Two supernovae discovered in 2009, known as PTF09atu [top right] and PTF09cnd [bottom right] are among a newfound class of very bright stellar explosions. The left frames show same regions of sky before the supernovae.
Image: Caltech/Robert Quimby/Nature
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From the outlook of a planet that resides next to a quiet, relatively predictable star, the circumstances that lead to dramatic stellar explosions elsewhere in the universe can sound somewhat improbable. Some such blasts, known as type Ia supernovae, occur when a small, dense star known as a white dwarf—roughly the diameter of Earth, but hundreds of thousands of times more massive—grows too large by siphoning material off a neighboring star, igniting a thermonuclear explosion. Other cataclysms, known as type II supernovae, occur when much heftier stars, some of them dozens of times as massive as the sun, implode under their own weight.
Luckily those circumstances arise infrequently enough to spare humankind the fallout of a nearby supernova. But the universe is a big place, and locally rare events such as type Ia and type II supernovae happen in relatively large numbers across the vast expanse of space. Now a sky survey has turned up a much rarer kind of supernova, one that defies the standard explanations for how such blasts work.
"They just don't look like normal supernovae," says Robert Quimby, a postdoctoral researcher at the California Institute of Technology, of the newfound phenomena. "That's the simplest way to put it." Quimby is part of the Palomar Transient Factory (PTF) project, which uses the 1.2-meter Oschin Telescope at Palomar Observatory in California to locate explosions in the universe, some of which are so distant that they occurred several billion years ago, but light from their detonation is only now reaching Earth. The PTF team described the new class of supernovae in a study published online June 8 in Nature. (Scientific American is part of Nature Publishing Group.)
Four new PTF supernovae, along with two events identified in the past several years that defied classification, all share the same unexplained traits: They are extraordinarily bright, and a spectral breakdown of their emitted light shows no trace of common supernova components such as hydrogen, iron and calcium. "If you look at thousands of supernova spectra, as I do, these immediately jump out to you as being peculiar," Quimby says. "They don't have the normal kinds of wiggles that you'd expect to see."
The extreme brightness of the new class of supernovae, some 10 times that of a typical type Ia supernova from an exploding white dwarf, rank them among the most luminous supernovae known. That luminosity enabled Quimby and his colleagues to spot a handful of the new supernovae among the 1,000-plus supernovae of all kinds that have been found by PTF, even though core-collapse supernovae appear to be 10,000 times more common.
But just what produces the brightness of the new class remains unknown. The way the supernovae fade from their peak brightness over time is inconsistent with the decay of radioactive elements, which is what powers the glow of a type Ia supernova. And in core-collapse cataclysms such as type II supernovae, heavy elements such as iron appear in the spectra, usually accompanied by hydrogen from the expanding supernova blast encountering ambient gas in the circumstellar medium.
One possible origin for the superluminous blasts is a very massive star, roughly 100 times the mass of the sun, that ejects a dense shell of hydrogen-depleted material. If it then undergoes core collapse to initiate a supernova, the supernova-driven ejecta would collide with the existing shell to glow brightly. Astronomers have found a precedent of a hydrogen-poor supernova preceded by an eruptive event, says Roger Chevalier, a professor of astronomy at the University of Virginia who did not contribute to the new research. But the scale of that eruption was far too small to explain the luminosity of the PTF group's supernovae.
Alternately, a supernova could have left behind a magnetar, a highly magnetized form of the dense stellar remnants known as neutron stars. The rapid spin of a magnetar could provide an internal power source to light up the supernova ejecta. But that scenario is wanting for observational backup as well; all known magnetars spin far too slowly to account for the glow of the superluminous blasts. "You want it to be formed with a spin rate of one to three milliseconds, and we don't have any evidence to show that magnetars form with those kinds of spin rates," Chevalier says. "So in principle at least you can produce the high luminosity in that way, but again there's a lot we don't understand."
Quimby and his colleagues are continuing to look for new events and to track fading supernovae over time to see how they evolve. They have even marshaled the Hubble Space Telescope to gather their ultraviolet spectra. "By building that whole sequence and incorporating the UV data, we can get a better handle on the physical origins of these things," Quimby says. But for the moment neither mechanism for the newfound supernova class is entirely convincing, Chevalier notes. "They both have their pluses and minuses, and I wouldn't say the community has come to an agreement about what is going on here," he says.
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19 Comments
Add CommentLikely a malfunctioning Imperial Death Star.
Reply | Report Abuse | Link to thisMaybe each of those ultra bright lights represent a baby god being born somewhere in a barn.
Reply | Report Abuse | Link to thisSince these incidents don't fit the scientific descriptions for supernovae, why couldn't they be something else? Has anyone tried to compare the specifics of these incidents to a black hole explosion, such as proposed by Hawking?
Reply | Report Abuse | Link to thisWhat if Alpha Centauri went into super Nova 4 years, 4 months ago? Would there be any advance warning. E.g. would there be any advance indication before the main shock/heat wave hit? Would we feel it? How much?
Reply | Report Abuse | Link to thisHey tharriss, Can you give us an example of how that wwould work?
Reply | Report Abuse | Link to thisThe right and left frames of the supernovae explosion are identical. Has this become a joke book?
Reply | Report Abuse | Link to thisYou might not want to play "Where's Wally?"
Reply | Report Abuse | Link to thisAmiable dave, you might want to take a closer look. Note the horizontal and vertical lines that point to the centre of the respective frames ; to the left the centre is dark, but to the right an extremely bright light sources is seen in both the upper and lower frames....
Reply | Report Abuse | Link to thisHenri
amiabledave, when did you last have your eyes checked?
Reply | Report Abuse | Link to thisWhat a Blast, Do you think this event have anything to do with Dec 12 2012.
Reply | Report Abuse | Link to thisSeveral months ago, I read an article on Eta Carina that proposed when extremely large stars go supernova, they may generate anti-matter and annihilate themselves completely in an unusually violent and bright explosion that leaves little or no remnants behind. There would be no neutron star or black hole remaining, total annihilation except for previously expelled shell material. As I read this article, I was reminded of this theoretical proposal. Such supernovas would not be very common and their spectra would differ from the familiar.
Reply | Report Abuse | Link to thisWhat happens if a pulsar collapses?
Reply | Report Abuse | Link to thisOur scientists need to start looking for white holes in our universe. Trying to understand these major explosions without factoring in the possibility of white hole influence is like trying to understand gravity without knowing black holes exist.
Reply | Report Abuse | Link to thisThe PTF Supernovae have no trace of hydrogen in their spectrum. This means that within the main reaction core, there is no hydrogen. A neutron star which has blasted away all the lighter gases around it? A Magnetar which has blasted away all the othr gasses around it? If I could throw in my own hypothesis, maybe a primordial particle mass incoming from behind the CMBR which never had hydrogen gas around it in the first place?
Reply | Report Abuse | Link to thisIs it possible that what we think of as the "Big Bang" may well be happening far away. Perhaps, rather than one "Big Bang", maybe there are many, but too far away to measure?
Reply | Report Abuse | Link to thisPerhaps ultrabright supernovae appear so bright because we are looking at the poles of these explosions. Perhaps these stars appear as supernovae but are stars that are suddenly pointing their poles at us. These "stars" may eject extra radiation at their poles like black holes.
Reply | Report Abuse | Link to thisseems as if the aliens have figured out how to introduce superdense elemts into the core of a star and create an artificial supernova, just like Major Carter did.
Reply | Report Abuse | Link to thisIt is possible that a "black hole" can only hold so much. At that point, perhaps it causes a "Big Bang"?
Reply | Report Abuse | Link to thisThere may be several "Big Bangs" rather than one big one!
My thoughts exactly...far less common than ordinary ones...one of the poles would need to point near us...
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