When will the Sun die?

JACKIE FAHERTY (Senior Scientist, Division of Physical Sciences, American Museum of Natural History): When will the Sun die?

[Text reads: “When will the Sun die?”]

[MUSIC] [BOOM]

[The American Museum of Natural History logo appears, with text below it reading “Space Vs Dinos” superimposed on illustrations of an asteroid and a dinosaur skull. FAHERTY appears, with text: “Jackie Faherty, Astrophysicist”]

FAHERTY: Stars don’t actually die, but rather they just morph into something else.

[To FAHERTY’s left, a glowing star starts to dim and a gravestone covers it. A red X appears over the gravestone. To her right, a glowing star spins and morphs into a ring of debris-like dots with a bigger single dot in the center. Both fade away after a few seconds.]

FAHERTY: And how long that takes really depends on how much hydrogen they have, and how efficient they are at burning that hydrogen.

[Text appears: “1. How much hydrogen they have” and “2. How fast they burn hydrogen”]

FAHERTY: In the case of a star like our own Sun,

[An illustrated glowing star comes down from the top of the screen. Label reads “The Sun.”]

FAHERTY: we can figure that part out by looking at it and seeing how bright it appears in the sky,

[The camera zooms out and an astronomical observatory drops down on the left and a human drops down on the right. Both look up at the sun above them. The human says “Ow, my eyes” and text below the human says “(Don’t do this)”. The observatory spits out the number “~4 x 10²⁶ Watts.”]

FAHERTY: and then measuring how far away it is.

[The observatory spits out the number “~93 million mi/150 million km” while the human hops up and down uselessly with a ruler.]

FAHERTY: And when you put those two things together,

[The camera zooms back in on just the Sun, with the two measurements below it.]

FAHERTY: what you discover is that our Sun is sort of a run of the mill, medium-sized G-type star,

[The Sun gets smaller and appears in a lineup of star types. The order, from largest on the left to smallest on the right, goes O, B, A, F, G (our Sun), K, and M. They also go in color from blue to pale red from left to right as well. Arrows indicate that the size, brightness, and temperature increase from right to left, and that lifespan increases in the opposite direction, from left to right. So the bigger stars are brighter, larger, and hotter, but live for shorter periods of time.]

FAHERTY: and these stars tend to live for roughly 9-10 billion years.

[A square is drawn around the G-type stars, of which our Sun is one. Text appears below: “9-10 billion years.” FAHERTY reappears on the screen.]

FAHERTY: But to find out how much time the Sun has left, you need to know how old it is now. And you can’t just ask the Sun how old it is.

[Two anthropomorphic stars drop from the top. One is sitting on a bench while the other holds a clipboard. The one on the bench says “How long have I got, doc?” The other says “Hmm. How old are you?” The first one [GASPS], crosses its arms and says “Wow, rude.”]

FAHERTY: So what astronomers and geologists do is we turn to the rocks of the solar system

[Illustrated icons of rocks pop up on the screen behind FAHERTY.]

FAHERTY: and specifically the best kinds for age-dating the solar system are meteorites. And those give us an indication

[Next to FAHERTY a circle is drawn, where an image of a small meteorite appears with the text “Meteorites” over it. The circle expands to show more of the meteorite particles. Text continues: “Meteorites – leftover rocks from when the solar system formed.”]

FAHERTY: that the solar system is about 4.5 billion years old.

[Text appears over the meteorite images: “Solar System: 4.5 billion years old.”]

FAHERTY: So when you take that into account with the fact that the Sun will live for about 10 billion years,

[The text minimizes into a circle in the center of the screen. Another circle appears to the left of it that reads: “Sun lifespan: 9-10B years.” A minus sign appears in between the two circles and an equals sign to the right of the solar system age circle.”]

FAHERTY: we know we’ve got 4.5-5.5 billion years of fuel left in the Sun.

[After the equals sign, a new circle appears with text inside: “Remaining: 4.5-5.5B years.” The circle enlarges to fill the screen and two fuel gauges appear on either side. They both point to halfway between full and empty. FAHERTY reappears onscreen.]

FAHERTY: But what happens when the Sun starts to run out of fuel? Up until this point, the Sun has been relatively stable with a very nice balance between two forces.

[The Sun appears over a set of scales, which are gently tipping back and forth.]

FAHERTY: There’s the inward force of gravity, which is trying to force the Sun together,

[On the left scale, the text “Gravity” appears. Inside the Sun, red arrows point from the outside of the Sun towards the center.]

FAHERTY: and the outward force of radiation pressure, which is pushing outward due to reactions that are going on at the core of the Sun.

[The red arrows fade away and are replaced by yellow arrows going in the opposite direction (pointing outward from the inside of the Sun). In the middle of the arrows, a glowing and bubbling white sphere churns. On the right scale, the text “Radiation pressure” appears. This graphic minimizes into a circle to the right of FAHERTY.]

FAHERTY: And as the Sun dies, as it’s running out of fuel, you start to lose that balance.

[The Sun flickers a little bit, and the scales start to tip back and forth more wildly and faster.]

FAHERTY: And initially, radiation pressure decreases, and the Sun starts to collapse in on itself, decreasing and shrinking in size.

[An illustration of the Sun with four planets orbiting around it appears on screen. At the bottom of the screen is the same text of “Gravity” and “Radiation pressure”. The text for “Gravity” gets much larger and the size of “Radiation pressure” decreases. Red arrows push inward on the sun as it starts to get smaller.]

FAHERTY: And when that happens, the core of the Sun actually gets hotter. You get another phase of burning and the Sun starts to expand again,

[An inset graphic from the center of the Sun expands to fill the screen with an orange glowing core in the center. A thermometer appears and shows temperature to be increasing. The core glows bright white and then gets large and fills the screen. This view of the core minimizes as we see the Sun with its planets in orbit starting to get larger again.]

FAHERTY: and the Sun will move into this phase that we call the red giant phase

[At the bottom of the screen, text for “Radiation pressure” now gets very large while the text for “Gravity” shrinks. Yellow arrows appear to push outward from the center of the Sun while it expands and goes from being white to a pale red. Text appears: “Red giant phase”]

FAHERTY: which will encompass Mercury and Venus

[As the Sun expands so much that it covers the orbits of the two innermost planets, they ignite and leave a trail of red flames as they continue to orbit. Beneath both planets, text appears: “AHHHHH!”]

FAHERTY: and spread all the way out to where the Earth is right now.

[The Sun stops expanding right at Earth’s orbit, so it too catches on fire and is left behind as a smoldering charred planet. Text appears: “Mars save yourself!” Mars, which has been untouched, has text appear next to it: “…guys?!”]

FAHERTY: Ultimately there’s just not enough fuel to sustain it, and so gravity collapses the sun down

[The inset view of the Sun’s core re-expands, so we can see that the core, once bright white and hot is now collapsing and turning orange and red. Text appears over the core: “so hungry… need more… hydrogen…”]

FAHERTY: to a fraction of its size, of its temperature, of its brightness,

[The text for “Gravity” gets large again, and “Radiation pressure” gets smaller. The red dwarf Sun starts to shrink again, with red arrows pointing inward from the outer edge of the Sun. As it shrinks, it becomes grey and dull.]

FAHERTY: and turns it into this object that we call a white dwarf,

[Text appears: “White dwarf phase.”]

FAHERTY: that’s really dense and has a strong gravitational field, but it’s faint, and would not be visible to the human eye.

[The background gets a little darker. Text appears beneath the white dwarf Sun: “*if humans are still around.” A pause and then more text: “(we won’t be)” FAHERTY reappears on screen.]

FAHERTY: Everyone wants to know how much longer the Sun has to go

[On her left, a star appears. On her right, a human scratching its head.]

FAHERTY: because without a Sun it really means big trouble for the Earth and for life on Earth.

[The Sun suddenly disappears and the human throws its hands to its head in surprise. It runs off screen with a high-pitched [SQUEAK]]

FAHERTY: But you don’t have to worry because we’ve got plenty of time.

[Text appears next to FAHERTY: “Reminder: 5.5 BILLION years until the show starts.”]

FAHERTY: Hopefully we’ll be out exploring the cosmos and looking for new worlds by the time the Sun runs out of fuel.

[On a background of stars, a spaceship shoots onscreen. Inside are two humans. They look around, then look at each other and high-five, as in the background our Sun shrinks and then rapidly expands into a red giant with an [EXPLOSION].]

[Credits roll. In the bottom right corner, FAHERTY continues to speak.]

FAHERTY: Thanks for watching, and be sure to subscribe to the AMNH channel so you can catch more videos like this, and you can click on the link above me if you want to catch this week’s dinosaurs video.

[END MUSIC]