Ask Ethan: How Many Generations Of Stars Formed Before Our Sun?
“[My professor] and I were discussing the status of our Sun. I was leaning towards the Sun being a third generation star and she was thinking the Sun was second. […] Any thoughts? And how might this be resolved with [future] technology?”
How many generations of stars formed before our Sun did? Surprisingly, this is not a questions astronomers know the answer to, nor is it one that we can envision coming up with a definitive answer for. In the modern Universe, we don’t have access to history or pre-history of the Solar System; all we can see is what remains today. The rest of it is up to us, the scientific community, to reconstruct.
But we’re pretty incredible at what we can say based on what we do know. The Sun cannot be a first-generation, pristine star, since none of those have ever been even discovered. It couldn’t be a second-generation star, because those are ubiquitous and have very different properties than our own Sun. But where are we then? And what do we know, and what remains mysterious?
It’s a great question with a remarkable set of facts behind what we know so far, all for your enjoyment on this week’s Ask Ethan!
A black hole is the most powerful astronomical object, because it can say the n word.
What Was It Like When The Universe Made Its Second Generation Of Stars?
“The very first stars live only an extremely short time, owing to their high masses and large luminosities and rates-of-fusion. When they die, the space around them becomes polluted with the fruits of their lives: heavy elements. These heavy elements enable the second generation of stars to form, but they now form differently. The heavy elements radiate heat away, giving rise to a less massive, more diverse generation of stars, some of which survive even to the present day.
When the James Webb Space Telescope begins operations, it may yet reveal a population of these first stars, likely to be found alongside polluted, second-generation stars. But once these second-generation stars begin to form, they make something else possible: the first galaxies. And that, in just a few years, is likely where the James Webb Space Telescope will truly shine.”
The first stars in the Universe, as astronomers define them, are stars made out of pristine materials left over from the Big Bang: almost exclusively hydrogen and helium. Because of this, their options are limited. They’re all very massive, they have no rocky planets around them, they live a short time, and they almost all die in a supernova. That’s not a life-friendly environment! But all of that changes with the second generation of stars, which forms just a few million years after the first. Some of these may even survive in the Milky Way to the present day… and we might have even found them already.
Come learn what the Universe was like when it form the second generation of stars, and why this is so important in our own cosmic story!
Emojis of the cosmos
Pareidolia is a psychological phenomenon in which the mind responds to a stimulus, usually an image or a sound, by perceiving a familiar pattern where none exists.
These are merely some images of stars and galaxies taken by the Hubble Space Telescope. But what do you see ?
What Happens When Planets, Stars, And Black Holes Collide?
“Brown dwarf collisions. Want to make a star, but you didn’t accumulate enough mass to get there when the gas cloud that created you first collapsed? There’s a second chance available to you! Brown dwarfs are like very massive gas giants, more than a dozen times as massive as Jupiter, that experience strong enough temperatures (about 1,000,000 K) and pressures at their centers to ignite deuterium fusion, but not hydrogen fusion. They produce their own light, they remain relatively cool, and they aren’t quite true stars. Ranging in mass from about 1% to 7.5% of the Sun’s mass, they are the failed stars of the Universe.
But if you have two in a binary system, or two in disparate systems that collide by chance, all of that can change in a flash.”
Nothing in the Universe exists in total isolation. Planets and stars all have a common origin inside of star clusters; galaxies clump and cluster together and are the homes for the smaller masses in the Universe. In an environment such as this, collisions between objects are all but inevitable. We think of space as being extremely sparse, but gravity is always attractive and the Universe sticks around for a long time. Eventually, collisions will occur between planets, stars, stellar remnants, and black holes.
What happens when they run into one another? Unbelievably, we not only know, we have the evidence to back it up!
Ask Ethan: Could The Energy Loss From Radiating Stars Explain Dark Energy?
“What happens to the gravity produced by the mass that is lost, when it’s converted by nuclear reactions in stars and goes out as light and neutrinos, or when mass accretes into a black hole, or when it’s converted into gravitational waves? […] In other words, are the gravitational waves and EM waves and neutrinos now a source of gravitation that exactly matches the prior mass that was converted, or not?”
For the first time in the history of Ask Ethan, I have a question from a Nobel Prize-winning scientist! John Mather, whose work on the Cosmic Microwave Background co-won him a Nobel Prize with George Smoot, sent me a theory claiming that when matter gets converted into radiation, it can generate an anti-gravitational force that might be responsible for what we presently call dark energy. It’s an interesting idea, but there are some compelling reasons why this shouldn’t work. We know how matter and radiation and dark energy all behave in the Universe, and converting one into another should have very straightforward consequences. When we take a close look at what they did, we can even figure out how the theory’s proponents fooled themselves.
Radiating stars and merging black holes do change how the Universe evolves, but not in a way that can mimic dark energy! Come find out how on this week’s Ask Ethan.
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.
Astronomers Confirm Second Most-Distant Galaxy Ever, And Its Stars Are Already Old
“Scientists have just confirmed the second most distant galaxy of all: MACS1149-JD1, whose light comes from when the Universe was 530 million years old: less than 4% of its present age. But what’s remarkable is that we’ve been able to detect oxygen in there, marking the first time we’ve seen this heavy element so far back. From the observations we’ve made, we can conclude this galaxy is at least 250 million years old, pushing the direct evidence for the first stars back further than ever.”
When it comes to the most distant galaxies of all, our current set of cutting-edge telescopes simply won’t get us there. The end of the cosmic dark ages and the dawn of the first cosmic starlight is a mystery that will remain until at least 2020: when the James Webb Space Telescope launches. Using the power of a multitude of observatories, we’ve managed to find a gravitationally lensed galaxy whose light comes to us from over 13 billion years ago. But unlike previous galaxies discovered near that distance, we’ve detected oxygen in this one, allowing us to get a precise measurement and to estimate its age.
For the first time, we have evidence from galaxies, directly, that the Universe’s first stars formed no later than 250 million years after the Big Bang. Here’s how we know.