The discussion revolves around how astronomers measure the distance that high-energy radio waves travel from distant parts of the universe. Participants explore various methods and concepts related to this measurement, including the role of observable sources, redshift, and triangulation, as well as the implications of specific radio bursts.
Participants express differing views on the methods used to measure distances of radio wave sources, with no consensus reached on the most effective approach. Some emphasize optical observations while others focus on the role of redshift and triangulation.
Participants note that the discussion involves complex concepts that may depend on specific definitions and assumptions, particularly regarding the measurement techniques and the nature of the radio bursts.
This discussion may be of interest to those studying astronomy, astrophysics, or anyone curious about the methods used to measure cosmic distances and the nature of radio wave sources in the universe.
this is the one that sparked my interest http://www.sciencemag.org/content/318/5851/777.fullSimon Bridge said:Well they can tell which direction they came from and then look back along that direction and see what is there.
There is a good chance that the strong radio source off thataway was where the radio burst came from, so the distance to the source is the distance the waves have travelled.
You get the distance to the source by a number of methods - one of which is the red-shift (for very distant sources) but mostly triangulation is used as well as comparing the brightness of the source compared with similar sources nearby.
That's a very simple picture ... the actual approach fills textbooks with the details.
Did you have particular radio bursts in mind?
Awesome! thanks dave, that answered my questiondavenn said:hi there psuedoben
no, it doesn't have to do with wavelength.
In most ( not all) cases there is an optically observable source at that point in "the sky"
eg, the Crab Nebula which is a supernova remnant with a pulsar in the middle, that pulsar is putting out bursts of radio signal at ~ 30 times a second
http://en.wikipedia.org/wiki/Crab_Nebula
There are lots and lots of SN remnants with all sorts of varying speed pulsars at their centre
In other cases its a galaxy that is emitting intense radio signals ... sometimes called radio galaxies
Centaurus A radio galaxy is an example
http://en.wikipedia.org/wiki/Centaurus_A
Generally, its the optical observations and measurements and will give the distance to the object
well let's say, it will give the MOST accurate distance measurements
Cepheid variable stars are commonly used for this purpose
http://en.wikipedia.org/wiki/Cepheid_variable
cheers
Dave
A Bright Millisecond Radio Burst of Extragalactic Origin
Pulsar surveys offer a rare opportunity to monitor the radio sky for impulsive burst-like events with millisecond durations. We analysed archival survey data and found a 30-jansky dispersed burst, less than 5 milliseconds in duration, located 3° from the Small Magellanic Cloud.
Pulsar surveys offer a rare opportunity to monitor the radio sky for impulsive burst-like events with millisecond durations. We analysed archival survey data and found a 30-jansky dispersed burst, less than 5 milliseconds in duration, located 3° from the Small Magellanic Cloud. The burst properties argue against a physical association with our Galaxy or the Small Magellanic Cloud. Current models for the free electron content in the universe imply that the burst is less than 1 gigaparsec distant. No further bursts were seen in 90 hours of additional observations, which implies that it was a singular event such as a supernova or coalescence of relativistic objects. Hundreds of similar events could occur every day and, if detected, could serve as cosmological probes.
amateur questions here, but 1) what do they mean when they refer to the "free-electron content in the universe" in the article 2) what is the SMC?davenn said:from that link you gave
If they only got that one burst, its going to be almost impossible to locate it, distance wise
as to whether it was within our galaxy or if it was actually associated with an event in the SMC
if as suggested it may be from a supernova event, then there is a chance that neutrino detectors also recorded a burst
They may possibly have already looked for that correlation ? :)
cheers
Dave
psuedoben said:amateur questions here, but 1) what do they mean when they refer to the "free-electron content in the universe" in the article 2) what is the SMC?
thank you that explains a great deal, and that analogy at the end did a wonderful job of helping me visualize what exactly they are dealing with when they try to calculate the distance!Simon Bridge said:Lorimer B. Bailes M. (2007) A bright millisecond radio burst of extragalactic origin
Full text: http://arxiv.org/abs/0709.4301
The universe is full of stuff, although there are big gaps between the bits.
Some of the bits are electrons - and there are electrons between the stars and between galaxies just flying around on their own. The paper talks about this as the galactic and intergalactic plasma (p2 etc).
This is what they mean by the free electron content of the Universe.
Radiation interacts with these electrons (and other charged particles) ... the electrons are very sparse, but over very long distances the effects add up.
Basically it's like looking at a light through a mist - you can tell how away it is from it's brightness and diffuseness if you have some idea about how light is affected by mist and how dense mists are. The researchers are basically saying they don't know how far away the source of the burst was, but the character of the burst was consistent with the best current guesses for how the intergalactic plasma affects radiation. Ergo: extragalactic origin - but still close enough to see it as well as we did.
Similarly, you can tell that a light you see outside the window was not in you backyard, because it looked like it was clearly affected by mist and the mist in your backyard is too diffuse for that.