Mega-star explosion most distant object ever seen

[The Spartan]

Yahoo News

Mega-star explosion most distant object ever seen
Wed Oct 28, 7:32 pm ET

PARIS (AFP) – It took 13 billion years to reach Earth, but astronomers have seen the light of an exploding mega-star that is the most distant object ever detected, two studies published Thursday reported.

The stunning gamma-ray burst (GRB) was observed by two teams of researchers in April, and opens a window onto a poorly known period when the Universe was in its infancy.

GRBs are the most violent explosions known to exist, and can be 10 million times more luminous than the brightest of galaxies.

They accompany the catastrophic death of a massive star, and are probably triggered by the collapse of the star's centre into a black hole.

Dubbed GRB 090423, the new discovery was first spotted by the NASA satellite Swift.

Astronomers alerted to the find trained several of Earth's largest telescopes skyward just in time to see the gamma-ray burst's fading afterglow.

The discovery is especially exciting for scientists because the explosion occurred during the so-called "cosmic dark ages", which started a mere 400,000 years after the Big Bang set the Universe in motion some 13.7 billion years ago.

During this period, free electrons and protons combined to form neutral atoms with the same number of positive and negative charges, resulting in an opaque -- or "dark" -- universe.

Not until 800 to 900 million years after the Big Bang were atoms and molecules "re-ionised", or electrically charged, resulting in the relatively transluscent inter-galactic medium we see today.

GRB 090423 flashed and crashed toward the end of these dark ages, making it the oldest object ever seen.

"This observation allows us to begin exploring the last blank space on our map of the Universe," said Nial Tanvir, a professor at the University of Leicester and lead author of one of the studies.

"It is tremendously exciting to be looking back in time to an era when the first stars were just switching on," said Andrew Levan, a professor at the University of Warwick in Britain and co-author of the same study.

The previous record holder for oldest object is at least 150 million years younger than the newly discovered gamma-ray burst.

Both studies were published in the British science journal Nature.

Not really much I can add, but I still thought it was interesting enough to share with the class.

Though this is the first I've heard of the cosmic dark ages, as they call it. I'd not heard about that before.

[Themightytom]

A mega star travelled that far in 400,000 years? That really gives you a sense of the power behind the big bang!

[Steel]

A mega star travelled that far in 400,000 years? That really gives you a sense of the power behind the big bang!

Eeerm... things dont travel as such due to the big bang. There never was a "bang" it was just that at a certain point in time space expanded so that points become further apart without objects actually moving. Strange concept. This megastar's location could have started well within sight of us in the very very early universe and then been carried away out of causal contact during cosmic inflation, and only now that the expansion of the universe has slowed has the point come back into contact with us (and in the intervening time a massive star formed and exploded).

[Sky Captain]

Now that has to be a real monster star if it burned out it`s nuclear fuel in few hundred thousand years and blew up.

[Rahvin]

The 400,000 year figure is being misunderstood. Read closer.

The discovery is especially exciting for scientists because the explosion occurred during the so-called "cosmic dark ages", which started a mere 400,000 years after the Big Bang set the Universe in motion some 13.7 billion years ago.

...

Not until 800 to 900 million years after the Big Bang were atoms and molecules "re-ionised", or electrically charged, resulting in the relatively transluscent inter-galactic medium we see today.

The explosion took place during the "cosmic dark age," which began approx. 400,000 years after T=0 and ended roughly 800-900 million years later.

That simply means the star had to be less than 800-900 million years old, by itself. Younger, obviously, because stellar formation didn't begin immediately...but not just 400,000 years. That's absurdly short for a star to form and die - formation alone is typically though to take hundreds of thousands to millions of years.

Even so, less than a billion years is still young for a star to die, but the bigger ones tend to burn out faster.

The important part of the article is that the even took place 13 billion lightyears away, and that it's the most distant (and thus oldest) event seen so far.

I dislike the way reporters discuss cosmology. They perpetuate the idea that "the Big Bang" was an "explosion" or that it ever stopped. Space expands. It's expanding right now. The distance between any two points is increasing without any actual motion involved. There was no "exploding singularity," the "Big Bang" was not some cosmic supernuke that exploded us all into existence. That's the Creationist version of the Big Bang, and it has prescious little to do with the real Universe. Hell, even the term "Big Bang" was coined in mockery by a man who was championing what was at the time a competing hypothesis. Unfortunately, it sounded too good and stuck.

[Serafina]

Holy shit - our universe is awesome. And so are we, if we can figure it out...
Seriously, i learned a lot about it just from this article.

Can someone elaborate on the whole "Dark Age"-stuff?

[Oskuro]

I'm also curious about that whole "opaqueness" bussiness. Is the article saying that the interstellar medium was opaque at some point? What are they talking about?

[CaptainChewbacca]

Holy shit - our universe is awesome. And so are we, if we can figure it out...
Seriously, i learned a lot about it just from this article.

Can someone elaborate on the whole "Dark Age"-stuff?

I'm also curious about that whole "opaqueness" bussiness. Is the article saying that the interstellar medium was opaque at some point? What are they talking about?

After the universe came into being (leaving aside the how for now) there was for the most part just a cloud of really energitic particles swirling around. All of these particles were atomic or subatomic, nothing bigger. Eventually, as the universe expanded and cooled, these particles formed hydrogen. From that point, you had a rougly-even distribution of hydrogen across the universe. Over time, gravity collapsed local sources of hydrogen into stars. Once the stars reached sufficient mass to ignite, there was suddenly light in the universe again, which had been absent since the hydrogen-forming process ended. There's your dark age. It was also 'opaque' because shit was alot more dense overall because mass hadn't been localized into stars, galaxies, and superclusters so there wasn't as much 'empty' space.*

Its quite sensible that this star would be so huge. There was literally NOTHING to inhibit its' growth, including a lack of materials due to the size of a nebular nursery. It was the absolute perfect growing conditions for a star.

*While perhaps not technically correct in the academic sense, this is the explanation I would give to my highschool students if asked. I can get more specific if you want.

[Themightytom]

A mega star travelled that far in 400,000 years? That really gives you a sense of the power behind the big bang!

Eeerm... things dont travel as such due to the big bang. There never was a "bang" it was just that at a certain point in time space expanded so that points become further apart without objects actually moving. Strange concept. This megastar's location could have started well within sight of us in the very very early universe and then been carried away out of causal contact during cosmic inflation, and only now that the expansion of the universe has slowed has the point come back into contact with us (and in the intervening time a massive star formed and exploded).

I know the big bang wasn't literally a big bang, maybe I should have used the word "magnitude" to describe the surreal scale of a star "moving". Sure you can learn that "Space is expanding" but this is a hell of a cocneptual bencchmark.

[Steel]

After the universe came into being (leaving aside the how for now) there was for the most part just a cloud of really energitic particles swirling around. All of these particles were atomic or subatomic, nothing bigger. Eventually, as the universe expanded and cooled, these particles formed hydrogen. From that point, you had a rougly-even distribution of hydrogen across the universe. Over time, gravity collapsed local sources of hydrogen into stars. Once the stars reached sufficient mass to ignite, there was suddenly light in the universe again, which had been absent since the hydrogen-forming process ended. There's your dark age. It was also 'opaque' because shit was alot more dense overall because mass hadn't been localized into stars, galaxies, and superclusters so there wasn't as much 'empty' space.*

I think when they refer to opaque they mean that the period when the universe was a very dense soup of particles, long before the formation of any kind of structure like stars or even atoms. That was the time when it was opaque because a photon couldnt travel anywhere without whacking straight into a particle, so everything was in thermal equilibrium. The cosmic microwave background was produced at the instant that the universe expanded such that it stopped being opaque (ie photons dropped out of thermal equilibrium with matter) so you got all the free photons at that time flying off in all directions. Interestingly due to that the CMB contains information about the state of the universe at that point in time.

[Oskuro]

That makes more sense, the way the article explained it, it almost sounded like the whole interstellar medium was opaque at one point, and then some electrochemical properties changed and BAM! Transparency.

[Rahvin]

That makes more sense, the way the article explained it, it almost sounded like the whole interstellar medium was opaque at one point, and then some electrochemical properties changed and BAM! Transparency.

Reporters aren't so good with the whole scientific accuracy thing.

[Simon_Jester]

After the universe came into being (leaving aside the how for now) there was for the most part just a cloud of really energitic particles swirling around. All of these particles were atomic or subatomic, nothing bigger. Eventually, as the universe expanded and cooled, these particles formed hydrogen. From that point, you had a rougly-even distribution of hydrogen across the universe. Over time, gravity collapsed local sources of hydrogen into stars. Once the stars reached sufficient mass to ignite, there was suddenly light in the universe again, which had been absent since the hydrogen-forming process ended. There's your dark age. It was also 'opaque' because shit was alot more dense overall because mass hadn't been localized into stars, galaxies, and superclusters so there wasn't as much 'empty' space.*

Not quite.

There was always light ricocheting around the particle soup. For a few hundred thousand years after the Big Bang, the average temperature of the universe (or, if you prefer, the average kinetic energy of the particle soup) was high enough that atoms could not form; protons and electrons bounced around freely and space was full of the resulting electron-proton plasma. The cosmic background radiation of photons was "coupled" with the plasma, because the plasma was very good at absorbing, scattering, and reradiating light. Over any long distance it was opaque (and glowy. Very glowy).

As space expanded the particles cooled off, eventually reaching the point where hydrogen atoms were stable at an average ambient temperature of ~3000 K. When that happened, the universe suddenly became transparent (and by 'suddenly' I mean 'only took a few millenia, tops'). Hydrogen gas is transparent at most wavelengths, and scatters only a little light compared to a charged particle plasma of the same density. So even without stars, you now had a transparent universe. The Cosmic Microwave Background we see is actually the very red-shifted Cosmic Infrared background of ambient light that was kicking around when this happened; its wavelength has gone up by about a factor of a thousand because the scale of the universe has expanded by that same factor since.

That makes more sense, the way the article explained it, it almost sounded like the whole interstellar medium was opaque at one point, and then some electrochemical properties changed and BAM! Transparency.

Thing is, that's more or less true. If you time-warped back to ~100000 years after the Big Bang and sat in the middle of unremarkable space (far from any unusually dense regions), you'd see what amounted to a red-hot vacuum all around you. Individual particles would be very energetic, but the overall density would still be relatively low. However, even a low density is still enough to block EM radiation over long distances, so you wouldn't be able to see anything except a uniform glowing fog all around you.

It really was an electrochemical shift, and the first combination of protons and electrons into hydrogen atoms, that allowed this to change.

[starslayer]

Even so, less than a billion years is still young for a star to die, but the bigger ones tend to burn out faster.

A star such as the one that produced this GRB lives less than a million years, and could very well have a life-time of only 400,000 years, although it would take almost as long or longer to form. However, it would not have formed until long after the dark ages began.

As for the opaqueness of the early universe, the others have pretty much covered it, but I would add that T=~400,000 years is properly known as the "surface of last scattering". After that point, but until the first stars formed, the universe was dark and opaque over very large distances. Once the first stars reionized the free gas in the universe with their radiation, the gas became fully transparent again. This has to do with quantum mechanics; it turns out that a free charged particle cannot absorb a photon, because doing so would violate energy/momentum conservation. Instead, the photon is scattered.

[Sriad]

Even so, less than a billion years is still young for a star to die, but the bigger ones tend to burn out faster.

A star such as the one that produced this GRB lives less than a million years, and could very well have a life-time of only 400,000 years, although it would take almost as long or longer to form. However, it would not have formed until long after the dark ages began.

As for the opaqueness of the early universe, the others have pretty much covered it, but I would add that T=~400,000 years is properly known as the "surface of last scattering". After that point, but until the first stars formed, the universe was dark and opaque over very large distances. Once the first stars reionized the free gas in the universe with their radiation, the gas became fully transparent again. This has to do with quantum mechanics; it turns out that a free charged particle cannot absorb a photon, because doing so would violate energy/momentum conservation. Instead, the photon is scattered.

Are there any estimates of the mega-star's mass? I wonder whether the cosmos-wide higher particle density could lead to the formation of much larger (and faster burning (and heavy-element producing)) stars than we see today. The universe was about 30 times more packed together at the time they're observing.

[starslayer]

Are there any estimates of the mega-star's mass? I wonder whether the cosmos-wide higher particle density could lead to the formation of much larger (and faster burning (and heavy-element producing)) stars than we see today. The universe was about 30 times more packed together at the time they're observing.

There are two possible mass ranges for this kind of progenitor star: ~50-140 M_sol, or >250 M_sol. In between, the supernova leaves no remnant, because the pair production instability that occurs in the core leads directly to an explosion; a GRB most likely requires a black hole.

For star formation, it wasn't so much the particle density as the lack of heavy elements that led to such massive stars. Even today, there are gas clouds massive enough to form a several hundred solar mass star, but their high metallicity prevents them from doing so (the CNO process dominates over the p-p chain in massive Pop I stars, greatly increasing the luminosity of the star, and thus greatly lowering the Eddington limit).

[Simon_Jester]

The Eddington limit is the upper bound on the stable mass of a star, right?

[starslayer]

The Eddington limit is the upper bound on the stable mass of a star, right?

Yes; it comes from the fact that eventually a star would be so bright that its radiation pressure would overcome its gravity, and it would gently puff off its outer layers until it regained equilibrium. This limit is also referred to as the "Eddington luminosity," although that's technically specific to each star.

[Wyrm]

The Eddington limit is the upper bound on the stable mass of a star, right?

Yes; it comes from the fact that eventually a star would be so bright that its radiation pressure would overcome its gravity, and it would gently puff off its outer layers until it regained equilibrium. This limit is also referred to as the "Eddington luminosity," although that's technically specific to each star.

Thing is, the Eddington limit depends on metallicity. The more metals in a star, the lower the limit. The young universe was almost pure hydrogen and helium — no metals to speak of, so the Eddington limit was much higher in the past than in the present, allowing for crazy huge stars that would go up in what we see today as CRBs.

[starslayer]

Thing is, the Eddington limit depends on metallicity. The more metals in a star, the lower the limit. The young universe was almost pure hydrogen and helium — no metals to speak of, so the Eddington limit was much higher in the past than in the present, allowing for crazy huge stars that would go up in what we see today as CRBs.

Which I mentioned, although I probably should have explained what the hell the CNO process and p-p chain actually are:

(the CNO process dominates over the p-p chain in massive Pop I stars, greatly increasing the luminosity of the star, and thus greatly lowering the Eddington limit)

[Steel]

Thing is, the Eddington limit depends on metallicity. The more metals in a star, the lower the limit. The young universe was almost pure hydrogen and helium — no metals to speak of, so the Eddington limit was much higher in the past than in the present, allowing for crazy huge stars that would go up in what we see today as CRBs.

Which I mentioned, although I probably should have explained what the hell the CNO process and p-p chain actually are:

(the CNO process dominates over the p-p chain in massive Pop I stars, greatly increasing the luminosity of the star, and thus greatly lowering the Eddington limit)

That and the quaint habit of astrophysicists to refer to everything that isn't hydrogen as 'metal'.

[Wyrm]

That and the quaint habit of astrophysicists to refer to everything that isn't hydrogen as 'metal'.

Stuff not hydrogen or helium is a metal. Get it right!

[Surlethe]

Funny, but not particularly on topic, guys.