terifyingly

wow, talk about supply and demand

*tries something out*
what we need now are pictures of hot girls getting soaked by a garden hose on a hot day

aaaaanyway.

How large would a GBR be and how fast would it...burst? i'm just trying to calculate the threat here. if one was 9bn light years away, surely we're safe, especially since we found out about something that happened 9bn years ago so if it WAS a threat, we would know about it already...unless we were affected in a minor way.

ooooh, what IF we found out what killed the dinosaurs 65 million years ago was some massive interstellar explosion who's shockwave traveled FTL and we're gonna see it in the heavens any day now. That would make a KILLER plotline for a movie, or at the very least, an episode plan for startrek.

What exactly are we discussing here indy? you kinda worded it like a statement of fact, where's the debate?

oooop. Sorry. Didn't think of making it a debate as I was just sucked into the current state of information and theory about the GRBs.

Sorry about that. I'll have to think these things through more carefully. I suppose you could argue whether its the merging of neutron stars versus a hyper nova but, frankly, I wasn't all that taken by the neutron star merger thing.... mainly 'cause I didn't understand it.

OK. No debate from me on this. Sorry. Don't know enought to debate it.

I'm trying to setup a linky for you but it's not working atm. Data source is Scientific American Special Edition on The Secret Lives Of Stars, Vol 14, No. 4.

How large is it? The "fireball" which precedes the GR burst is estimated to reach a size of between 10bn to 100bn kms in diameter at which point gamma rays begin to escape the fireball as the photon density of the ball finally has to dropped off sufficiently. The fireball's rate of expansion to that point is estimated to be near the speed of light. The gamma ray emissions are speed of light. And there's more but I'm gonna try to get that linky going instead.

Edited by - Indy11 on 11/5/2004 9:17:09 PM

Which makes sense, because if it fireball is expanding at c and Gamma rays travel at c , then there is a massive buildup of gamma ray radiation by the time the fireball ceases to expand, the radiation overlaps.
This also brings up some interesting mathematical calculations, because if the radation front is at the same point as the radiation emitter, then the pulse of gamma radiation lasts for a total time of zero (i think), and would, in theory, cause the pulse of energy that was emitted to be zero also...
Correct me if im wrong (probably)


Now, assuming that the pulse lasts longer than time=0 what amount of energy are we talking about here? terajoules? exajoules? any significant figure would be more than capable of completely annihilating any stellar object within a few trillion kilometres...
Now, bear thet in mind, look at the Cygnug X1 star, it is believed to be coupled with a black hole that is slowly siphoning its gases away into its graviitational well...
Now, if the Cygnus black hole was the product of one of these 'hypernovas' as we are led to believe, wouldnt Cygnus X1 have been destroyed?

Im not saying its not right... but i dont think that a hypernova would be the couse of a balck hole... maybe its the mythical 'end' of a star, where there is nothing left...

Arania - As far as you Cygnus question is concerned you must remember that "hypernovae" are not the only possible causes of black holes. Simple supernovae can have the same effect. Not only that but black holes can last a very long time so Cygnus may have formed subsequent to the black hole's birth.

Indy - Is there any mention of how long the black holes born out of GRBs last? I know that in some supercolliders here on earth, black hole-like conditions exist but only for fractions of a second. If the case of GRBs is the same, or similar, I wouldn't worry too much. Then again, I wouldn't worry much anyway; it's not like we could do anything about it.

not necessarily.

off the top of my head, there's 3 sources of gamma ray bursts.

formation of blackholes, 'hyper novae', and pulsars. pulsars emit gamma ray bursts preiodically, rapidly at that. blackholes are usually detected by the constant gamma stream thats emited from its axis. vertical to its material plane (whatever its called)

oh, the gamma burst may also have been from neutron stars when they build up enough density in their accredition (sp?) disk that they get rid of it by ... exploding them. releasing intense energy. including those going deep into the gamma spectrum. i kinda forgot the term.

My astronomy book, in a pdf format, i did not type all of this...:

What are Gamma-ray bursts, and what are gamma rays?

Gamma ray bursts (GRBs for short) are intense and short (approximately 0.1-100 seconds long) bursts of gamma-ray radiation that occur all over the sky approximately once per day at very large distances from Earth. Gamma rays are very energetic photons (E>10^5 eV), which represent the most extreme portion of the electromagnetic spectrum (ranging from radio waves at the lowest energies through visible optical light at higher energies, to gamma rays at the highest energies).


Where do Gamma-ray bursts occur?

Up until the 1990s and the launch of the Compton Gamma Ray Observatory (CGRO; see next question) there was a heated debate in the astronomical community about the source of, and distance to gamma ray bursts. One group claimed that gamma ray bursts occur in our own galaxy (the Milky Way), while others claimed that they occur in very distant galaxies. The main reason put forward by the group which claimed a local origin was the extreme energy release that is necessary to explain the observed emission from gamma ray bursts (see question 10). However, from the information gathered by CGRO, and later confirmation from observations of gamma-ray burst afterglows (see below), it was determined unambiguously that gamma-ray bursts take place in very distant galaxies (several billion light years away). The most distant Gamma-ray burst detected so far occured 13 billion light years away. This means that the gamma ray emission from gamma ray bursts that we observe now has been emitted billions of years ago, when the Universe was much younger.


How are gamma-ray bursts detected?

Gamma ray bursts are detected by satellites orbiting the Earth and travelling through the Solar system. They can only be detected from space because the Earth's atmosphere absorbs gamma rays and therefore we cannot observe them from the ground. The first gamma ray bursts were detected by the Vela satellites, which were launched in the 1960s to ensure compliance with the Nuclear Test Ban Treaty. Since then several thousand gamma ray bursts have been detected by satellites such as the Compton Gamma Ray Observatory (CGRO) and the Interplanetary Network (IPN).

(Meaning GRBs cannot hurt Earth, atmosphere)

Gamma ray bursts release extremely large amount of energy - approximately 10^52 ergs (or 10^45 joules), with the most extreme bursts releasing up to 10^54 ergs. This is the equivalent of turning a star like the Sun into pure energy (using Einstein's famous equation E=mc^2). This is also the amount of energy released by 1000 stars like the Sun over their entire lifetime! In practice, over the few seconds that a gamma ray burst occurs, it releases almost the same amount of energy as the entire Universe! This exteremly large energy release is the reason that astronomers initially believed that gamma ray bursts come from our own galaxy (see question 6). For those of us who live with rolling blackouts (i.e. Californians), the energy from a gamma ray burst (if it was converted to electricity) could supply the entire world's energy needs for a billion billion billion (that's 1 with 27 zeroes after it) years!

What is the source (progenitor) of gamma-ray bursts?

In the first years of gamma ray burst research there were more proposed sources (or progenitors) for gamma ray bursts than the actual number of gamma ray bursts detected! However, ever since it was determined that gamma ray bursts occur at very large distances (and therefore release huge amounts of energy) the list of proposed progenitors shrunk into two main classes: very massive stars, and binary (2 star) systems composed of neutron stars or black holes. It is now thought that the "long and soft" bursts come from massive stars, while the "short and hard" bursts come from binary systems. Recently, observations of GRB 011121 (Bloom et al. 2002; Price et al. 2002) revealed a SN explosion which accompanied the GRB, and a circumburst environment typical of what is usually found around massive stars (see more on this intersting burst below). These results support the idea that the "long and soft" bursts are the end product of massive stars.

How are massive stars thought to produce gamma ray bursts?

Astronomers now think that the iron cores of some very massive stars (at least 30 times more massive than the Sun) can collapse into black holes several million years after they form. The energy released in the formation of the black hole emerges out of the collapsed star in the form of a gamma ray burst. Gamma ray burst astronomers call this the "collapsar" model. Other names are "hypernova" or "failed supernova" models. These names hint that there may be a connection between gamma ray bursts and supernovae (see below).

Gamma ray bursts could also be created by the final "evaporation" of black holes. According to Stephen Hawking, black holes gradually emit radiation (don't say it - yes, nothing can escape from a black hole. They still emit radiation). This decreses their mass, and once their mass is small enough, they finally disappear in a massive final burst of Hawking radiation. That would register as fairly large, IIRC. Most black holes live for time on the scale of 10^30 years, far longer than the universe itself, but massive black holes created by the conditions of the Big Bang should be exploding about now.

Black holes emmit radiation because of the few particles that have a high enough orbital velocity to exceed the gravatational pull. We useually see this in the X-ray band of the Electromagnetic Spectrum.

I was under the impression that it wasn't the blackhole itself that emits the radiation but the colliding destruction of the matter collapsing into the event horizon.

no particle can escape the event horizon... The particles that I stated in my last post never enter the event horizon, they orbit it then get shot off because of high velocities.

The only particle that can escape the event horison is the theoretical 'tachyon' particle, because, by definition, its speed is higher than the speed of light.
Ive done a fair bit of theory on tachyon particles, in particular thier theroetical use in weaponry and their colission effects on stationary matter (very interesting, if i do say so myself)

@darkstone: Yes, black holos do indeed emit electromagnetic radiation inside the event horison, but they just get sucked back into the singularity after thier emission.
If the singularity were to somehow lose the gravitational pull holdin it together, one of three things could happen:
1) the singularity stays formed because if its immense density, doing nothing.
2) it will cease to exist
3) the matter contained in the singularity will dissipate (i.e. explode), causing a fair bit of destruction

Nertz. The best I can do with a linky is this

@Code, no specific discussion on the duration of the black hole. Implication in the text is that these are the "permanent" variety ... at least as respects a hyper nova.

Theory is that a GRB "hyper nova" has such a super high mass that its collapse results in a huge neutron star that, as a result, collapses into a black hole as there is a limit to how large a neutron star can be. The rest of the stellar mass is ejected as a super nova explosion. This may explain the high coincidence of a super nova alongside the detected GRBs that has been noted.

this 'tachyon' particle arania mentioned.. im gonna have to look into it. never heard of it before

@Arania,

I'm not talking about radiation emanating from the black hole. Hawking radiation originates just outside the event horizon. Virtual particle - antiparticle pairs spring into existence all the time, as the Uncertainty principle means that there can never be no energy at all anywhere. What happens is that every so often, the pair is created, but one gets sucked into the black hole and the other is free to go, rather than annihilating with its partner, which it would usually do.

So, to any observer, it looks as if the black hole has emitted a particle. In addition, the particle that falls into the black hole has negative energy. So, according to E=mc², the mass of the black hole decreases, making the effect even more convincing.

Changing topics: tachyons are hypothetical particles with real momentum and energy, but imaginary mass, IIRC. Not only can tachyons travel faster than light, but they can in fact never slow down to c or slower. The most interesting property of tachyons is that the lower their energy, the faster they travel - a direct contradiction of what we see around us.