Most Extreme Gamma-Ray Blast Yet Detected 128
Matt_dk sends in a quote from a story at NASA:
"The first gamma-ray burst to be seen in high-resolution from NASA's Fermi Gamma-ray Space Telescope is one for the record books. The blast had the greatest total energy, the fastest motions and the highest-energy initial emissions ever seen. ... Gamma-ray bursts are the universe's most luminous explosions. Astronomers believe most occur when exotic massive stars run out of nuclear fuel. As a star's core collapses into a black hole, jets of material — powered by processes not yet fully understood — blast outward at nearly the speed of light. The jets bore all the way through the collapsing star and continue into space, where they interact with gas previously shed by the star and generate bright afterglows that fade with time. ...Fermi team members calculated that the blast exceeded the power of approximately 9,000 ordinary supernovae, if the energy was emitted equally in all directions."
Re:how do they know (Score:1, Informative)
Parallax and red shift, I would imagine. They know the speed of light, and the rate (roughly) that red-shifting happens. Parallax measurements allow them to determine how far away it is to at least a modicum of accuracy.
Note: The above is a guess, but it seems plausible.
Re:how do they know (Score:3, Informative)
Power of Gamma Ray Bursts (Score:5, Informative)
My favorite comparison to illustrate the power of Gamma Ray Bursts: A Gamma Ray Burst puts out the same amount of power (while it is bursting) as all the stars in the universe together.
(Usually comparisons made in the media are rather lame, i.e. Libraries of Congress, but this one really impressed me)
Re:coloured dots!!! (Score:3, Informative)
Actually, it is worse. It is a 6-second .mov Quicktime movie, all 7 MB of it. Considering it is a 6-second movie of colored dots, it would have been a lot more efficient to represent it in a different format. Perhaps an animated GIF?
Re:how do they know (Score:3, Informative)
parallax only works for stars very close (astronomically speaking) to us... few dozen light-years at most. Even then they have to use the whole width of earth's orbit around the sun, taken 6 months apart, to calculate the parallax.... closing your left eye then your right eye aint gonna cut it for measuring light-year distances :P
Redshift is how they measure galaxy distances, and by some process they determine that this gamma ray burst occurred in galaxy X, so that's how far they come up with the distance here. I think, I haven't RTFA :-/
GROND (Score:3, Informative)
In this particular case, it was this [eso.org].
Method is explained a little in the eso.org link, but here's a wikipedia article, too: http://en.wikipedia.org/wiki/Photometric_redshift [wikipedia.org].
Also, awesome Tolkien reference apparently acknowledged by Jochen Greiner.
Re:And make it relative! (Score:4, Informative)
That very same graph with a third axis (axee? axen? Arg!) that shows this burst/time graph relative to an energy source I can somewhat comprehend.
The plural of axis is axes.
That said, you're talking about a single one (the third in a set, but it's still singular) so axis is correct.
Re:how do they know (Score:5, Informative)
i've always wondered how they know the size and distance of these objects. short of running a tape measure out, how the hell do you calculate the size of something an unknown distance away?
The chain of logic is vast and complex, but I'll try to summarize:
1) First, we used radar and the speed of light to figure out the distances of things in our solar system. These calculations helped us figure out the diameter of the Earth's orbit, which is used in the next step, parallax.
2) Once we know the diameter of Earth's orbit, we used parallax to determine the distance to nearby stars. Parallax is a process of triangulation, where we use the earth at two extremes and the star we are looking at as the three points of a triangle. Knowing two angles and one side lets us solve for the distance to the star. But the resolution of our telescopes only lets us use this method with any accuracy for stars in our immediate vicinity.
3) Once we could figure our how far away nearby stars are, we began focusing in on types of stars that have fairly consistent outputs of energy in comparison to their other measurable traits, such as color. We call these consistent types of stars (and other astronomical objects) standard candles.
4) Once we are sure that these standard candles do indeed have consistently predictable outputs, we can guess how far away stars of these types are by noting that luminosity (total light output) and apparent brightness are related by a simple inverse distance squared relationship. This lets us estimate the distance to any type of star that has a fairly estimable luminosity.
5) After we have our standard candles mapped out in space, we can note the absorption lines in the light spectrum which indicates various types of dust and gasses. With this data we can make a rough map of where dust and gasses are floating around. This map will let us look at light from stars and objects that aren't standard candles and figure out how far away they should be to account for the absorption lines we see in their light spectrum.
6) After mapping out many of the nearby galaxies using supernovae as our key standard candle, we notices that is seems that there is a linear correlation between how far away an object is and how fast it is moving away from us (we can tell how fast an object is moving away from us using red-shift). This observation seems to show that the universe is expanding, but more important to the discussion at hand, it gives us another tool with which to estimate and map the distances of objects -- this time at any arbitrary distance.
Using the many of the above methods we can get estimates for how far away objects are, but the margin of error is huge because of all of the assumptions we've made. Plus of minus a magnitude or two is considered fairly precise in astronomical terms. This might have been more of an answer than you bargained for, but there you have it.
Re:And no-one knows why they go bang. (Score:3, Informative)
The "speed" is how long the burst lasts for - not how fast the gamma rays go!
Re:how do they know (Score:4, Informative)
The host or counterpart galaxy was too faint (the GRB was 12.8Gly away, and models predict that the host galaxy wouldn't be detectable). But apparently, there is now enough confidence in the models for GRBs to get a good fix on the distance anyway. It's awesome that they can do this without observing a host galaxy now.
The same team that measured this also confirmed the most distant GRB to date last September, and this is within the most distant 5% of observed GRBs.
Arxiv paper [arxiv.org]
Re:how do they know (Score:5, Informative)
I don't think you made the part about standard candles very clear, so I'll elaborate on that point.
The term doesn't refer to a specific type of star. Standard candles are any stellar objects that have some quality that allows them to be used to measure distance.
One of the most famous examples are Cepheid variable stars. These stars all vary in brightness over some predictable period of time. There is a relationship between how fast they "pulse" and how bright they are. The faster they pulse, the dimmer they are (in absolute terms). If one is pulsing really slow, and it looks dim (relatively speaking), it's probably very far away since it should be relatively bright. If it looks bright and pulses quickly, it's probably close by since they don't get very bright (absolutely speaking).
Other standard candles include planetary nebula, supergiants, globular clusters, H II regions, and supernova. Each of them has a different maximum range over which they can be detected, but there is some overlap. The ones in the overlapping regions are used to calibrate the distances for the rest.
It's called "EIRP" (Score:3, Informative)
A common acronym you'll find in engineering and physics texts is EIRP, which stands for equivalent isotropic radiated power. This means you take the direction with the highest intensity of radiation and calculate what would be the total power if it was radiated with equal intensity in all directions.
This system of calculation is very convenient in communications engineering, because you buy amplifiers and antennas separately. Antennas which emit tighter beams are called "high gain", because using one such antenna allows you to use a smaller amplifier to get the same effect at one direction.
In microwaves it's very common to trade off the cost of a smaller antenna against the higher cost of a more powerful amplifier when designing a point to point link. When you calculate the needed signal intensity at the receiver, you represent the result as an EIRP and calculate the loss due to the signal spreading out to get the needed EIRP at the transmitter. Then you check out how much different antennas and amplifiers cost to get the cheapest combination that gives the needed EIRP.
Since radio astronomy uses basically the same formulas, it only stands to reason that astronomers would use the same terminology.
Re:Big Bang (Score:4, Informative)
No, this was just a little Bang. The big one, we had already found. You can see a picture here [nasa.gov].
Re:coloured dots!!! (Score:2, Informative)
And the largest bomb ever exploded is 5x10^8 tons of TNT.
Not quite. You are thinking of the sowjet "Tsar Bomba" [wikipedia.org] - with an estimated
blast of about 50Mt TNT-equivalent. That would be 50e6, or 5*10^7.
This factor of ten of yours of course doesn't change the fact that the amounts of energy involved in cosmic
explosions are mindbogglingly huge.