What Was It Like When Galaxies Formed The Greatest Number Of Stars?
“The star-formation rate declined slowly and steadily for a few billion years, corresponding to an epoch where the Universe was still matter-dominated, just consisting of more processed and aged material. There were fewer mergers by number, but this was partially compensated for by the fact that larger structures were merging, leading to larger regions where stars formed.
But right around 6-to-8 billion years of age, the effects of dark energy began to make their presence known on the star formation rate, causing it to plummet precipitously. If we want to see the largest bursts of star formation, we have no choice but to look far away. The ultra-distant Universe is where star formation was at its maximum, not locally.”
In a myriad of locations, throughout our galaxy and almost all the galaxies in the known Universe, new stars form wherever a cloud of gas is triggered into collapsing. From the Orion Nebula to dozens of others in our own galaxy, new stars form thousands-at-a-time in regions all throughout our local neighborhood. But as spectacular as these sights are, they’re much, much rarer than they were a long time ago. In fact, we formed stars at a rate that was 30 times faster than today back when the Universe was young. For the last 11 billion years, we’ve been forming fewer and fewer stars everywhere we look.
The Universe is changing even today, and fewer and fewer stars are being newly created as time goes on. There are many reasons why; come learn them today!
Remnants Of Our Solar System’s Formation Found In Our Interplanetary Dust
“Our naive picture of a disk that gets very hot, fragments, and cools to then form planets may be hopelessly oversimplified. Instead, we’ve learned that it may actually be cold, outer material that holds the key to our planetary backyard. If the conclusions of the Ishii et al. paper stand the test of time, we may have just revolutionized our understanding of how all planetary systems come into being.”
How did Earth (and the other planets) form? According to conventional wisdom, a molecular cloud collapsed, formed a protoplanetary disk, funneled material into the center, and gave birth to a star. This star then blew off the gas and light elements from the inner Solar System, with the planets we have today representing the survivors from these hot, early stages. Only, what if that picture weren’t correct after all? What if the material that gave rise to our (and other) worlds wasn’t forged in an inferno, but in a colder, more distant environment that only fell into the inner reaches at a later time?
The way to decide would be to identify and examine material left over from these early stages of Solar System formation in enough detail. For the first time, we’ve done exactly that. Don’t miss the results!
New Stars Turn Galaxies Pink, Even Though There Are No ‘Pink Stars’
“New star-forming regions produce lots of ultraviolet light, which ionizes atoms by kicking electrons off of their nuclei.
These electrons then find other nuclei, creating neutral atoms again, eventually cascading down through its energy levels.
Hydrogen is the most common element in the Universe, and the strongest visible light-emitting transition is at 656.3 nanometers.
The combination of this red emission line — known as the Balmer alpha (or Hα) line — with white starlight adds up to pink.”
When you look through a telescope’s eyepiece at a distant galaxy, it will always appear white to you. That’s because, on average, starlight is white, and your eyes are more sensitive to white light than any color in particular. But with the advent of a CCD camera, collecting individual photons one-at-a-time, you can more accurately gauge an astronomical object’s natural color. Even though new stars are predominantly blue in color, star-forming regions and galaxies appear pink. The problem compounds itself when you realize there isn’t any such thing as a pink star! And yet, there’s a straightforward physical explanation for what we see.
It’s a combination of ultraviolet radiation, white starlight, and the physics of hydrogen atoms that turn galaxies pink. Find out how, with some incredible visuals, today!
Hubble Catches New Stars, Individually, Forming In Galaxies Beyond The Milky Way
“There are a massive variety of star-forming regions nearby, and Hubble’s new Legacy ExtraGalactic UV Survey (LEGUS) is now the sharpest, most comprehensive one ever.
By imaging 50 nearby, star-forming spiral and dwarf galaxies, astronomers can see how the galactic environment affects star-formation.”
Within galaxies, new stars are going to be formed from the existing population of gas. But how that gas collapses and forms stars, as well as the types, numbers, and locations of the stars that will arise, is highly dependent on the galactic environment into which they are born. Dwarf galaxies, for example, tend to form stars when a nearby gravitational interaction triggers them. These bursts occur periodically, leading to multiple populations of stars of different ages. Spirals, on the other hand, form their new stars mostly along the lines traced by their arms, where the dust and gas is densest. Thanks to the Hubble Space Telescope, we’re capable of finding these stars and resolving them individually, using a combination of optical and ultraviolet data.
The best part? These are individually resolved stars from well outside our own galaxy: in 50 independent ones. Here’s what Hubble’s new LEGUS survey is revealing.
Mysterious Light Seen Around A Newly Forming Star; Here’s What Astronomers Think It Means
“In order to reproduce the signatures we see, the disk has to be practically edge-on to our line of sight. Which seems weird, because the main binary system that is CS Cha has a disk that’s inclined, somewhere between edge-on and face-on. This wouldn’t be the first time we’ve seen such a misalignment, as dusty, misaligned binary and trinary systems have been seen before. But it already marks the very first time we’ve detected a polarized companion outside of one of these protoplanetary disks! Because so much of the light is blocked by this dust disk, though, we have a hard time telling what the mass of this companion is. Is it a Jupiter-class planet? A super-Jupiter? Or, as the authors conjecture, is it a low-mass brown dwarf: a failed star?
With a dusty disk around the companion, there’s a near-certainty that whatever it is, it will be developing its own orbiting companions in the imminent future!”
600 light years away, in a small constellation in the southern skies, there’s a new binary star system that’s just in the process of forming: CS Cha. It’s only 2 or 3 million years old, a blip in a star’s lifetime. And all around it for billions of kilometers is a dusty, protoplanetary disk. But far outside that disk is a surprise: a companion object. Most companions will be either large planets or brown dwarfs, and that’s not a surprise. But when you look at the light, it should barely be polarized at all: 1% at most. Yet when we looked at the companion with SPHERE, a new instrument aboard the Very Large Telescope in Chile, we found that a whopping 14% of the light was polarized!
This was no mistake, but the implications are tremendous. After some very careful research, scientists think they know the answer to what’s going on: there’s a dusty disk around the companion object, too!
The Earliest Galaxies Spin Just Like Our Milky Way, Defying Expectations
“As our data sets improve, we should begin to measure the internal motions of large numbers of galaxies like this, which will answer many questions and raise others. Do most/all galaxies at these early stages rotate in a whirlpool-like plane? Is there a variety and multiple sets of populations that exhibit different behaviors? What are the actual effects of gas infall, supernovae, and small-scale motions? What is the velocity profile of these rotation curves, and can they teach us anything about the interplay of radiation, normal matter, and dark matter?
While we hope to learn these answers, we can now ask these questions sensibly in the aftermath of having measured the movement and internal motions of a galaxy so far away. At least for the first two, they rotate very similarly to their much older cousins, a quite unexpected result. Thanks to ALMA, we’re taking those coveted next steps into the final frontier.”
It wasn’t supposed to be this way. When you form galaxies in the very young Universe, it’s supposed to be a chaotic, turbulent place. Sure, you have gravitation, pulling matter in and creating a pancake-like shape. But then you form stars, and everything goes haywire. Supernovae go off, gas falls in, protogalaxies merge and get swallowed, motions get stirred up, and turbulence should permeate the galaxy. It ought to take billions of years for them to quiet down into a Milky Way-like whirlpool. Well, for the first time, owing to ALMA and Renske Smit’s team, the internal motions of galaxies less than a billion years old were measured, and – surprise! – their movement is smooth and not chaotic at all.
They’re less than a billion years old. And, thanks to ALMA observing them, they might finally pave the way to understand how galaxies form altogether.
‘Direct Collapse’ Black Holes May Explain Our Universe’s Mysterious Quasars
“In a theoretical study published in March of this year, a fascinating mechanism for producing direct collapse black holes from a mechanism like this was introduced. A young, luminous galaxy could irradiate a nearby partner, which prevents the gas within it from fragmenting to form tiny clumps. Normally, it’s the tiny clumps that collapse into individual stars, but if you fail to form those clumps, you instead can just get a monolithic collapse of a huge amount of gas into a single bound structure. Gravitation then does its thing, and your net result could be a black hole over 100,000 times as massive as our Sun, perhaps even all the way up to 1,000,000 solar masses.”
Some of the most distant, luminous objects in our entire Universe, quasars, are a mystery. How does our Universe get an active, supermassive black hole that forms so early, especially given how relatively small the stars that make black holes are known to be? Even given the earliest, most massive stars that can theoretically form, you’d only expect seed black holes of a few hundred solar masses, yet these early quasars have almost a billion Suns worth of mass to begin with. You’d need a seed 1,000 times as massive to get there. Well, that’s exactly what the scenario known as ‘direct collapse’ could get you. If a massive galaxy is close by another cloud of gas, it can suppress the formation of stars all while that cloud collapses, potentially leading to a black hole directly, without any stars. That black hole could be up to a million solar masses, providing a path to the earliest quasars with no further hitches. With the technology coming online in the next few years, we might yet see this process in action for the first time.
Come learn about the huge strides we’ve made in direct collapse black holes and finding the origin of the Universe’s quasars. The way you view our Universe may never be the same!
When Did The First Stars Appear In The Universe?
“But there’s more science to be done. Even with James Webb, we likely won’t get all the way to the very first star of all, but we’re very likely to gain a much better handle on exactly where they are and when they are. And as for the first pristine stars? The first stars verified to have nothing other than hydrogen and helium in them? If nature is kind to us, James Webb won’t only bring us the very first one of those, but will bring us many examples.
The Universe is out there, waiting for us to discover it. If we want to know the answer, all we need to do is look. As we build better observatories and take better data, our understanding of all that’s out there will only improve.”
If we look out as far as we can, there’s a big gap between what we know and what must be there. The most distant galaxy we’ve ever found is GN-z11, whose light comes from when the Universe was only 400 million years old. The next picture we have is the cosmic microwave background, emitted from when the Universe was a mere 380,000 years old. At that point, there were no stars; by time we get to 400 million years of age, we have quite large and bright galaxies. So when did the first stars actually, truly appear? It’s a question that we know an awful lot about what the answer must look like, but we’re still a few steps away from actually finding them.
Come find out all we know, and check out a video that Paul Matt Sutter and I made together explaining what we know… and what comes next!
Ask Ethan: Why Was The Universe Dark For So Long?
“One thing I wonder though is why did the dark ages last hundreds of millions of years? I would have expected an order of magnitude smaller, or more.”
There’s a troubling puzzle when it comes to the Universe: the so-called ‘dark ages’ don’t come to an end until 550 million years after the Big Bang. But this is a big problem when you consider that we’ve already imaged a galaxy from when the Universe was only 400 million years old, and that we fully anticipate the first stars to form when the Universe is only 50-100 million years old. So what’s with all the darkness, then? And how do we expect the James Webb Space Telescope to see back to the very first galaxies? The answer lies in two parts. First, even though you have stars, the Universe is still filled with neutral atoms, which block visible and ultraviolet light. We need to ionize those atoms in order to have a transparent Universe, and that takes lots of time. But the second key is that the Universe, even with neutral atoms, is quite transparent to other wavelengths of light, like infrared light. And that’s where an observatory like James Webb is going to be looking!
The Universe was dark for so long because it doesn’t just need light, it needs for all the light-blocking material to disappear. But we’re going to overcome that obstacle in less than two years anyway, and that’s something we should all be excited about!