Supernova Alert! Astronomers Developing Explosion Predictors
Each century, about two massive stars in our own galaxy explode, producing magnificent supernovae. In the Universe at large, a supernova event occurs every second. Astrophysicists at the level of Stephen Hawking believe that these massive explosions may be resonsible for killing off advanced civilization --a major factor perhaps in the "Great Silence" of the Fermi Paradox.
If we are to understand that data, however, scientists will need to know in advance how to interpret the information the detectors collect. To that end, researchers at the California Institute of Technology (Caltech) have found via computer simulation what they believe will be an unmistakable signature of a feature of such an event: if the interior of the dying star is spinning rapidly just before it explodes, the emitted neutrino and gravitational-wave signals will oscillate together at the same frequency.
"We saw this correlation in the results from our simulations and were completely surprised," says Christian Ott, an assistant professor of theoretical astrophysics at Caltech and the lead author on a paper describing the correlation, which appears in the current issue of the journal Physical Review D. "In the gravitational-wave signal alone, you get this oscillation even at slow rotation. But if the star is very rapidly spinning, you see the oscillation in the neutrinos and in the gravitational waves, which very clearly proves that the star was spinning quickly—that's your smoking-gun evidence."
Scientists do not yet know all the details that lead a massive star—one that is at least 10 times as massive as the Sun—to become a supernova. What they do know (which was first hypothesized by Caltech astronomer Fritz Zwicky and his colleague Walter Baade in 1934) is that when such a star runs out of fuel, it can no longer support itself against gravity's pull, and the star begins to collapse in upon itself, forming what is called a proto-neutron star. They also now know that another force, called the strong nuclear force, takes over and leads to the formation of a shock wave that begins to tear the stellar core apart. But this shock wave is not energetic enough to completely explode the star; it stalls part way through its destructive work.
There needs to be some mechanism—what scientists refer to as the "supernova mechanism"—that completes the explosion. But what could revive the shock? Current theory suggests several possibilities. Neutrinos could do the trick if they were absorbed just below the shock, re-energizing it. The proto-neutron star could also rotate rapidly enough, like a dynamo, to produce a magnetic field that could force the star's material into an energetic outflow, called a jet, through its poles, thereby reviving the shock and leading to explosion. It could also be a combination of these or other effects. The new correlation Ott's team has identified provides a way of determining whether the core's spin rate played a role in creating any detected supernova.
It would be difficult to glean such information from observations using a telescope, for example, because those provide only information from the surface of the star, not its interior. Neutrinos and gravitational waves, on the other hand, are emitted from inside the stellar core and barely interact with other particles as they zip through space at the speed of light. That means they carry unaltered information about the core with them.
The ability neutrinos have to pass through matter, interacting only ever so weakly, also makes them notoriously difficult to detect. Nonetheless, neutrinos have been detected: twenty neutrinos from Supernova 1987a in the Large Magellanic Cloud were detected in February 1987. If a supernova went off in the Milky Way, it is estimated that current neutrino detectors would be able to pick up about 10,000 neutrinos. In addition, scientists and engineers now have detectors—such as the Laser Interferometer Gravitational-Wave Observatory, or LIGO, a collaborative project supported by the National Science Foundation and managed by Caltech and MIT—in place to detect and measure gravitational waves for the first time.
Ott's team happened across the correlation between the neutrino signal and the gravitational-wave signal when looking at data from a recent simulation. Previous simulations focusing on the gravitational-wave signal had not included the effect of neutrinos after the formation of a proto-neutron star. This time around, they wanted to look into that effect.
"To our big surprise, it wasn't that the gravitational-wave signal changed significantly," Ott says. "The big new discovery was that the neutrino signal has these oscillations that are correlated with the gravitational-wave signal." The correlation was seen when the proto-neutron star reached high rotational velocities—spinning about 400 times per second.
Future simulation studies will look in a more fine-grained way at the range of rotation rates over which the correlated oscillations between the neutrino signal and the gravitational-wave signal occur. Hannah Klion, a Caltech undergraduate student who recently completed her freshman year, will conduct that research this summer as a Summer Undergraduate Research Fellowship (SURF) student in Ott's group. When the next nearby supernova occurs, the results could help scientists elucidate what happens in the moments right before a collapsed stellar core explodes.
Most of the computations were completed on the Zwicky Cluster in the Caltech Center for Advanced Computing Research. Ott built the cluster with a grant from the National Science Foundation. It is supported by the Sherman Fairchild Foundation.
The image below shows the inner regions of a collapsing, rapidly spinning massive star. The colors indicate entropy, which roughly corresponds to heat: Red regions are very hot, while blue regions are cold. The black arrows indicate the direction of the flow of stellar material. The two white curves with black outlines indicate the neutrino (top) and gravitational-wave (bottom) signals. This frame shows a simulation about 10.5 milliseconds after the stellar core has become a dense proto-neutron star.
Journal reference: Physical Review D
The Daily Galaxy via California Institute of Technology
Image Credit top of page: X-ray: NASA/CXC/U.Illinois/R.Williams & Y.-H.Chu; Optical: NOAO/CTIO/U.Illinois/R.Williams & MCELS coll.; Radio: ATCA/U.Illinois/R.Williams et al.) This composite image of DEM L316 combines data from Chandra (X-ray, blue), the Curtis-Schmidt telescope at CTIO (optical, red) & ATCA, the Australia Telescope Compact Array (radio, green).
Comments
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This is cool. How would we protect ourselves from these stellar explosions? Could we build a graphine shield of some sort.
Posted by: Justin | July 12, 2012 at 09:55 PM
Not sure about about nearby explosions, but I think it near impossible to protect ourselve from our own star exploding! The only solution to this is faster than light travel and migrate to a different solar system before this happens.
Posted by: Greg | July 13, 2012 at 08:58 AM
Each century, about two massive stars in our own galaxy explode, producing magnificent supernovae. In the Universe at large, a supernova ...
Posted by: abercrombie france | July 13, 2012 at 08:16 PM
Well this the most threat I think we have to start preparing right away.
We could solve this but the person studying this concept should have life of 200 yrs without any illness.
Posted by: Vallabh,India | July 14, 2012 at 06:55 AM
Supernovae have nothing to do with the Great Silence they are too rare. In our case there is no large enough star near enough to do anything but give us a really nice light show. And by the time our Solar System's trek thru (sic: coinage thru usage) the galaxy does bring us close enough to a star that might pose a threat our technology will allow us to tinker with the star's evolution, i.e. the timing of the supernova, think of Jupiter sized gas giants mostly hydrogen/helium gas bags (with a fair bit of carbon) thrown into the star with enough velocity to reach the stellar core before assimilation. How about megaton iron slugs whose velocity gets them into nice tight inner-core orbits before total vaporization. Both of these scenarios are believed to mess up fusion reactions. We will likely reach that level of technology in less than a thousand years (very likely a lot, lot less). Our planet-fryer super-jumbo civilization killing nemesis (I've named it Fat Albert (apologies Bill)) is hundreds of thousands of years in our future. It is so far into the future that even Christmas will be long forgotten and no one will think to time the explosion so that the nova's first light reaches us in time for the Magi to start their journey.
The Great Silence is easy enough to explain if you grant the following: Our type of society places selection pressure towards higher IQ. Note that almost all standardized IQ tests and professional school admission tests and high school SAT scores are acceptable to Mensa as proof of meeting eligibility criteria. In the near future gene therapy will allow in utero cures to a vast array of genetic maladies, including sub-normal intelligence. (This intelligence boosting will take off like a rocket). These two items make progressively higher intelligence a given and so let us turn our attention to limits and consequences.
If there is a limit to the intelligence that one entity can have then all intelligent species wait until they hit that limit to communicate with others. Why? Given the slow speed of light, communications will cause conversations to last hundreds of years, differential rates of approaching the intelligence limit will make that slow conversation boring to one of them and unintelligible to the other. If on the other hand there is no limit to intelligence then every intelligent species is on its own. The only thing to do would be to broadcast in the simplest code possible the contents of your civilization's current state if knowledge, repeat every 50 to 100 years.
So, where is the human race? We have reached the very lowest rung on that ladder which climbs to the pinnacle of intelligence. We do not know how tall the ladder may be, nor the spacing between rungs (I like the common ancestor to Pan Troglodytes and Homo Sapiens to now as the spacing, completely arbitrary, but somehow satisfying.)
Before we get to the second rung our understanding of intelligence and its limits, an appropriate rung spacing, and a keener understanding of communications theory will allow us to answer Fermi's Paradox with greater clarity.
But for now the answer seems to be that people are talking, but we haven't learned to listen yet.
Posted by: farticustheelder | July 14, 2012 at 01:32 PM
Supernovae have nothing to do with the Great Silence they are too rare. In our case there is no large enough star near enough to do anything but give us a really nice light show. And by the time our Solar System's trek thru (sic: coinage thru usage) the galaxy does bring us close enough to a star that might pose a threat our technology will allow us to tinker with the star's evolution, i.e. the timing of the supernova, think of Jupiter sized gas giants mostly hydrogen/helium gas bags (with a fair bit of carbon) thrown into the star with enough velocity to reach the stellar core before assimilation. How about megaton iron slugs whose velocity gets them into nice tight inner-core orbits before total vaporization. Both of these scenarios are believed to mess up fusion reactions. We will likely reach that level of technology in less than a thousand years (very likely a lot, lot less). Our planet-fryer super-jumbo civilization killing nemesis (I've named it Fat Albert (apologies Bill)) is hundreds of thousands of years in our future. It is so far into the future that even Christmas will be long forgotten and no one will think to time the explosion so that the nova's first light reaches us in time for the Magi to start their journey.
The Great Silence is easy enough to explain if you grant the following: Our type of society places selection pressure towards higher IQ. Note that almost all standardized IQ tests and professional school admission tests and high school SAT scores are acceptable to Mensa as proof of meeting eligibility criteria. In the near future gene therapy will allow in utero cures to a vast array of genetic maladies, including sub-normal intelligence. (This intelligence boosting will take off like a rocket). These two items make progressively higher intelligence a given and so let us turn our attention to limits and consequences.
If there is a limit to the intelligence that one entity can have then all intelligent species wait until they hit that limit to communicate with others. Why? Given the slow speed of light, communications will cause conversations to last hundreds of years, differential rates of approaching the intelligence limit will make that slow conversation boring to one of them and unintelligible to the other. If on the other hand there is no limit to intelligence then every intelligent species is on its own. The only thing to do would be to broadcast in the simplest code possible the contents of your civilization's current state if knowledge, repeat every 50 to 100 years.
So, where is the human race? We have reached the very lowest rung on that ladder which climbs to the pinnacle of intelligence. We do not know how tall the ladder may be, nor the spacing between rungs (I like the common ancestor to Pan Troglodytes and Homo Sapiens to now as the spacing, completely arbitrary, but somehow satisfying.)
Before we get to the second rung our understanding of intelligence and its limits, an appropriate rung spacing, and a keener understanding of communications theory will allow us to answer Fermi's Paradox with greater clarity.
But for now the answer seems to be that people are talking, but we haven't learned to listen yet.
Posted by: farticustheelder | July 14, 2012 at 01:33 PM
Well, aside from all that I would like to know should I plan for Spring Break this coming year or not? Thanks in advance
Posted by: denbenenki | December 21, 2012 at 10:21 AM