Inside a Black Hole

01Say you were floating towards the black hole.

02Basically, the first part of you that was starting to get closer and closer to the black hole would start to experience the really extreme gravity that was near the black hole.

03Your body would basically start to be stretched like a spaghetti, stretching to get into the black hole where we would never see you again.

04Once you're in, you're stuck and that becomes your universe.

05This is NASA's Curious Universe.

06Our universe is a wild and wonderful place.

07I'm Patti Boyd, and in this podcast, NASA is your tour guide.

08This week's adventure will give you a front row seat to some of the universe's most perplexing wonders.

09We're exploring black holes.

10Really, these are some of the most extreme environments in the universe.

11That's Regina Caputo.

12She's an astrophysicist at NASA, and she studies black holes, mysterious and fascinating cosmic objects.

13We can't make anything like a black hole on Earth to study it.

14And so if we really want to understand how gravity interacts with all of the other forces in the universe, like, it's really a playground for understanding how gravity works, how fundamental particles work, how stars collapse in on themselves.

15Black holes truly are one of a kind.

16But what exactly is a black hole?

17Let's start with the word black.

18The name comes from the fact that nothing can escape the gravity of a black hole, not even light.

19How can they keep such a tight hold on everything?

20Well, they are extremely massive.

21And so they have very strong gravitational attractive forces.

22And so they really don't, like, suck things in.

23They pull things in.

24Because that's how gravity works.

25It's things that have mass are all attracted to each other.

26And the more mass, the more gravity.

27Even though light travels so quickly, it is no match for the gravity of a black hole.

28So now you know why they're black, let's talk about why they're called holes.

29This is actually a misleading word to describe these massive objects.

30While they may seem like a hole in the sky because they don't produce light, a black hole is not empty.

31It's actually a lot of matter condensed into a single point.

32This point is known as a singularity.

33So how do we get such a large amount of mass to come together at one point in space?

34Step one, get yourself a large star.

35Big stars burn up their fuel really fast because they have more gravity, which makes the centers of them hotter and denser.

36So they can go through a lot more nuclear reactions.

37And they burn it all up really, really fast.

38That's Jeremy Schnittman, a research astrophysicist at NASA.

39He's going to explain how a star gives rise to a black hole as it eats up its fuel.

40They build up a big pile of ashes in the center of the star.

41Those ashes, actually, it's iron.

42That iron doesn't do nuclear burning, so it doesn't give off extra heat.

43It just sits there and it's getting bigger and bigger and bigger.

44And now you have these two forces that are battling against each other.

45One force comes from whatever fuel is left to be burned.

46And another force is from the gravity of the iron pulling everything inward.

47And eventually you run out of this pressure that's holding up the center of the star.

48And the gravity just keeps getting bigger and the pressure stays more or less the same.

49And so the gravity wins.

50When the gravity wins, everything just starts collapsing.

51At that moment, two things are happening.

52Some star stuff is being shot off into space, causing the light shows we call supernovae.

53And the rest of it condenses into one point, the singularity.

54And that is how you make a stellar mass black hole.

55It's called stellar because it was made from a star.

56Our sun is a star.

57So you may be asking, will it ever become a black hole?

58As far as our sun becoming a black hole, it's unlikely that our sun is massive enough in order to actually become a black hole.

59Our sun will never form an iron core massive enough to collapse into a black hole.

60In fact, the smallest black hole we've ever observed was about four times the mass of the sun.

61Instead of a black hole, our sun will evolve into something else.

62At some point in our sun's lifetime, it will puff up into a red giant phase.

63And so it'll get really, really, really big.

64Future humans will have to deal with that.

65But it's very, very far in the future.

66By far in the future, Regina means really far.

67About four billion years.

68If our sun were magically replaced by a black hole of the same mass, here's what would happen.

69Earth and all of the other planets would stay in their same orbits, experiencing the same amount of gravity as before.

70We wouldn't even notice.

71Like, the Earth would still rotate around.

72The major difference?

73No light.

74A solar system in darkness.

75Not a fun scenario.

76So Jeremy took you through the birth of a stellar mass black hole.

77But that's not the only kind of black hole that we know of.

78There's another kind of black hole that makes a stellar mass black hole look like a blip in the universe.

79There are these supermassive black holes that are millions or even billions of times more massive than the sun.

80And those are in the centers of almost every galaxy.

81We still don't really know where those come from, but they seem to be quite universal.

82In fact, we have one of these mysterious giants at the center of our galaxy.

83About 26,000 light-years from Earth, the equivalent of 150 quadrillion miles, is the Milky Way's supermassive black hole called Sagittarius A-star.

84It's called that because it's located in the constellation Sagittarius.

85And you might be surprised to know that it wasn't discovered until 1974, which raises the question.

86If you were hunting for a black hole, how would you know when you had found one?

87After all, they are black.

88You can't actually see a black hole because they don't produce light like stars do.

89However, black holes can be some of the brightest objects in the sky.

90That's because of what can happen before black holes gobble up star stuff.

91Around a black hole is a boundary called the event horizon.

92Anything that passes the event horizon is trapped within the black hole.

93But right as the gas and dust get closer and closer to the event horizon, the gravity from the black hole makes them spin really fast, forming lots of radiation.

94And so we see that last little bits of light escaping from the event horizon.

95Another clue that there is a black hole is when you see a star orbiting what appears to be nothing at a very fast pace.

96That's how Cygnus X-1, the first ever confirmed black hole, was found in the 70s.

97We saw this star orbiting around something.

98And we didn't know what it was orbiting around.

99There were a lot of x-rays coming from it.

100And we figured, well, the only way it could be moving that fast is if there's a really strong gravitational field pulling on it.

101Since there was really nothing else that it could have been and it was more or less invisible, that's how we concluded that it was in fact a black hole.

102Cygnus X-1 was a big deal.

103Finding it confirmed what until then had only been a mathematical prediction based on Einstein's theory of relativity.

104Since then, we've found black holes through other means.

105Like sometimes a black hole can reveal itself if it comes between Earth and a bright star.

106Gravity actually bends light, bends the trajectory of photons.

107The gravity of the black hole bends the space surrounding it.

108So the light from the star travels through this warped space and looks very strange.

109Kind of like a cosmic donut.

110It's a phenomenon called gravitational lensing.

111And finally, there's one more way we can detect black holes.

112One that requires that two black holes get very close to each other.

113And then they start orbiting around each other and basically get closer and closer and closer and closer together as they're spiraling towards each other.

114And at some point, their event horizons merge and they smash into each other.

115And this process literally shakes the fabric of space-time.

116We've observed this before, and in some ways we've heard it too.

117We've detected these waves with LIGO, the Laser Interferometer Gravitational Wave Observatory.

118LIGO is funded by the National Science Foundation and operated by Caltech and MIT.

119That smashing together of these very, very massive objects sends out ripples in space-time.

120And those ripples are just like sound waves.

121And LIGO is built to detect those ripples.

122Scientists took those ripples and translated them into audio waves so that we can hear it.

123Take a listen.

124First, you'll hear the sound at the original frequency corresponding to the gravitational waves.

125Now here is the sound played at a higher frequency that is easier for us to hear.

126Did you hear the whoop?

127That was the waves getting faster and faster as the black holes merged.

128And so that's how we get the sounds of the universe.

129All of these ways of detecting black holes require that some other object be present.

130But if the black hole is flying solo, with nothing nearby orbiting it, and nothing nearby to eat, there is little chance that we will ever notice it.

131We will likely only get to know a fraction of the millions, if not billions, stellar mass black holes that are estimated to live in the Milky Way alone.

132Stellar mass and supermassive black holes are vastly different in mass.

133And for a while, scientists thought there might be no black holes with masses in between these two extremes.

134But recently, with the help of the Hubble Space Telescope, astrophysicists found the best evidence yet of intermediate mass black holes.

135NASA's Chandra and New Star telescopes have also been exploring these newly discovered middleweights.

136Now it's time for us to explore a black hole up close and personal.

137Let's take a journey into one.

138Say you were floating towards the black hole.

139Now let's suppose that you are approaching a stellar mass black hole, and that it isn't actively consuming star stuff, because if it were, even being near the black hole could be deadly.

140I certainly would not want to be in the path of a black hole that's actively eating up these stars.

141They eat things, and then they kind of like, you know, burp up particles, you know, at the speed of light.

142Lots of high-energy particles do not mix well with life.

143So let's just assume you approach a lonely black hole by chance, because you wouldn't see it.

144Now as you get closer, all of a sudden, you start feeling this tugging on one side of your body, but not on the other.

145Basically, the first part of you that was starting to get closer and closer to the black hole would start to experience the really extreme gravity that was near the black hole.

146Say if you were going feet first, you know, your feet would start to be stretched apart.

147Your body would basically start to be stretched like a spaghetti.

148There's even a technical term for it.

149It's called spaghettification.

150Basically just rip you to pieces.

151You probably wouldn't survive.

152But just for fun, let's say you did survive.

153Part of you would cross over into the event horizon, and the rest of you would probably be following pretty soon after.

154This only happens with stellar mass black holes, where you can feel that change in gravity.

155But if you found yourself entering a supermassive black hole, you wouldn't feel a thing.

156All of a sudden, you would just be inside the black hole, never to be seen again.

157Well, kind of.

158Here's the crazy part.

159If your friend were watching this happen to you, they might see you get stretched.

160But it would happen really slowly, until at some point it might look like you were frozen in time, like you never passed through the event horizon.

161That's because time gets stretched out by the immense gravity that a black hole produces.

162Really, it bends the reality of our universe.

163And the reverse happens from your vantage point.

164So if you were looking out at your friend, it would seem like they were moving through life at warp speed.

165If somehow you weren't ripped apart by the gravity, or managed to survive the radiation near the black hole's event horizon, well then you would get to enter the black hole.

166Once you're in, you're stuck, and that becomes your universe.

167What would you see and feel?

168We don't really know.

169We can only theorize.

170But at some point, you would become one with the singularity.

171Essentially, you'd be compressed into a tiny speck.

172So I would not recommend traveling to black holes.

173At least not that close.

174And luckily, it shouldn't be too tricky to avoid them.

175The nearest black holes we know of are thousands of light years away from us, meaning it would take thousands of years to get to them if we could travel at the speed of light, which we can't.

176So not only will they not be eating earth, they're too far away for a visit from earthlings.

177By now, the universe is peppered with black holes, with new ones forming all the time.

178And some black holes keep expanding as they consume more gas.

179But how and when does a black hole die?

180Even the ones that are creating hot gas and are very bright, they only do that for a very short part of their lifetime.

181But eventually, they'll all just run out of fuel.

182Even if they have a star orbiting around them, that won't last forever.

183They really, there's nothing left for them to do.

184They're just going to, they're just going to sit there.

185And for the most part, all of the matter inside the black hole will stay there as well.

186What happens in a black hole stays in a black hole.

187There's only one theorized way that anything can escape a black hole's gravitational grip.

188There's an interesting result from Stephen Hawking, the famous theoretical physicist, who showed that because of these quantum mechanical effects, a tiny bit of radiation can actually leak out of a black hole.

189It's called Hawking radiation.

190But in practice, it's such a tiny, tiny, tiny effect.

191First, we will never be able to observe it.

192And second, if you have a star that's 10 or 15 times the size of the sun, it would take trillions and trillions of years before it even changed a little bit because of the Hawking radiation.

193Once you hit black hole, you're black hole for the rest of the universe, it seems like.

194The long-lasting nature of black holes leads scientists to speculate that towards the end of the universe, when there's no stuff left to make new stars, and when all of the existing stars have burnt up, the universe will be dominated by black holes, a dark and uninviting scenario.

195Until eventually, those dissipate trillions upon trillions of years later, more time than we can fathom.

196And then, there will be nothing.

197This is NASA's Curious Universe.

198This episode was written by Margo Wall and Maddie Arnold.

199The Curious Universe team includes Michaela Sosby and Vicki Woodburn.

200Our executive producer is Katie Atkinson.

201Special thanks to Claire Andreoli, Ryland Hegey, Barb Mattson, Aaron Cara, and the astrophysics team.

202If you liked this episode, please let us know by leaving us a review, tweeting about the show at NASA, and sharing us with a friend.

203To keep up with the latest black hole science from NASA, check out nasa.gov slash black hole.

204Still curious about NASA?

205You can send us questions about this episode or a previous one, and we'll try to track down the answers.

206You can email a voice recording or send a written note to nasa-curiousuniverse at mail.nasa.gov.

207Go to nasa.gov slash curiousuniverse for more information.

208Thank you for listening to the second season of NASA's Curious Universe.

209We've enjoyed taking you along with us as we've explored everything from the International Space Station to our asteroid hunting mission.

210We're taking a break now, but we'll be back before you know it.

211Until then, you can continue exploring the universe and discovering our home planet with NASA by visiting nasa.gov.

212You can also follow NASA on Twitter, Instagram, and Facebook.

213And find more NASA podcasts in your app or at nasa.gov slash podcasts.

214Before we sign off, we've asked our scientists to do their best impression of the sounds we can make from black hole data.

215Here's what they gave us.

216We'll see you next time.

217We'll see you next time.

218We'll see you next time.

219We'll see you next time.

220We'll see you next time.

221We'll see you next time.

222We'll see you next time.

223We'll see you next time.

224We'll see you next time.

225We'll see you next time.

226We'll see you next time.

227Bye.