THE LIFE OF A STAR: A DAY IN THE LIFE
THE LIFE OF A STAR: A DAY IN THE LIFE
Stars are born, and then they live. If a body is large enough and has enough pressure in its core, it will squeeze to fuse hydrogen. The hydrogen in a star's core fuses into helium, releasing photons and fueling the star. The heat created in this process attempts to expand the star, but as their gravity is so strong which threatens to collapse them (making it a problem once fusion stops - we'll get to this later!), this creates an equilibrium. And while stars have some things in common, they do have unique qualities of their own.
Here are the properties that all main sequence stars share: hydrogen fusion, hydrostatic equilibrium ("the inward acting force, gravity, is balanced by outward acting forces of gas pressure and the radiation pressure"), the mass-luminosity relationship (in other words, the more massive a star, the brighter it is), it is the stage where stars spend the most of their lives, and a composition made almost entirely of hydrogen and helium (ATNF - Australia Telescope National Facility).
Like the planets and our sun, stars have structure. The layers of a star are as follows, from the innermost to the outermost: the core, the radiative and convective zones, the photosphere, the chromosphere, and the corona. The structure of our Sun is illustrated above.
The core of a star undergoes fusion in order to maintain hydrostatic equilibrium, and prevent the star from collapsing in on itself. As such, the core is the hottest and most dense region of a star (Universe Today). Thermonuclear energy spreads from the core through convection, the process by which heat moves: heat moves up and cold moves down because cold has a higher density than hot (Britannica: convection). Furthermore, some stars are fully convective, while others just have regions of convection. "The location of convection zones is strongly dependent on the star’s mass. Cool and low-mass stars are fully convective ... Stars slightly more massive and warmer than the Sun, also form a convective core." (Stellar Convection). I'll touch on this in the next chapter, where small stars such as Red Dwarfs are fully convective and are able to avoid the Red Giant phase, due to a lack of build-up of particles in their cores.
In radiative zones, this energy is carried by radiation. In convective zones, it is carried by convection. These zones are not hot or dense enough to undergo nuclear fusion. The photosphere is the surface of a star, then the inner atmosphere (colored red due to the abundance of hydrogen) is the chromosphere, and the outermost atmosphere is the corona (space.com).
In terms of stellar composition, they are mainly composed of hydrogen and helium (which also happen to be some of the most abundant elements in the universe and are the fuel behind a star's nuclear fusion), but also include heavier elements (such as carbon and oxygen). As observed by spectrums and other observations, stars with a greater amount of heavier elements are typically younger because older stars give these elements off due to mass-loss (ATNF - Australia Telescope National Facility).
Stars also undergo atomic and molecular processes internally to maintain their hydrostatic equilibrium:
The Proton-Proton Cycle is the main source of energy for cool main-sequence stars, such as the Sun. This cycle fuses four hydrogen nuclei (aka, protons) into one helium nucleus and two neutrinos (some of the original mass is converted into heat energy). Two hydrogen nuclei combine and emit a positron (a positively charged electron) and a neutrino. The hydrogen-2 nucleus captures a proton to become hydrogen-3 and emit a gamma-ray. There are multiple paths after which, but it always results in the same (Britannica: proton-proton cycle).
The CNO Cycle (aka the Carbon-Nitrogen-Oxygen Cycle) is the main source of energy for warmer main-sequence stars. This cycle has the same resultants but the process is much different. *SKIP AHEAD TO AVOID MY NERD RANT* It fuses a carbon-12 nucleus with a hydrogen nucleus to form a nitrogen-13 nucleus and a gamma-ray emission. The nitrogen-13 emits a positron and becomes carbon-13, which captures another proton/hydrogen nucleus and becomes nitrogen-14 and another gamma-ray. The nitrogen-14 captures a proton to form oxygen-15 and then ejects a positron and becomes nitrogen-15. This, of course, captures another proton and then breaks down into a carbon-12 nucleus and a helium nucleus (an alpha particle). *JUST IN CASE YOU SKIPPED AHEAD* TLDR, it ends up as helium. Nuclear fusion, folks, it's weird (Britannica: CNO cycle).
The products of these processes aren't just automatically transferred and radiated away from the star. No, first they must make their way through the radiative and convective zones. Neutrinos travel almost at the speed of light, and so are the least affected. Photons also lose some energy during the journey, due to interactions with other particles. This energy heats up the surrounding plasma and keeps it flowing, in turn the convection currents transport energy to the surface (ATNF - Australia Telescope National Facility).
Even though a star spends most of its life in the main-sequence stage, this cycle of processes and equilibrium ends eventually. In the next chapter, we'll be talking about what happens after a star runs out of hydrogen to fuse - Giant and Super-Giant Stars.
The rate at which a star runs through its hydrogen is proportional to its mass: the greater the mass, the faster it runs through hydrogen, and vice versa (Britannica: star). Then the star will begin to fuse the heavier elements until it meets its match: iron. Then things get real ... explosive.
First - Chapter 1: An Introduction
Previous - Chapter 4: A Star is Born
Next - Chapter 6: The End (But Not Really)
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That’s a great explanation of particle physics xD
But really, this stuff is so interesting! I love reading about stuff like this - so good work NASA!
If you liked the four forces governing the universe, you might like this book I just finished reading for the seventh time (Neil DeGrasse Tyson’s “Astrophysics for People in a Hurry”). It talks about these forces and a lot of other really cool concepts, like dark energy and chemistry-related-to-space.
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May the Four Forces Be With You!
May the force be with you? Much to learn you still have, padawan. In our universe it would be more appropriate to say, “May the four forces be with you.”
There are four fundamental forces that bind our universe and its building blocks together. Two of them are easy to spot — gravity keeps your feet on the ground while electromagnetism keeps your devices running. The other two are a little harder to see directly in everyday life, but without them, our universe would look a lot different!
Let’s explore these forces in a little more detail.
Gravity: Bringing the universe together
If you jump up, gravity brings you back down to Earth. It also keeps the solar system together … and our galaxy, and our local group of galaxies and our supercluster of galaxies.
Gravity pulls everything together. Everything, from the bright centers of the universe to the planets farthest from them. In fact, you (yes, you!) even exert a gravitational force on a galaxy far, far away. A tiny gravitational force, but a force nonetheless.
Credit: NASA and the Advanced Visualization Laboratory at the National Center for Supercomputing and B. O'Shea, M. Norman
Despite its well-known reputation, gravity is actually the weakest of the four forces. Its strength increases with the mass of the two objects involved. And its range is infinite, but the strength drops off as the square of the distance. If you and a friend measured your gravitational tug on each other and then doubled the distance between you, your new gravitational attraction would just be a quarter of what it was. So, you have to be really close together, or really big, or both, to exert a lot of gravity.
Even so, because its range is infinite, gravity is responsible for the formation of the largest structures in our universe! Planetary systems, galaxies and clusters of galaxies all formed because gravity brought them together.
Gravity truly surrounds us and binds us together.
Electromagnetism: Lighting the way
You know that shock you get on a dry day after shuffling across the carpet? The electricity that powers your television? The light that illuminates your room on a dark night? Those are all the work of electromagnetism. As the name implies, electromagnetism is the force that includes both electricity and magnetism.
Electromagnetism keeps electrons orbiting the nucleus at the center of atoms and allows chemical compounds to form (you know, the stuff that makes up us and everything around us). Electromagnetic waves are also known as light. Once started, an electromagnetic wave will travel at the speed of light until it interacts with something (like your eye) — so it will be there to light up the dark places.
Like gravity, electromagnetism works at infinite distances. And, also like gravity, the electromagnetic force between two objects falls as the square of their distance. However, unlike gravity, electromagnetism doesn’t just attract. Whether it attracts or repels depends on the electric charge of the objects involved. Two negative charges or two positive charges repel each other; one of each, and they attract each other. Plus. Minus. A balance.
This is what happens with common household magnets. If you hold them with the same “poles” together, they resist each other. On the other hand, if you hold a magnet with opposite poles together — snap! — they’ll attract each other.
Electromagnetism might just explain the relationship between a certain scruffy-looking nerf-herder and a princess.
Strong Force: Building the building blocks
Credit: Lawrence Livermore National Laboratory
The strong force is where things get really small. So small, that you can’t see it at work directly. But don’t let your eyes deceive you. Despite acting only on short distances, the strong force holds together the building blocks of the atoms, which are, in turn, the building blocks of everything we see around us.
Like gravity, the strong force always attracts, but that’s really where their similarities end. As the name implies, the force is strong with the strong force. It is the strongest of the four forces. It brings together protons and neutrons to form the nucleus of atoms — it has to be stronger than electromagnetism to do it, since all those protons are positively charged. But not only that, the strong force holds together the quarks — even tinier particles — to form those very protons and neutrons.
However, the strong force only works on very, very, very small distances. How small? About the scale of a medium-sized atom’s nucleus. For those of you who like the numbers, that’s about 10-15 meters, or 0.000000000000001 meters. That’s about a hundred billion times smaller than the width of a human hair! Whew.
Its tiny scale is why you don’t directly see the strong force in your day-to-day life. Judge a force by its physical size, do you?
Weak Force: Keeping us in sunshine
If you thought it was hard to see the strong force, the weak force works on even smaller scales — 1,000 times smaller. But it, too, is extremely important for life as we know it. In fact, the weak force plays a key role in keeping our Sun shining.
But what does the weak force do? Well … that requires getting a little into the weeds of particle physics. Here goes nothing! We mentioned quarks earlier — these are tiny particles that, among other things, make up protons and neutrons. There are six types of quarks, but the two that make up protons and neutrons are called up and down quarks. The weak force changes one quark type into another. This causes neutrons to decay into protons (or the other way around) while releasing electrons and ghostly particles called neutrinos.
So for example, the weak force can turn a down quark in a neutron into an up quark, which will turn that neutron into a proton. If that neutron is in an atom’s nucleus, the electric charge of the nucleus changes. That tiny change turns the atom into a different element! Such reactions are happening all the time in our Sun, giving it the energy to shine.
The weak force might just help to keep you in the (sun)light.
All four of these forces run strong in the universe. They flow between all things and keep our universe in balance. Without them, we’d be doomed. But these forces will be with you. Always.
You can learn more about gravity from NASA’s Space Place and follow NASAUniverse on Twitter or Facebook to learn about some of the cool cosmic objects we study with light.
Make sure to follow us on Tumblr for your regular dose of space: http://nasa.tumblr.com
I love supermassive black holes!!!
Expect this in the chapter about black holes lol
The relationship between SBHs and their host galaxies are so cool!
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AAS NOVA
A Young Population of Hidden Jets
By Susanna Kohler
Looking for a fireworks show this 4th of July? Try checking out the distant universe, where powerful jets flung from supermassive black holes slam into their surroundings, lighting up the sky.
Though these jets are hidden behind shrouds of gas and dust, a new study has now revealed some of these young powerhouses.
A Galaxy–Black-Hole Connection
In the turbulent centers of active galaxies (active galactic nuclei, or AGN), gas and dust rains onto supermassive black holes of millions to billions of solar masses, triggering dramatic jets that plow into the surrounding matter and light up across the electromagnetic spectrum.
The growth of a supermassive black hole is thought to be closely tied to the evolution of its host galaxy, and feedback like these jets may provide that link. As the jets collide with the gas and dust surrounding the galaxy’s nucleus, they can trigger a range of effects — from shock waves that drive star formation, to gas removal that quenches star formation.
To better understand the connections between supermassive black holes and their host galaxies, we’d especially like to observe AGN at a time known as Cosmic Noon. This period occurred around 10 billion years ago and marks a time when star formation and supermassive black hole growth was at its strongest.
The Hidden World of Cosmic Noon
But there’s a catch: around Cosmic Noon, galaxies were heavily shrouded in thick gas and dust. This obscuring material makes it difficult for us to observe these systems in short wavelengths like optical and X-ray. Instead, we have to get creative by searching for our targets at other wavelengths.
Since AGN emission is absorbed by the surrounding dust and re-radiated in infrared, we can use infrared brightness to find obscured but luminous sources. To differentiate between hidden clumps of star formation and hidden AGN, we also look for a compact radio source — a signature that points to a jet emitted from a central black hole.
A team of scientists led by Pallavi Patil (University of Virginia and the National Radio Astronomy Observatory) has now gone on the hunt for these hidden sources at Cosmic Noon.
Newly-Triggered Jets Caught in the Act
Patil and collaborators observed a sample of 155 infrared-selected sources, following up with high-resolution imaging from the Jansky Very Large Array to identify compact radio sources. From their observations and modeling of the jets, the authors estimate these sources’ properties.
The authors find bright luminosities, small sizes, and high jet pressures — all of which suggest that we’ve caught newly-triggered jets in a short-lived, unique phase of AGN evolution where the jets are still embedded in the dense gas reservoirs of their hosts. The jets are expanding slowly because they have to work hard to push through the thick clouds of surrounding material. Over time, the jets will likely expand to larger scales and clear out the surrounding matter, causing the sources to evolve into more classical looking radio galaxies.
What’s next? The authors are currently working on a companion study to further explore the shapes of the jets and their immediate environments. These young, hidden sources will provide valuable insight into how supermassive black holes evolve alongside their host galaxies.
Citation “High-resolution VLA Imaging of Obscured Quasars: Young Radio Jets Caught in a Dense ISM,” Pallavi Patil et al 2020 ApJ 896 18. doi:10.3847/1538-4357/ab9011
TOP IMAGE….Artist’s impression of a galaxy forming stars, as powerful jets that are flung from its central black hole collide with the surrounding matter. [ESO/M. Kornmesser]
CENTRE IMAGE….This composite image of Centaurus A shows an example of large-scale jets launched from an AGN, which can eventually extend far beyond the galaxy, as seen here. [ESO/WFI (Optical); MPIfR/ESO/APEX/A.Weiss et al. (Submillimetre); NASA/CXC/CfA/R.Kraft et al. (X-ray)]
LOWER IMAGE….The redshift distribution of the authors’ sample, based on spectroscopic redshifts of 71 sources. The sources span the period of peak star formation and black hole fueling around Cosmic Noon. [Patil et al. 2020]
BOTTOM IMAGE….The JVLA 10 GHz radio continuum observations for four sources in the authors’ sample. The cyan plus symbol marks the infrared-obtained source position. The color bars indicate flux in mJy/beam. [Adapted from Patil et al. 2020]
That’s how I want the world to end
better than us all getting killed by a pandemic or a nuke
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On November 12, 1833, there was such an intense meteor shower that it was possible to see up to 100,000 meteors crossing the sky every hour. At the time, many thought it was the end of the world, so much that inspired this wood engraving by Adolf Vollmy.
Ooo, that’s pretty cool
Also - a nice little teaser - we’ll be covering brown dwarfs in the next chapter of the Life of a Star!
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ASTRONOMERS FIND JUPITER-LIKE CLOUD BANDS ON CLOSEST BROWN DWARF
A team of astronomers has discovered that the closest known brown dwarf, Luhman 16A, shows signs of cloud bands similar to those seen on Jupiter and Saturn. This is the first time scientists have used the technique of polarimetry to determine the properties of atmospheric clouds outside of the solar system, or exoclouds.
Brown dwarfs are objects heavier than planets but lighter than stars, and typically have 13 to 80 times the mass of Jupiter. Luhman 16A is part of a binary system containing a second brown dwarf, Luhman 16B. At a distance of 6.5 light-years, it’s the third closest system to our Sun after Alpha Centauri and Barnard’s Star. Both brown dwarfs weigh about 30 times as much as Jupiter.
Despite the fact that Luhman 16A and 16B have similar masses and temperatures (about 1,900°F, or 1,000°C), and presumably formed at the same time, they show markedly different weather. Luhman 16B shows no sign of stationary cloud bands, instead exhibiting evidence of more irregular, patchy clouds. Luhman 16B therefore has noticeable brightness variations as a result of its cloudy features, unlike Luhman 16A.
“Like Earth and Venus, these objects are twins with very different weather,” said Julien Girard of the Space Telescope Science Institute in Baltimore, Maryland, a member of the discovery team. “It can rain things like silicates or ammonia. It’s pretty awful weather, actually.”
The researchers used an instrument on the Very Large Telescope in Chile to study polarized light from the Luhman 16 system. Polarization is a property of light that represents the direction that the light wave oscillates. Polarized sunglasses block out one direction of polarization to reduce glare and improve contrast.
“Instead of trying to block out that glare, we’re trying to measure it,” explained lead author Max Millar-Blanchaer of the California Institute of Technology (Caltech) in Pasadena, California.
When light is reflected off of particles, such as cloud droplets, it can favor a certain angle of polarization. By measuring the preferred polarization of light from a distant system, astronomers can deduce the presence of clouds without directly resolving either brown dwarf’s cloud structure.
“Even from light-years away, we can use polarization to determine what the light encountered along its path,” added Girard.
“To determine what the light encountered on its way we compared observations against models with different properties: brown dwarf atmospheres with solid cloud decks, striped cloud bands, and even brown dwarfs that are oblate due to their fast rotation. We found that only models of atmospheres with cloud bands could match our observations of Luhman 16A,” explained Theodora Karalidi of the University of Central Florida in Orlando, Florida, a member of the discovery team.
The polarimetry technique isn’t limited to brown dwarfs. It can also be applied to exoplanets orbiting distant stars. The atmospheres of hot, gas giant exoplanets are similar to those of brown dwarfs. Although measuring a polarization signal from exoplanets will be more challenging, due to their relative faintness and proximity to their star, the information gained from brown dwarfs can potentially inform those future studies.
NASA’s upcoming James Webb Space Telescope would be able to study systems like Luhman 16 to look for signs of brightness variations in infrared light that are indicative of cloud features. NASA’s Wide Field Infrared Survey Telescope (WFIRST) will be equipped with a coronagraph instrument that can conduct polarimetry, and may be able to detect giant exoplanets in reflected light and eventual signs of clouds in their atmospheres.
IMAGE….Astronomers have found evidence for a striped pattern of clouds on the brown dwarf called Luhman 16A, as illustrated here in this artist’s concept. The bands of clouds were inferred using a technique called polarimetry, in which polarized light is measured from an astrophysical object much like polarized sunglasses are used to block out glare. This is the first time that polarimetry has been used to measure cloud patterns on a brown dwarf. The red object in the background is Luhman 16B, the partner brown dwarf to Luhman 16A. Together, this pair is the closest brown dwarf system to Earth at 6.5 light-years away. CREDITS: Caltech/R. Hurt (IPAC)
Omg particles are such players - JUST CHOOSE ONE!!!
But yeah wave-particle duality is kinda confusing sometimes lol
Like, how is it both? I dunno! Maybe I’ll read up on that later ...
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Photons : Hello I’m a particle . Oh yeah but i behave like a wave too , isn’t that beautiful !!
It’s easy to forget that thousands of comets, asteroids, and meteors are near us everyday. They seem like such a rarity.
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Cosmonaut Ivan Vagner obtained this image of the comet NEOWISE a few hours ago from the International Space Station. He says that the dust tail looks very good from there. It is worth enlarging the image.
via reddit
I mean, the song really isn’t accurate.
Also that’s a bit unfair. I’m pretty super that’s a Red Super Giant. Not all stars are that huge xD (even though I’d wouldn’t describe any star as “little”)
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Little star : am I a joke to you?
More nebulae!!!
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M27: Not a Comet : While hunting for comets in the skies above 18th century France, astronomer Charles Messier diligently kept a list of the things he encountered that were definitely not comets. This is number 27 on his now famous not-a-comet list. In fact, 21st century astronomers would identify it as a planetary nebula, but it’s not a planet either, even though it may appear round and planet-like in a small telescope. Messier 27 (M27) is an excellent example of a gaseous emission nebula created as a sun-like star runs out of nuclear fuel in its core. The nebula forms as the star’s outer layers are expelled into space, with a visible glow generated by atoms excited by the dying star’s intense but invisible ultraviolet light. Known by the popular name of the Dumbbell Nebula, the beautifully symmetric interstellar gas cloud is over 2.5 light-years across and about 1,200 light-years away in the constellation Vulpecula. This impressive color composite highlights details within the well-studied central region and fainter, seldom imaged features in the nebula’s outer halo. It incorporates broad and narrowband images recorded using filters sensitive to emission from hydrogen and oxygen atoms. via NASA
I’m so hype for this telescope though
They say it might be able to see back to when the first stars were born - how exciting!
Eat shit Hubble telescope
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The launch of the James Webb Telescope – the successor of the Hubble Telescope – has been delayed until 2021 but damn it’s going to be awesome.
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