The Hubble Space Telescope, to which we owe our current estimates for the age of the universe and the first detection of organic matter on an exoplanet, is very much doing science and still alive. It’s latest masterpiece remixes an old hit – apparently a growing trend in space science as well as space music.Continue reading “A new Hubble Image Reveals a Shredded Star in a Nearby Galaxy”
Gamma rays are useful for more than just turning unassuming scientists into green-skinned behemoths. They can also shine a light on the deaths of some of the earliest stars in the universe. More accurately, they are some of the light caused by the deaths of the earliest stars in the universe. Now, a team of scientists led by Nicholas White of George Washington University, and formerly of NASA’s Goddard Space Flight Center, has proposed an observatory mission that would scan the sky for evidence of Gamma-ray bursts (GRBs) and use them to understand the early universe.Continue reading “The Gamow Explorer Would be a new Gamma-ray Observatory to Search for the First Stars in the Universe… as They Explode”
Just a couple of weeks ago, astronomers from Caltech announced their third detection of gravitational waves from the Laser Interferometer Gravitational-Wave Observatory or LIGO.
As with the previous two detections, astronomers have determined that the waves were generated when two intermediate-mass black holes slammed into each other, sending out ripples of distorted spacetime.
One black hole had 31.2 times the mass of the Sun, while the other had 19.4 solar masses. The two spiraled inward towards each other, until they merged into a single black hole with 48.7 solar masses. And if you do the math, twice the mass of the Sun was converted into gravitational waves as the black holes merged.
These gravitational waves traveled outward from the colossal collision at the speed of light, stretching and compressing spacetime like a tsunami wave crossing the ocean until they reached Earth, located about 2.9 billion light-years away.
The waves swept past each of the two LIGO facilities, located in different parts of the United States, stretching the length of carefully calibrated laser measurements. And from this, researchers were able to detect the direction, distance and strength of the original merger.
Seriously, if this isn’t one of the coolest things you’ve ever heard, I’m clearly easily impressed.
Now that the third detection has been made, I think it’s safe to say we’re entering a brand new field of gravitational astronomy. In the coming decades, astronomers will use gravitational waves to peer into regions they could never see before.
Being able to perceive gravitational waves is like getting a whole new sense. It’s like having eyes and then suddenly getting the ability to perceive sound.
This whole new science will take decades to unlock, and we’re just getting started.
As Einstein predicted, any mass moving through space generates ripples in spacetime. When you’re just walking along, you’re actually generating tiny ripples. If you can detect these ripples, you can work backwards to figure out what size of mass made the ripples, what direction it was moving, etc.
Even in places that you couldn’t see in any other way. Let me give you a couple of examples.
Black holes, obviously, are the low hanging fruit. When they’re not actively feeding, they’re completely invisible, only detectable by how they gravitational attract objects or bend light from objects passing behind them.
But seen in gravitational waves, they’re like ships moving across the ocean, leaving ripples of distorted spacetime behind them.
With our current capabilities through LIGO, astronomers can only detect the most massive objects moving at a significant portion of the speed of light. A regular black hole merger doesn’t do the trick – there’s not enough mass. Even a supermassive black hole merger isn’t detectable yet because these mergers seem to happen too slowly.
This is why all the detections so far have been intermediate-mass black holes with dozens of times the mass of our Sun. And we can only detect them at the moment that they’re merging together, when they’re generating the most intense gravitational waves.
If we can boost the sensitivity of our gravitational wave detectors, we should be able to spot mergers of less and more massive black holes.
But merging isn’t the only thing they do. Black holes are born when stars with many more times the mass of our Sun collapse in on themselves and explode as supernovae. Some stars, we’ve now learned just implode as black holes, never generating the supernovae, so this process happens entirely hidden from us.
Is there a singularity at the center of a black hole event horizon, or is there something there, some kind of object smaller than a neutron star, but bigger than an infinitely small point? As black holes merge together, we could see beyond the event horizon with gravitational waves, mapping out the invisible region within to get a sense of what’s going on down there.
We want to know about even less massive objects like neutron stars, which can also form from a supernova explosion. These neutron stars can orbit one another and merge generating some of the most powerful explosions in the Universe: gamma ray bursts. But do neutron stars have surface features? Different densities? Could we detect a wobble in the gravitational waves in the last moments before a merger?
And not everything needs to merge. Sensitive gravitational wave detectors could sense binary objects with a large imbalance, like a black hole or neutron star orbiting around a main sequence star. We could detect future mergers by their gravitational waves.
Are gravitational waves a momentary distortion of spacetime, or do they leave some kind of permanent dent on the Universe that we could trace back? Will we see echoes of gravity from gravitational waves reflecting and refracting through the fabric of the cosmos?
Perhaps the greatest challenge will be using gravitational waves to see beyond the Cosmic Microwave Background Radiation. This region shows us the Universe 380,000 years after the Big Bang, when everything was cool enough for light to move freely through the Universe.
But there was mass there, before that moment. Moving, merging mass that would have generated gravitational waves. As we explained in a previous article, astronomers are working to find the imprint of these gravitational waves on the Cosmic Microwave Background, like an echo, or a shadow. Perhaps there’s a deeper Cosmic Gravitational Background Radiation out there, one which will let us see right to the beginning of time, just moments after the Big Bang.
And as always, there will be the surprises. The discoveries in this new field that nobody ever saw coming. The “that’s funny” moments that take researchers down into whole new fields of discovery, and new insights into how the Universe works.
The LIGO project was begun back in 1994, and the first iteration operated from 2002 to 2012 without a single gravitational wave detection. It was clear that the facility wasn’t sensitive enough, so researchers went back and made massive improvements.
In 2008, they started improving the facility, and in 2015, Advanced LIGO came online with much more sensitivity. With the increased capabilities, Advanced LIGO made its first discovery in 2016, and now two more discoveries have been added.
LIGO can currently only detect the general hemisphere of the sky where a gravitational wave was emitted. And so, LIGO’s next improvement will be to add another facility in India, called INDIGO. In addition to improving the sensitivity of LIGO, this will give astronomers three observations of each event, to precisely detect the origin of the gravitational waves. Then visual astronomers could do follow up observations, to map the event to anything in other wavelengths.
A European experiment known as Virgo has been operating for a few years as well, agreeing to collaborate with the LIGO team if any detections are made. So far, the Virgo experiment hasn’t found anything, but it’s being upgraded with 10 times the sensitivity, which should be fully operational by 2018.
A Japanese experiment called the Kamioka Gravitational Wave Detector, or KAGRA, will come online in 2018 as well, and be able to contribute to the observations. It should be capable of detecting binary neutron star mergers out to nearly a billion light-years away.
Just with visual astronomy, there are a set of next generation supergravitational wave telescopes in the works, which should come online in the next few decades.
The Europeans are building the Einstein Telescope, which will have detection arms 10 km long, compared to 4 km for LIGO. That’s like, 6 more km.
There’s the European Space Agency’s space-based Laser Interferometer Space Antenna, or LISA, which could launch in 2030. This will consist of a fleet of 3 spacecraft which will maintain a precise distance of 2.5 million km from each other. Compare that to the Earth-based detection distances, and you can see why the future of observations will come from space.
And that last idea, looking right back to the beginning of time could be a possibility with the Big Bang Observer mission, which will have a fleet of 12 spacecraft flying in formation. This is still all in the proposal stage, so no concrete date for if or when they’ll actually fly.
Gravitational wave astronomy is one of the most exciting fields of astronomy. This entirely new sense is pushing out our understanding of the cosmos in entirely new directions, allowing us to see regions we could never even imagine exploring before. I can’t wait to see what happens next.
When we do finally learn the full truth about our place in the galaxy, and we’re invited to join the Galactic Federation of Planets, I’m sure we’ll always be seen as a quaint backwater world orbiting a boring single star.
The terrifying tentacle monsters from the nightmare tentacle world will gurgle horrifying, but clearly condescending comments about how we’ve only got a single star in the Solar System.
The beings of pure energy will remark how only truly enlightened civilizations can come from systems with at least 6 stars, insulting not only humanity, but also the horrifying tentacle monsters, leading to another galaxy spanning conflict.
Yes, we’ll always be making up for our stellar deficit in the eyes of aliens, or whatever those creepy blobs use for eyes.
What we lack in sophistication, however, we make up in volume. In our Milky Way, fully 2/3rds of star systems only have a single star. The last 1/3rd is made up of multiple star systems.
We’re taking binary stars, triple star systems, even exotic 7 star systems. When you mix and match different types of stars in various Odd Couple stellar apartments, the results get interesting.
Consider our own Solar System, where the Sun and planets formed together out a cloud of gas and dust. Gravity collected material into the center of the Solar System, becoming the Sun, while the rest of the disk spun up faster and faster. Eventually our star ignited its fusion furnace, blasting out the rest of the stellar nebula.
But different stellar nebulae can lead to the formation of multiple stars instead. What you get depends on the mass of the cloud, and how fast it’s rotating.
Check out this amazing photograph of a multiple star system forming right now.
In this image, you can see three stars forming together, two at the center, about 60 astronomical units away from each other (60 times the distance from the Earth to the Sun), and then a third orbiting 183 AU away.
It’s estimated these stars are only 10,000 to 20,000 years old. This is one of the most amazing astronomy pictures I ever seen.
When you have two stars, that’s a binary system. If the stars are similar in mass to each other, then they orbit a common point of mass, known as the barycenter. If the stars are different masses, then it can appear that one star is orbiting the other, like a planet going around a star.
When you look up in the sky, many of the single stars you see are actually binary stars, and can be resolved with a pair of binoculars or a small telescope. For example, in a good telescope, Alpha Centauri can be resolved into two equally bright stars, with the much dimmer Proxima Centauri hanging out nearby.
You have to be careful, though, sometimes stars just happen to be beside each other in the sky, but they’re not actually orbiting one another – this is known as an optical binary. It’s a trap.
Astronomers find that you can then get binary stars with a third companion orbiting around them. As long as the third star is far enough away, the whole system can be stable. This is a triple star system.
You can get two sets of binary stars orbiting each other, for a quadruple star system.
In fact, you can build up these combinations of stars up. For example, the star system Nu Scorpii has 7 stars in a single system. All happily orbiting one another for eons.
If stars remained unchanging forever, then this would be the end of our story. However, as we’ve discussed in other articles, stars change over time, bloating up as red giants, detonating as supernovae and turning into bizarre objects, like white dwarfs, neutron stars and even black holes. And when these occur in multiple star systems, well, watch the sparks fly.
There are a nearly infinite combinations you can have here: main sequence, red giant, white dwarf, neutron star, and even black holes. I don’t have time to go through all the combinations, but here are some highlights.
For starters, binary stars can get so close they actually touch each other. This is known as a contact binary, where the two stars actually share material back and forth. But it gets even stranger.
When a main sequence star like our Sun runs out of hydrogen fuel in its core, it expands as a red giant, before cooling and becoming a white dwarf.
When a red giant is in a binary system, the distance and evolution of its stellar companion makes all the difference.
If the two stars are close enough, the red giant can pass material over to the other star. And if the red giant is large enough, it can actually engulf its companion. Imagine our Sun, orbiting within the atmosphere of a red giant star. Needless to say, that’s not healthy for any planets.
An even stranger contact binary happens when a red giant consumes a binary neutron star. This is known as a Thorne-Zytkow object. The neutron star spirals inward through the atmosphere of the red giant. When it reaches the core, it either becomes a black hole, gobbling up the red giant from within, or an even more massive neutron star. This is exceedingly rare, and only one candidate object has ever been observed.
When a binary pair is a white dwarf, the dead remnant of a star like our Sun, then material can transfer to the surface of the white dwarf, causing novae explosions. And if enough material is transferred, the white dwarf explodes as a Type 1A supernova.
If you’re a star that was unlucky enough to be born beside a very massive star, you can actually kicked off into space when it explodes as a supernova. In fact, there are rogue stars which such a kick, they’re on an escape trajectory from the entire galaxy, never to return.
If you have two neutron stars in a binary pair, they release energy in the form of gravitational waves, which causes them to lose momentum and spiral inward. Eventually they collide, becoming a black hole, and detonating with so much energy we can see the explosions billions of light-years away – a short-period gamma ray burst.
The combinations are endless.
It’s amazing to think what the night sky would look like if we were born into a multiple star system. Sometimes there would be several stars in the sky, other times just one. And rarely, there would be an actual night.
How would life be different in a multiple star system? Let me know your thoughts in the comments.
In our next episode, we try to untangle this bizarre paradox. If the Universe is infinite, how did it start out as a singularity? That doesn’t make any sense.
We glossed over it in this episode, but one of the most interesting effects of multiple star systems are novae, explosions of stolen material on the surface of a white dwarf star. Learn more about it in this video.
We’ve written quite a few articles on what happens when massive stars fail as supernovae. Here’s a quick recap.
A star with more than 8 times the mass of the Sun runs out of usable fuel in its core and collapses in on itself. The enormous amount of matter falling inward creates a dense remnant, like a neutron star or a black hole. Oh, and an insanely powerful explosion, visible billions of light-years away.
There are a few other classes of supernovae, but that’s the main way they go out.
But it turns out some supernovae just don’t bring their A-game. Instead hitting the ball out of the park, they choke up at the last minute.
They’re failures. They’ll never amount to anything. They’re a complete and utter disappointment to me and your mother. Oh wait, we were talking about stars, right.
So, how does a supernova fail?
In a regular core collapse supernova, the infalling material pushes the star denser and denser until it reaches the density of 5 billion tons per teaspoon of matter. The black hole forms, and a shockwave ripples outward creating the supernova.
It turns out that the density and energy of the shockwave on its own isn’t enough to actually generate the supernova, and overcome the gravitational force pulling it inward. Instead, it’s believed that neutrinos created at the core pile up behind the shockwave, and give it the push it needs to blast outward into space.
In some cases, though, it’s believed that this additional energy doesn’t show up. Instead of rebounding from the core of the star, the black hole just gobbles it all up. In a fraction of a second, the star is just… gone.
According to astronomers, it might be the case that 1/3rd of all core collapse supernovae die this way, which means that a third of the supergiant stars are just disappearing from the sky. They’re there, and then a moment later, they’re not there.
Seriously, imagine the forces and energy it must take to swallow an entire red supergiant star whole. Black holes are scary.
Astronomers have gone looking for these things, and they’ve actually been pretty tricky to find. It’s like one of those puzzles where you try to figure out what’s missing from a picture. They studied images of galaxies taken by the Hubble Space Telescope, looking for bright supergiant stars which disappeared. In one survey, studying a large group of galaxies, they only turned up a single candidate.
But they only surveyed a handful of galaxies. To really get serious about searching for them, they’ll need better tools, like the Large Synoptic Survey Telescope due for first light in just a few years. This amazing instrument will survey the entire sky every few nights, searching for anything that changes. It’ll find asteroids, comets, variable stars, supernovae, and now, supergiant stars that just disappeared.
We’ve talked about failed supernovae. Now let’s take a few moments and talk about the complete opposite: super successful supernovae.
When a star with more than 8 times the mass of the Sun explodes as a supernova, it leaves behind a remnant. For the lower mass star explosions, they leave behind a neutron star. If it’s a higher mass star, they leave behind a black hole.
But for the largest explosions, where the star had more than 130 times the mass of the Sun, the supernova is so powerful, so complete, there’s no remnant behind. There’s an enormous explosion, and the star is just gone.
No black hole ever forms.
Astronomers call them pair instability supernovae. In a regular core collapse supernova, the layers of the star collapse inward, producing the highly dense remnant. But in these monster stars, the core is pumping out such energetic gamma radiation that it generates antimatter in the core. The star explodes so quickly, with so much energy, it totally overpowers the gravity pulling it inward.
In a moment, the star is completely and utterly gone, just expanding waves of energy and particles.
Only a few of these supernovae have ever been observed, and they might explain some hypernovae and gamma ray bursts, the most powerful explosions in the Universe.
Beyond 250 times the mass of the Sun, however, gravity takes over again, and you get enormous black holes.
As always, the Universe behaves more strangely than we ever thought possible. Some supernova fail, completely imploding as a black hole. And others detonate entirely, leaving no remnant behind. Trust the Universe to keep mixing it up on us.
Gamma ray bursts are the most energetic explosions in the Universe, outshining the rest of their entire galaxy for a moment. So, it stands to reason you wouldn’t want to be close when one of these goes off.
If comics have taught me anything, it’s that gamma powered superheroes and villains are some of the most formidable around.
Coincidentally, Gamma Ray bursts, astronomers say, are the most powerful explosions in the Universe. In a split second, a star with many times the mass of our Sun collapses into a black hole, and its outer layers are ejected away from the core. Twin beams blast out of the star. They’re so bright we can see them for billions of light-years away. In a split second, a gamma ray burst can release more energy than the Sun will emit in its entire lifetime. It’s a super-supernova.
You’re thinking “Heck, if the gamma exposure worked for Banner, surely a super-supernova will make me even more powerful than the Hulk.” That’s not exactly how this plays out.
For any world caught within the death beam from a gamma ray burst, the effects are devastating. One side of the world is blasted with lethal levels of radiation. Our ozone layer would be depleted, or completely stripped away, and any life on that world would experience an extinction level event on the scale of the asteroid that wiped out the dinosaurs.
Astronomers believe that gamma ray bursts might explain some of the mass extinctions that happened on Earth. The most devastating was probably one that occurred 450 million years ago causing the Ordovician–Silurian extinction event. Creatures that lived near the surface of the ocean were hit much harder than deep sea animals, and this evidence matches what would happen from a powerful gamma ray burst event. Considering that, are we in danger from a gamma ray burst and why didn’t we get at least one Tyrannosaurus Hulk out of the deal?
There’s no question gamma ray bursts are terrifying. In fact, astronomers predict that the lethal destruction from a gamma ray burst would stretch for thousands of light years. So if a gamma ray burst went off within about 5000-8000 light years, we’d be in a world of trouble.
Astronomers figure that gamma ray bursts happen about once every few hundred thousand years in a galaxy the size of the Milky Way. And although they can be devastating, you actually need to be pretty close to be affected. It has been calculated that every 5 million years or so, a gamma ray burst goes off close enough to affect life on Earth. In other words, there have been around 1,000 events since the Earth formed 4.6 billion years ago. So the odds of a nearby gamma ray burst aren’t zero, but they’re low enough that you really don’t have to worry about them. Unless you’re planning on living about 5 million years in some kind of gamma powered superbody.
We might have evidence of a recent gamma ray burst that struck the Earth around the year 774. Tree rings from that year contain about 20 times the level of carbon-14 than normal. One theory is that a gamma ray burst from a star located within 13,000 light-years of Earth struck the planet 1,200 years ago, generating all that carbon-14.
Clearly humanity survived without incident, but it shows that even if you’re halfway across the galaxy, a gamma ray burst can reach out and affect you. So don’t worry. The chances of a gamma ray burst hitting Earth are minimal. In fact, astronomers have observed all the nearby gamma ray burst candidates, and none seem to be close enough or oriented to point their death beams at our planet. You’ll need to worry about your exercise and diet after all.
So what do you think? What existential crisis makes you most concerned, and how do gamma ray bursts compare?
Gamma ray bursts (GRBs) are some of the brightest, most dramatic events in the Universe. These cosmic tempests are characterized by a spectacular explosion of photons with energies 1,000,000 times greater than the most energetic light our eyes can detect. Due to their explosive power, long-lasting GRBs are predicted to have catastrophic consequences for life on any nearby planet. But could this type of event occur in our own stellar neighborhood? In a new paper published in Physical Review Letters, two astrophysicists examine the probability of a deadly GRB occurring in galaxies like the Milky Way, potentially shedding light on the risk for organisms on Earth, both now and in our distant past and future.
There are two main kinds of GRBs: short, and long. Short GRBs last less than two seconds and are thought to result from the merger of two compact stars, such as neutron stars or black holes. Conversely, long GRBs last more than two seconds and seem to occur in conjunction with certain kinds of Type I supernovae, specifically those that result when a massive star throws off all of its hydrogen and helium during collapse.
Perhaps unsurprisingly, long GRBs are much more threatening to planetary systems than short GRBs. Since dangerous long GRBs appear to be relatively rare in large, metal-rich galaxies like our own, it has long been thought that planets in the Milky Way would be immune to their fallout. But take into account the inconceivably old age of the Universe, and “relatively rare” no longer seems to cut it.
In fact, according to the authors of the new paper, there is a 90% chance that a GRB powerful enough to destroy Earth’s ozone layer occurred in our stellar neighborhood some time in the last 5 billion years, and a 50% chance that such an event occurred within the last half billion years. These odds indicate a possible trigger for the second worst mass extinction in Earth’s history: the Ordovician Extinction. This great decimation occurred 440-450 million years ago and led to the death of more than 80% of all species.
Today, however, Earth appears to be relatively safe. Galaxies that produce GRBs at a far higher rate than our own, such as the Large Magellanic Cloud, are currently too far from Earth to be any cause for alarm. Additionally, our Solar System’s home address in the sleepy outskirts of the Milky Way places us far away from our own galaxy’s more active, star-forming regions, areas that would be more likely to produce GRBs. Interestingly, the fact that such quiet outer regions exist within spiral galaxies like our own is entirely due to the precise value of the cosmological constant – the factor that describes our Universe’s expansion rate – that we observe. If the Universe had expanded any faster, such galaxies would not exist; any slower, and spirals would be far more compact and thus, far more energetically active.
In a future paper, the authors promise to look into the role long GRBs may play in Fermi’s paradox, the open question of why advanced lifeforms appear to be so rare in our Universe. A preprint of their current work can be accessed on the ArXiv.
If too close to an environment harboring complex life, a gamma ray burst could spell doom for that life. But could GRBs be the reason we haven’t yet found evidence of other civilizations in the cosmos? To help answer the big question of “where is everybody?” physicists from Spain and Israel have narrowed the time period and the regions of space in which complex life could persist with a low risk of extinction by a GRB.
GRBs are some of the most cataclysmic events in the Universe. Astrophysicists are astounded by their intensity, some of which can outshine the whole Universe for brief moments. So far, they have remained incredible far-off events. But in a new paper, physicists have weighed how GRBs could limit where and when life could persist and evolve, potentially into intelligent life.
In their paper, “On the role of GRBs on life extinctions in the Universe”, published in the journal Science, Dr. Piran from Hebrew University and Dr. Jimenez from University of Barcelona consider first what is known about gamma ray bursts. The metallicity of stars and galaxies as a whole are directly related to the frequency of GRBs. Metallicity is the abundance of elements beyond hydrogen and helium in the content of stars or whole galaxies. More metals reduce the frequency of GRBs. Galaxies that have a low metal content are prone to a higher frequency of GRBs. The researchers, referencing their previous work, state that observational data has shown that GRBs are not generally related to a galaxy’s star formation rate; forming stars, including massive ones is not the most significant factor for increased frequency of GRBs.
As fate would have it, we live in a high metal content galaxy – the Milky Way. Piran and Jimenez show that the frequency of GRBs in the Milky Way is lower based on the latest data available. That is the good news. More significant is the placement of a solar system within the Milky Way or any galaxy.
The paper states that there is a 50% chance of a lethal GRB’s having occurred near Earth within the last 500 million years. If a stellar system is within 13,000 light years (4 kilo-parsecs) of the galactic center, the odds rise to 95%. Effectively, this makes the densest regions of all galaxies too prone to GRBs to permit complex life to persist.
The Earth lies at 8.3 kilo-parsecs (27,000 light years) from the galactic center and the astrophysicists’ work also concludes that the chances of a lethal GRB in a 500 million year span does not drop below 50% until beyond 10 kilo-parsecs (32,000 light years). So Earth’s odds have not been most favorable, but obviously adequate. Star systems further out from the center are safer places for life to progress and evolve. Only the outlying low star density regions of large galaxies keep life out of harm’s way of gamma ray bursts.
The paper continues by describing their assessment of the effect of GRBs throughout the Universe. They state that only approximately 10% of galaxies have environments conducive to life when GRB events are a concern. Based on previous work and new data, galaxies (their stars) had to reach a metallicity content of 30% of the Sun’s, and the galaxies needed to be at least 4 kilo-parsecs (13,000 light years) in diameter to lower the risk of lethal GRBs. Simple life could survive repeated GRBs. Evolving to higher life forms would be repeatedly set back by mass extinctions.
Piran’s and Jimenez’s work also reveals a relation to a cosmological constant. Further back in time, metallicity within stars was lower. Only after generations of star formation – billions of years – have heavier elements built up within galaxies. They conclude that complex life such as on Earth – from jelly fish to humans – could not have developed in the early Universe before Z > 0.5, a cosmological red-shift equal to ~5 billion years ago or longer ago. Analysis also shows that there is a 95% chance that Earth experienced a lethal GRB within the last 5 billion years.
The question of what effect a nearby GRB could have on life has been raised for decades. In 1974, Dr. Malvin Ruderman of Columbia University considered the consequences of a nearby supernova on the ozone layer of the Earth and on terrestrial life. His and subsequent work has determined that cosmic rays would lead to the depletion of the ozone layer, a doubling of the solar ultraviolet radiation reaching the surface, cooling of the Earth’s climate, and an increase in NOx and rainout that effects biological systems. Not a pretty picture. The loss of the ozone layer would lead to a domino effect of atmospheric changes and radiation exposure leading to the collapse of ecosystems. A GRB is considered the most likely cause of the mass extinction at the end of the Ordovician period, 450 million years ago; there remains considerable debate on the causes of this and several other mass extinction events in Earth’s history.
The paper focuses on what are deemed long GRBs – lGRBs – lasting several seconds in contrast to short GRBs which last only a second or less. Long GRBs are believed to be due to the collapse of massive stars such as seen in supernovas, while sGRBs are from the collision of neutron stars or black holes. There remains uncertainty as to the causes, but the longer GRBs release far greater amounts of energy and are most dangerous to ecosystems harboring complex life.
The paper narrows the time and space available for complex life to develop within our Universe. Over the age of the Universe, approximately 14 billion years, only the last 5 billion years have been conducive to the creation of complex life. Furthermore, only 10% of the galaxies within the last 5 billion years provided such environments. And within only larger galaxies, only the outlying areas provided the safe distances needed to evade lethal exposure to a gamma ray burst.
This work reveals how well our Solar System fits within the ideal conditions for permitting complex life to develop. We stand at a fairly good distance from the Milky Way’s galactic center. The age of our Solar System, at approximately 4.6 billion years, lies within the 5 billion year safe zone in time. However, for many other stellar systems, despite how many are now considered to exist throughout the Universe – 100s of billions in the Milky Way, trillions throughout the Universe – simple is probably a way of life due to GRBs. This work indicates that complex life, including intelligent life, is likely less common when just taking the effect of gamma ray bursts into consideration.
On the role of GRBs on life extinction in the Universe, Tsvi Piran, Raul Jimenez, Science, Nov 2014, pre-print
Following the late night news yesterday of a possible gamma ray burst in our next door neighboring galaxy Andromeda, it was an “Oh darn!” moment this morning to find out the big event was likely a false alarm. The false alert — and the ensuing false excitement — was due to an unlikely combination of Swift’s Burst Alert Telescope (BAT) detecting what was a previously known object and a power outage at Goddard Space Flight Center and Swift Data Center, so that the data couldn’t be analyzed by the regular team of astronomers around the world.
Also, according to a blog post by Phil Evans, a post-doctoral research assistant from the University of Leicester and a member of the support team for Swift, the Swift team never actually announced a claim of such an event, and it turns out that the tentative data that triggered this story was overstated.
“Interestingly, the Swift team never claimed it was [a GRB]; indeed, I haven’t seen any professional communication claiming that this was a GRB,” Evans wrote on his blog. “Why it has been reported throughout the web as a GRB is something I can only speculate on, but Swift has been fabulously successful studying GRBs.”
Definitely read Evans’ entire analysis of the event.
A circular posted from the Swift-XRT team” on NASA’s Gamma-ray Coordinates Network (GCN) system at says that the astronomers “do not believe this source to be in outburst”. On the Nature blog, Alexandra Witze spoke with Swift team member Kim Page, also from the University of Leicester, who told Nature “that the source had been initially mistaken for a new outburst, and that its intensity had been overestimated due to measurement error. Instead, she says, it was a relatively common, persistent x-ray source — possibly a globular cluster — that had previously been catalogued.”
Here’s the circular in its entirety:
We have re-analysed the prompt XRT data on Swift trigger 600114 (GCN Circ.
16332), taking advantage of the event data.
The initial count rate given in GCN Circ. 16332 was based on raw data from
the full field of view, without X-ray event detection, and therefore may
have been affected by other sources in M31, as well as background hot
pixels. Analysis of the event data (not fully available at the time of the
initial circular) shows the count rate of the X-ray source identified in
GCN Circ. 16332 to have been 0.065 +/- 0.012 count s^-1, consistent with
the previous observations of this source [see the 1SXPS catalogue (Evans
et al. 2014): http://www.swift.ac.uk/1SXPS/1SXPS%20J004143.1%2B413420].
We therefore do not believe this source to be in outburst. Instead, it was
a serendipitous constant source in the field of view of a BAT subthreshold
This circular is an official product of the Swift-XRT team.
The event caused a tweet-storm last night on Twitter (see #GRBM31) and as many have said, the excitement was magnified because of the ability to spread news quickly via social media:
— Jonathan McDowell (@planet4589) May 28, 2014
— Robert Rutledge (@rerutled) May 28, 2014
— Robert Rutledge (@rerutled) May 28, 2014
— Robert Rutledge (@rerutled) May 28, 2014
— Robert Rutledge (@rerutled) May 28, 2014
— Robert Rutledge (@rerutled) May 28, 2014
— Robert Rutledge (@rerutled) May 28, 2014
— Robert Rutledge (@rerutled) May 28, 2014
— Robert Rutledge (@rerutled) May 28, 2014
Update (5/28/14 9:20 am EDT): This alert may have been a false alarm. Further analysis showed the initial brightness was overestimated by a factor of 300. An official circular from the Swift-XRT team says “therefore do not believe this source to be in outburst. Instead, it was a serendipitous constant source in the field of view of a BAT subthreshold trigger.” Please read our subsequent article here that provides further information and analysis.
Something went boom in the Andromeda Galaxy, our next door neighbor. The Swift Gamma-Ray Burst telescope detected a sudden bright emission of gamma rays. Astronomers aren’t sure yet if it was a Gamma-Ray Burst (GRB) or an Ultraluminous X-Ray (ULX) or even an outburst from a low-mass x-ray binary (LMXB), but whatever it turns out to be, it will be the closest event of this kind that we’ve ever observed.
One of the previous closest GRBs was 2.6 billion light-years away, while Andromeda is a mere 2.5 million light years away from Earth. Even though this would be the closest burst to Earth, there is no danger of our planet getting fried by gamma rays.
According to astronomer (Bad Astronomer!) Phil Plait, a GRB would have to be less than 8,000 light years away cause any problems for us.
This event is providing astronomers with a rare opportunity to gain information vital to understanding powerful cosmic explosions like this.
If it is a GRB, it likely came from a collision of neutron stars. If it is a ULX, the blast came from a black hole consuming gas. If the outburst was from a LMXB, a black hole or neutron star annihilated its companion star.
Astronomers should be able to determine the pedigree of this blast within 24-48 hours by watching the way the light fades from the burst.
How this Blast was Detected
The Swift Burst Alert telescope watches the sky for gamma-ray bursts and, within seconds of detecting a burst Swift relays the location of the burst to ground stations, allowing both ground-based and space-based telescopes around the world the opportunity to observe the burst’s afterglow. As soon as it can, Swift will swiftly shift itself to observe the burst with its X-ray and ultraviolet telescopes.
The burst alert came at 21:21 pm Universal time on May 27, 2014; three minutes later, the X-ray telescope aboard Swift was observing a bright X-ray glow.
News of the event quickly spread across the astronomical community and on Twitter, sending astronomers scrambling for their telescopes.
Remember scene in Contact where they got a weird signal & called up astronomers all over the world to look? That happens for GRBs. #GRBm31
— Katie Mack (@AstroKatie) May 27, 2014
According to astronomer Katie Mack on Twitter, if this is indeed a GRB, this gamma-ray burst looks like a short GRB.
No two GRBs are the same, but they are usually classified as either long or short depending on the burst’s duration. Long bursts are more common and last for between 2 seconds and several minutes; short bursts last less than 2 seconds, meaning the action can all be over in just milliseconds.
As we noted earlier, more should be known about this blast within a day or so and we’ll keep you posted. In the meantime, you can follow the hashtag #GRBM31 on Twitter to see the latest. Katie Mack or Robert Rutledge (Astronomer’s Telegram) have been tweeting pertinent info about the burst.