Test- star birth, Evolution, and Death

The white dwarf is less than _.

1.4 M

When a star dies and if the core of the star is between _ , it collapses even further (than a white dwarf). A star will become a neutron star. A neutron star is approximately only _.

1.4 and 2.8 times the Sun's mass, ... , 20km

The hottest stars are O-type stars, slightly cooler are B, followed by A, F, G, K, and M. Each letter grouping is divided into _, again according to temperature. We've also discovered even cooler stars in the past few decades, and these are assigned the letters _.

10 subgroups, ... ,L, T, and Y.

Cooler stars are red, and so the Sun will (eventually) be too. But the core still isn't done. The details are complicated, but the core continues to contract and heat up. It gets so hot that the outer layers swell even more, and the Sun can bloat up to a fantastic _ its present size! It will then be a red giant.

10 to 150 times

The total energy carried by little neutrinos is almost beyond reason: In a fraction of a second, they carry away _ as much energy as the Sun will produce over its entire lifetime. That's an incredible amount of energy!

100 times

The expanding material, called the supernova remnant, forms fantastic shapes. The most famous is the Crab nebula, from a star we saw blow up in the year _. The tendrils form as the material expands into the gas and dust that surrounded the progenitor star.

1054

The supernova that left the crab nebula was recorded by many civilizations in _.

1054

For the Sun, that total lifespan is about _ years.

12 billion

Given that mass is the key factor here, let's start with a low-mass star. This would range from the smallest that stars can be, meaning the smallest amount of material that can sufficiently trigger nuclear fusion so as to qualify as a star, which is about _ Jupiter masses, to a star somewhere in the ballpark of our sun's mass.

13

Both hydrogen and helium rise up through the star and then fall back down. The star can't fuse the helium, but the hydrogen that makes it back to the center is just more grist for the mill. Even after a long, long time, these stars (low mass stars) can still shine as the hydrogen mixed throughout the star eventually makes it down to the center. So how long can a really low mass red dwarf last? A trillion years. A trillion! The Universe itself is less than _, so even the oldest red dwarf stars are basically infants.

14 billion years old

One teaspoon of a white dwarf would weigh around _ tons.

15

There is not necessarily an upper limit to how big a star can be. Whatever mass of gas and dust happens to have accumulated to form the star, that's the mass of the star. Some propose a limit of _.

150 solar masses

A neutron star, with its immense gravity, can have an escape velocity of _ - that's half the speed of light!

150,000 km/sec

The core has to be more than about _ to form a black hole.

2.8 times the Sun's mass

When it's neutron star-sized the escape velocity is half the speed of light, but if it's more than _ , the core will keep collapsing. When its size drops just a little bit more, down to roughly _, an amazing thing happens: The escape velocity at its surface is equal to _.

2.8 times the mass of the Sun, ... ,18 km, ... , the speed of light

The original star must have something like _ the Sun's mass or more to become a black hole.

20 times

Red giants are fantastically bright because of all the energy percolating up from their interiors, coupled with their enormous size. When it turns into a red giant, the Sun will increase its luminosity by an incredible _.

2000 times

In March _, in a distant galaxy, a star apparently got too close to a black hole, and was torn apart by the ferocious tides. As the star was disrupted, it flared in brightness, momentarily blasting out a trillion times the Sun's energy! That's how we were able to see it even though it was several billion light years away.

2011

That extra heat works its way out through our star, heating up the outer layers, too. A hotter gas shines more brightly, so the Sun has been steadily increasing in brightness too. It's an incredibly slow but inexorable process; the Sun's increased in luminosity by about _ since it was born.

40%

The Sun is nearly _ old now, so it's approaching middle age.

5 billion years

These are incredibly huge stars, some over a billion kilometers across! And they are luminous. For example, Betelgeuse in Orion is a red supergiant, and one of the brightest stars in the sky despite being over _ away.

600 light years

The main sequence star of _ solar masses will leave the white dwarf.

8

A star like the Sun can happily fuse hydrogen into helium for over 10 billion years. But a star twice as massive as the Sun runs out of hydrogen in just 2 billion years. A star with _ the Sun's mass runs out in only 100 million years or so.

8 times

Lower-mass stars like the Sun stop fusion at carbon. Once that builds up in the core, the star's fate is sealed. But if the star has more than about _ the Sun's mass, it can create temperatures in its core in excess of _ million degrees Celsius, and then carbon will fuse. There are actually a lot of steps in this process, but in the end you get carbon fusing into neon, magnesium, and some sodium.

8 times, ... , 500

Sirius, the brightest star in the night sky, is much hotter than the Sun, and is classified as an _.

A0

One of _ biggest ideas is that space isn't just emptiness, it's an actual thing, like _ in which all matter and energy is embedded.

Albert Einstein's, ... , a fabric

At first, stars were classified by the strengths of their hydrogen lines. The strongest were called A stars, the next strongest B, then C, and so on. But in 1901, a new system was introduced by spectroscopist _, who dropped or merged a few of the old classifications, and then rearranged them into one that classified stars by the strengths and appearances of many different absorption lines in their spectra.

Annie Jump Cannon

As the core switches back and forth from one fusion reaction to the next the outer layers respond by contracting and expanding, so a red supergiant can shrink and become a _ supergiant.

BLUE

The brilliant astronomer _ put all the pieces together. She showed that the spectra of stars depended on the temperature and elements in their atmospheres.

Cecelia Payne-Gaposchkin

Whatever happens in a black hole STAYS in a black hole. That region of space, that surface around the black hole where the escape velocity is the speed of light, is called the _ for that reason.

EVENT HORIZON

Space and time are basically two parts of the same thing, what we now call space-time. You can't affect one without affecting the other. _ calculated that when a massive object warps space, it also warps time; someone deep inside the gravitational influence of an object perceives time as ticking _ than someone far away from that object.

Einstein, ... , more slowly

Stars make energy in their cores by fusing helium into hydrogen.

False

The Sun has a surface temperature of about 5500° Celsius, and is a _ star.

G2

The data regarding temperature and luminosity, as well as indirect information on mass and radius, can be represented on something called an _ diagram for short.

H-R

So from hottest at around 25,000 Kelvin to coolest at around 3,500 Kelvin, we now have a letters for stars, a classification system called the _, which was developed by early astronomer Annie Jump Cannon.

Harvard system (O, B, F, G, K, M)

This is called an HR Diagram, after _.

Hertzsprung and Russell

Betelgeuse, which is red and cool, is classified as an _.

M2

A black hole has incredibly intense gravity, so the tides it can inflict are serious indeed. They're so strong that if you fell into a stellar mass black hole feet first, the force of gravity on your feet can be _ than the force on your head.

MILLIONS OF TIMES STRONGER

When a star dies and if the core of the star is _, the gravity of the core can actually overcome the tremendous resistance of the neutrons and continue its collapse. What force can possibly stop it now? It turns out, none. None more force. There is literally nothing in the Universe that can stop the collapse.

MORE than 2.8 times the Sun's mass

There's that thick line running diagonally down the middle, the clump to the upper right, and the smaller clump to the lower left. This took a long time to fully understand, but now we know this diagram is showing us how stars live their lives. Most stars fall into that thick line, and that's why astronomers call it the _.

Main Sequence

The idea that huge black holes could form in the centers of galaxies was first proposed in the 1970s, and it wasn't much later that the first one was found, in the center of our own _. We've measured its mass at a whopping _ times the Sun's mass!

Milky Way galaxy, ... , 4.3 million

_ after the big bang stars exist within galaxies.

One billion years

An example of a red dwarf star would be _.

Proxima Centauri Star

is happening so fast this literally takes a fraction of a second once it gets started. The core gets its legs kicked out from under it. It doesn't shrink, it _. The gravity of the core is so mind-bogglingly strong that the outer parts crash down on the inner parts at a significant fraction of the speed of light.

Silicon fusing into iron, ... , collapses

The nearest star that might explode in this way is _, in Virgo, and it's well over 100 light years away

Spica

All the heavier elements are synthesized during this event.

Supernova

A supernova does not leave behind a white dwarf.

True

At first glance, stars pretty much all look alike. Twinkly dots, scattered across the sky. But when you look more closely you see differences. The most obvious is that some look bright and some faint. Sometimes that's due to them being at different distances, but it's also true that stars emit different amounts of light, too

True

Iron is different. When it fuses it actually sucks up energy instead of creating it. Instead of providing energy for the star, it removes it

True

Massive stars versus low-mass stars age differently, and go to different parts of the HR diagram as they die.

True

So your clock ticks a bit slower than someone far away from Earth, for example. The effect is tiny, but real, and we've actually measured it on Earth with extremely precise clocks!

True

Stars also have atmospheres, thinner layers of gas above the denser inner layers.

True

Stars can change position on H-R diagram.

True

The HR diagram plots stars' luminosity versus temperature, and most stars fall along the main sequence, where they live most of their lives.

True

The gravity crushing the star inwards increases exponentially with its radius, so larger stars have to generate much more outward pressure to prevent collapse.

True

The red SUPERgiants are massive stars beginning their death stage.

True

Today you learned that stars can be categorized using their spectra.

True

Very roughly speaking, we can divide stars into two groups: low mass stars and high mass stars.

True

"The largest star that we know of" - The current title belongs to _.

UY Scuti

As we can't stick a thermometer into a star to see how hot it is, this classification based on temperature is actually derived from _ regarding blackbody radiation.

Wien's law

These are technically not stars, and are thus referred to as sub-stellar objects

a brown dwarf stars

The smallest type of star that is sufficiently massive so as to trigger the type of nuclear fusion we see in familiar stars is _.

a red dwarf star

The material stops its infall, reverses course, and blasts outward. The star explodes. It explodes. This is called _, and it is one of the most violent and terrifying events the Universe can offer. An entire star tears itself to shreds, and the expanding gas blasts outward at 10% the speed of light. The energy released is so huge they can be seen literally halfway across the Universe; they outshine all the stars in the rest of the galaxy combined.

a supernova

For the Earth, the escape velocity is _. Get something moving that quickly, and it's gone; it'll never fall back.

about 11 km/sec

Interpreting stellar spectra was a tough problem. The spectrum we measure from a star is a combination of two different kinds of spectra. Stars are hot, dense balls of gas, so they give off a continuous spectrum; that is, they emit light _.

at all wavelengths.

Hotter stars put out more light _ of the spectrum, while cooler ones _.

at the blue end, ..., peaked in the red

The star will be a red giant for around a _ years.

billions

Rigel, another star in Orion, is a _ supergiant, putting out over _ times as much energy as the Sun!

blue, ... , 100,000

Stars come in almost every color of the rainbow. Hot stars are _, cool stars _. In between there are orange and even some yellow stars.

blue, ... , red

Also, hotter stars tend to be larger and burn _, with the additional heat resulting from the fact that so much more fuel is being burned.

brighter

What happens if we go lower than this limit of 80 Jupiter masses? Then we can get something called a _.

brown dwarf

Ever since the Sun was born it's been fusing hydrogen into helium in its core. The helium is trapped there, unable to be used as fuel, and is _ like ash in a fireplace. As it does, the density in the Sun's core slowly increases. When you compress a gas it _. That means, every day, the Sun's core gets a wee bit .

building up in the core, ..., heats up, ... , hotter

The _ in your bones? The_ in your blood? The _ in your DNA? All created in the heart of the titanic death of a star. That star blew up more than 5 billion years ago, but parts of it go on in you.

calcium, ... , iron, ... , phosphorus

After being a red supergiant. At some point, the core contracts and heats up so much that the conditions will finally be primed for helium fusion. Suddenly, helium is converted into _, releasing a lot of energy. Then, in a weird twist, due to a lot of very complicated physics, the core itself winds up expanding, absorbing most of that energy. In the end, less energy is pumped into the outer layers, so the Sun's outer layers contract. The Sun shrinks.

carbon

Eventually, though, low-mass stars do run out of fuel (after some 990 billion years or so ). When one does, the star itself will be nearly pure helium (plus whatever heavier elements it was born with), and fusion will _.

cease

Stars are in a constant struggle between gravity trying to _ and their internal heat trying to _.

collapse them, ... , inflate them

Now that we are about a billion years into the history of the universe, we can see a panorama of stars swirling around in galaxies, and galaxies have in turn collected into clusters and superclusters. So what happened next? We started to observe stars in telescopes, we divided them first into _ classes.

color

The stars on the upper right are luminous but _. They must therefore be huge. These are red giants, also part of the dying process of stars like the Sun.

cool

In the lowest mass stars, _ , the rate is so slow they last a long, long time. But there's more to it than that. They fuse hydrogen only in their very centers, and their cores aren't very big. Outside of this small region the gas is _, which means the hot stuff rises all the way to the surface, cools, then falls back to the core. That's important, because it means the entire star is available for fuel.

cool red dwarfs, ... , convective

In the lowest mass stars, _ , the rate is so slow they last a long, long time. But there's more to it than that. They fuse hydrogen only in their very centers, and their cores aren't very big. Outside of this small region the gas is _ , which means the hot stuff rises all the way to the surface, cools, then falls back to the core. That's important, because it means the entire star is available for fuel.

cool red dwarfs, ..., convective

The closest you can get to the Sun is by touching it, being on its surface, about 700,000 km from its center. If you get any closer to its center, you're INSIDE it. The material OUTSIDE of your position is no longer pulling you down and so the gravity you feel will actually _.

decrease

Stars also have atmospheres, thinner layers of gas above the denser inner layers. These gases absorb light at specific wavelengths from the light below depending on the elements in them. The result is that the continuous spectrum of a star has gaps in it, darker bands where _.

different elements absorb different colors.

That huge increase in luminosity does more than just make the Sun bright, though. As a red giant, the Sun will be so swollen that the gravity at its surface will _ substantially from what it is now. The force of gravity holding it down is weak, but the force from all that light blasting out from below is strong, easily overpowering gravity. Material on the surface will get blown off like a leaf in a hurricane. Think of it as a super solar wind. That means the Sun will shed mass, a lot faster than it does now. While it's a red giant, it'll _ fully a third of its mass.

drop, ... , lose

The velocity at which you need to fling something off the surface of an object to get it to escape it's called _.

escape velocity

The Sun can become a black hole.

false

The shock wave, together with a huge swarm of protons, blast through the star's outer layers, causing it to explode.

false

Like the Sun, stars generate energy by fusing hydrogen into helium in their cores. A star that fuses hydrogen faster will be hotter, because it's making more energy. The rate of fusion depends on the pressure in a star's core. More massive stars can squeeze their cores harder, so they fuse _ than low mass stars. It's pretty much that simple. And that explains the main sequence!

faster and get hotter

The hotter star means _.

faster fusion

Stars make energy in their cores by fusing hydrogen into helium. This is actually a pretty complicated process with lots of steps, but in the end _ plus some other ingredients get turned into one helium nucleus. Each time this happens a little bit of energy is released, but in the core of a star it happens countless times every second. It adds up to a LOT of energy: enough to power a star, in fact.

four protons

The gravity causes the gas cloud to contract until _ begins.

fusion

Only by colliding nuclei together and fusing them in its ultra-hot core can a star release enough outward energy to counter the effects of _ relentlessly crushing inward.

gravity

When more massive stars go out, they go out with a bang -- a very, very big bang. In the core of a star, pressure and temperature are high enough that atomic nuclei can get squeezed together and fuse. This releases energy, and creates _ elements. Hydrogen fusion makes helium, helium fusion makes carbon, and each _ element, in general, takes higher temperatures and pressures to fuse.

heavier, ... , heavier

A star will slowly be fusing all of the hydrogen in its core into _, and maintaining a relatively steady size, temperature, and luminosity as it does so, until almost all of the hydrogen is gone.

helium

A black hole is the ultimate end state for the core of a _.

high mass star

The strength of gravity you feel from an object depends on _ and _.

how massive it is, ... , your distance from its center

The fusion in the core continues as long as there is _ to fuel it.

hydrogen

As we already know, any star will begin as a cloud of gas and dust at least a few light-years across. In the earliest era of star formation, this material was almost exclusively _, as this was what remained after the brief seventeen minutes of nucleosynthesis soon after the Big Bang.

hydrogen and helium

Stars spend most of their lives fusing _, which is why the main sequence has most of the stars on it; those are the ones merrily going about their starry business of making energy.

hydrogen into helium

Low-mass stars will eventually run out of fuel ( _ ). When one does, the star itself will be nearly pure _ (plus whatever heavier elements it was born with), and fusion will cease. It'll then cool, which will take many more billions of years. Finally, it will be a cold, black, dead star. And for them, that'll be pretty much that. Or so we think; the Universe is far too young for any of these red dwarfs to have run out of fuel yet.

hydrogen, ... , helium

There is a limit to how small a star can be, or rather, we know the minimum mass that is required for a gas cloud such that the _ is sufficient to trigger nuclear fusion, which is the process that defines every star.

inward gravitational pressure

Among a pile of other elements, silicon fusion creates _.

iron

As the core switches back and forth from one fusion reaction to the next the outer layers respond by contracting and expanding. It now looks like an onion, with multiple layers: _is building up in the center, surrounded by fusing _. Outside that is a layer of fusing _, then _, then , then _ , and finally _. You might think massive stars would last longer because they have more fuel than lower-mass stars. But the cores of these monsters are far hotter, and fuse elements at far higher rates, running out of fuel more quickly.

iron, ... , silicon, ... , oxygen, ... , neon, ... , carbon, ... , helium, ... , hydrogen

If the star's core is _, it will become a white dwarf. A white dwarf is a very hot ball of super-compressed matter. A white dwarf is about the size of the Earth. A white dwarf is what stars like the Sun become after they have exhausted their nuclear fuel. Near the end of its nuclear burning stage, this type of star expels most of its outer material, creating a planetary nebula.

less than 1.4 times the mass of the Sun

Silicon fuses into a bunch of different elements, including iron. This slams down on the central core, collapsing from several hundred kilometers across down to a couple of dozen kilometers across in just a few thousandths of a second! If the star has _ the Sun's mass, the core collapse stops when it's still 20 or so kilometers wide. It forms what's called _.

less than about 20 times, ... , a neutron star

So we can use spectra to determine a lot about a star. But if you combine that with knowing a star's distance, things get amazing. You can measure how bright the star appears to be in your telescope, and by using the distance you can calculate how much energy it's actually giving off — what astronomers call its _.

luminosity

A century ago astronomers Ejnar Hertzsprung and Henry Norris Russell made a graph, in which they plotted a star's _. When they did, they got a surprise: a VERY strong trend

luminosity versus its temperature

The core heats up, and when it reaches about a billion degrees, neon will fuse. Neon fusion creates more _, as well as some _.

magnesium, ... , oxygen

In the H-R diagram, we can see that the majority of stars fall on a continuous curve, which we call _. Ninety percent of all stars follow this trend, including our own sun, which is part of this yellow region here.

main-sequence stars

We talked about what happens to low mass stars like our own sun, which eventually become white dwarfs, and we talked about what happens to high mass stars, which become neutron stars, or even black holes above a certain mass. So clearly, the _ of a star is the primary variable in determining its behavior and the remnant it leaves behind.

mass

About a _ Earths could fit inside the Sun.

million

The light from the Sun is white, but some of the shorter wavelengths like purple and blue and some green get scattered away by _. Those appear to be coming from every direction but the Sun, which is why the sky looks blue. The Sun doesn't emit much purple, so the sky doesn't look purple, and the green doesn't scatter as well as blue.

molecules of nitrogen in our air

Larger stars are always _ luminous.

more

If two stars are the same size, but one is hotter, the hotter one will be_.

more luminous

If two stars are the same temperature, but one is bigger, the bigger one will be _.

more luminous

Massive stars are hotter and _, so they fall on the upper left of the main sequence.

more luminous

Silicon fuses into a bunch of different elements, including iron. If the star is _ the Sun's mass, then the collapse cannot be stopped by any force in the Universe. The core collapses all the way down. Down to a point. The gravity becomes so intense that not even light can escape. A _ is born.

more than 20 times, ... , black hole

The rate at which hydrogen fusion occurs depends on how _ the star has in its core.

much pressure

In the H-R graph, really bright stars are _, fainter ones _.

near the top, ... , near the bottom

Stars are fueled by_.

nuclear fusion

When the star explodes, the gas gets so hot and is compressed so violently by the blast that it undergoes fusion, what astronomers call explosive _ : Literally, creating heavy elements explosively.

nucleosynthesis

Hot, blue stars are _, and cool, red stars on _.

on the left, ... , on the right

The hotter the star, the more of the hydrogen and helium nuclei that have been stripped of their electrons, forming the phase of matter known as _.

plasma

Hotter objects like O and B stars are blue, and cooler objects like K and M stars are _.

red

Like the Sun, a massive star changes when hydrogen fusion stops, its core contracts, and then helium fusion begins. It swells up just as the Sun will, but instead of becoming a red giant, it generates so much energy it becomes a _.

red supergiant

What happens when the core collapses and suddenly stops? The core of the star, whether it's a neutron star or a black hole, is now extremely small with terrifyingly strong gravity. It pulls on the star's matter above it, HARD. This stuff comes crashing down at a fantastic speed and gets hugely compressed, ferociously heating up. At the same time, two things happen in the core. While this stuff is falling in, a monster _ created by the collapse of the core moves outward, and slams into the incoming material. The explosive energy is so insane it slows that material substantially. The second event is that the complicated quantum physics brewing in the core generates vast numbers of subatomic particles called _.

shock wave, ... , neutrinos

When hydrogen runs out the core will begin to _.

shrink

When the core of the high-mass star heats up to about 1.5 billion degrees, then oxygen fuses, creating _.

silicon

As you fall in a black hole, your feet are pulled so much harder than your head that you stretch, pulled like taffy. You'd become a long, thin, noodle, kilometers in length, but narrower than a hair wide. Astronomers call this - and no, I'm not kidding - _.

spaghettification

A _ is the result when you divide the incoming light from an object into individual colors, or wavelengths.

spectrum

The Sun, which has much _ gravity than Earth, has an escape velocity of over _.

stronger , ... , 600 km/sec

When a star dies and the collapsing core of the star shrinks, its gravity gets _. That means its escape velocity gets_.

stronger and stronger, ... , higher and higher

This slowing of time is _ the _ of the object is.

stronger, ... , stronger the gravity

Later it was realized that things made more sense if stars were categorized by _, but this letter system was retained because all the work to classify stars had already been done.

surface temperature

A few years later, physicist Max Planck solved a thorny problem in physics, showing how objects like stars give off light of different colors based on their _.

temperature

The classification scheme proposed by Cannon and decoded by Payne-Gaposchkin is still used today, and arranges stars by their _, assigning each a letter. Because they were rearranged from an older system the letters aren't alphabetical: So the hottest are O-type stars, slightly cooler are B, followed by A, F, G, K, and M. It's a little weird, but many people use the mnemonic, "Oh Be A Fine Guy, Kiss Me," or "Oh Be A Fine Girl, Kiss Me,"

temperature

Around the same time, Bengali physicist Meghnad Saha solved another tough problem: how atoms give off light at different _.

temperatures

Black holes come in different sizes, but for all of them,_, so nothing can escape, not matter or light.

the escape velocity is greater than the speed of light

A higher mass star squeezes hydrogen harder, so it fuses far more quickly. The rate is so much higher, in fact, that even though they're a lot bigger than low mass stars, high mass stars run out of hydrogen fuel in their cores more quickly! The lower mass a star is, _.

the longer it lives

Stars like the Sun, work a little differently than the Low-mass stars. Their cores are bigger, and hotter, and denser. The different conditions inside them means _, the hot stuff _ .

the material in them doesn't convect, ... , doesn't rise away from the core

A stellar mass black holes form when a very massive star dies, and its core collapses.

true

As remnants expand and age they become more tenuous. Some have bright rims as they push into material between the stars; others form complex webs of filaments.

true

Black holes have powerful gravity, yeah, but only when you're very close to one. The power of a black hole comes from its mass, certainly, but just as important is its SIZE. Or, really, its LACK of size.

true

However, if you get near a black hole, the effect gets a lot stronger. In fact, black holes warp space-time so much that, at the event horizon, time essentially stops! You'd see your clock running normally, and you'd just fall in — bloop, gone. But someone far away would see your clock ticking more slowly as you fell in. And this isn't a mechanical or perception effect; it's actually woven into the fabric of space. To someone outside looking down on you, your fall would literally take forever.

true

However, if you get near a black hole, the effect gets a lot stronger. In fact, black holes warp space-time so much that, at the event horizon, time essentially stops! You'd see your clock running normally, and you'd just fall in — bloop, gone. But someone far away would see your clock ticking more slowly as you fell in. And this isn't a mechanical or perception effect; it's actually woven into the fabric of space. To someone outside looking down on you, your fall would literally take forever. When you're right at the event horizon, just when an outside observer would see your clock stop, they'd also see the light coming from you infinitely redshift!

true

If you could turn the Sun into a black hole, which you can't, but let's pretend you could, then the Earth would orbit it pretty much exactly as it does now. From 150 million kilometers away, the Earth doesn't care if the Sun is big or tiny.

true

Iron robs critical energy from the core, causing it to collapse.

true

It takes a stellar core at least about three times the mass of the Sun to overcome neutron degeneracy pressure.

true

Massive stars fuse heavier elements in their cores than lower mass stars.

true

One single neutrino could pass through trillions of kilometers of lead without even noticing.

true

Orbiting a ten-solar-mass black hole would be just like orbiting a ten-solar-mass star... except not so hot and bright.

true

So from far away, a black hole with, say, ten times the Sun's mass would pull on you just as hard as a normal star with that same mass.

true

So, if the Sun were crushed down to about 6 km across it would be a black hole. You could get much closer than 700,000 km to it, and as you did you'd feel a stronger and stronger pull as you approached it.

true

Star mass determines the faith of the star.

true

Stars with more mass than Low-mass stars, stars more like the Sun itself, work a little differently. Their cores are bigger, and hotter, and denser. The different conditions inside them means the material in them doesn't convect, the hot stuff doesn't rise away from the core. What's in the core stays in the core. Outside the core there is a very deep and active convection zone, but that doesn't interact with the material in the core itself.

true

The heavy elements created in the supernova will become part of the next generation of stars and planets. Supernovae are how the majority of heavy elements in the Universe are created and scattered.

true

The resulting supernova creates even more heavy elements, scattering them through space.

true

We think of time as just... flowing, and everyone should see it move at the same rate. But the Universe is under no obligation to obey our preconceptions.

true

What we perceive as gravity is really just a warping of space, like the way a bowling ball on top of a bed warps the shape of the mattress. The more massive an object, the more it warps space.

true

You can orbit a black hole, too, as long as you keep a safe distance between you and it.

true

High-mass stars are incredibly huge stars! And that's nothing compared to VY Canis Majoris, the largest known star, which is a staggering _ billion kilometers across. We even have a special term for it: _.

two, ... , a hypergiant

If you look through binoculars or take pictures of stars, you'll see that they're all different colors, too. Some appear _, some red, orange, blue, and for a long time, the reason for this was a mystery.

white

Finally, though, we approach the endgame. The Sun doesn't have enough mass to squeeze carbon atoms enough to fuse them. They build up in the core until there's no more helium, and fusion stops. By this time the Sun will have literally blown off all its outer layers. It's essentially a naked core: a hot, intensely bright super-compact ball, not much bigger than Earth. We call this a _.

white dwarf

Without fuel (hydrogen), fusion in the core will stop. Helium can be fused into carbon (and a little bit of oxygen and neon), but it has to be incredibly hot to do so, and the Sun's core _. Still, half the Sun's mass is bearing down on the core, so even though fusion stops, the core will continue to contract and heat up. It'll get so hot that the temperature outside the core will get to hydrogen fusion temperatures. Like igniting a match by holding it near a flame, the hydrogen outside the core will start to fuse. That'll occur in a shell surrounding the core, adding its heat to the outer layers of the Sun as well. When you heat a gas it _. The Sun's outer layers will do just that, and our star will grow to well over twice its current size. Astronomers call a star like this a subgiant.

won't be anywhere near those conditions, ... , expands