Astrophysics - Blog Posts

Yeah, Mercury did kinda kick Newton in the balls, didn’t it?

Guess that’s why it’s my favorite planet

WANT MORE? GET YOUR HEAD STUCK IN THE STARS AT MY BLOG!

Ah yes, the science

THE LIFE OF A STAR: THE END (BUT NOT REALLY)

In our last chapter, we discussed the main-sequence stage of a star. In this chapter, we'll be discussing when the main-sequence stage ends, and what happens when it does.

        In order to live, stars are required to maintain a hydrostatic equilibrium - which is the balance between the gravitational force and the gas pressure produced from nuclear fusion within the core. If gravity were to be stronger than this pressure, the star would collapse. Likewise, if the pressure were to be stronger than gravity, the star would explode. It's the balance - the equilibrium - between these two forces which keeps a star stable. Stars contain hydrogen - their primary fuel for fusion - in their core, shell, and envelope. The heat and density in the core is the only area in a main-sequence star that has enough pressure to undergo fusion. However, what happens once hydrogen runs out in the core is where things start to get ... explosive.

        For this, we'll be having two discussions: what happens in low-mass stars, versus what happens in high-mass stars.

                                                                      ~ Low-Mass Stars ~

        Low-mass stars are classified as those less than 1.4 times the mass of the sun (NASA). While low-mass stars last a lot longer than their higher-mass counterparts, these stars will eventually have fused all of the hydrogens in their core. Because the core doesn't have enough pressure to fuse helium (as it takes more pressure and heat to fuse heavier elements than less), gas pressure stops and gravity causes the core to contract. This converts gravitational potential energy into thermal energy, which heats up the hydrogen shell until it is hot enough to begin fusing. It also produces extra energy, which overcomes gravity in small amounts and causes the star to swell up a bit. As it expands, the pressure lessens and it cools. The increased energy also causes an increase in luminosity. This is what is now called a Red Giant star (ATNF). 

        Red Giants grow a lot, averagely reaching sizes of 100 million to 1 billion kilometers in diameter, which is 100-1,000 times larger than the sun. The growth of the star causes energy to be more spread out, and so cools it down to only around 3,000 degrees Celsius (still though, pretty hot). Because energy correlates with heat, and the red part of the electromagnetic spectrum is less energized, the stars glow a reddish color. Hence, the name Red Giant. Due to the current size of the sun, we can conclude that it will eventually become a Red Giant. This could be a big problem (literally), as the sun will grow so large that it will either consume Earth or become so close that it would be too hot to live. However, this won't be happening for around 5 billion years, so there's nothing immediately to worry about (Space.com).

        As more hydrogen is fused within the shell of the Red Giant, the produced helium falls down into the core. The increased mass leads to increased pressure, which leads to increased heat. Once the temperature in the core reaches 100 K (at which point the helium produced has enough energy to overcome repulsive forces), helium begins to fuse. This process is called the Triple Alpha Process (as the helium being fused are actually alpha particles, helium-4 nuclei), where three of the helium particles combine to form carbon-12, and sometimes a fourth fuses along to form oxygen-16. Both processes release a gamma-ray photon. In low-mass stars, the Triple Alpha Process spreads so quickly that the entire helium ore is fusing in mere minutes or hours. This is, accurately called, the Helium Flash. 

        After millions of years, the helium in the core will run out. Now the core is made entirely of the products of helium fusion: carbon and oxygen nuclei. As the fusion stops, gas pressure shrinks, and gravity causes the star to contract yet again. The temperature needed to fuse carbon and oxygen is even higher, as heavier elements require more energy to fuse (because, with more protons, there's more Coulombic Repulsion). However, this temperature cannot be reached, because the gravity acting on the core is not strong enough to create enough heat. The core can burn no longer.

        The helium shell of the star begins to fuse, as gravity IS strong enough to do that. The extra energy and gas pressure created causes the star to expand even more so now. The helium shell is not dense enough to cause one single helium flash, so small flashes occur every 10,000-100,000 years (due to the energy released, this is called a thermal pulse). Radiation pressure blows away most of the outer layer of the star, which gravity is not strong enough to contain. The carbon-rich molecules form a cloud of dust which expands and cools, re-emitting light from the star at a longer wavelength (ATNF).

        But what happens after the shell is fused? We'll get back to that in Chapter 7, where we'll discuss White Dwarfs and Planetary Nebulae.

        It's also important to note that not every low-mass star needs to become a Red Giant. Stars that are smaller than half the mass of the Sun (like, Red Dwarfs) are fully convective, meaning that the surface, envelope, shell, and core of star materials all mix. Because of this mixing, there is no helium buildup in the core. This means that there is not enough pressure to fuse the helium in fully convective stars, and so they skip the contraction and expansion phases of Red Giant Stars. Instead, with no gas pressure to counteract gravity, the star collapses in on itself and forms a White Dwarf (Cosmos).

                                                                     ~ High-Mass Stars ~

         High-mass stars are classified as those more than 1.4 times the mass of the sun (NASA). High-Mass Stars, as opposed to their Low-Mass counterparts, use up their hydrogen fast, and as such have much shorter lives. Just like Low-Mass Stars, they'll eventually run out of hydrogen in both their core and their shell, and this will cause the star to contract. Their density and pressure will become so strong that the core becomes extremely hot, and helium fusion starts quickly (there is no helium flash because the process of fusion will begin slowly, rather than in "a flash"). The release of energy will cause it to expand and cool into a Red Supergiant, and will also begin the fusion of the helium shell. 

        Once all of the helium is gone, leaving carbon and oxygen nuclei, the star contracts yet again. The mass (and the gravity squeezing it into a very small space with a very large density) of a high-mass star will be enough to generate the temperatures needed for carbon fusion. This produces sodium, neon, and magnesium. The neon can also fuse with helium (whose nuclei is released in the neon fusion) to create magnesium. Once the core runs out of neon, oxygen fuses. This process keeps going, creating heavier and heavier elements, until it stops at iron. At this point, the supergiant star resembles an onion. It is layered: with the heavier elements being deeper within the star, and the lighter elements closer to the surface (ATNF).

        But what happens after the star finally gets to iron? We'll get back to that in Chapters 8, 9, and 10 - where we'll discuss Supernovae, Neutron Stars, and Black Holes.

        We’re nearing the end of our star’s life, and now it’s time to look into the many ways it can go out.

        If our first five chapters were all about life, these next five will be all about death.

First -  Chapter 1: An Introduction

Previous -  Chapter 5: A Day in the Life

Next - Chapter 7: What Goes Around, Comes Around

WANT MORE? GET YOUR HEAD STUCK IN THE STARS AT MY BLOG!

Dark matter is one of my favorite mysteries in Astrophysics, oh I would just love to study it. Some are using particle accelerators to try to study DM and figure out what it is - and it’s so so exciting!!!

WANT MORE? GET YOUR HEAD STUCK IN THE STARS AT MY BLOG!

I love this meme format

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)

WANT MORE? GET YOUR HEAD STUCK IN THE STARS AT MY BLOG!

It surprises me how disinterested we are today about things like physics, space, the universe and philosophy of our existence, our purpose, our final destination. Its a crazy world out there. Be curious.

Stephen Hawking

WANT MORE? GET YOUR HEAD STUCK IN THE STARS AT MY BLOG!

Hubble has discovered a dwarf star that devours its own solar system. It's like a cosmic cannibal

Astronomers used archival data from the Hubble Space Telescope and other observatories to analyze the spectral properties of the white dwarf star G238-44.

Detected elements show that the dead star swallows debris from both the inside and the outside of its system. It's a case of "cosmic cannibalism," say the study's authors, published on the Hubble Telescope website.

G238-44 was a Sun-like star that lost its outer layers and no longer burned fuel through nuclear fusion. The discovery that stellar debris simultaneously captures matter from its asteroid belt and Kuiper belt-like regions at the edge of the solar system, including ice bodies, is significant because it suggests that a "water tank" may be a common feature in outer areas. of planetary systems.

‼️When a star like the Sun expands and becomes a red giant, at the end of its life, it loses mass by releasing its outer layers.

➡️A consequence of this may be the gravitational scattering of small objects, such as asteroids, comets and satellites, to the large planets in the system. Hit in this way, surviving objects can be thrown into very eccentric orbits.‼️

☑️ "After the phase of the red giant, the remaining white dwarf star is compact - no bigger than Earth. The planets get very close to the star and experience strong forces of attraction that break them to pieces, creating a disk of gas and dust that eventually falls on the surface of the white dwarf star, "said Johnson.

Thinking of making a weekly post about astrophysics and/or math and other subjects.

I'm in a science club in Uni and the people they bring are extremely knowledgeable and since they gave me their approval I'm thinking of publishing some of it here !

Alright.

NASA Camera Shows Moon Crossing Face of Earth for 2nd Time in a Year

For only the second time in a year, a NASA camera aboard the Deep Space Climate Observatory (DSCOVR) satellite captured a view of the moon as it moved in front of the sunlit side of Earth. 

The images were captured by NASA’s Earth Polychromatic Imaging Camera (EPIC), a four-megapixel CCD camera and telescope on the DSCOVR satellite orbiting 1 million miles from Earth. From its position between the sun and Earth, DSCOVR conducts its primary mission of real-time solar wind monitoring for the National Oceanic and Atmospheric Administration (NOAA).

The first image is from July 2016 and the second image (moon traveling diagonally Northeast in the image) is from July 2015

Credits: NASA

Grades don’t determine your intelligence.

Grades don’t determine your intelligence.

Grades don’t determine your intelligence.

Grades don’t determine your intelligence.

Dale & Karlie | Gold Coast 🇦🇺 on Instagram

Audience member: “does this have any practical applications?”

Math lecturer: “probably not”

brilliant binaries 3/6/2019

M🌑🌑N ~ 3/1/2019

5 Facts About Earth's Radiation Donuts 🍩

Did you know that our planet is surrounded by giant, donut-shaped clouds of radiation?

Here’s what you need to know.

1. The radiation belts are a side effect of Earth’s magnetic field

The Van Allen radiation belts exist because fast-moving charged particles get trapped inside Earth’s natural magnetic field, forming two concentric donut-shaped clouds of radiation. Other planets with global magnetic fields, like Jupiter, also have radiation belts.

2. The radiation belts were one of our first Space Age discoveries

Earth’s radiation belts were first identified in 1958 by Explorer 1, the first U.S. satellite. The inner belt, composed predominantly of protons, and the outer belt, mostly electrons, would come to be named the Van Allen Belts, after James Van Allen, the scientist who led the charge designing the instruments and studying the radiation data from Explorer 1.

3. The Van Allen Probes have spent six years exploring the radiation belts

In 2012, we launched the twin Van Allen Probes to study the radiation belts. Over the past six years, these spacecraft have orbited in and out of the belts, providing brand-new data about how the radiation belts shift and change in response to solar activity and other factors.

4. Surprise! Sometimes there are three radiation belts

Shortly after launch, the Van Allen Probes detected a previously-unknown third radiation belt, created by a bout of strong solar activity. All the extra energy directed towards Earth meant that some particles trapped in our planet’s magnetic field were swept out into the usually relatively empty region between the two Van Allen Belts, creating an additional radiation belt.

5. Swan song for the Van Allen Probes

Originally designed for a two-year mission, the Van Allen Probes have spent more than six years collecting data in the harsh radiation environment of the Van Allen Belts. In spring 2019, we’re changing their orbit to bring the perigee — the part of the orbit where the spacecraft are closest to Earth — about 190 miles lower. This ensures that the spacecraft will eventually burn up in Earth’s atmosphere, instead of orbiting forever and becoming space junk.

Because the Van Allen Probes have proven to be so hardy, they’ll continue collecting data throughout the final months of the mission until they run out of fuel. As they skim through the outer reaches of Earth’s atmosphere, scientists and engineers will also learn more about how atmospheric oxygen can degrade satellite measurements — information that can help build better satellites in the future.

Keep up with the latest on the mission on Twitter, Facebook or nasa.gov/vanallenprobes.

vintage book shopping. came across this curiosity(?)/monstrosity(?). no idea what to make of it.

THIS is what i study

andenes, norway 2/22/2019

So long, Oppy.

crab contours 2/6/2019

have I mentioned that one week ago TODAY i launched a sounding ROCKET? (model pictured above)

andøya, norway 1/24/2019

We made it, friends.

GR 🙈

recreational reading

Hi, I’m proud of this one. 10/23/2018

10/12/2018

Let’s just talk about how much I love space... and my Nikon. 1/12/2018

Why not just buid a solar panel around the sun to solve all energy problemss?

Behold the Dyson Sphere

Dyson sphere is a hypothetical mega-structure that completely encompasses a star and captures most or all of its power output.

Over the years many variants have been explored:

The simplest such arrangement is the Dyson ring, in which all ‘energy harvesting structures’ share the same orbit.

Add multiple Dyson ring structures and you will get a Dyson swarm.

Now what if you didn’t like a consistent orbit for your structures, you could employ a solar sail to continuously modify its orbit( called a statite ).

Such an arrangement would be known as a Dyson Bubble

Then there is the fictionally popular version - The Dyson Shell, where a uniform solid shell of matter just encapsulates the entire star.

And many many more. But you get the gist.

Could there be Dyson Spheres out there?

When scientists were monitoring the brightness from some stars, they found that it fluctuated in some odd ways like so:

                          Brightness v/s time for KIC 8462852

It is common for such dips to occur since when a planet eclipses a star, there would a drop in the brightness observed from the star.

                       Brightness v/s time for a binary star system

But what was baffling was the duration and period of occurrence of these dips.

Although the main line of rationale remains as asteroid impact remnants or interstellar collisions causing these aberrations in data.

But to say that these could the signs of an alien civilization does remain to be the more entertaining interpretation.

Great Question. Thanks for asking !

** For more information. check out this TED talk

some of my favourite absolutely SICK facts about the trappist-1 exoplanets: - theyre all very close to one another and to their star, so the length of a year on them varies from 1 to 20 DAYS - since they’re so close, the star appears a lot bigger than our sun from earth, and from one planet you could easily see the rest, some would even appear bigger than the moon from earth. you could literally see the surface of another planet with the naked eye!!! - they’re probably tidally locked to their star like our moon is locked to earth, meaning only one side of a planet ever faces the star, and on the other side it’s always night. the sun never sets or rises on any of the planets - the star is red, so the sunlight is red/orange, meaning if, for example, plants were to grow there, they could be black and that’s just what we know now, imagine how much cool stuff we have yet to discover about the trappist-1 system

The origin of the universe was not by a singularity, since in a singularity, the laws of nature are not valid or do not exist,