05.02 – Jets

Loading...

Do curso por University of Alberta

Astro 101: Black Holes

25 classificações

University of Alberta

Astro 101: Black Holes

25 classificações

What is a black hole? Do they really exist? How do they form? How are they related to stars? What would happen if you fell into one? How do you see a black hole if they emit no light? What’s the difference between a black hole and a really dark star? Could a particle accelerator create a black hole? Can a black hole also be a worm hole or a time machine? In Astro 101: Black Holes, you will explore the concepts behind black holes. Using the theme of black holes, you will learn the basic ideas of astronomy, relativity, and quantum physics. After completing this course, you will be able to: • Describe the essential properties of black holes. • Explain recent black hole research using plain language and appropriate analogies. • Compare black holes in popular culture to modern physics to distinguish science fact from science fiction. • Describe the application of fundamental physical concepts including gravity, special and general relativity, and quantum mechanics to reported scientific observations. • Recognize different types of stars and distinguish which stars can potentially become black holes. • Differentiate types of black holes and classify each type as observed or theoretical. • Characterize formation theories associated with each type of black hole. • Identify different ways of detecting black holes, and appropriate technologies associated with each detection method. • Summarize the puzzles facing black hole researchers in modern science.

Na lição

Approaching a Black Hole

What would you see as you approached a black hole, using a black hole binary as a vehicle to explore black holes? In this module students will follow material as it is transferred from a companion star to a black hole via Roche lobe overflow or wind fed accretion. They will then follow that material down through the accretion disc to explore tidal forces to learn about the ways in which black holes can rip apart surrounding material. This material will then pass through the innermost stable orbit of the disc, before falling in. Students will also get the opportunity to look at jets - the outflow of material from the innermost regions of this structure. Module Objective: Introduce properties of black holes from the outside in, through the context of a journey into the event horizon of a black hole. What would we see as we are far away? What will we see and experience as we get closer? What is a disc? What is a jet?

05.01 – Journey to a Black Hole2:54

05.02 – Jets6:45

05.03 – Black Hole Companions1:09

05.04 – Mass Transfer in Binaries8:20

05.05 – Have a Corona!2:26

05.06 – So What is Accretion?8:33

05.07 – Spinning Through the Disc10:13

05.08 – Innermost Stable Circular Orbit4:44

05.09 – Teetering on the Edge1:05

Interviews with experts - How can a star be like a vampire?1:20

Conheça os instrutores

Sharon Morsink
Associate Professor
Department of Physics, University of Alberta

[MUSIC]

From a distance, you might expect that there isn't much to see when looking at

a black hole like Cygnus X-1.

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

This is not due to the black hole itself emitting light, but

is an indirect result of the effects the black hole has on the space around it.

The bright lights that we see emanating from the regions around black holes

are due to the material the black hole is feeding on.

And from any material escaping from its mouth.

If the black hole's gravity is so strong, how can some of this material escape?

One of the first things we detect from Cygnus X-1 are the radio waves and

X-rays being produced from cone-like structures that

seem to originate from the area around its rotational axis.

These structures are called astrophysical jets, and they are one of the few

structures associated with black holes that have been imaged directly.

These cone-like structures can funnel material away from the black hole, and

in the case of Cygnus X-1, release the power of more than 1,000 suns.

Astrophysical jets are thought to be powered by material falling

onto the black hole or another compact object, but

the formation of jets is not yet fully understood.

Imagine water cascading over a waterfall.

The turbulence at the bottom and

the resulting mist are analogous to the way jets are formed.

We still don't know what jets are composed of, but leading theories suggest

that they are either electrically neutral combinations of electrons,

atomic nuclei and positrons, or a positron-electron plasma.

This material is responsible for creating the light that we detect when we see jets.

Near the inner edge of the accretion disk,

hot material interacts with the magnetic fields generated within the disc.

Due to these extreme conditions,

not only is the material hot enough to be in a state of matter called plasma.

But this plasma strongly interacts with magnetic fields to produce

light in a process called synchrotron radiation.

Although the precise mechanism of the interaction is still unknown,

there is no doubt that huge amounts of energy escape from the enfolding material

in the form of a jet.

In fact, there is so much energy within the escaping material that it can reach

10% of the speed of light.

When this occurs, we say that the jets are relativistic.

Relativistic jets can be seen emanating from compact objects like neutron

stars and black holes.

Jets originate at the magnetic poles of the compact objects and are,

in general, aligned with the spin axis of the compact object.

This is not always the case however,

as jets can be slightly offset from the spin axis.

The magnetic pulls of the Earth, for example,

are offset from the rotational pulls.

This slight offset in jets can be observed as a wobble or a lighthouse effect.

The lighthouse effect occurs as light from the jet sweeps across the field of view.

Just like light from a lighthouse sweeps past you as it rotates.

While this effect can be seen in any type of compact object, including Cygnus X-1,

the lighthouse effect is more commonly associated with a class of neutron stars

known as pulsars.

The jets from Cygnus X-1 are 100 times longer than the distance

between the Earth and our sun when imaged in x-rays.

On the other hand, if we look at the radio emission from Cygnus X-1,

there is evidence that the jets extend even further,

possibly 600,000 times the distance between the Earth and our sun.

If a jet is not pointed towards us, the wobble can be seen through other effects.

A good example can be seen in the relativistic jet

originating from the elliptical galaxy M87.

M87 contains one of the largest known supermassive black holes.

Which powers itself by devouring material at a rate equal to one

solar mass every ten years.

M87's jet is a jaw-dropping 5,000 light years in length,

spanning more than 4% of its host galaxy.

These NASA images of M87 show clear bends and

kinks that come both from the wobble of the jets and

from their interactions with the material in the surrounding space.

Since the material within a jet is traveling so

quickly, we'd expect it to have features related to its motion.

And indeed, it does.

Material from the jets is subject to the same Doppler shifts that we discussed in

module one.

Which is evidenced by the fact that material traveling away from us

appears to be redder and dimmer.

Versus the brighter and bluer jets that are directed towards us.

A good example of this was a recent survey by NASA Chandra Observatory

of Piktar-A galaxy containing a supermassive black hole.

NASA calls this black hole The Death Star because of

the powerful beams of energy it generates.

This is one of the best images we have of a complete system around a supermassive

black hole.

In this image, the central black hole of Piktar-A is obscured by an intense

X-ray source, depicted by the color blue, which is also the source of the jets.

The blue jet that is visible on the right-hand side of the image is pointed

roughly towards us.

But the counter jet on the other side is pointed away.

Due to Doppler shifting, we aren't able to see the counter jet.

The red clouds, labeled in this picture,

are also an important part of the environment around black holes.

They are called radio lobes because they produce significant amounts

of radio frequency radiation.

We mentioned earlier that the size of the jet in M87,

is more than 5,000 light years long.

The jets emanating from Piktar-A have been estimated to be 800,000 light

years in length, more than 8 times the span of the entire Milky Way galaxy.

With some jets from black holes exceeding the size of most galaxies,

it's safe to say that some jets generated from black holes are among

the biggest structures in our universe.

Explore nosso catálogo

Registre-se gratuitamente e obtenha recomendações, atualizações e ofertas personalizadas.

O Coursera proporciona acesso universal à melhor educação do mundo fazendo parcerias com as melhores universidades e organizações para oferecer cursos on-line.

© 2018 Coursera Inc. Todos os direitos reservados.

Baixar na App Store

Baixar no Google Play