Harvey Black Hole Show:
What are black holes and can we travel through them?
Lets start with density, some rocks are denser than others (two rocks the same size, one feels heavier):
handle, sulfur, quartz, pyrite, large iron nut
The Iron sinks to
the center of the earth.
We can tell cuz the earth is heavier than if it were just made of
rock! Also we can tell something is down there because earthquake
waves travel funny when they get close to the center.
But some things are even denser than iron! There are white dwarf stars like Sirius b.
where is Sirius and Sirius b in the night sky this winter?
https://arabiannightsrum.com/stars/winter-constellations/orion/
Sirius b is very dim because it is very small, the size of the earth, but it is still as massive as the sun and very hot, so it is bright for its size. Anyway it is therefore at least 10^6 times as dense as our sun. Here is the sun compared to Earth. Imagine squishing all the sun stuff into the size of the earth! a teaspoon of sirius b stuff would weigh as much as a truck!
The gravity is so strong that if we tried to walk on sirius b... we would be so heavy that we would be squished flat like a pancake!
https://upload.wikimedia.org/wikipedia/commons/thumb/c/cb/Planets2013.svg/1280px-Planets2013.svg.png
https://en.wikipedia.org/wiki/Sirius#Sirius_B
how does it happen, why do stars go nova? At first they are balanced.
They burn up their hydrogen fuel by nuclear fusion into helium and that produces a lot of gamma ray radiation pushing outward. But they are so heavy that all that gravity pushes inward. They are balanced. but then they use up the hydrogen and burn helium to carbon, and then carbon to silicon, and then silicon to iron. And that's as dense as the fusion burning can go, and when that happens: KABLOOIE! A supernova.
The crab nebula
https://en.wikipedia.org/wiki/Crab_Nebula#/media/File:Crab_Nebula.jpg
A star that went Nova: the crab nebula, where to find it? In the constellation Taurus, near Orion!
https://theskylive.com/sky/deepsky/messier-1-the-crab-nebula-object
Inside there is a kind of star discovered by Jocelyn Bell and her radio telescope. Neutron stars, or pulsars.
https://www.newscientist.com/people/jocelyn-bell-burnell/
Here is the record of what her radio telescope heard:
The pulsar inside the crab nebula is a sun squished down to about 12 miles wide!!!
https://en.wikipedia.org/wiki/Crab_Pulsar
But even though it is as big as a large city it is spinning around 30 times a second, so that's how we detect them with our radio telescopes.
It's so squished that the electrons and protons are squishd out of their atoms and all that's left is one giant atom of neutronium. And it is 500million times as dense as sirius b!!! If you tried to walk on a neutron star it would squish you not only into a pancake but POOF, you would be atomized into more neutronium.
crab nebula pulsar nova
https://www.youtube.com/watch?v=aysiMbgml5g
there is a record of when it exploded from a few places on earth in 1054CE
https://en.wikipedia.org/wiki/SN_1054
BLACK HOLE
But if a much bigger sun goes supernova then maybe it can turn into something even more squished together than a neutron star. But physicists think that it is impossibl to squish something that much. It would completely collapse into a kind of NOTHINGNESS that has so much gravity that even light wouldn't be able to escape: a "black hole"! is it possible? For a long time, physicists weren't sure.
If no light comes out how can we see one? 3 ways.
first they might suck in other star stuff and produce accretion discs and jets. Here is an artists conception of a black hole sucking in it's neighboring star stuff
https://en.wikipedia.org/wiki/Accretion_disk
Note that if we got anywhere near a black hole we would be vaporized and smeared out PUFF and would not be able to travel through it if it made a worm hole like in science fiction stories. We would have to invent a REALLY ADVANCED kind of spacecraft to make that work! Maybe in th future!
2) looking at
stars orbiting around an unseen object. Like these orbiting near the
center of our own galaxy. The speed of their rotation tells us that
the object at their focus of orbit is 4 million times the mass of our
sun! but the stars are so close to that focus that the object in
that focus is smaller than the orbit of Uranus. There is no way that
4 million suns can pack in that tightly, so it must be a supermassive
black hole.
3) gravitational wave detection. If two black holes swirl around each other, they are so massive and they swirl around so fast that they make ripples in space-time itself and after 30 years of building, we've made a detector to detect that:
LIGO!
https://www.ligo.caltech.edu/page/ligo-detectors
we made TWO of them on opposite sides of the country to make sure it really works. The arms are 2.5 miles long!
One of LIGO's mirrors. It uses laser beams traveling back and forth through th arms.
When LIGO detects two black holes swirling around each other and then finally smashing into each other... it sounds like a chirp, Listen:
https://www.youtube.com/watch?v=QyDcTbR-kEA
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