This image shows the afterglow of GRB 090423 (red source in the centre) and was created from images taken in the z, Y and J filters at Gemini-South and VLT (credit: A. J. Levan).

More Observations of GRB 090423, the Most Distant Known Object in the Universe

28 Oct , 2009 by

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This image shows the afterglow of GRB 090423 (red source in the centre) and was created from images taken in the z, Y and J filters at Gemini-South and VLT (credit: A. J. Levan).

On April 23, 2009 the Swift satellite detected a gamma ray burst and as we reported back in April, scientists soon realized that it was more than 13 billion light-years from Earth. GRB 090423 occurred 630 million years after the Big Bang, when the Universe was only four percent of its current age of 13.7 billion years. Now, continued observations of the GRB by astronomers around the world have yielded more information about this dramatic and ancient event: the GRB didn’t come from a monster star, but it produced a fairly sizable explosion.

Several of the world’s largest telescopes turned to the region of the sky within the next minutes and hours after Swift’s announcement of the GRB’s detection, and were able to locate the faint, fading afterglow of the GRB. Detailed analysis revealed that the afterglow was seen only in infrared light and not in the normal optical. This was the clue that the burst came from very great distance.

The Very Large Array radio telescope first looked for the object the day after the discovery, detected the first radio waves from the blast a week later, then recorded changes in the object until it faded from view more than two months later.

Images of the afterglow of GRB 090423 taken (left to right) with the Y, J, H and K filters. The absence of any flux in the Y filter is a strong indication that the GRB is very high redshift (Credit: A. J. Levan & N. R. Tanvir)

Images of the afterglow of GRB 090423 taken (left to right) with the Y, J, H and K filters. The absence of any flux in the Y filter is a strong indication that the GRB is very high redshift (Credit: A. J. Levan & N. R. Tanvir)

Astronomers have thought that the very first stars in the Universe might be very different — brighter, hotter, and more massive — from those that formed later.

“This explosion provides an unprecedented look at an era when the Universe was very young and also was undergoing drastic changes. The primal cosmic darkness was being pierced by the light of the first stars and the first galaxies were beginning to form. The star that exploded in this event was a member of one of these earliest generations of stars,” said Dale Frail of the National Radio Astronomy Observatory.

Universe Today spoke with Edo Berger with the Gemini Telescope shortly after the GRB was detected, and he said the burst itself was not all that unusual. But even that can convey a lot of information. “That might mean that even these early generations of stars are very similar to stars in the local universe, that when they die they seem to produce similar types of gamma ray bursts, but it might be a little early to speculate.”

“This happened a little more than 13 billion years ago,” said Berger. “We’ve essentially been able to find gamma ray bursts throughout the Universe. The nearest ones are only about 100 million light years away, and this most distant one is 13 billion light years away, so it seems that they populate the entire universe. This most distant one demonstrates for the first time that massive stars exist at those very high red shifts. This is something people have suspected for a long time, but there was no direct observational proof. So that is one of the cool results from this observation.”

The scientists concluded the explosion was more energetic than most GRBs, but was certainly not the most energetic ever detected. The blast was nearly spherical that expanded into a tenuous and relatively uniform gaseous medium surrounding the star.

Antennas of the Very Large Array CREDIT: NRAO/AUI/NSF

Antennas of the Very Large Array CREDIT: NRAO/AUI/NSF


“It’s important to study these explosions with many kinds of telescopes. Our research team combined data from the VLA with data from X-ray and infrared telescopes to piece together some of the physical conditions of the blast,” said Derek Fox of Pennsylvania State University. “The result is a unique look into the very early Universe that we couldn’t have gotten any other way,” he added.

Sources: NRAO, University of Leicester



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The Eclectic Exterminator of Stupid Electricians
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The Eclectic Exterminator of Stupid Electricians
October 28, 2009 1:24 PM
According to the released paper “GRB 050904 at redshift 6.3: observations of the oldest cosmic explosion after the Big Bang” > “We present optical and near-infrared observations of the afterglow of the gamma-ray burst GRB 050904. We derive a photometric redshift z = 6.3, estimated from the presence of the Lyman break falling between the I and J filters. This is by far the most distant GRB known to date. Its isotropic-equivalent energy is 3.4 × 10^53 erg in the rest-frame 110-1100 keV energy band.” Why doesn’t the article here mention the actual redshift? Clearly the central part of the story is the staggering measurement of a redshift that is 6.3!! (Knowing this, the means we can easily… Read more »
Jon Hanford
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Jon Hanford
October 28, 2009 2:53 PM

Congrats to Nancy for another thought provoking article on GRB 050904. Again, well confirmed spectroscopic redshifts are generally more precise than photometric redshifts, due to the more precise determinations of redshift available to astrophysicists.

Congratulations to all involved making such sensitive and rigorously counterchecked data determination before all the facts are in.

The Eclectic Exterminator of Stupid Electricians
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The Eclectic Exterminator of Stupid Electricians
October 28, 2009 3:18 PM

@ Jon Hanford

You are right. The redshift of this is 8.1 not 6.2!

Still, without any redshift at all, it is so easy to confuse!

The paper is of course “GRB 090423 reveals an exploding star at the epoch of re-ionization” by R.Salverra, et.al.

(Apologies for the mix-up – a little too early in the morning!)

Jon Hanford
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Jon Hanford
October 28, 2009 3:47 PM

Thanks for the update and reference paper regarding this peculiar GRB, SBC smile

Aqua4U
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October 28, 2009 4:16 PM

“”It’s important to study these explosions with many kinds of telescopes. Our research team combined data from the VLA with data from X-ray and infrared telescopes to piece together some of the physical conditions of the blast,” said Derek Fox of Pennsylvania State University. ”

And what did the spectra say about what elements were present? Any metals?

Lawrence B. Crowell
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Lawrence B. Crowell
October 28, 2009 8:36 PM
The value for z is z = a(T)/a(t) – 1, for a(t) the radius of a region at time T and a(t) the radius much earlier. The Hubble relationship v = Hd indicates an approximate linear relationship with that radius and time. So for a(t) = 13.7 a(t) = .7 this would give z = 18.6, which is rather astounding. Of course out to the CMB with t = 3e5 and T = 1.37e10 one gets a z ~ 10^5. So an optical ~ 1 micron photon gets expanded into a .1cm photon, which is about right. I would tend to think that a z = 8.1 would put this back to about z = a(T)/a(t) – 1,… Read more »
Black WiD/Oe H/Oe
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October 29, 2009 2:06 AM

The fact that this GRB explosion is so uniform in shape, why wouldn’t they at least speculate on the”texture” of the space surrounding it?
One would think being so soon after the BANG that EVERYTHING would be different at that time, wouldn’t it?

HeadAroundU
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October 29, 2009 3:46 AM

” the GRB didn’t come from a monster star”

I’m so confused. From where did it come from?

Lawrence B. Crowell
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Lawrence B. Crowell
October 29, 2009 5:00 AM

GRB’s probably come from the inspiral collision of two neutron stars. The two neutron stars are in a mutual orbit that inspirals as it loses energy by emitting gravity waves. The Hulse-Taylor observation confirmed this. Eventually the two compact bodies crash into each other with an enormous release of energy.

LC

Lawrence B. Crowell
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Lawrence B. Crowell
October 29, 2009 5:19 AM

I made a statement last night that:

So an optical ~ 1 micron photon gets expanded into a .1cm photon, which is about right.

where I should have written it gets expanded to .1 meter or 10 cm. So this means for 300nm to 600 nm optical wavelength photons the redshifted photons would be stretched out to 3-6 cm. That is about the measured blackbody peak of the CMB.

My estimate on the z, where I got this to be about double the quoted value probably reflects the limits to which the low redshift approximation works. I would have to work with the more general calcuation from the FLRW cosmology spacetime metric .

Cheers LC

SteveZodiac
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SteveZodiac
October 29, 2009 7:32 AM

I can’t wait until we see one that is redshifted to before the big bang

Lawrence B. Crowell
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Lawrence B. Crowell
October 29, 2009 7:43 AM

That would be in the words of Buzz Lightyear, to infinity and beyond! smile

LC

Jon Hanford
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Jon Hanford
October 29, 2009 11:28 AM

I am confused as to some of the observable quantities quoted in the article While GRB 09043 may hold the distance record for GRBs, several papers recently published have found what appears to be galaxies with redshifts over 8! (check out this recent paper made with the newly refurbished HST as evinced here: http://arxiv.org/PS_cache/arxiv/pdf/0909/0909.1803v1.pdf ). And it’s not just galaxies in the HUDF-N but other deep fields (COSMOS, GOODS, Chandra, etc.). Farthest known GRB, possibly. Farthest known object in the universe, highly improbable.

Btw, Thanks to Salacious B. Crumb for a link to the original paper :0

Lawrence B. Crowell
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Lawrence B. Crowell
October 29, 2009 1:03 PM

I just ran a calculation using the more exact formula. A linear redshift grows faster than the general relativistic one. I got z = 7.89 for the distance claimed. That appears to be pretty close.

LC

BeckyWS
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BeckyWS
October 29, 2009 4:00 PM

A little confused by things: if this was entirely observed in the infrared, how do we know it is a GRB? Is it possible it could be a closer object giving off only infrared? Or is there another measure of distance taken that I am missing ?
Apologies if my question is very basic.

Nereid
Member
Nereid
October 29, 2009 4:58 PM

@BeckyWS: it is, as always, entirely possible that we have been fooled by some cosmic coincidence …

However, the location (position on the sky; (RA, Dec)) of the IR object is well within the error circle of the Swift GRB localisation, and there’s nothing with a light curve that resembles a fading GRB nearby … ergo, the IR source IS the GRB.

(there’s a lot more, but it’s more indirect; hopefully the above is enough to get you started …)

Lawrence B. Crowell
Member
Lawrence B. Crowell
October 30, 2009 4:55 AM
The clincher is that atomic spectra, which we know well, are redshifted. So an .5 microns transition line from an atomic species is redshifted to the wave length L = z(5nm), which for z = 8 is 4. microns. That is in the infrared region. This is one reason infrared astronomy is so important. Now we infer these distances and times by observing more local objects and their redshifts. A galaxy 100 million light years away is observed to have Cepheid variables. These have a luminosity/periodicity relationship and from that the distance can be backed out. This was how Ed Hubble came up with his V = Hd relationship, for d = distance H = 71Mpc/(km/sec) and v=… Read more »
BeckyWS
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BeckyWS
October 30, 2009 6:43 AM

Thanks for the replies Nereid and Lawrence.

I have now realised I mis-read the article and thought that the initial burst was only in infra-red, as well as the afterglow, hence my confusion about how it could be termed a GRB…. :-S
Quick astro-blog catch up sometimes not a good idea!

Jon Hanford
Member
Jon Hanford
October 30, 2009 9:44 AM

A quick reply to Aqua’s question of the composition of the GRB derived from its spectra. My guess (after reading the paper) is that the spectra were too low in resolution to reliably infer the presence of other possibly constituents (which I believe were gathered with the 2.1m TNG scope). Of course followup with larger ground-based and orbiting observatories are probably already being planned. Due to its extreme distance, GRB 090423 would probably exhibit a low metallicity.

Jon Hanford
Member
Jon Hanford
October 30, 2009 10:55 AM
Some followup work on this GRB got me thinking (for once!), might this observation tie into the long-sought but currently undetected Pop III stars, presumably short-lived, massive, extremely powerful sources, already invoked to some degree by some astronomers to (partially, at least) have some role in the universe re-ionization epoch? Or is there good evidence in favor of a distant GRB popping up at this time? Clearly time to perform an extensive, deep multiwavelength study of this object. I strongly feel that GRB 0909423 originated in a galaxy (as almost all GRBs detected). I suspect the host galaxy is located in a newly forming galaxy cluster (too faint currently for our ground-based or space-based observatories). Telescopes like the… Read more »
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