When Was the First Light in the Universe?

When Was the First Light in the Universe?


The speed of light gives us an amazing tool for studying the Universe. Because light only travels a mere 300,000 kilometers per second, when we see distant objects, we’re looking back in time.

You’re not seeing the Sun as it is today, you’re seeing an 8 minute old Sun. You’re seeing 642 year-old Betelgeuse. 2.5 million year-old Andromeda. In fact, you can keep doing this, looking further out, and deeper into time. Since the Universe is expanding today, it was closer in the past.

Run the Universe clock backwards, right to the beginning, and you get to a place that was hotter and denser than it is today.  So dense that the entire Universe shortly after the Big Bang was just a soup of protons, neutrons and electrons, with nothing holding them together.

Illustration of the Big Bang Theory
The Big Bang Theory: A history of the Universe starting from a singularity and expanding ever since. Credit: grandunificationtheory.com

In fact, once it expanded and cooled down a bit, the entire Universe was merely as hot and as dense as the core of a star like our Sun. It was cool enough for ionized atoms of hydrogen to form.

Because the Universe has the conditions of the core of a star, it had the temperature and pressure to actually fuse hydrogen into helium and other heavier elements. Based on the ratio of those elements we see in the Universe today: 74% hydrogen, 25% helium and 1% miscellaneous, we know how long the Universe was in this “whole Universe is a star” condition.

It lasted about 17 minutes. From 3 minutes after the Big Bang until about 20 minutes after the Big Bang.  In those few, short moments, clowns gathered all the helium they would ever need to haunt us with a lifetime of balloon animals.

The fusion process generates photons of gamma radiation. In the core of our Sun, these photons bounce from atom to atom, eventually making their way out of the core, through the Sun’s radiative zone, and eventually out into space. This process can take tens of thousands of years. But in the early Universe, there was nowhere for these primordial photons of gamma radiation to go. Everywhere was more hot, dense Universe.

The Universe was continuing to expand, and finally, just a few hundred thousand years after the Big Bang, the Universe was finally cool enough for these atoms of hydrogen and helium to attract free electrons, turning them into neutral atoms.

Artist's impression of how huge cosmic structures deflect photons in the cosmic microwave background (CMB). Credit: ESA and the Planck Collaboration
Artist’s impression of how huge cosmic structures deflect photons in the cosmic microwave background (CMB). Credit: ESA and the Planck Collaboration

This was the moment of first light in the Universe, between 240,000 and 300,000 years after the Big Bang, known as the Era of Recombination. The first time that photons could rest for a second, attached as electrons to atoms. It was at this point that the Universe went from being totally opaque, to transparent.

And this is the earliest possible light that astronomers can see. Go ahead, say it with me: the Cosmic Microwave Background Radiation. Because the Universe has been expanding over the 13.8 billion years from then until now, the those earliest photons were stretched out, or red-shifted, from ultraviolet and visible light into the microwave end of the spectrum.

If you could see the Universe with microwave eyes, you’d see that first blast of radiation in all directions. The Universe celebrating its existence.

After that first blast of light, everything was dark, there were no stars or galaxies, just enormous amounts of these primordial elements. At the beginning of these dark ages, the temperature of the entire Universe was about 4000 kelvin. Compare that with the 2.7 kelvin we see today. By the end of the dark ages, 150 million years later, the temperature was a more reasonable 60 kelvin.

Artist's concept of the first stars in the Universe turning on some 200 million years after the Big Bang. These first suns were made of almost pure hydrogen and helium. They and later generations of stars cooked up the heavier elements from these simple ones. Credit: NASA/WMAP Science Team
Artist’s concept of the first stars in the Universe turning on some 200 million years after the Big Bang. These first suns were made of almost pure hydrogen and helium. They and later generations of stars cooked up the heavier elements from these simple ones. Credit: NASA/WMAP Science Team

For the next 850 million years or so, these elements came together into monster stars of pure hydrogen and helium. Without heavier elements, they were free to form stars with dozens or even hundreds of times the mass of our own Sun. These are the Population III stars, or the first stars, and we don’t have telescopes powerful enough to see them yet. Astronomers indirectly estimate that those first stars formed about 560 million years after the Big Bang.

Then, those first stars exploded as supernovae, more massive stars formed and they detonated as well. It’s seriously difficult to imagine what that time must have looked like, with stars going off like fireworks. But we know it was so common and so violent that it lit up the whole Universe in an era called reionization. Most of the Universe was hot plasma.

Scientists have used ESO’s Very Large Telescope to probe the early Universe at several different times as it was becoming transparent to ultraviolet light. This brief but dramatic phase in cosmic history — known as reionisation — occurred around 13 billion years ago. By carefully studying some of the most distant galaxies ever detected, the team has been able to establish a timeline for reionisation for the first time. They have also demonstrated that this phase must have happened quicker than astronomers previously thought.
Scientists have used ESO’s Very Large Telescope to probe the early Universe at several different times as it was becoming transparent to ultraviolet light. This brief but dramatic phase in cosmic history — known as reionisation — occurred around 13 billion years ago.

The early Universe was hot and awful, and there weren’t a lot of the heavier elements that life as we know it depends on. Just think about it. You can’t get oxygen without fusion in a star, even multiple generations. Our own Solar System is the result of several generations of supernovae that exploded, seeding our region with heavier and heavier elements.

As I mentioned earlier in the article, the Universe cooled from 4000 kelvin down to 60 kelvin. About 10 million years after the Big Bang, the temperature of the Universe was 100 C, the boiling point of water. And then 7 million years later, it was down to 0 C, the freezing point of water.

This has led astronomers to theorize that for about 7 million years, liquid water was present across the Universe… everywhere. And wherever we find liquid water on Earth, we find life.

An artists illustration of the early Universe. Image Credit: NASA
An artists illustration of the early Universe. Image Credit: NASA

So it’s possible, possible that primitive life could have formed with the Universe was just 10 million years old. The physicist Avi Loeb calls this the habitable Epoch of the Universe. No evidence, but it’s a pretty cool idea to think about.

I always find it absolutely mind bending to think that all around us in every direction is the first light from the Universe. It’s taken 13.8 billion years to reach us, and although we need microwave eyes to actually see it, it’s there, everywhere.

How Many Galaxies Are There in the Universe?

How Many Galaxies Are There in the Universe?


The wonderful thing about science is that it’s constantly searching for new evidence, revising estimates, throwing out theories, and sometimes discovering aspects of the Universe that we never realized existed.

The best science is skeptical of itself, always examining its own theories to find out where they could be wrong, and seriously considering new ideas to see if they better explain the observations and data.

What this means is that whenever I state some conclusion that science has reached, you can’t come back a few years later and throw that answer in my face. Science changes, it’s not my fault.

I get it, VY Canis Majoris isn’t the biggest star any more, it’s whatever the biggest star is right now. UY Scuti? That what it is today, but I’m sure it’ll be a totally different star when you watch this in a few years.

What I’m saying is, the science changes, numbers update, and we don’t need to get concerned when it happens. Change is a good thing. And so, it’s with no big surprise that I need to update the estimate for the number of galaxies in the observable Universe. Until a couple of weeks ago, the established count for galaxies was about 200 billion galaxies.

Jacinta studies distant galaxies like those shown in this image from the Hubble Space Telescope, using the new 'stacking' technique to gather information only available through radio telescope observations. Credit: NASA, STScI, and ESA.
Jacinta studies distant galaxies like those shown in this image from the Hubble Space Telescope, using the new ‘stacking’ technique to gather information only available through radio telescope observations. Credit: NASA, STScI, and ESA.

But a new paper published in the Astrophysics Journal revised the estimate for the number of galaxies, by a factor of 10, from 200 billion to 2 trillion. 200 billion, I could wrap my head around, I say billion all the time. But 2 trillion? That’s just an incomprehensible number.

Does that throw all the previous estimates for the number of stars up as well? Actually, it doesn’t.

The observable Universe measures 13.8 billion light-years in all directions. What this means is that at the very edge of what we can see, is the light left that region 13.8 billion years ago. Furthermore, the expansion of the Universe has carried to those regions 46 billion light-years away.

Does that make sense? The light you’re seeing is 13.8 billion light-years old, but now it’s 46 billion light-years away. What this means is that the expansion of space has stretched out the light from all the photons trying to reach us.

What might have been visible or ultraviolet radiation in the past, has shifted into infrared, and even microwaves at the very edge of the observable Universe.

Since astronomers know the volume of the observable Universe, and they can calculate the density of the Universe, they know the mass of the entire Universe. 3.4 x 10^54 kilograms including regular matter and dark matter.  They also know the ratio of regular matter to dark matter, so they can calculate the total amount of regular mass in the Universe.

In the past, astronomers divided that total mass by the number of galaxies they could see in the original Hubble data and determined there were about 200 billion galaxies.

Now, astronomers used a new technique to estimate the galaxies and it’s pretty cool. Astronomers used the Hubble Space Telescope to peer into a seemingly empty part of the sky and identified all the galaxies in it. This is the Hubble Ultra Deep Field, and it’s one of the most amazing pictures Hubble has ever captured.

The Hubble Ultra Deep Field seen in ultraviolet, visible, and infrared light. Image Credit: NASA, ESA, H. Teplitz and M. Rafelski (IPAC/Caltech), A. Koekemoer (STScI), R. Windhorst (Arizona State University), and Z. Levay (STScI)
The Hubble Ultra Deep Field seen in ultraviolet, visible, and infrared light. Image Credit: NASA, ESA, H. Teplitz and M. Rafelski (IPAC/Caltech), A. Koekemoer (STScI), R. Windhorst (Arizona State University), and Z. Levay (STScI)

Astronomers painstakingly converted this image of galaxies into a 3-dimensional map of galaxy size and locations. Then, they used their knowledge of galaxy structure closer to home to provide a more accurate estimate of what the galaxies must look like, out there, at the very edge of our observational ability.

For example, the Milky Way is surrounded by about 50 satellite dwarf galaxies, each of which has a fraction of the mass of the Milky Way.

By recognizing which were the larger main galaxies, they could calculate the distribution of smaller, dimmer dwarf galaxies that weren’t visible in the Hubble images.

In other words, if the distant Universe is similar to the nearby Universe, and this is one of the principles of modern astronomy, then the distant galaxies have the same structure as nearby galaxies.

It doesn’t mean that the Universe is bigger than we thought, or that there are more stars, it just means that the Universe contains more galaxies, which have less stars in them. There are the big main galaxies, and then a smooth distribution curve of smaller and smaller galaxies down to the tiny dwarf galaxies. The total number of stars comes out to be the same number.

The Fornax dwarf galaxy is one of our Milky Way’s neighbouring dwarf galaxies. The Milky Way is, like all large galaxies, thought to have formed from smaller galaxies in the early days of the Universe. These small galaxies should also contain many very old stars, just as the Milky Way does, and a team of astronomers has now shown that this is indeed the case. This image was composed from data from the Digitized Sky Survey 2. Credit: ESO
The Fornax dwarf galaxy is one of our Milky Way’s neighbouring dwarf galaxies. Credit: ESO

The galaxies we can see are just the tip of the galactic iceberg. For every galaxy we can see, there are another 9, smaller fainter galaxies that we can’t see.

Of course, we’re just a few years away from being able to see these dimmer galaxies. When NASA’s James Webb Space Telescope launches in October, 2018, it’s going to be carrying a telescope mirror with 25 square meters of collecting surface, compared to Hubble’s 4.5 square meters.

Furthermore, James Webb is an infrared telescope, a specialized tool for looking at cooler objects, and galaxies which are billions of light-years away. The kinds of galaxies that Hubble can only hint at, James Webb will be able to see directly.

So, why don’t we see galaxies in all directions with our eyeballs?  This is actually an old conundrum, proposed by Wilhelm Olbers in the 1700, appropriately named Olber’s Paradox.  We did a whole article on it, but the basic idea is that if you look in any direction, you’ll eventually hit a star. It could be close, like the Sun, or very far away, but whatever the case, it should be stars in all directions. Which means that the entire night sky should be as bright as the surface of a star. Clearly it isn’t, but why isn’t it?

In fact, with 10 times the number of galaxies, you could restate the paradox and say that in every direction, you should be looking at a galaxy, but that’s not what you see.

A partial map of the distribution of galaxies in the SDSS, going out to a distance of 7 billion light years. The amount of galaxy clustering that we observe today is a signature of how gravity acted over cosmic time, and allows as to test whether general relativity holds over these scales. (M. Blanton, SDSS)
A partial map of the distribution of galaxies in the SDSS, going out to a distance of 7 billion light years. The amount of galaxy clustering that we observe today is a signature of how gravity acted over cosmic time, and allows as to test whether general relativity holds over these scales. (M. Blanton, SDSS)

Except you are. Everywhere you look, in all directions, you’re seeing galaxies. It’s just that those galaxies are red-shifted from the visible spectrum into the infrared spectrum, so your eyeballs can’t perceive them. But they’re there.

When you see the sky in microwaves, it does indeed glow in all directions. That’s the Cosmic Microwave Background Radiation, shining behind all those galaxies.

It turns out the Universe has 10 times more galaxies than previously estimated – 2 trillion galaxies. Not 10 times the stars or mass, those numbers have stayed the same.

And, once James Webb launches, those numbers will be fine-tuned again to be even more precise. 1.5 trillion? 3.4 trillion? Stay tuned for the better number.

Dark Energy Ignited By Gamma-Ray Bursts?

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Dark energy… We’re still not exactly sure of what it is or where it comes from. Is it possible this mysterious force is what’s driving the expansion of the Universe? A group of astronomers from the universities in Warsaw and Naples, headed by Dr. Ester Piedipalumbo, are taking a closer look at a way to measure this energetic enigma and they’re doing it with one of the most intense sources they can find – gamma-ray bursts.

“We are able to determine the distance of an explosion on the basis of the properties of the radiation emitted during gamma-ray bursts. Given that some of these explosions are related to the most remote objects in space that we know about, we are able, for the first time, to assess the speed of space-time expansion even in the relatively early periods after the Big Bang,” says Prof. Marek Demianski (FUW).

What spawned this new method? In 1998, astronomers were measuring the energy given off by Type Ia supernovae events and realized the expelled forces were consistent. Much like the standard candle model, this release could be used to determine cosmic distances. But there was just one caveat… The more remote the event, the weaker the signature.

While these faint events weren’t lighting up the night, they were lighting up the way science thought about things. Perhaps these Type Ia supernovae were farther away than surmised… and if this were true, perhaps instead of slowing down the expansion of the Universe, maybe it was accelerating! In order to set the Universal model to rights, a new form of mass-energy needed to be introduced – dark energy – and it needed to be twenty times more than what we could perceive. “Overnight, dark energy became, quite literally, the greatest mystery of the Universe,” says Prof. Demianski. In a model put forward by Einstein it’s a property of the cosmological constant – and another model suggests accelerated expansion is caused by some unknown scalar field. “In other words, it is either-or: either space-time expands by itself or is expanded by a scalar physical field inside it,” says Prof. Demianski.

So what’s the point behind the studies? If it is possible to use a gamma-ray burst as a type of standard candle, then astronomers can better assess the density of dark energy, allowing them to further refine models. If it stays monophonic, it belongs to the cosmological constant and is a property of space-time. However, if the acceleration of the Universe is the property of a scalar field, the density of dark energy would differ. “This used to be a problem. In order to assess the changes in the density of dark energy immediately after the Big Bang, one needs to know how to measure the distance to very remote objects. So remote that even Type Ia supernovae connected to them are too faint to be observed,” says Demianski.

Now the real research begins. Gamma-ray bursts needed to have their energy levels measured and to do that accurately meant looking at previous studies which contained verified sources of distance, such as Type Ia supernovae. “We focused on those instances. We knew the distance to the galaxy and we also knew how much energy of the burst reached the Earth. This allowed us to calibrate the burst, that is to say, to calculate the total energy of the explosion,” explains Prof. Demianski. Then the next step was to find statistical dependencies between various properties of the radiation emitted during a gamma-ray burst and the total energy of the explosion. Such relations were discovered. “We cannot provide a physical explanation of why certain properties of gamma-ray bursts are correlated,” points out Prof. Demianski. “But we can say that if registered radiation has such and such properties, then the burst had such and such energy. This allows us to use bursts as standard candles, to measure distances.”

Dr. Ester Piedipalumbo and a team of researchers from the universities in Warsaw and Naples then took up the gauntlet. Despite this fascinating new concept, the reality is that distant gamma-ray bursts are unusual. Even with 95 candidates listed in the Amanti catalogue, there simply wasn’t enough information to pinpoint dark energy. “It is quite a disappointment. But what is important is the fact that we have in our hands a tool for verifying hypotheses about the structure of the Universe. All we need to do now is wait for the next cosmic fireworks,” concludes Prof. Demianski.

Let the games begin…

Original Story Source: University of Warsaw Press Release. For Further Reading: Cosmological models in scalar tensor theories of gravity and observations: a class of general solutions.