04.07 – Intermediate Mass Black Holes

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Del curso dictado por University of Alberta

Astro 101: Black Holes

86 calificaciones

University of Alberta

Astro 101: Black Holes

86 calificaciones

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.

De la lección

Sizing Up Black Holes

So far discussion has focussed on either the general case for black holes, of the stellar mass variety (endpoint of a star's life). In this module students will explore the various sizes of black holes and their measurable properties. Students will learn that there are four major types of astrophysical black holes (primordial/mini black hole’s, stellar mass, intermediate mass and supermassive black holes), and discover current theories on their formation, and what might feed them. Students will also gain an knowledge of ‘no-hair’ theorem and gravitational lensing. We will also explore the formation of supermassive black holes, intermediate mass black holes, and mini black holes in particle accelerators.

04.01 – Introduction1:07

04.02 – May the Schwarz(schild) Be With You6:34

04.03 – Dancing With the Stars12:57

04.04 – Weight Training5:30

04.05 – Stellar Mass Black Holes3:12

04.06 – Supermassive Black Holes10:53

04.07 – Intermediate Mass Black Holes8:27

04.08 – Super Tiny Black Holes2:43

04.09 – Summary: Preparing to Explore1:10

Interviews with experts - How do supermassive black holes form?3:11

Conoce a los instructores

Sharon Morsink
Associate Professor
Department of Physics, University of Alberta

So far, we have looked at the extremes of the astrophysical black hole scale,

stellar-mass black holes and supermassive black holes.

There is a good reason for this.

These extremes are the most well-known cases.

If we consider all the measured masses of black holes to date,

so as of late 2017,

we see a cluster of objects in the range of

about 5-20 solar masses with some reaching as high as possibly 70-80 solar masses.

These are the stellar-mass black holes.

There are also a large number of objects towards the right side of this plot,

at the highest mass end.

These are the supermassive black holes that are

thought to reside in the centers of most galaxies.

Masses have also been obtained for many other low-mass compact objects.

These low-mass stellar remnants populate the far left of

this plot and are classified as either neutron stars or white dwarfs.

In the middle of this plot,

there is a great deal of empty space.

Should there not be something lying in the middle?

This is one of the many questions perplexing astronomers today.

If we were to find black holes lying in the center of this plot,

they would be known as intermediate-mass black holes.

Although the search for these sources is ongoing,

intermediate-mass black holes have proven themselves to be very elusive.

Intermediate-mass black holes are just that.

They have masses that lie between

the heaviest stellar-mass black holes and the lightest supermassive black holes,

making them intermediate on the mass scale of

the astrophysical black holes, hence the name.

But what are these objects,

how are they made and why should we care about them?

Intermediate-mass black holes weigh more than 100 times the mass of our sun,

reaching up to 100,000 times the mass of our sun.

They are thought to be too big to form from

the death of stars that exist in our universe today.

If this is the case,

how are they made?

One theory suggests that these behemoths were formed

early in the universe when it was a much simpler place,

chemically speaking that is.

The first stars formed when the universe was only about 100 million years old.

At this time, the universe contained only the simplest elements,

so that was just hydrogen and helium.

This early in the universe,

stars could become much larger than they are today,

sometimes containing upwards of hundreds of solar masses.

We have already learned that massive stars burn hotter,

brighter, and quicker than their low-mass counterparts.

This was true for those first stars too.

Such huge stars would have very short lives indeed.

We have also seen that massive stars can lose their mass through winds.

What we have not yet mentioned though,

is that the power of this wind is a function of the star's chemistry.

Astronomers have found that the metallicity of

a star or the amount of metals it contains,

affect the strength of the star's wind.

Here is where I should point out a quirk of astronomy.

Forget the high school chemistry class for the moment, according to astronomers,

the universe is made up of hydrogen, helium, and metals.

Anything that contains more than two protons is a metal,

strange but true in the astronomical circles.

Anyway, back to stellar winds.

Therefore, the metallicity of a star or a region give you

an indication of how much of these metals are present.

When the metallicity is essentially zero,

we find that a star loses little to no mass via it's wind,

irrespective of its size.

This means that those first stars would have

lost very little mass by the ends of their lives.

At the end of the short life, well,

here's another place where it changes from a life of stars today.

Given the huge mass contained in these first stars,

astronomers think that they may not have ended in

a huge explosion as massive stars do today.

Instead, it is thought that once the star ran out of fuel,

the force of gravity would be so strong that all of

the star would collapse directly down to a black hole.

The outer envelope of the star,

would not be blown away as it is today,

it will be dragged down into the black hole to join the core of the star.

This stellar death is called direct collapse.

This means that the first stars in the universe may have

collapsed to form black holes weighing hundreds of solar masses,

they would have created intermediate-mass black holes.

Now that we know a possible direct way to make intermediate-mass black holes,

are there more indirect ways? Well, yes.

We can make intermediate-mass black holes by

combining two smaller stellar-mass black holes.

Stellar-mass black holes are the easiest to see when they are

actively feeding from their companion star in a binary system.

If the companion is a massive star,

then it may also create a black hole at the end of its life.

If this happens, we would end up with a black hole binary containing two black holes.

Over time, these black holes can spiral in,

getting closer and closer together until they merge.

When that happens, the merging black holes

combine to form single more massive black hole.

This is an idea that has been around for a while but recently,

has gained traction due to this discovery of black hole mergers with LIGO,

the Laser Interferometer Gravitational Wave Observatory.

We will be going into more detail about the facilities such as

LIGO and the physics behind them in a later module.

By combining stellar-mass black holes in this way,

it's possible to step up the mass scale to intermediate-mass black hole range.

So, for example, if two black holes came

together that each weighed in at about 60 solar masses,

the result would be a black hole lying in the intermediate-mass black hole range.

Some theoretical astronomers have suggested that

intermediate-mass black holes could also form by a process known as runaway formation.

Runaway formation can only occur in dense regions.

Dense regions are areas in space where many stars are clumped closely together,

as they are in some stellar clusters.

Within the central region of the cluster,

you can think of the stars as dancers in a club.

They are moving around each other as they travel under the influence of gravity.

If two of these stars get too close together,

they can start orbiting as binaries do,

or they can spiral in towards each other and merge.

This new star will have more gravity and attract other nearby stars.

As they spiral in and merge,

the object at the center will have even more gravity,

and the cycle will continue,

allowing this object to grow and grow until the gravity of this object is so

strong that the supermassive star is

forced to collapse to make an intermediate-mass black hole.

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