Posted on 12/02/2018 5:13:05 AM PST by LibWhacker
Have you ever stopped to wonder exactly how much light has been produced by all the stars in the Universe, over all the time that has passed? Well, now you can wonder no more. An international team of astronomers has actually calculated the amount of starlight in the cosmos.
And it's teaching us new things about the early years of our Universe. In the time since the Big Bang - roughly 13.7 billion years - our Universe has produced many, many galaxies, and many more stars. Perhaps around two trillion galaxies, containing around a trillion-trillion stars. For decades, scientists have known that knowing how much light these stars have produced over the course of the Universe's lifespan would be a powerful tool for understanding the early Universe, as well as the history of star formation. But, well, it's not exactly an easy thing to measure. While there are a lot of stars out there, producing many photons, space is incredibly vast, and starlight incredibly dim. There's also interference from zodiacal light and the Milky Way's own faint glow. The Universe's starlight cannot really be observed directly. But astrophysicist Marco Ajello of Clemson University and his team discovered an indirect method of quantifying starlight. They used gamma ray photons. "These are photons that are high energy, typically a billion times the energy of visible light," Ajello told ScienceAlert.
"While travelling through space, gamma rays can be absorbed through interactions with starlight photons. And if there are many starlight photons, there will be more absorptions; so we can count the number of absorptions that we see to understand the density of the starlight of the photon field between us and the gamma ray source." Using nine years' worth of data from NASA's Fermi Gamma-ray Space Telescope, Ajello and his team analysed the light from 739 blazars (strong gamma-ray sources) throughout the Universe to determine the rate of absorption into the extragalactic background light (EBL), the Universe's accumulated background radiation. This gave them the density of starlight photons in the EBL - and, because the blazars are at different distances, they were able to do so across a range of time periods. Once they accounted for and subtracted light from other sources, such as the glowing accretion discs around supermassive black holes, they could multiply this density by the volume of the Universe to arrive at the number of photons produced by stars since the beginning of time.
"We basically have a tool, like a book, to tell the stories of starlight across the history of the Universe, and finally we found it, and we can just read it," Ajello said. "So we did. We measured the entire star formation history of the Universe." It is pretty simple to explain, but it was painstaking and complex to actually do. It took the team three years - and it was worth it. We now know that, as of the time Fermi's data was collected, the Universe's stars had produced 4x1084 photons. Do you need that spelled out? Here: 4,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000. Yep, it's a four followed by 84 zeroes. That's a pretty cool trivia fact, so file it up your sleeve for later. But you bet the science actually gets much cooler. Because that cool number actually lifts the veil on a particularly mysterious time in our Universe's history - the Epoch of Reionisation, which started around 500 million years after the Big Bang. We often hear the term "holy grail" chucked around, but the EoR really IS one.
It's basically when the Universe's lights switched on. Before the EoR, space was opaque. Then something came along and ionised all the neutral hydrogen, so that radiation - including light - could stream freely through the Universe. "With our measurement, we can reach the very first billion years of the Universe, and that's a very interesting time of the Universe, so distant from us that all the really powerful telescopes can't really see. The objects there are so far away and so faint that we can't really see them. Instead, we still see the light from those objects," Ajello explained. The team found two things of note in that time: a very large number of UV photons, which was expected for the reionisation process; and that the sources of those UV photons were populations of irregular galaxies - small, blobby, asymmetrical galaxies that produce a lot of UV radiation. These could be the drivers behind reionisation. It's expected that the James Webb Space Telescope, scheduled for a 2021 launch, could tell us more about the EoR. Meanwhile, Ajello and his team are going to apply their book of the stars to a deeper study of the cosmos - such as the rate of the Universe's expansion, the Hubble constant, which has been really difficult to pin down. "It turns out our measurement is very sensitive to the expansion rate of the Universe," Ajello said. "This can be used to make a measurement of the Hubble Constant right now, so that's something that we're going to do." The team's research has been published in the journal Science .
Thank you for being so intellectually honest as to include the proviso "as far as I can see."
The question is now: How far can you see?
I don't wish to denigrate your academic accomplishments (you don't cite them, so for all I know you could have a Bachelor's in Agriculture, etc.) - but are you really qualified at all to even begin to understand the Science behind this data, and its possible implications?
Regards,
Fiat Lux
you know when you look in a hole and see the bottom it is only the beginning..man knows nothing
Not many on FR.
Anyhow, 52! is another really cool number.
What is that number, you might ask?
52! can also be written as 8.0658175e+67.
Most of us would know this number as the possible combinations when shuffling a deck of cards. It is a number that is so massively huge that it is unlikely that any two decks of cards, ever, in all of humanity, have been shuffled the same, or ever will.
I was curious and looked it up. Most on FR would ask, "Who cares?" I cared.
Why?
Before the EoR (Epoch of Reionisation), space was opaque. - Darkness was upon the face of the waters.
Then something came along and ionised all the neutral hydrogen, so that radiation - including light - could stream freely through the Universe. - And God said, "Let there be light."
That’s almost as many as fraudulent demonrat ballots.....
The were used to bias the grid on vacuum tubes in battery powered radios.
The advent of transistors ultimately removed the need. No need, no market, no market, no more production...
To be fair, the exponent is 84, that’s twice as good as 42...
“O Deep Thought computer," he said, "the task we have designed you to perform is this. We want you to tell us...." he paused, "The Answer."
"The Answer?" said Deep Thought. "The Answer to what?"
"Life!" urged Fook. "The Universe!" said Lunkwill. "Everything!" they said in chorus.
Deep Thought paused for a moment's reflection. "Tricky," he said finally. "But can you do it?" Again, a significant pause. "Yes," said Deep Thought, "I can do it."
"There is an answer?" said Fook with breathless excitement.
"Yes," said Deep Thought. "Life, the Universe, and Everything. There is an answer. But, I'll have to think about it."
... Fook glanced impatiently at his watch. ;“How long?;” he said.
;“Seven and a half million years,;” said Deep Thought.
Lunkwill and Fook blinked at each other. ;“Seven and a half million years...!;” they cried in chorus.
;“Yes,;” declaimed Deep Thought, ;“I said I;’d have to think about it, didn;’t I?"
[Seven and a half million years later.... Fook and Lunkwill are long gone, but their descendents continue what they started]
"We are the ones who will hear," said Phouchg, "the answer to the great question of Life....!"
"The Universe...!" said Loonquawl.
"And Everything...!"
"Shhh," said Loonquawl with a slight gesture.
"I think Deep Thought is preparing to speak!"
There was a moment's expectant pause while panels slowly came to life on the front of the console. Lights flashed on and off experimentally and settled down into a businesslike pattern. A soft low hum came from the communication channel.
"Good Morning," said Deep Thought at last.
"Er..good morning, O Deep Thought" said Loonquawl nervously, "do you have...er, that is..."
"An Answer for you?" interrupted Deep Thought majestically. "Yes, I have."
The two men shivered with expectancy. Their waiting had not been in vain. "There really is one?" breathed Phouchg.
"There really is one," confirmed Deep Thought. "To Everything? To the great Question of Life, the Universe and everything?"
"Yes." Both of the men had been trained for this moment, their lives had been a preparation for it, they had been selected at birth as those who would witness the answer, but even so they found themselves gasping and squirming like excited children.
"And you're ready to give it to us?" urged Loonsuawl.
"I am."
"Now?"
"Now," said Deep Thought.
They both licked their dry lips.
"Though I don't think," added Deep Thought. "that you're going to like it."
"Doesn't matter!" said Phouchg. "We must know it! Now!"
"Now?" inquired Deep Thought.
"Yes! Now..."
"All right," said the computer, and settled into silence again.
The two men fidgeted. The tension was unbearable.
"You're really not going to like it," observed Deep Thought.
"Tell us!"
"All right," said Deep Thought. "The Answer to the Great Question..."
"Yes..!"
"Of Life, the Universe and Everything..." said Deep Thought.
"Yes...!"
"Is..." said Deep Thought, and paused.
"Yes...!"
"Is..."
"Yes...!!!...?"
"Forty-two," said Deep Thought, with infinite majesty and calm.”
from Douglas Adams, The Hitchhiker's Guide to the Galaxy
Given all the variables and all the assumptions, this is the epitome of “scientific wild-a**ed guess” or SWAG...
They must have a lot of extra fingers and toes to count that high....
The unaided eye can discern the Andromeda galaxy.
That's 780 kiloparsecs (2.5 million light-years) from Earth.
If you that’s a big number, it’s nothing to the odds that it’s right.
They forgot to count anti-photons that are traveling in the opposite direction.
“At some point, don’t you have enough zeroes?” To paraphrase The Big Zero.
How long does it take a trillion monkeys to count to a trillion?
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