Starship Asterisk*

Just how small of an explosion can we detect from across the galaxy. Does it have to be "star" size?

Going into the realm of sci-fi for a second. Say on the otherside of the Milky Way a Star Wars scenario was going on, and the rebels blew-up the Death Star. Would our instruments be able to detect an explosion like that? Or in the Star Trek universe, something like the Paraxis explosion? Obviously accounting that these things would have happened in the past.

According to this picture, we can detect the radiation and even see an explosion that occurred billions of years ago (13 or 14+). Routinely, it seems, they find some far off ancient explosion.

I did notice one thing that most of these detections seem to have in common seems to be Gamma. Is that the key? If it is rich in Gamma, we could detect it.

Lastly, food for discussion...would an all out nuclear war on a planet be detectable from across the galaxy? Say, every nuclear warhead was detonated at the same time...

-Windquake

http://apod.nasa.gov/apod/ap090429.html

My question is: how early does this explosion occur? If this is a gamma ray burst from an exploding star, does that mean a g.r.b. will outshine it's containing galaxy? Or is this too early in the universe for the formation of galaxies?

@windquake: Regarding your discussion of nuclear war on another planet ... Being as we can positively identify and now visibly see planets, I would imagine we'd only be able to pick up on a nuclear explosion if it caused extreme atmospheric changes on the planet (which an all out nuclear war would).

The Most Distant Object Yet Discovered in the Universe
ESO 17/09 - Science Release - 2009 April 28 - VLT

New Gamma-Ray Burst Smashes Cosmic Distance Record
NASA Swift Mission News - 2009 April 28

http://asterisk.apod.com/vie ... =8&t=16791

I am no genius, so excuse me if I have missed the obvious. I have my doubts regarding all astronomical caluclations anyway. So, this one is really confusing me.
I do not understand the time given for the "explosion". If it was 630 million years after the "big bang", then how could this have been seen now? Light travels faster, and with our current date being billions of years after this explosion, how could we see it now? Please, explain?
Thank you, and I apologize for wasting someones time, if I am missing something.
Thanks!!!

Unless, I guess, we are a greater distance away than the number of years in creation. 11 billion years old, but trillions of light years away, but that still seems as if the light should have passed by before this universe was even being created. That would mean that the expansion of the universe would be growing faster than light. In that case no light from anything in the center would ever be seen, unless the universe is now collapsing back on itself allowing us to come back into "view" of the past.

windquake wrote:Just how small of an explosion can we detect from across the galaxy. Does it have to be "star" size?

There is no lower limit on size. We only observe the energy; these events are far too small spatially to actually resolve. So the limitation on our ability to detect them is determined by the sensitivity and S/N of our detectors, and the energy emitted by the source, not its physical size.

" . . the gamma-ray burst recorded last week was clocked at redshift 8.2, making it the farthest explosion of any type yet detected. "

Let's stick with the facts please. This gamma ray burst was received by us with a redshift of z=8.2, making it the highest redshift ever recorded. period.
Redshift has not been proven to be caused by recessional velocity alone, so that does not make this the furthest object ever seen, nor 830 million years post the erroneously preconceived concept of a Big Bang.

I would say that this gamma ray burst observation conclusively falsifies the conceptual theory of the Big Bang. period. end of story for the Big Bang Theory.

DistantViewer wrote:I do not understand the time given for the "explosion". If it was 630 million years after the "big bang", then how could this have been seen now? Light travels faster, and with our current date being billions of years after this explosion, how could we see it now? Please, explain?...

Unless, I guess, we are a greater distance away than the number of years in creation.

When the explosion occurred, it was much closer to us. It is now something like 30 billion light years away, and the light is just reaching us. That is a result of the expansion of the Universe between the time of the explosion and our observing it. Indeed, our actual distance from this object is greater than 13.7 billion light years. The Universe itself has a radius of more than 46 billion light years, because of its expansion over its 13.7 billion years of existence.

kovil wrote:Redshift has not been proven to be caused by recessional velocity alone, so that does not make this the furthest object ever seen, nor 830 million years post the erroneously preconceived concept of a Big Bang.

Nor will it ever be proven. Nevertheless, the relationship between redshift, distance, and cosmological expansion is very strongly supported by theory and multiple avenues of observation. This represents the view of almost all astronomers, and is considered the standard model. It is certainly the interpretation that best supports observation, and it is entirely appropriate to take it for granted in a general science forum like this one.

Chris Peterson wrote:

windquake wrote:Just how small of an explosion can we detect from across the galaxy. Does it have to be "star" size?

There is no lower limit on size. We only observe the energy; these events are far too small spatially to actually resolve. So the limitation on our ability to detect them is determined by the sensitivity and S/N of our detectors, and the energy emitted by the source, not its physical size.

Well yes, I understand it is energy and not physical size of the event...

But my question remains...just how sensitive are the instruments? Let's say the Death Star was to explode an Earth-like planet or even a sun-like star...could we detect that 10 light years away? 100 light years away? Across the galaxy? In another galaxy? (again given the appropriate amount of time for energy travel.)

I realize this is all hypothetical and just brain fun, so no need to get extremely technical or specific.

Perhaps, just being a run of the mill geek, I am just babbling a bunch of junk, but my curiosity has been piqued.

-Windquake

windquake wrote:But my question remains...just how sensitive are the instruments?

SWIFT can detect events which deposit about 2e-15 joules at its sensors.

Let's say the Death Star was to explode an Earth-like planet or even a sun-like star...could we detect that 10 light years away?

I'm afraid that R2D2 hasn't shown up here with the plans for the Death Star, so I'm a bit vague on how efficiently it can convert a planet to energy. However, using the above stated instrument sensitivity and the inverse square law, you can experiment with different scenarios of energy versus distance.

windquake wrote:...just how sensitive are the instruments? -Windquake

The Chinese are building the world's biggest radio telescope which will pretty much dwarf all other radios. They are moving VERY quickly towards supremacy in the sciences.

Thanks Aristarcus, I had no idea about the Chinese radio telescope, and google found it quick !

http://www.universetoday.com/2009/01/31 ... telescope/

This distant echo made me think along other kind of loose lines.

How likely it is that we are (or once where) inside a cloud of explosion like this one (dissipated long time ago)? Try to make sense out of that in whichever way you find appropriate . I have gotten something published on things called space-time codes (telcomm jargon), but have occasionally problems moving in the real spacetime.

Hmm. My understanding about the production of elements in the early universe became more than a little bit hazy, when the author (of the book I was studying) was trying to explain, why it is difficult to move from helium to carbon (and beyond). But our bodies contain heavier elements - iron at least.

I have a *very* hazy recollection that supernova scale of explosions are needed to produce heavier nucleids.

So let me rephrase my question. Where explosions like this the first generation of supernovae producing heavier elements, and should we thus see ourselves as one of the by-products of explosions like the one depicted in today's APOD?

In case you are oblivious as I am sometimes, you may have missed the link to the original article: http://www.cfa.harvard.edu/news/2009/pr200911.html

aristarchusinexile wrote:

windquake wrote:...just how sensitive are the instruments? -Windquake

The Chinese are building the world's biggest radio telescope which will pretty much dwarf all other radios. They are moving VERY quickly towards supremacy in the sciences.

However, in the context of this discussion, that doesn't matter. Radio telescopes aren't used for detecting GRBs. For that you need space based detectors, and the U.S. and Europe are way ahead in that area.

Chris Peterson wrote: Radio telescopes aren't used for detecting GRBs. For that you need space based detectors, and the U.S. and Europe are way ahead in that area.

Please explain why ground based radio telescopes are not used to detect stellar explosions.

GRBs were first detected in 1967 by the Vela satellites, a series of satellites designed to detect nuclear explosions in space. Since then, hundreds of theoretical models have been proposed to explain these bursts, such as collisions between comets and neutron stars. Little information was available to support any of these models until the discovery of X-ray and optical afterglows and the determination of the redshift of GRB 970508. http://en.wikipedia.org/wiki/Gamma-ray_burst
"Gamma rays (denoted as γ) are electromagnetic radiation of high energy." http://en.wikipedia.org/wiki/Gamma_Ray

aristarchusinexile wrote:

Chris Peterson wrote: Radio telescopes aren't used for detecting GRBs. For that you need space based detectors, and the U.S. and Europe are way ahead in that area.

Please explain why ground based radio telescopes are not used to detect stellar explosions.

GRB's produce gamma rays- electromagnetic radiation that is ten or more orders of magnitude shorter wavelength than radio receivers can detect, and which is largely unable to make it through the atmosphere. GRBs are the first indication of an event; once one has been detected and located, it is possible to aim other types of instruments at them, including radio telescopes, and make measurements of the afterglow. A primary detection by a radio telescope would not occur until the event was nearly over, so much information would be lost. Also, radio telescopes are not wide angle imaging devices, so they would be nearly impossible to use as a search tool for brief events.

BTW, GRBs are primarily associated with the collapse of a star into a black hole, and with black hole jets. Those are different from stellar explosions.

Chris Peterson wrote: GRB's produce gamma rays- electromagnetic radiation that is ten or more orders of magnitude shorter wavelength than radio receivers can detect, and which is largely unable to make it through the atmosphere. GRBs are the first indication of an event; once one has been detected and located, it is possible to aim other types of instruments at them, including radio telescopes, and make measurements of the afterglow. A primary detection by a radio telescope would not occur until the event was nearly over, so much information would be lost. Also, radio telescopes are not wide angle imaging devices, so they would be nearly impossible to use as a search tool for brief events.

BTW, GRBs are primarily associated with the collapse of a star into a black hole, and with black hole jets. Those are different from stellar explosions.

Thanks Chris. I Wiki'd GRBs and see why space based instruments will have an advantage, but enough GRs penetrate the atmosphere to effect life here, so would a huge Radio Telescope 'tuned' to GRBs detect them? GRBs are still categorized as electro magnetic, correct? (Or not?)

aristarchusinexile wrote:Thanks Chris. I Wiki'd GRBs and see why space based instruments will have an advantage, but enough GRs penetrate the atmosphere to effect life here, so would a huge Radio Telescope 'tuned' to GRBs detect them? GRBs are still categorized as electro magnetic, correct? (Or not?)

You can't tune a radio telescope to detect GRBs, anymore than you can tune an optical telescope to detect radio waves. Gamma ray detectors operate on fundamentally different principles than radio detectors. Even if you put a gamma ray detector at the focus of a radio telescope, you wouldn't get any signal, since gamma rays aren't reflected by the radio telescope's dish.

SWIFT is capable of detecting very low energy gamma rays, which are not detectable at ground level. Even more energetic gamma rays are highly attenuated by the atmosphere, so detecting them from space is really the only practical approach for most applications.

Chris Peterson wrote:

aristarchusinexile wrote:Thanks Chris. I Wiki'd GRBs and see why space based instruments will have an advantage, but enough GRs penetrate the atmosphere to effect life here, so would a huge Radio Telescope 'tuned' to GRBs detect them? GRBs are still categorized as electro magnetic, correct? (Or not?)

You can't tune a radio telescope to detect GRBs, anymore than you can tune an optical telescope to detect radio waves. Gamma ray detectors operate on fundamentally different principles than radio detectors. Even if you put a gamma ray detector at the focus of a radio telescope, you wouldn't get any signal, since gamma rays aren't reflected by the radio telescope's dish.

SWIFT is capable of detecting very low energy gamma rays, which are not detectable at ground level. Even more energetic gamma rays are highly attenuated by the atmosphere, so detecting them from space is really the only practical approach for most applications.

Thanks Chris.

Does anybody know if gamma ray bursts come from any particular direction -or- if you tried to plot them on a star chart, would they be fairly randomly distributed? I tried to look this up, but could only find the coordinates of 2 of them.

By the way, this is a pretty nifty tool. I don't know how valid it is, though --> http://www.atlasoftheuniverse.com/universe.html

brett_w7 wrote:Does anybody know if gamma ray bursts come from any particular direction -or- if you tried to plot them on a star chart, would they be fairly randomly distributed? I tried to look this up, but could only find the coordinates of 2 of them.

brett_w7 wrote:Does anybody know if gamma ray bursts come from any particular direction -or- if you tried to plot them on a star chart, would they be fairly randomly distributed? I tried to look this up, but could only find the coordinates of 2 of them.

They appear to be distributed over the entire sky, with no preferential direction.



(This is data from the BATSE instrument on the Compton Gamma Ray Observatory, so it's about 10 years old. But I don't think the distribution has changed with SWIFT. The raw data is available here if you want to plot it yourself.)

Thanks Art and Chris!

Brett