source and the observer, the gravitational constant G, the speed of light, c, and the geometry of the system. The geometry is that light has to be passing near the gravitating body before it gets to the observer for the effect to occur at all so the vector that points from the observer to the source, R, and the vector that points from the observer to the gravitating mass are vital. Pulsar J1614-2230 is a nearly edge on, 89 degrees, system meaning that when the white dwarf passes in front of the pulsar during the binary orbit the Shapiro effect will be very strong. I ran a quick calculation of the time delay and found it to be exactly on the order of a few microseconds. The first figure in the paper shows the geometry and the measured effect.
With this data in hand the standard Keplerian orbital parameters are calculated for this clean binary system and the masses of the objects are calculated. The mass of the neutron star was found to be 1.97 +/- 0.04 solar masses which is the most precise measurement of neutron star mass to date. Unfortunately this measurement technique does not provide any information about the radius of the neutron star, but because the mass was so high it already set a limit on the equation of state of the neutron star matter. This means that we can begin to answer what a neutron star is really made of. Different kinds of matter have a different behavior as you add more mass to them which is intuitive if you thought how discrepant with respect to size a planet made out of cotton candy versus rock would be. This result indicates that exotic models of hadronic matter including hyperons, kaon condensates are ruled out. Condensed quark matter is not ruled out, but highly constrained with this data. This is a big deal for particle physicists because this kind of system is an experiment that could never be carried out in a lab, but is necessary to probe fundamental physics.
This cool result on neutron stars glosses over another application of precise pulsar measurements that the authors of this Nature paper regarded as noise. The plot above is very neat and clean, but before the data looks like that a timing analysis must take into account the time delays associated with many more mundane effects. Effects that change the time of arrival of the pulsar include the variations in the Euclidean distance between the Earth and the pulsar resulting from Earth’s orbital motion, the proper motion of the pulsar, and its binary motion, dispersive delays in the interstellar medium, and time dilation of clocks in the observatory and pulsar frames and along the propagation path. The Earth's orbital motion about the solar system barycenter (known as the Roemer delay) is up to 500 seconds and so must be removed from the data. The powerful thing is that the Earth's orbital motion tells us about the mass and orbits of all the bodies in our solar system. A paper published in the Astrophysical Journal states that with ten years of careful observation of 20 pulsars the masses and orbits of solar system bodies could be determined better than with any other method and even undiscovered trans-Neptunian objects could be found.
Precise pulsar measurements are powerful. The first extrasolar planet ever discovered was actually made with pulsar measurements. Pulsars can tell us about the nature of neutron stars, the properties of own solar system, oh and even gravitational waves. If only astronomers had the money to build a pulsar timing array...
References
Demorest PB, Pennucci T, Ransom SM, Roberts MS, & Hessels JW (2010). A two-solar-mass neutron star measured using Shapiro delay. Nature, 467 (7319), 1081-3 PMID: 20981094
D. J. Champion, G. B. Hobbs, R. N. Manchester, R. T. Edwards, D. C. Backer, M. Bailes, N. D. R. Bhat, S. Burke-Spolaor, W. Coles, P. B. Demorest, R. D. Ferdman, W. M. Folkner, A. W. Hotan, M. Kramer, A. N. Lommen, D. J. Nice, M. B. Purver, J. M. Sarkissian, I. H. Stairs, W. van Straten, J. P. W. Verbiest, & D. R. B. Yardley (2010). Measuring the mass of solar system planets using pulsar timing ApJ arXiv: 1008.3607v1
Check out this lovely art by Jeremy Geddes. He is a Melbourne artist who works with mostly oil paints. His paintings have glowing colors and he has this recurrent cosmonaut theme that vaguely makes them seem relevant. Below are three of my favorite images that I have seen: The White Cosmonaut, The Red Cosmonaut, and Heat Death. Of his cosmonaut series he himself is vague,
I wanted to construct my own reality through my paintings, a quiet melancholic space that operates by it’s own set of underlying rules and runs it’s own oblique narrative. With each successive painting, I try to build the world and uncover it’s form. The cosmonaut paintings are the first step in this.
And on his piece Heat Death he again lets your mind linger on meaning and reasoning,
Hopefully, I communicate everything I want to say through the painting itself. I’m not interested in giving it a didactic final meaning. I just want to spark questions in the viewer.
Artists have the luxury of letting their art speak so that they don't have to. Scientists don't have this luxury and generally must have a didactic (although, not intending to imply moral) explanation of nature; an explanation which may or may not be close to the truth. Science ultimately doesn't self explain its emphases on truth seeking. Truth is like art, sought for its own sake. Oh and please, if someone wants to buy me the Red/White Cosmonaut diptych print feel free.
Once upon a time there was a planet named Earth. It orbited exactly one astronomical unity away from a G2V type star. Billions of years went by and Earth found that it lived right in the habitable zone where liquid water was maintained on it surface and life spontaneously arose. Pretty soon life on Earth became restless, questioned its own existence, and looked for life on Gliese 581. Earthlings found many planets and exclaimed, 'Gliese 581 b is too hot, Gilese 581 c is slightly too hot, Gliese 581 d is slightly too cold, Gliese 581 e is way too hot, Gliese 581 f is too cold, but Gliese 581 g is just right!' so the story goes.
Gliese 581 is an unassuming star: it is relativity close at 20 light years away (the 87th closest cataloged star to earth), it is only a third the mass of the sun, and it is relativity quiet in terms of stellar activity (which is beneficial for life because flares scorch planets). It is the sixth planet from Gliese 581 denoted merely as g that harbors so much potential. It is not to hot, not too cold, it is just right. It is the Goldilocks planet. Vogt et al. 2010 recently reported on the discovery of this planet which is a 3.1 Earth mass (or larger) planet orbiting in the habitable zone of the M3V type star Gliese 581. The problem is that this planet may not exist.
The Media
I did not immediately discuss Gliese 581 here at The Astronomist because I wanted to read the paper before weighing in. However the authors were compelled to issue a press release about their findings before making their peer reviewed paper available. After I finally looked at the paper I was somewhat disappointed. The whole thing was a science journalism media circus. A selection of some of my favorite excerpts:
“Found: An Earth like Planet, at Last” Time magazine
“The chances of life on this planet are 100 percent,” Steven Vogt
“Could contain more gold than we could ever imagine” PR Fire
Media coverage is a double edged sword for science. Scientists strive to come up with compelling results that often fall flat when presented to the media or public, but other stories make waves disproportionately large relative to their scientific impact. Arguably the discovery of an earth like planet should have been accompanied by a much larger amount of media attention. The misinformation spread about Gliese 581 g is a symptom of the real problem which is the science. This is not a confirmed planet detection, there is no evidence this planet has a hospitable atmosphere anything like Earth, and there is certainly no evidence of life. This wont stop the media from speculating or spreading dangerous misinformation (like the idea we could travel there if we trash Earth). The quote from Steven Vogt is an example of poor journalism where he prefaced the statement by saying, 'my own personal feeling is that the chances of life on this planet are 100 percent,' but the crucial context was thrown away for headlines.
The Science
All the planets around Gliese 581 were discovered using the radial velocity technique. In any gravitationally bound system the bodies orbit their common center of mass. It is a subtle effect in a star-planet system where the central star dominates the mass. The central star will move at a characteristic speed depending on the orbits of the planets around it. The movement of the star is measured through the Doppler shift of the light emitted by the star. Modern instruments are super sensitive to even the smallest movements of stars down to as little as 1 m/s. Observations of the radial velocity of the star over a period of time (usually several years) is analyzed using Fourier analysis. The Fourier analysis identifies periodic signals in the data corresponding to the orbital period of the planet or planets.
The researchers used two data sets spanning almost two decades. Most of the data came from the researcher's own instrument HIRES, and additional data came from a Swiss group with the HARPS instrument. The HIRES data spans a larger time range, but the HARPS data is more precise. This combined data set is how the researchers identified two new planets f and g.
The Problems
A little after this new Goldilocks planet was announced the Swiss group announced that they could find no evidence of Gliese 581 g in their data. Does this mean it doesn't exist? Well this is tricky. A planetary researcher in my department, Rory Barnes, spoke to the New York times before the Swiss group had spoke up and said that the planet looked like the 'real deal'. After the announcement was made I spoke to Barnes again and he said that he would have to hold off further judgment until more information was available.
The onus of proof in science is upon those who make extraordinary claims. Vogt et al. were only able to find this planet by combing the available data sets; they actually state in their paper that they did not detect the planet in either of the data sets independently, only in combination. The damning part of the Swiss groups statement is that they say they have much more data available at this point that Vogt et al. did no have access to during their analysis. When the Swiss team forces planet g to fit their complete data they actually get a negative fit indicating that planet g really isn't there. The thing about this paper that I am least happy with is the quoted false alarm probability. The false alarm probability appears to be 1% based on the figures in the paper (see figure 3 specifically), but in the text it is quoted as ~10-5. I don't know what is going on.
Then there is their error analysis (warning this is about to get technical feel free to skip this paragraph). Vogt et al. used the peaks in the power spectrum to identify the planets in the system then subtracted off the highest power modes corresponding to the planets they had found. The power spectrum for each planet carried with it a false alarm probability, but once the planet had been subtracted out of the power spectrum its false alarm probability was washed away (you can see this happening in figure 3). They compound their errors after the 1st, 2nd, 3rd, 4th, and 5th planets which have varying false alarm rates. The proper way to do this is a joint fit model to all planets in the system using Bayesian analysis.
The strangest thing about all this is that when this paper was first submitted to The Astrophysical Journal the Swiss group was reviewing the paper and it was rejected. This Vogt paper meta chronicles its own history and discusses why it was retracted previously over concern of systematics. Unfortunatly the quality of the paper may not have improved. The Swiss group has actually leveled one specific concern, Vogt used perfectly circular orbits to find planet g, but the evidence shows the orbits are probably slightly elliptical. In fact in 2009 Vogt used elliptical orbits, but in this new paper circular orbits have been adopted. The image above illustrates this and makes a pictorial argument as to how circular vs elliptical orbits could introduce errors.
The discovery of an Earth-like planet seems imminent. I do not know if this is it. I will hold off further judgment until more information was available.
References:
Steven S. Vogt, R. Paul Butler, Eugenio J. Rivera, Nader Haghighipour, Gregory W. Henry, & Michael H. Williamson (2010). The Lick-Carnegie Exoplanet Survey: A 3.1 M_Earth Planet in the
Habitable Zone of the Nearby M3V Star Gliese 581 ApJ accepted : arXiv: 1009.5733v1
Also thanks to Amit and Rory for discussion and figures.
ATALAS commissioned an impressive mural of their detector that has just been completed. Artist Josef Kristofoletti created the massive mural of the Large Hadron Collider's ATLAS detector on the outside wall of loop point 01. The mural was commissioned by the ATALAS experiment after Kristofoletti first painted a similar, though much smaller, mural on the side of the Redux Contemporary Art Center in Charleston, South Carolina. Kristofoletti found inspiration for the art by merging his enjoyment of classic Italian Renaissance murals and his life long fascination with science. He says that the humongous size of ATALAS and the tiny particles it finds make the Large Hadron Collider fascinating, like an unprecedented modern cathedral of science. The event depicted in the mural shows an actual event recorded by ATALAS of a Z boson decay into two muons.
There are more concept pictures here or finished pictures from CERN here.
Making good decisions is complicated. Game theory applies logic and mathematics to determine the optimal course of action for individuals when acting in the presence of other participants. Now, individual actions must take into account logic, morals, and personal preference, but there are general rules or situations in which the optimal course of action is clear. This comic (or infographic?) by SMBC illustrates the application of game theory to a classic problem, the prisoners dilemma, and by extension morality.
The prisoners dilemma is a great way to find your moral compass. We can apply a similar decision matrix as used above to many different kinds of situations, like Pascal's wager, where one attempts to bet on the existence of God. The logic of pascal's wager concludes that one should believe, or at least act as if one believes in God (this result is unsatisfactory to many, but wait I have a response). I was recently considering applying a decision matrix to answer the question, 'Should you believe in science?' There are other ways to phrase the question, like 'Should you be a skeptic?' or 'Should you follow logic?' Decision theory gets tricky here. In order to answer the question I recalled an analogy a professor used in a philosophy class I took long ago. My professor wanted us to consider a philosophical umpire calling a game. The umpire could either state that she was very vigilant such that she, 'calls em as I see em' (admitting fallibility), or the umpire could say that, 'I call them as they are' (denial of fallibility). In the situation before replays I could almost see the umpire taking either stance with reason because they are the final arbiter on the field. In this modern age it is completely untenable for an umpire to state that she calls everything'as they are because replays are available. In life any experience that can be repeated is like a game with replays; an experiment is a game with replays. We all must be like the philosophical umpire and we can reason out how to behave using these ideas.
Below I have made a logic table. On the left vertical axis is the true outcome of an event with respect to how you perceived it and on the top horizontal axis is how you see yourself judging the event. The conclusion of the table is that application of the scientific method is really powerful. Admitting that you make errors in judgement means that you always allow potential for improvements in the future outcomes, but insistence on being right leads you to a false world view. I think that scientists, skeptics, and atheist have essentially the same goal and are all standing in the top right corner there jumping up and down trying to get people to choose to be skeptical.
'calls em as I see em' (skeptic)
'calls em as they are'
right
positive result, skeptic world view, positive future results
positive result, superficially correct world view, positive future results
negative result, skeptic world view, potential for improved future results
negative result, false world view, negative future results
wrong
It almost seem to be a tautology that logic says you should use logic to understand the world. This decision matrix casts doubt on the result of all other decision matrices like Pascal's wager such that we can escape being certain that belief in God is best, but simultaneously this result casts doubt on itself. Paradoxically what this really seems to say is that you should be skeptical about being skeptical.
The existence of magnetic fields on cosmologically large scales is an unsolved problem in astrophysics. Theory favors a universe that did not begin with any magnetic fields present and classical magnetohydrodynamics restricts the spontaneous emergence of a magnetic state under the influence of ideal forces. In a paper entitled Twisting Space-Time: Relativistic Origin of Seed Magnetic Field and Vorticity appearing Physical Review letters Swadesh Mahajan and Zensho Yoshida propose a universal magnetic field generating effect using ideal special relativistic fluid dynamics. Mahajan and Yoshida's insight was that in describing magnetic fields, which are mathematically equivalent to a vorticity, a careful application of ideal dynamics in the framework of distortions caused by special relativity may result in the spontaneous emergence of a magnetic state in contrast to the previous theoretical result.
Magnetic fields are found to be important in every scale hierarchy of the universe. Most notably detailed images of galaxies paradoxically display regions of chaotic turbulence and beautiful grand coherent designs at once. Thus it is clear that turbulent motion on scales below hundreds of parsecs does not necessarily destroy coherent optical or magnetic features over scales of kiloparsecs. Indeed, magnetic fields are indirectly observed at optical and radio wavelengths by detecting the polarization of the electromagnetic field through the Faraday effect and also by the Zeeman splitting effect. The Faraday effect is the rotation of the linear polarization vector of light which occurs when polarized radiation passes through a magnetized and ionized medium. Radio observations are the most powerful technique and by measuring both the dispersion and polarization rotation the mean of the magnetic field along the line of sight can be measured. Such observations indicate a wide range of magnetic field are present in astrophysics. The image at right below shows the magnetic fields present in M51 which are likely similar in structure and strength to that of the Milky Way.
The total radio continuum emission from the "whirlpool" galaxy M51 (distance estimates range between 13 and 30 million light years) is strongest at the inner edges of the optical spiral arms, probably due to the compression of magnetic fields by density waves. The vectors give the orientations of the regular magnetic fields as derived from the polarized emission. The field lines follow nicely the optical spiral arms. Unexpectedly, strong polarized emission is observed also between the optical arms which indicates the action of a dynamo. This image was observed with the VLA in its most compact configuration at 6cm radio wavelength (broadband continuum). As the VLA cannot detect the diffuse, large-scale radio emission, data from the Effelsberg 100-m telescope in Germany at the same wavelength was added. Investigator(s): Rainer Beck (MPIfR Bonn, Germany), Cathy Horellou (Onsala Space Observatory). Image courtesy of NRAO/AUI
Microguass fields are present in galaxies at scales of a few kiloparsecs and on the much larger scales of megaparsecs ordered fields of perhaps a few orders of magnitude less are present in galaxy clusters. Magnetic fields in astronomy are controlled by induction of partially ionized gas. A common model for creating these magnetic fields is the dynamo effect wherein an electrically conductive fluid accelerated by some kinetic force generates convective motions in the fluid; it is plausible that a turbulent hydromagnetic dynamo of some kind coupled to an inverse cascade of magnetic energy wold give rise to regular galactic magnetic fields. Following the basic dynamo theory magnetic field lines can be simulated for galaxies which are consistent with observations. The dynamo theory is actually a mechanism for maintaining or growing fields rather than creating them, but it is expected that minuscule primordial magnetic field seeds in the early universe of cosmological origin drive the magnetic fields observed today.
The magnetic dynamo and the primordial magnetic seed theories are both unsatisfactory. The model wherein the the large scale magnetic field in galaxies is the result of the twisting of a cosmological magnetic fields by galactic differential rotation is not satisfactory because a primordial field wound up by differential rotation ultimately decays in an effect known as flux expulsion. The primordial seed theory must explain the presence of large magnetic fields in higher redshift objects when the universe was much younger when the fields should not have had sufficient time to grow. Researchers disagree over what initial primordial field strength is necessary to create the magnetic fields seen today; estimates vary from as large as 10-9 gauss [1] to 10-30 gauss [2], but either way an alternative model would be welcome.
Mahajan and Yoshida's work was motivated by the search for a universal mechanism for magnetic field generation. They key to creating a magnetic field is the vorticity of an ionized material which is analyzed in this paper with topological constraints. In mathematical terms fundamental cosmology requires a topological constraint on the vorticity of the universe (consider that you wouldn't expect the universe to have a preferred rotation), however this constraint can be broken by the application of special relativity. The problem of magnetic fields lies in the fact that vorticity must vanish for every ideal force such as the entropy conserving thermodynamic forces (this can be proven though the governing Hamiltonian dynamics of an ideal fluid where ultimately Kelvin's circulation theorem shows that if the initial state has no circulation the later sate will also be vorticity-free). Introduction of the Lorentz factor γ=(1-(v/c)2)-1/2 from special relativity destroys the exactness of the ideal thermodynamic force and allows spontaneous vorticity.
The authors find a new term that provides a magnetic field growing mechanism as long as the kinetic energy is inhomogeneous. The authors mechanism can provide a finite seed for even mildly relativistic flows. They provide an example for very standard parameters (electron density n=1010 cm3, temperature T= 20 eV and velocity, v, compared to c of v/c=10-2) and find their relativistic drive mechanism remains dominate over other effects until magnetic fields of 1 gauss or so which is much larger than most magnetic fields ever observed, thus the relativistic drive is the only dominant effect. The relativistic drive mechanism will likely help us understand, among other things, the origin of magnetic fields in astrophysical and cosmic settings.
References:
[1] Beck, R., Brandenburg, A., Moss, D., Shukurov, A., & Sokoloff, D. (1996). GALACTIC MAGNETISM: Recent Developments and Perspectives Annual Review of Astronomy and Astrophysics, 34 (1), 155-206 DOI: 10.1146/annurev.astro.34.1.155
[2] Davis, A., Lilley, M., & Törnkvist, O. (1999). Relaxing the bounds on primordial magnetic seed fields Physical Review D, 60 (2) DOI: 10.1103/PhysRevD.60.021301
[3] Mahajan, S., & Yoshida, Z. (2010). Twisting Space-Time: Relativistic Origin of Seed Magnetic Field and Vorticity Physical Review Letters, 105 (9) DOI: 10.1103/PhysRevLett.105.095005
Current observations of our universe indicate that the universe is expanding at an accelerating rate. The expansion of the universe will eventually place all galaxies which are not gravitationally bound to the Milky Way beyond our observable horizon (yet I caution that the notion of a horizon is a subtle point and a source of expanding confusion). Galaxies will cease to be brilliant. The passing of time will see stars exhaust all of their fuel. Stars will cease to shine. Black holes will evaporate due to Hawking radiation dispersing a bath of dull photons into the universe. Black holes will cease to exist. The universe will cool as it expands to a uniformly frigid temperature. Entropy will be maximized. The universe will be cold, dark, and lonely.
The future history of the universe described above is an implicit result of the standard cosmology accepted today. It is an extrapolation of accepted theory into the distant future. There is good reason to be skeptical of extraordinary predictions which is why the big bang and the past expansion history of the universe is the major focus of cosmology and not predicting the future of the universe. We need to know exactly what happened in the past to understand the reasons for the accelerating expansion (what is dark energy?). The current observations and the 'standard cosmology' I speak of are part of what is known in physics as the concordance model of cosmology. Every peer reviewed research paper that discusses the universe has this one sentence in it that goes something like this (taken from generic research paper on cosmology and extragalactic astrophysics):
If you lived forever it would be hard to avoid the situation where eventually you and your fellow space travelers were huddled around a few dieing stars in a bland galaxy in an exhausted void. There are small stars which are burning today and will be burning in 100 billion years and more stars will form for a while. But eventually, stars really will shut down and cool. You could try to travel to another galaxy, but that would take a long time (if the distance to our neighbor galaxy Andromeda was held constant it would take about 2.5 million years to travel there at the speed of light), and even then there would be few stars and most problematically most other galaxies would have receded beyond our horizon. Where would you want to head in this barren universe? Recent studies of the entropy of the universe indicate that the majority of the entropy in the universe is actually contributed by super massive black holes. Interestingly gravity is rather unlike most systems in thermodynamics. Generally entropy is increased by say smashing something into many pieces, but for gravity when energy is uniformly distributed gravity is quite low compared to the state where matter has collapsed into stars or to the extreme state of a black hole. There is one more step in producing more entropy which occurs as black holes slowly emit radiation in the form of Hawking radiation. A black hole the mass of the sun would emit Hawking radiation for 2 × 1067 years which is much longer than the current age of the universe at 13.7 × 109 years. A super massive black hole of 100 billion solar masses, about the mass of our entire Milky Way galaxy, would emit Hawking radiation for 2 × 10100years. You could hang out near one of these black holes for a while as a source of energy because the black hole would still be producing entropy. Finally, all the black holes would also evaporate and the universe would consist of a diffuse gas of photons and leptons. Any activity in the universe would be very limited at this point and what did occur would take truly epic time scales.
The concordance cosmology, the theoretical models, and the measured parameters implicitly assume that the end of the universe is cold, dark, and lonely. The universe ending as cold void in which life can no longer be sustained is sometimes known as the Big Chill. At this point there is only speculation, perhaps it is philosophical. The universe may expand again in a secondary inflationary epoch or the vacuum may decay into an even lower energy state. Actually, there are other possible scenarios such as the Big Rip in which dark energy pulls apart the fabric of space through some exponentially increasing expansion. Revisionist history is the best kind of history, so when talking about the future history revisions are always welcome. There may already be information about universe which has been erased that would change our expectations. One example of the universe erasing information is if the radius of curvature of the universe is much greater than the horizon distance then observing this curvature would be like trying perceive the curvature of the earth just by looking at the horizon so as the universe, or earth, expanded observing curvature could more difficult. Paradoxically, conceding that there is information about the universe which has been erased which would indicate an ultimate fate other than the one outlined here also supports the argument that the ultimate fate of the universe is an extremely high entropy state.
Conceding that the universe may not be infinite or that the end is simply cold and lonely is very difficult for some. This theme was explored in Issac Asimov's story The Last Question in my previous post. In this story man ponders how the heat death of the universe can be avoided. Man asks the greatest computer created how the second law of thermodynamics can be reversed. [spoiler alert] After hundreds of billions of years the computer still cannot answer the humans. Ultimately all of humanities mental facilities from the trillions of humans spread throughout the universe merge their minds with this ultimate computer to from a singular unified mental process. The question is asked again and there is still no answer. Time goes on until space and time cease to exist, however the ultimate mind continues to ponder the question in hyperspace and eventually finds an answer. There is no one or no thing left to report the answer to so the mind decides to show the answer by demonstrating the reversal of entropy. The mind spends another eternity determining how to do this and writing a careful program to execute. Upon execution of the program the mind reverses entropy and thus creates the universe anew.
The last question was asked for the first time, half in jest, on May 21, 2061, at a time when humanity first stepped into the light. The question came about as a result of a five dollar bet over highballs, and it happened this way:
Alexander Adell and Bertram Lupov were two of the faithful attendants of Multivac. As well as any human beings could, they knew what lay behind the cold, clicking, flashing face -- miles and miles of face -- of that giant computer. They had at least a vague notion of the general plan of relays and circuits that had long since grown past the point where any single human could possibly have a firm grasp of the whole.
It is interesting to note that different versions of this story I have encountered state the the sun will burn for ten billion years or 20 billion years. The written story above says twenty while the spoken story says ten. I don't know what the original version said (does anyone out there?). Perhaps this reflects our changing understanding of our sun which suggests that ten billion years is more appropriate.
The era of complex planetary systems is here. The solar-type star HD 10180 is just 39 parsecs away and hosts at least 5 extrasolar planets; this is the richest planetary system yet discovered. The ESO 3.6 meter telescope in La Silla, Chile made the observations of HD 10180 with the precise High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph for six years to confirm their findings.
Are there planets outside of our solar system? Is there life on other planets? Is life on other planets like life on Earth? These are questions that astronomers, astrobiologists, chemists, and geologists are trying to answer with current experiments. In order to answer these questions we must observe distant planets and we must determine what life on those planets may be like. Detecting extrasolar planets is tricky enough, but imaging what alien life is like may well be stranger than science fiction. Yesterday evening I attended a lecture sponsored by the Seattle Astronomical Society given by Shawn Domagal-Goldman titled Cylons and Smelloscopes: False Positives and False Negatives in the Search for Extraterrestrial Life. It was an excellent lecture and filled with interesting topics. Shawn touched on the philosophical problem of defining life in the broadest of senses (is Number Six alive?) and he pointed out that the verification of life on distant planets faces technical challenges and basic scientific limitations (a smelloscope sure would help!).
Dimitar Sasselov set off minor shock waves of gossip and rumors in the media and astronomy communities when claimed that the NASA Kepler mission had found 140 Earth-like planets a few weeks ago during a talk he gave at the TED Global 2010 meeting in Oxford. The media thought we had found earth's twin, but astronomers knew that Sasselov had exaggerated the situation. Sasselov had to post a redaction of sorts on the Kepler blog in order to clarify what he said. What he should have said is that the Kepler mission will find and verify the presence of potentially habitable planets and that Kepler currently had 140 candidate extrasolar planets. The candidates are not confirmed and so a pessimistic outcome could be that half of the candidates will be false. The difficulty in finding extrasolar planets or life is fraught with false positive and false negatives. A false positive is a detection that seems like exactly what you were looking for, and maybe it is, but the detection was either bad data or you were looking for the wrong thing. A false negative is a detection which you conclude is not what you were looking for, but either your data was fouled or your detection threshold was too constrictive.
How do we find planets outside of our solar system? There are at least five methods to find planets: Doppler shift, astrometric measurement, transit method, gravitational microlensing, and direct detection. Shawn discussed in depth the Kepler mission that is currently monitoring more than 150,000 stars in the direction of the Cygnus constellation for any signs of extrasolar planets that may be orbiting those stars. So, what method does Kepler use to find planets? It watches for eclipses! When a planet orbiting a distant star crosses in front of the star some of the light from the host star is blocked. The planet will transit (astronomers often use the world transit not eclipse for exoplanets) in front of the the star once an orbit and thus the period of orbit can be determined. A secondary eclipse also occurs when the day side of the planet is blocked by the star. The video below illustrates the whole process.
Yes, there are planets outside of our solar system. The current exoplanet detection count is 473 and counting; you can watch that count go up over at Planet Quest. Kepler may double that number, but more importantly it has the ability to find earth size planets. Most of the planets found to date have been large, hot, and inhospitable to most kinds of life anyone can fathom.
How do we detect signs of life on other planets? Astronomers look for bio-markers in the planet's atmosphere. Bio-markers are molecular signatures of certain compounds that could not be produced by non-biological process; bio-markers indicate that dynamic non-equilibrium chemistry is present on the surface of that planet. Astronomers can measure the light emitted as a function of wavelength, the spectra, that a planet emits to determine the molecular species present in the atmosphere. For example the Earth's atmosphere has the spectral signature of water which means it has conditions in which life as we know it can thrive. If we found an earth size planet that had water in its atmosphere which wasn't too hot we would say we had found a habitable planet. If we found oxygen or ozone (03) in an atmosphere it would almost certainly mean life was present on the planet because 03 is quickly removed from atmospheres through standard geological processes such as oxidation of iron, but it may remain present in an atmosphere if it is continually replenished by the photosynthesis mechanism of algae and plants. One of the topics Shawn talked about in his talk and a focus of his research was the problem of being certain that non-biological processes are not creating the oxygen rich atmospheres. The runaway greenhouse effect combined with the photo-disassociation of carbon dioxide can produce oxygen in a similar way to biological life. This is where the smelloscope would be useful: ozone along with other non-equilibrium species such as nitrous oxide and methane in specific ratios would be the scent we are looking for. Bio-signatures were not present on the early Earth. In fact the Earth probably looked a lot more like Venus. The diagram above shows that Venus, Earth, and Mars all have distinct spectral features that tell us about their atmospheres. The hardest part of looking for bio-signatures is that we do not have a telescope that is sensitive enough. Trying to take the spectra of a planet orbiting a bright star is like trying to tell the color of the wings on a gnat hovering around a spotlight on the moon. Like a baseball player holding up one hand to block the sun from his eyes as he focuses on the ball an occulter or star shade working with an existing telescope in space would do the trick. The current funding situation in astronomy is dire, but there is hope that a mission called New Worlds will one day work with the James Webb Space Telescope to allow us to take a closer look at planets which Kepler is finding.
Is there life on other planets? We don't know and it may be a more complicated question than is suspected. There is a bias towards looking for life that is similar to what life on Earth is like. There is a bias towards looking for life that alters its host planet's atmosphere significantly enough to detect it with telescopes on earth. There is a bias towards looking for life that is alive as we define it. These biases may lead to false negatives in the search for life, but as Shawn pointed out the possibilities for life to exist are much grander than our imaginations so we do the best we can. Also, despite the difficulties for finding life on other planets and the gulf between the public's perception of aliens and reality scientists are taking this as a serious venture. Scientists from diverse fields are coming together to forge a path forward. One such project is the Virtual Planet Laboratory which employs scientists in fields such as geology, chemistry, biology, and astronomy. The Virtual Planet Laboratory is a team of scientists who are building computer simulated planets to discover the likely range of planetary environments for planets around other stars so we can better look for habitable planets and distinguish between planets with and without life. However, we can't even discern with certainty the presence of life on Mars or Europa at this point, what hope do we have for finding life on distant planets?
I think there is a lot of hope and I am not alone in that sentiment. I don't search for planets or life in my research, but I think that the search for life, particularly intelligent life, is a fundamental question. It is natural to wonder about the Universe on the grandest of scales, but it is wise to be concerned with what happens on the smallest of scales because that is where we will find life. We expect to find the unexpected in the search for life.
References:
Beichman, C. A., Woolf, N. J., & Lindensmith, C. A. (1999). The Terrestrial Planet Finder (TPF) : a NASA Origins Program to search for habitable planets JPL publication
