Mysterious rare five-hour space explosion explained

The X-ray image from the Swift X-ray Telescope of the gamma-ray burst GRB 130925. 

The white object in the center is the gamma-ray burst. 

The large diffuse region to the right is a cluster of galaxies. 

The other objects are X-ray-emitting celestial objects, most likely supermassive black holes at the centers of distant galaxies. 

The full image is approximately the size of the full moon. 

Credit: Phil Evans/ University of Leicester

Next week in St. Petersburg, Russia, scientists on an international team that includes Penn State University astronomers will present a paper that provides a simple explanation for mysterious ultra-long gamma-ray bursts, a very rare form of the most powerful explosions in the universe.

"The recent discovery of ultra-long gamma-ray bursts raised questions about whether some new physics is required to explain them, but our work suggests a much simpler explanation," said David Burrows, a Penn State professor of astronomy and astrophysics.

"Our analysis reveals that these rare gamma-ray bursts, which can last for hours, can be explained as standard explosions occurring in a region with a low density of matter that is located behind a cloud of dust when viewed from Earth."

Dick Willingale, an astronomer at the University of Leicester and a co-author of the study, said, "Not only is this result significant scientifically, but it shows the importance of international collaborations to build observatories, and of sharing information between those observatories."

Burrows is the lead scientist for the X-Ray Telescope on board the Swift satellite, one of two space observatories that the scientists used to collect data from the gamma-ray burst named GRB 130925A, which they observed last year while the energy from its explosion streamed toward Earth for more than five hours.

Swift is a NASA-led collaboration with Penn State in the United States, the University of Leicester and University College-London in the United Kingdom, and the Italian space agency and Brera Observatory in Italy.

The scientists also observed the ultra-long gamma-ray burst with the US/Russian satellite Konus-Wind.

"We could not have reached our conclusions without the Swift and Konus teams working together," Willingale said.

Burrows said it is not surprising that some gamma-ray bursts occur in a low-density region, nor is it surprising when one occurs behind a dust cloud.

"Our analysis of the observations from the two observatories shows that these two conditions existing simultaneously can explain our observations of the ultra-long gamma-ray burst GRB 130925A," Burrows said.

"One reason that these results are satisfying is that scientists generally prefer to find the simplest explanations for mysterious phenomena," he said.

Astronomers detect Light from Gamma Ray Burst from huge explosion 12 billion years ago

Light from the explosion 12 billion years ago of a massive star at the end of its life reached Earth recently. 

An image of its peak afterglow, circled with blue and yellow, was captured by Southern Methodist University's ROTSE-IIIb telescope at McDonald Observatory, Fort Davis, Texas. 

A bright star sits alongside the afterglow from GRB 140419A. 

Credit: ROTSE-IIIb, SMU

Known as a gamma-ray burst, the intense light captured in the night sky resulted from one of the biggest and hottest explosions in the universe, occurring shortly after the Big Bang.

Intense light from the enormous explosion of a star more than 12 billion years ago, shortly after the Big Bang, recently reached Earth and was visible in the sky.

Known as a gamma-ray burst, light from the rare, high-energy explosion traveled for 12.1 billion years before it was detected and observed by a telescope owned by Southern Methodist University, Dallas.


Gamma-ray bursts (GRBs) are believed to be the catastrophic collapse of a star at the end of its life. SMU physicists report that their telescope was the first on the ground to observe the burst and to capture an image, said Farley Ferrante, a graduate student in SMU's Department of Physics, who monitored the observations along with two astronomers in Turkey and Hawaii.

Recorded as GRB 140419A by NASA's Gamma-ray Coordinates Network, the burst was spotted at 11 p.m. April 19 by SMU's robotic telescope, ROTSE-IIIb, at the McDonald Observatory in the Davis Mountains of West Texas.

Gamma-ray bursts (GRBs) are not well understood by astronomers, but they are considered important, Ferrante said.

"As NASA points out, gamma-ray bursts are the most powerful explosions in the universe since the Big Bang," he said. "These bursts release more energy in 10 seconds than our Earth's sun during its entire expected lifespan of 10 billion years."

Some of these gamma-ray bursts appear to be related to supernovae, and correspond to the end-of-life of a massive star, said Robert Kehoe, physics professor and leader of the SMU astronomy team.

"Gamma-ray bursts (GRBs) may be particularly massive cousins to supernovae, or may correspond to cases in which the explosion ejecta are more beamed in our direction. By studying them, we learn about supernovae," Kehoe said.

Scientists weren't able to detect optical light from gamma-ray bursts until the late 1990s, when telescope technology improved.

Among all lights in the electromagnetic spectrum, gamma rays have the shortest wavelengths and are visible only using special detectors.

SMU's ROTSE-IIIb at the McDonald Observatory, Fort Davis, Texas had the earliest and brightest observation from the ground of a gamma-ray burst that occurred more than 12 billion years ago. 

The telescope is part of the Robotic Optical Transient Search Experiment, which has telescopes in four locations on Earth to cover the entire sky in search of gamma-ray bursts. 

Credit: ROTSE Collaboration.

Gamma-ray bursts (GRBs) result from hot stars that measure as enormous as 50 solar masses. The explosion occurs when the stars run out of fuel and collapse in on themselves, forming black holes.

Outer layers detonate, shooting out material along the rotation axis in powerful, high-energy jets that include gamma radiation.

As the gamma radiation declines, the explosion produces an afterglow of visible optical light. The light, in turn, fades very quickly, said Kehoe.

Physicists calculate the distance of the explosion based on the shifting wavelength of the light, or redshift.

"The optical light is visible for anywhere from a few seconds to a few hours," Kehoe said. "Sometimes optical telescopes can capture the spectra."

"This allows us to calculate the redshift of the light, which tells us how fast the light is moving away from us. This is an indirect indication of the distance from us."

Cosmic explosion spotted in neighbouring galaxy - video

NASA's Swift satellite reported an enormous explosion occurred this morning at 8.15 AEST in our neighbouring galaxy, Andromeda. This explosion is known as a Gamma Ray Burst (GRB), one of the most powerful explosions in the Universe.

The exact cause is unknown but thought to be an explosion from when two Neutron Stars collide.

These Neutron Stars are the dead cores of massive stars, with the mass of our Sun crushed into the size of a small city. When they merge together, the explosion is so powerful it can be seen from across the Universe.

Swinburne University of Technology astronomer Dr Alan Duffy says these GRBs explosions are so large that if they occur within our galaxy they can potentially trigger mass extinctions on Earth.

"Telescopes around the world are currently trained on the Andromeda galaxy looking in all wavelengths of light to learn more about this once-in-a-lifetime event."

"The explosion seen in light will also potentially be visible in gravitational waves, a key prediction of Einstein, ending a long quest to detect these ripples in space time."

"Unfortunately the world-wide facility for detecting these events, LIGO, is currently shut down for an upgrade, missing out on the explosion and a potential Nobel Prize winning discovery."

This animation shows the merger of two neutron stars from a horizontal perspective. Theory predicts that these kinds of collisions would not produce a long afterglow because there isn't much "fuel" dust and gas from the objects and in the region to sustain an afterglow. 

Credit: NASA

"The night sky seen in high-energy light is continuously flashing as titanic explosions, bright enough to be seen from across the length of the Universe, erupt and travel to us. It's a violent world out there.

"The most astounding aspect of today is that colliding Neutron Stars exploded in less than a second, shining out in Gamma Rays which have travelled undisturbed for 2.5 million years until hitting NASA's Swift satellite, within minutes telescopes across the globe were tracking it and an hour later people around the world were following it on Twitter. It's been hectic.

Stellar explosion on outer reaches of Universe provides clues about black hole formation

Top left box (a): Image of the field of the GRB121024A captured by the Very Large Telescope (VLT), Chile. 

The GRB121024A is the point marked by the dotted lines.

The glow of the GRB121024A in the image does not correspond to its distance from the Earth. 

In fact, as can be seen, the GRB121024A is one of the brightest objects in the field, despite being one of the most distant, if not the most distant one, in the image.

So the point marked corresponds to the explosion of a star about ~11,000 million years ago when the age of the Universe was only one third of what it is now. 

General box (b): Artist's impression of the GRB121024A.

It is possible to see the jets emerging from the dying star in the center of which a black hole would form. The blue wave spread by the jet represents the circular polarization detected.

Acknowledgements: NASA, Goddard Space Flight Center/S. Wiessinger. Credit: UPV/EHU

On 24 October 2012 observatories across the world were alerted about a huge stellar explosion, the GRB121024A.

However, only the European Southern Observatory using its Very Large Telescope located in Chile managed to take accurate polarimetric measurements of the phenomenon.

The data obtained on that explosion, which took place about 11,000 million years ago, have made it possible to reconstruct how a black hole is formed.

The work, which has had the participation of the Ikerbasque researcher Javier Gorosabal, co-director of the Associated Unit with the Institute of Astrophysics of Andalusia /CSIC-UPV /EHU, has been published in the prestigious journal Nature.

There is no other event in the cosmos that can compete in terms of energy and intensity with stellar explosions on the outer reaches of the universe and which are known as LGRBs (Long Gamma-Ray Bursts): in just one second a single GRB can emit as many as hundreds of stars like the Sun during its 10,000-million-year-lifetime.

For the last decade astrophysicists have been in possession of strong evidence that LGRBs occur when the so-called massive stars burst; these are huge stars with masses of up to hundreds of times bigger than that of the Sun and which, moreover, spin rapidly on a rotation axis.

As these stars are massive and spin, they do not explode like a normal star, which does so radially, as a ball does when it deflates, for example.

The implosion of these huge stars would produce, according to theoretical models, a huge spinning top, which would turn in the way that water rotates down the plughole of a basin, until a black hole is finally formed.

The energy given off by this gigantic explosion would be emitted in two jets displaying a high level of energy and which would be aligned with the rotation axis of the dying star.

What is more, all these stars have magnetic fields. And these are intensified further if they rotate rapidly, as in the case of the LGRBs.

So during the internal collapse of the star towards the central black hole, the magnetic fields of the star would also swirl around the star's rotation axis, and during the collapse of the star, a powerful "magnetic geyser" would be produced and be ejected from the environment of the black hole that is being formed; the effects of this can be felt at distances of billions of kilometres.

Image of the GRB121024A captured by means of the polarimeter fitted onto the FORS2 instrument of the VLT. 

The polarimeter provides two images for each object in the field of vision.

The polarized objects appear considerably brighter in one band than in the other. The non-polarized objects, the vast majority, display the same intensity in the upper and lower band.

The object indicted by the arrow is the GRB121024A which displayed a circular polarization of 0.6%. 

Credit: Wiersema et al. 2014, Nature, DOI 10.1038/nature13237.

This complex scenario led one to predict that the light emitted during the explosion of the star must have been circularly polarized as if it were a screw, and that is what, for the first time, the authors have detected in Chile: a circularly polarized light that is the direct consequence of a black hole "recently" created on the outer reaches of the Universe and which has been confirmed by the theoretical model.

What is more, an optical circular polarization to such a high degree had never been detected, and nor had one been detected in such a distant source. All this indicates that the GRB121024A is an extraordinary event.

The VLT is one of the largest and best equipped telescopes in the world; it makes use of the exceptional astronomical observation conditions of the Atacama desert.

That is why the use of the VLT is very limited and is regulated by a highly competitive process in which every six months an international committee selects the best proposals for observation submitted.

So the only way to access these technologically state-of-the-art facilities is by means of powerful international consortia. 27 institutions belonging to 13 countries have participated in the study published by the prestigious journal Nature.

More information: K. Wiersema, S. Covino, K. Toma, A.J. van der Horst, K. Varela, M. Min, J. Greiner, R.L.C. Starling, N.R. Tanvir, R.A.M.J. Wijers, S. Campana, P.A. Curra, Y. Fan, J.P.U. Fynbo, J. Gorosabel, A. Gomboc, D. Götz, J. Hjorth, Z.P. Jin, S. Kobayashi, C. Kouveliotou, C. Mundell, P.T.O'Brien, E. Pian, A. Rowlinson, D.M. Russell, R. Salvaterra, S. Di Serego Alighieri, G. Tagliafferri, S.D. Vergani, J. Eliott, C. Fariña, O.E. Hartoog, R. Karjalainen, S. Klose, F. Knust, A.J. Levan, P. Schady, V. Sudilovsky, & R. Willingale. "Circular Polarization in the optical afterglow of GRB121024A". Nature, 2014, DOI: 10.1038/nature13237

SKA and CAASTRO: Forecast Sky bubbling with exploding stars

It is hard to imagine that any astronomical phenomenon could escape our latest and most powerful telescopes, but an international research team has now forecast some of the exotic discoveries that will only be able to be studied with the forthcoming Square Kilometre Array (SKA).

Giancarlo Ghirlanda

The team, led by Dr Giancarlo Ghirlanda at the National Institute for Astrophysics (INAF) in Italy and including CAASTRO members Dr Davide Burlon and Dr Tara Murphy from the University of Sydney, has calculated that the SKA will reveal the lingering footprints of tens of thousands of enigmatic cosmic explosions known as "gamma-ray bursts".

Davide Burlon

"With current telescopes, we see a bright gamma-ray burst somewhere in the Universe around once per day, but new radio telescopes will soon be able to see an afterglow of the explosion after the initial burst has faded away," explains CAASTRO postdoctoral researcher Dr Burlon.

"This afterglow can generally take weeks to gradually decay and teaches us incredible amounts about both the initial explosion and its neighbourhood."

The catch is that a gamma-ray burst is not an explosion that we can see from all directions but is comprised of a very narrow, energetic jet, so we need to be looking down the barrel of the jet at the right time.

Otherwise it is invisible, equivalent to only seeing the beam of a laser pointer when it points directly at us.

The radio afterglow should be visible from any direction though and for long periods of time, even if we missed the burst.

Tara Murphy

These afterglows without a burst are known as "orphan" afterglows, they're a phenomenon that astronomers have until now been looking for without success.

"From the rate at which we detect gamma-ray bursts, we were able to predict that with the power of a sensitive new telescope like the SKA, orphan afterglows should be seen 700 times more often than their gamma-ray bursts." says Dr Burlon.

"The unprecedented sensitivity and wide field-of view of the SKA means that orphan afterglows should be visible for months or even years before eventually disappearing, bubbling across the sky more than ten thousand times per year."

Of course, the SKA's view of the sky will be full of all sorts of objects and events, such as supernova explosions and flaring black holes that are more common than orphan afterglows.

"In this new era of radio astronomy, one of the challenges will be to disentangle these different classes of radio sources." says Dr Tara Murphy, CAASTRO Associate Investigator and project leader of the "Variables and Slow Transients (VAST)" survey with the Australian SKA Pathfinder (ASKAP).

The SKA will join the Australian SKA precursor telescope ASKAP and the South African SKA precursor MeerKAT in painting an entirely new picture of the "radio sky".

"The SKA will not only allow us to finally see these orphan afterglows but help us understand how gamma-ray bursts (GRB) produce such powerful, narrow jets and will cast new light on the big question of just what causes gamma-ray bursts in the first place," concludes Dr Ghirlanda.

More information: G. Ghirlanda, D. Burlon, G. Ghisellini, R. Salvaterra, M. G. Bernardini, S. Campana, S. Covino, P. D'Avanzo, V. D'Elia, A. Melandri, T. Murphy, L. Nava, S. D. Vergani, G. Tagliaferri: "GRB orphan afterglows in present and future radio transient surveys" in The Publications of the Astronomical Society of Australia (PASA). arXiv:1402.6338 [astro-ph.HE] arxiv.org/abs/1402.6338

Gamma-ray bursts (GRB): Afterglow discovery surprises scientists

Measurements of polarized light in the afterglow of GRB 120308A by the Liverpool Telescope and its RINGO2 instrument indicate the presence of a large-scale stable magnetic field linked with a young black hole, as shown in this illustration. 

Credit: NASA's Goddard Space Flight Center /S. Wiessinger

Research from an international team of scientists led by the University of Leicester has discovered for the first time that one of the most powerful events in our universe, Gamma-Ray Bursts (GRB), behave differently than previously thought.

The study, published in the prestigious scientific journal Nature, uses evidence from observation of a GRB to rule out most of the existing theoretical predictions concerning the afterglow of the explosions.

Klaas Wiersema

For Dr Klaas Wiersema, of the University of Leicester's Department of Physics and Astronomy, it was handy that he was up in the middle of the night tending to his three-year-old son which is when he got the alert that a GRB had occurred.

He said: "When a suitable GRB is detected by a satellite, I get a text message on my phone, and then I have to very quickly tell the observatory in Chile exactly which observations I want them to take, and how.

"This is usually a rather stressed and frantic few hours of working, as fast as possible, on my laptop throughout our night-time, and I remember very well that my son, who was three at the time, was up a lot that night too, so I kept on running back and forth between my laptop, my phone to call the observatory in Chile, and my son's cot!"

The effort was worth it- and has led to scientific findings that will change theoretical understandings of the afterglows of GRBs.

Dr Wiersema explains: "About once per day, a short, very bright flash of gamma-rays (the most energetic form of light) is detected by satellites. These flashes are called gamma-ray bursts (GRBs), and take place in galaxies far away, when a massive star collapses at the end of its life.

"These GRBs are followed by a so-called "afterglow", slowly fading emission that can be seen at all wavelengths (including visible light), for a few days to weeks."

"We know that the afterglow emission is formed by a shockwave, moving at very high velocities, in which electrons are being accelerated to tremendous energies."

"These fast moving electrons then produce the afterglow light that we detect.

When a massive star dies it explodes as a supernova. 

The core of the star collapses into a black hole, and in care cases a jet is formed along the rotation axis of the newly formed black hole. 

Processes in this jet emits gamma radiation, which we observe as a so-called gamma-ray burst. 

Typically gamma-ray bursts last a few minutes. 

When the jet hits material surrounding the dying star an afterglow is formed. 

New observations of the degree of polarisation of the afterglow light has shown that the afterglow behaves differently than expected 

Credit: NASA

"However, how this acceleration process actually works is very hard to study on Earth in laboratories, or using computer simulations."

"What we do, is study the polarised light of the afterglow using large optical telescopes, and special filters, that work much like the filters in Polaroid sunglasses."

Gamma-ray burst 121024A, as seen on the day of burst by ESO's Very Large Telescope (VLT) in Chile. Only a week later the source had faded completely. 

Credit: Dr Klaas Wiersema, University of Leicester, UK and Dr Peter Curran, ICRAR.

Dr Wiersema says it is important to remember that light is a wave, when light is linearly polarised, it means that the wave vibrations lie in a plane; and when light is circularly polarised, it means that that this plane rotates on the sky.

He added: "Different theories for electron acceleration and light emission within the afterglow all predict different levels of linear polarisation, but theories all agreed that there should be no circular polarisation in visible light."

Peter Curran, ICRAR

"This is where we come in: we decided to test this by carefully measuring both the linear and circular polarisation of one afterglow, of GRB 121024A, detected by the Swift satellite."

"Using the ESO Very Large Telescope (VLT) in Chile, we measured both the linear and circular polarisation of an afterglow with high accuracy."

"Much to our surprise we clearly detected circular polarisation, while theories predicted we should not see any at all."

"We believe that the most likely explanation is that the exact way in which electrons are accelerated within the afterglow shockwave is different from what we always thought."

"It is a very nice example of observations ruling out most of the existing theoretical predictions – exactly why observers like me are in this game!

More information: Paper: Circular polarisation in the optical afterglow of GRB 121024A, Nature, DOI: 10.1038/nature13237

Liverpool telescope Ringo 02: Glimpsing the infrastructure of a Gamma-Ray Burst jet

Measurements of polarized light in the afterglow of GRB 120308A by the Liverpool Telescope and its RINGO2 instrument indicate the presence of a large-scale stable magnetic field linked with a young black hole, as shown in this illustration. 

Credit: NASA's Goddard Space Flight Center/S. Wiessinger

A new study using observations from a novel instrument provides the best look to date at magnetic fields at the heart of gamma-ray bursts, the most energetic explosions in the universe.

An international team of astronomers from Britain, Slovenia and Italy has glimpsed the infrastructure of a burst's high-speed jet.

Gamma-ray bursts are the most luminous explosions in the cosmos. Most are thought to be triggered when the core of a massive star runs out of nuclear fuel, collapses under its own weight, and forms a black hole.

The black hole then drives jets of particles that drill all the way through the collapsing star and erupt into space at nearly the speed of light.

On March 8, 2012, NASA's Swift satellite detected a 100-second pulse of gamma rays from a source in the constellation Ursa Minor.

The spacecraft immediately forwarded the location of the gamma-ray burst, dubbed GRB 120308A, to observatories around the globe.

The world's largest fully autonomous robotic optical telescope, the 2-meter Liverpool Telescope located at Roque de los Muchachos Observatory on La Palma in the Canary Islands, automatically responded to Swift's notification.

"Just four minutes after it received Swift's trigger, the telescope found the burst's visible afterglow and began making thousands of measurements," said lead researcher Carole Mundell, who heads the gamma-ray burst team at the Astrophysics Research Institute at Liverpool John Moores University in the U.K.

The telescope was fitted with an instrument named RINGO2, which Mundell's team designed to detect any preferred direction, called polarization, in the vibration of light waves from burst afterglows.

More information: Nature paper: "Highly polarized light from stable ordered magnetic fields in GRB 120308A," C. Mundell et al., www.nature.com/nature/journal/v504/n7478/full/nature12814.html

Cosmic Flash may reveal Birth of a Black Hole

A computer-generated image of the light distortions created by a black hole. Credit: Alain Riazuelo, IAP/UPMC/CNRS

When a massive star exhausts its fuel, it collapses under its own gravity and produces a black hole, an object so dense that not even light can escape its gravitational grip.

According to a new analysis by an astrophysicist at the California Institute of Technology (Caltech), just before the black hole forms, the dying star may generate a distinct burst of light that will allow astronomers to witness the birth of a new black hole for the first time.

Tony Piro

Tony Piro, a postdoctoral scholar at Caltech, describes this signature light burst in a paper published in the May 1 issue of the Astrophysical Journal Letters.

While some dying stars that result in black holes explode as gamma-ray bursts, which are among the most energetic phenomena in the universe, those cases are rare, requiring exotic circumstances, Piro explains.

"We don't think most run-of-the-mill black holes are created that way." In most cases, according to one hypothesis, a dying star produces a black hole without a bang or a flash: the star would seemingly vanish from the sky—an event dubbed an unnova. "You don't see a burst," he says. "You see a disappearance."

But, Piro hypothesizes, that may not be the case. "Maybe they're not as boring as we thought," he says.

According to well-established theory, when a massive star dies, its core collapses under its own weight. As it collapses, the protons and electrons that make up the core merge and produce neutrons.

For a few seconds—before it ultimately collapses into a black hole—the core becomes an extremely dense object called a neutron star, which is as dense as the sun would be if squeezed into a sphere with a radius of about 10 kilometers (roughly 6 miles).

This collapsing process also creates neutrinos, which are particles that zip through almost all matter at nearly the speed of light.

As the neutrinos stream out from the core, they carry away a lot of energy—representing about a tenth of the sun's mass (since energy and mass are equivalent, per E = mc2).

According to a little-known paper written in 1980 by Dmitry Nadezhin of the Alikhanov Institute for Theoretical and Experimental Physics in Russia, this rapid loss of mass means that the gravitational strength of the dying star's core would abruptly drop.

When that happens, the outer gaseous layers—mainly hydrogen—still surrounding the core would rush outward, generating a shock wave that would hurtle through the outer layers at about 1,000 kilometers per second (more than 2 million miles per hour).

Stan Woosley

Using computer simulations, two astronomers at UC Santa Cruz, Elizabeth Lovegrove and Stan Woosley, recently found that when the shock wave strikes the outer surface of the gaseous layers, it would heat the gas at the surface, producing a glow that would shine for about a year—a potentially promising signal of a black-hole birth.

Although about a million times brighter than the sun, this glow would be relatively dim compared to other stars.

"It would be hard to see, even in galaxies that are relatively close to us," says Piro.

But now Piro says he has found a more promising signal. In his new study, he examines in more detail what might happen at the moment when the shock wave hits the star's surface, and he calculates that the impact itself would make a flash 10 to 100 times brighter than the glow predicted by Lovegrove and Woosley.

"That flash is going to be very bright, and it gives us the best chance for actually observing that this event occurred," Piro explains. "This is what you really want to look for."

Such a flash would be dim compared to exploding stars called supernovae, for example, but it would be luminous enough to be detectable in nearby galaxies, he says.

The flash, which would shine for 3 to 10 days before fading, would be very bright in optical wavelengths—and at its very brightest in ultraviolet wavelengths.

Piro estimates that astronomers should be able to see one of these events per year on average. Surveys that watch the skies for flashes of light like supernovae—surveys such as the Palomar Transient Factory (PTF), led by Caltech—are well suited to discover these unique events, he says.

The intermediate Palomar Transient Factory (iPTF), which improves on the PTF and just began surveying in February, may be able to find a couple of these events per year.

Neither survey has observed any black-hole flashes as of yet, says Piro, but that does not rule out their existence. "Eventually we're going to start getting worried if we don't find these things." But for now, he says, his expectations are perfectly sound.