GRBs

What is a Gamma Ray Burst?

We define a gamma-ray burst based on its observational properties: an intense flash of gamma rays, lasting anywhere from a fraction of a second to up to a few minutes.

Gamma-ray bursts have a few other common features. We believe them to be beamed - the energy does not escape from the explosion everywhere equally, but is focused into a narrow jet (or more likely, two oppositely-directed jets.) The burst itself is also normally followed by a much longer-lived (but also much fainter) signal, visible at optical and other wavelengths. This so-called “afterglow”, discovered only in the 1990s, allows us to pinpoint the origin of the GRB - something not possible from the short-lived gamma-ray signal alone.1

History

Cosmic gamma ray bursts (GRBs) were discovered by accident in the late 1960’s by satellites designed to detect gamma rays produced by atomic bomb tests on Earth. The GRBs appear first as a brilliant flash of gamma rays, that rises and falls in a matter of minutes. These bursts are often followed by afterglows at X-ray, optical and radio wavelengths.

A major leap forward in understanding the source of cosmic GRBs was made when the Burst and Transient Source Experiment (BATSE) was launched aboard the Compton Gamma Ray Observatory in 1991.

BATSE had an all-sky monitor that was capable of detecting a GRB virtually anywhere in the sky. Over a period of 9 years BATSE recorded thousands of GRBs, about 1 per day. Among other things, these results showed that the bursts occurred at random all over the sky. If the bursts were associated with objects in our Milky Way Galaxy, they would not show such a universal distribution. Rather, they would be concentrated along the plane of our galaxy like most of the matter in the Milky Way. The BATSE data was so good that it allowed astronomers to also rule out the possibility that the GRBs might be originating in the halo of our galaxy.2

GRB Progenitors

Black Holes

3

The most powerful explosions in the universe are caused by the births of black holes rather than dense neutron stars called magnetars, new evidence confirms.4

White Dwarfs

5

Very old compact stars called white dwarfs are known to flare as well, but the amount of energy is not enough to explain distant GRBs.  Other GRB progenitors include neutron stars (magnetar, pulsars or a hybrid), starquakes, cannonballs or strange stars (stars composed of strange matter).Wolf-Rayet stars have also been proposed.7

1 http://astro.berkeley.edu/research/grbs/grbinfo.html

2 http://chandra.harvard.edu/xray_sources/grb.html

3 https://en.wikipedia.org/wiki/File:BH_LMC.png

4 http://www.newscientist.com/article/dn19681-most-powerful-gammaray-bursts-linked-to-black-holes.html

5 https://en.wikipedia.org/wiki/File:Sirius_A_and_B_Hubble_photo.jpg

6 http://www.space.com/3724-alternative-theories-gamma-ray-bursts.html

7 http://cds.cern.ch/record/482530/files/0012512.pdf

illustration: artist’s impression of a gamma-ray burst shining through two young galaxies in the early Universe

An international team of astronomers has used the brief but brilliant light of a distant gamma-ray burst as a probe to study the make-up of very distant galaxies. Surprisingly the new observations, made with ESO’s Very Large Telescope, have revealed two galaxies in the young Universe that are richer in the heavier chemical elements than the Sun. The two galaxies may be in the process of merging. Such events in the early Universe will drive the formation of many new stars and may be the trigger for gamma-ray bursts.

Gamma-ray bursts are the brightest explosions in the Universe. They are first spotted by orbiting observatories that detect the initial short burst of gamma rays. After their positions have been pinned down, they are then immediately studied using large ground-based telescopes that can detect the visible-light and infrared afterglows that the bursts emit over the succeeding hours and days. One such burst, called GRB 090323, was first spotted by the NASA Fermi Gamma-ray Space Telescope. Very soon afterwards it was picked up by the X-ray detector on NASA’s Swift satellite and with the GROND system at the MPG/ESO 2.2-metre telescope in Chile and then studied in great detail using ESO’s Very Large Telescope (VLT) just one day after it exploded.

The VLT observations show that the brilliant light from the gamma-ray burst had passed through its own host galaxy and another galaxy nearby. These galaxies are being seen as they were about 12 billion years ago. Such distant galaxies are very rarely caught in the glare of a gamma-ray burst.

As light from the gamma-ray burst passed through the galaxies, the gas there acted like a filter, and absorbed some of the light from the gamma-ray burst at certain wavelengths. Without the gamma-ray burst these faint galaxies would be invisible. By carefully analysing the tell-tale fingerprints from different chemical elements the team was able to work out the composition of the cool gas in these very distant galaxies, and in particular how rich they were in heavy elements.

credit: ESO (text); L. Calçada (image)

Going Nova: Star Explosions Unleash Gamma-Ray Blasts

Gamma-rays, the most powerful form of light, may erupt from star explosions called novas surprisingly often, but the way these gamma-rays form remains a mystery, scientists say.

High-energy gamma-rays are typically associated with supernovas, the explosive deaths of stars. These explosions are bright enough to momentarily outshine their entire galaxies.

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SPACE Thoughts: GRBs

I like outer space. Or perhaps I should call it SPACE, to appropriate the unfathomable vastness of the cosmos. I didn’t major in astronomy at Uni, so all my knowledge comes from nights of research and a few classes I took that were, in the end, way out of my league. But I want to write about it now, as part of a general writing exercise. I’m out of practice. Again.

So, SPACE thoughts #1: Gamma Ray Bursts or; How the World Could End at Any Moment and There’s Not a Damn Thing We Could Do to Prevent It.

One of the more famous space phenomena are black holes, incredibly dense celestial bodies that have such a strong gravitational pull that not even light can escape its grasp. And, as such, they are black, invisible. There are tons of black holes in our galaxy, including one supermassive black hole (what up, Muse) in the center. But black holes get a bad rap. I mean, they’re still an incredibly destructive force that sucks matter away into an unknown space. But they’re not quite the “Hoovers of Outer Space” that they’ve been touted to be. Black holes don’t move. The reason why things get sucked into black holes is due to something getting too close to the black hole. This is the equivalent of tearing a hole in a bed sheet. If you drop something onto the sheet, the object may fall through the hole. The hole doesn’t move towards the object. That would be impossible. But I digress. We’re supposed to be talking about Gamma Ray Bursts.

Wait wait, a bit more prologue. Sorry.

Black holes themselves are a product at the end of a massive star dying. And while the black hole may be more fascinating to the everyman, the actual process of a star dying is just as incredible.

Our sun is an average star. A boring star. A C+ star. When the sun dies, it’ll puff up to a humongous size, become a red giant, and likely swallow the earth in its expanded radius, assuming we haven’t blown the world up before that. Then it will cool and shrink in size, as it expends the last bits of its energy, and eventually becomes a red dwarf. Red dwarves are small, relatively cold stars. Yawn. 

The big stars, though, are quite the spectacle. These huge stars are, uh, rock stars, in a way. They live fast and die young, shining brightly for millions of years before ending their lives in a fantastic explosion. On the molecular level, here’s what happens: every star is a balance of two forces. One is gravity, which pulls all matter towards the center of the star, and the other is nuclear fusion, which keeps pushing the mass and energy out into space. As the star continues to burn its energy, the helium atoms caused by nuclear fusion begin to then fuse together, creating the more complicated elements: carbon, oxygen, sodium, etc. As the heavier elements are created, the star becomes more dense, thus the gravitational pull becomes stronger. Concurrently, the star’s available hydrogen needed for fusion is dwindling, and at some point something has to give.

Gravity wins out, and all the dense matter collapses in on itself, squeezing itself into as compact of an object as possible. The collapse causes a shockwave, and all the material not sucked into the star is jettisoned out into space. Thus, a supernova occurs. Supernovae are very pretty and leave absolutely gorgeous nebulae. They also cause gamma ray bursts.

We’re 600 words into this post, and I finally get to what a gamma ray burst is. Go me.

Anyways, as a star explodes, a gamma ray burst is emitted from its poles, shooting out far into space. A GRB is a narrow beam of extremely energetic rays, the power being something equivalent to the amount of energy the sun will expend in its entire lifetime. These things are very powerful and, potentially, very dangerous.

Most of the GRBs scientists have witnessed are very far away, somewhere in the billion-light-year range. But, if a GRB occurred close to us, say, in the thousand-light-year range, and we just happened to be in the beam’s path, things would go bad very fast. A GRB can be as short as two seconds, but there would be enough energy in those two seconds to irrevocably alter the earth.

Theoretical models have the intense wave of radiation slicing through the atmosphere and depleting up to 25% of the ozone layer. This would be a disastrous amount lost in one sitting. Those living on the side of Earth facing the blast would be subjected to lethal amounts of radiation immediately. The side facing away from Earth wouldn’t be as bombarded by harmful gamma rays, but the ozone depletion and UV radiation would likely kill them eventually. On top of that, a dramatic change to the atmosphere would disrupt many food chains and elemental cycles, leading to many species dying due to food shortages. So those humans who happen to not die of radiation poisoning would die of starvation. It wouldn’t be a pretty sight. 

The thing is, we can’t predict this. We don’t know which massive stars have their poles pointed towards us. We don’t know when they’re going to explode. For many other natural disasters, we’d have projection models and years of warning. A catastrophic meteor would at least be observed a year before impact (though we wouldn’t be able to do anything about it. Sorry, Bruce Willis). We’re in the midst of extreme climate change and can observe it directly. A gamma ray burst, though, can happen at any moment. The radiation travels at near speed of light, so as soon as we see the star exploding, it would already be too late. Once the light arrives, so does the radiation. 

You may say that the likelihood of a GRB hitting us is very slim. True, it is. However, it’s likely that Earth experienced a gamma ray burst in the past. It’s been theorized that the Ordovician–Silurian extinction event, the second largest extinction event in the history of earth, was due to a GRB. It’s not impossible.

So what’s to be learned from all of this? Probably nothing you haven’t heard before. Cherish every moment; live every day as if it were your last; life is fleeting; etc. But now you can append “because at any moment you could be bombarded by one billion nuclear bombs’ worth of radiation and die a painful death” to all of that!

Science is magical.

%Title%

Gamma-ray bursts (GRBs) are flashes of gamma rays (electromagnetic radiation of high frequency) that come from energetic explosions in distant galaxies. They are known to be the most radiating electromagnetic events in the Universe. The bursts can last from ten milliseconds to several minutes (a typical burst lasts 20-40 seconds). GRBs were discovered in the lats 1960s; however, this was not an intentional discovery. They were discovered by the U.S. Vela satellites that were actually built to detect gamma radiation pulses emitted by nuclear weapons tested in Space. Why? Well, the USA suspected that the USSR might attempt to conduct secret nuclear tests after signing the Nuclear Test Ban Treaty in 1963.

Learn about how they were discovered at:
http://www.fromquarkstoquasars.com/what-are-gamma-ray-bursts-and-how-did-we-discover-them/

Image source:
http://www.nsf.gov/news/news_images.jsp?cntn_id=104440&org=NSF

Detection of the Cosmic Gamma Ray Horizon: Measures All the Light in the Universe Since the Big Bang

May 24, 2013 — How much light has been emitted by all galaxies since the cosmos began? After all, almost every photon (particle of light) from ultraviolet to far infrared wavelengths ever radiated by all galaxies that ever existed throughout cosmic history is still speeding through the Universe today. If we could carefully measure the number and energy (wavelength) of all those photons – not only at the present time, but also back in time – we might learn important secrets about the nature and evolution of the Universe, including how similar or different ancient galaxies were compared to the galaxies we see today.

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(Space.com) ‘Dark’ and Powerful Space Explosions May Be Cloaked by Cosmic Dust

Astronomers using a giant radio telescope to investigate the most violent explosions in the universe, known as gamma-ray bursts (GRBs), found something surprising in two distant galaxies: more dust and less gas than they expected.

So-called “dark GRBs” may explain a curious phenomenon for astronomers mapping out these powerful explosions in space. While most gamma-ray bursts have an afterglow, sometimes scientists don’t see that luminescence. It is possible that thick interstellar dust may mask the light from dark GRBs.

(more…)

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5° Gaia Science Alerts Workshop 2014

5° Gaia Science Alerts Workshop 2014

Gaia is the cornerstone mission of the European Space Agency, successfully launched in December 2013. Its main goal is to map the entire Galaxy, but thanks to repetitive observations of the entire sky it also acts as a unique time-domain space survey, suitable for real-time detections of transients. In recent years the astronomy of transient phenomena has became a very vivid area of research.…

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Kings step aside when the Emperor comes…

You guys ever heard of the Large Quasar Group? It’s literally the biggest fuckin’ thing in the known universe. Four billion lightyears across, 1600x the distance between the Milky Way and Andromeda. The only thing that comes close in size is the CMB cold spot at one billion lightyears and the Great GRB Wall, which would be bigger if we could definitively prove it’s actually there.

I wanted to make LQG a character for a suuuuuuper long time, and now divine-retributi0n gave me an excuse, so, here, giant space bara nerd who doesn’t know how to properly interact with things because he lives SO FAR AWAY that no one ever talks to him. He swaggers around like he’s a god, but then probably trips over his own feet or some dumb shit, help him, he is too large.

Pansexual/Demiromantic

Thirsty hippo.
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