Ask Ethan: Can Gamma-Ray Jets Really Travel Faster Than The Speed Of Light?
“What gives? Is it really possible for gamma-rays to exceed the speed of light and thereby “reverse” time? Is the time reversal just a theoretical claim that allows these hypothetical super-light speed particles to conform with Relativity or is there empirical evidence of this phenomenon?”
Very recently, a paper came out claiming that gamma-ray bursts, and the jets that give them off, can travel faster than the speed of light. If that sounds too fantastic to be true, there’s a reason for that: particles can travel faster than light, but only in a medium, where the speed of light is less than the speed of light in a vacuum. Gamma-ray bursts, when they occur, exhibit a strange property: the signal is mostly a large peak, but when you subtract that peak out, parts of the residual signal are symmetric: if you flip it, part of it going forwards in time is identical to the remainder going backwards in time.
Sound weird? Well, we’re just getting started! Come find out the true story behind this fascinating phenomenon, and what just became our best explanation of what makes it so!
What Would The Milky Way Look Like If You Could See All Of Its Light?
“When you look at the Milky Way in visible light, you might see billions of stars, but you miss so much more. The human eye is only sensitive to a tiny fraction of the entire electromagnetic (light) spectrum. Each wavelength range showcases a novel view of all that’s out there.”
If you looked out at our galaxy with your eyes and the wavelengths they’re sensitive to alone, there’s an incredible amount of information you’d miss no matter how powerful you became at gathering light or resolving individual objects. That’s because visible light only occupies a narrow range of electromagnetic wavelengths, meaning that what you can see is limited to what emits visible light (stars and some reflective clouds) and constrained by dust, which can absorb all the visible light behind it.
But there are other wavelengths than these, and they reveal a series of fascinating details. What do they all look like? Come get a fuller picture today!
Newest LIGO Signal Raises A Huge Question: Do Merging Black Holes Emit Light?
“The second merger held no such hints of electromagnetic signals, but that was less surprising: the black holes were of significantly lower mass, so any signal arising from them would be expected to be correspondingly lower in magnitude. But the third merger was large in mass again, more comparable to the first than the second. While Fermi has made no announcement, and Integral again reports a non-detection, there are two pieces of evidence that suggest there may have been an electromagnetic counterpart after all. The AGILE satellite from the Italian Space Agency detected a weak, short-lived event that occurred just half a second before the LIGO merger, while X-ray, radio and optical observations combined to identify a strange afterglow less than 24 hours after the merger.”
Whenever there’s a catastrophic, cataclysmic event in space, there’s almost always a tremendous release of energy that accompanies it. A supernova emits light; a neutron star merger emits gamma rays; a quasar emits radio waves; merging black holes emit gravitational waves. But if there’s any sort of matter present outside the event horizons of these black holes, they have the potential to emit electromagnetic radiation, or light signals, too. Our best models and simulations don’t predict much, but sometimes the Universe surprises us! With the third LIGO merger, there were two independent teams that claimed an electromagnetic counterpart within 24 hours of the gravitational wave signal. One was an afterglow in gamma rays and the optical, occurring about 19 hours after-the-fact, while the other was an X-ray burst occurring just half a second before the merger.
Could either of these be connected to these merging black holes? Or are we just grasping at straws here? We need more, better data to know for sure, but here’s what we’ve got so far!
No, Mysterious Signals From Space Are Not Dark Matter
“When you see something unexpected, there’s always a chance it’s something novel and exciting, like dark matter. But more often than not, if there’s a chance that the physics and astrophysical objects we already know of can account for it, that’s where the answer lies. Our minds may instinctively be drawn to the most fantastic and exciting possibilities, but that’s our own bias. In the end, as it did in this case, the key to doing good science is discriminating between the signatures of different possible mechanisms. In this case, it’s pulsars, not dark matter, that explain the incredible energy signal coming from our galaxy’s center.”
When NASA’s Fermi satellite began operations, it didn’t take long before we had constructed the most accurate, comprehensive gamma ray map of the galaxy. While many outstanding astrophysics findings ensued, including the discovery of many new pulsars, there was one particular mystery that came about as well: an unexplained excess of gamma rays from the galactic center. Many possible explanations emerged, but one gathered a disproportionately large and exciting amount of attention: that of dark matter annihilations. In some models of dark matter, it’s a particle that’s its own antiparticle. If dark matter/dark matter annihilation occurs, it could produce excessive gamma rays, as well as cascades of new particle/antiparticle pairs that would result in a photon signal peaked at 511 keV, as positrons annihilated with electrons. After a huge effort to uncover the nature of this gamma ray excess, Fermi finally has an answer.
Did you bet on dark matter? You shouldn’t have! Come find out how pulsars are likely responsible, and why dark matter is disfavored for the gamma ray excess seen in the Milky Way.