Why Quasars are so Awesome | Space Time

Summary

This script delves into the mysteries of quasars, the most luminous and energetic phenomena in the universe, powered by supermassive black holes. It recounts the history of quasar discovery and explains their formation through the accretion of gas into a whirlpool around the black hole, emitting light brighter than entire galaxies. The video also touches on the role of quasars in shaping the universe, their influence on star formation, and the potential for a new quasar to emerge from the collision of the Milky Way and Andromeda galaxies.

Takeaways

• 🌌 Quasars are among the most powerful and distant astrophysical phenomena, with their immense energy output being a subject of fascination and research.
• 🌀 They consist of supermassive black holes surrounded by a whirlpool of superheated plasma, which emits light brighter than entire galaxies.
• 🔭 The discovery of quasars began with mysterious radio light sources, with 3C273 being a pivotal example identified through an occultation event.
• 🌈 The term 'quasar' comes from 'quasi-stellar radio source', reflecting their star-like appearance and strong radio emissions.
• 🌌 The redshift in their spectrum indicates that quasars are located billions of light-years away, yet emit an extraordinary amount of light from a very small region.
• 🌪️ Quasars are thought to form when gas is driven into the core of a galaxy, where it forms an accretion disk around a supermassive black hole, converting motion into intense heat and light.
• 💥 Some quasars emit jets of particles at near light speed, which can create large radio plumes in the surrounding universe.
• 👁️ The appearance of a quasar can vary greatly depending on the viewer's angle, with some appearing obscured by dust and others showing bright accretion disks or powerful jets.
• 🌍 Quasars have played a significant role in shaping the universe, possibly contributing to the regulation of star formation and the conditions necessary for life.
• 🚀 The study of quasars is ongoing, with modern observations revealing details about their formation, behavior, and the environments in which they exist.
• 🔮 The future may hold the formation of new quasars, such as the potential merging of the Andromeda and Milky Way galaxies, which could trigger a final burst of quasar activity.

Q & A

What is a quasar and why are they considered enigmatic?

A quasar is a type of active galactic nucleus powered by a supermassive black hole, millions to billions of times the mass of the sun. They are considered enigmatic due to their immense luminosity and the complex phenomena surrounding them, such as superheated plasma whirlpools and near light speed jets.

What is the significance of quasars in the context of the universe's history?

Quasars played a significant role in the universe's history by influencing the formation of stars and galaxies. Their intense radiation helped to heat the gas in galaxies, which in turn reduced the rate of star formation, allowing for the potential development of life.

What was the first quasar discovered and how was it identified?

The first quasar discovered was 3C273. It was identified through an event known as an occultation, where the moon passed in front of the radio source, allowing astronomers to pinpoint its location and later observe its unique spectrum.

What causes the redshift observed in the light from quasars?

The redshift observed in the light from quasars is caused by the expansion of the universe. As light travels vast distances, its wavelength is stretched out, indicating the quasar's immense distance from us.

What is an accretion disk and how is it related to quasars?

An accretion disk is a rotating disk of gas and other material that forms around a massive object, such as a supermassive black hole. In quasars, the accretion disk is where the gas is heated to high temperatures, emitting intense light that makes the quasar visible across vast cosmic distances.

How do quasars emit light equivalent to many galaxies, despite their small size?

Quasars emit light equivalent to many galaxies due to the energy released by the accretion of material onto the supermassive black hole. The conversion of gravitational potential energy into radiation in the accretion disk is highly efficient, resulting in an incredibly bright light output.

What are the jets observed in some quasars and what role do they play?

The jets in quasars are streams of particles moving at near light speed, often perpendicular to the accretion disk. They play a role in distributing energy and matter into the surrounding space, and their presence can significantly affect the appearance of the quasar from different viewing angles.

What is the term for the phenomenon where light from a jet is magnified due to its near light speed motion?

The phenomenon is called relativistic beaming, and it occurs when the jet from a quasar is pointed towards the observer, resulting in the light from the jet being significantly magnified.

What is the difference between a quasar and a Seyfert galaxy in terms of their activity?

While both quasars and Seyfert galaxies are types of active galactic nuclei, quasars are typically much more luminous and have a higher level of activity. Seyfert galaxies are less powerful and more common in the modern universe compared to the more rare and powerful quasars.

How might the future collision of the Milky Way and Andromeda galaxies affect the formation of a new quasar?

The collision of the Milky Way and Andromeda galaxies could lead to the merging of their supermassive black holes, potentially providing a surge of fuel to the combined galactic core. This could result in the formation of a new quasar, illuminating the local spacetime.

What is the Great Courses Plus and how does it relate to the script?

The Great Courses Plus is a digital learning service offering a wide range of video lectures from professors worldwide. It is mentioned in the script as the sponsor of the episode, providing an opportunity for viewers to learn about various topics, including those related to space and time.

Outlines

00:00

🌌 The Enigma of Quasars

This paragraph delves into the fascinating world of quasars, which are among the most intriguing astrophysical phenomena. The speaker, who is also a researcher in this field, introduces quasars as having supermassive black holes at their center, millions to billions of times the mass of the sun. These black holes are surrounded by a whirlpool of superheated plasma, which emits light brighter than an entire galaxy. The paragraph also touches on the history of quasar discovery, starting with early radio telescope observations and leading to the identification of 3C273 as the first quasi-stellar radio source, or quasar. The unique spectral redshift of quasars indicates their immense distance and the extraordinary amount of light they emit from a very small region in space. The explanation of quasars as a result of black holes accreting gas and transforming it into radiant energy concludes this summary.

05:04

🌠 The Dynamics of Quasar Visibility

The second paragraph explores the factors that affect how quasars appear to observers. It discusses the role of the black hole's magnetic field and the importance of the viewer's perspective. When viewed from above, the bright accretion disk of a quasar is visible in all its splendor, but from the side, the disk is obscured by a ring of dusty gas. The paragraph also explains how the presence of jets and their orientation can lead to the formation of radio galaxies or blazars, depending on their alignment with the observer. The summary touches on the concept of relativistic beaming, which magnifies the light from jets moving at near light speed. The paragraph concludes with a discussion of the evolution of quasars and their role in the universe's history, including their impact on star formation and the potential for future quasar activity following galactic collisions.

10:06

📚 The Educational Sponsorship of The Great Courses Plus

The final paragraph shifts focus to the educational aspect of the video, acknowledging the sponsorship by The Great Courses Plus. It describes the platform as a digital learning service offering a wide range of topics taught by professors and educators worldwide. Viewers are encouraged to visit the website for access to a vast library of video lectures on various subjects, including science, math, history, and even practical skills like cooking and photography. The paragraph highlights the convenience of the service, allowing unlimited access to lectures without the pressure of tests or exams. It concludes with a special thank you to Patreon supporters and a humorous note about a 'personal spacetime quasar' being sent to a specific supporter.

Keywords

💡Quasar

A quasar, short for quasi-stellar radio source, is an extremely bright and distant active galactic nucleus powered by a supermassive black hole. In the video's theme, quasars are depicted as some of the most fascinating and powerful objects in the universe, with the capability to emit light brighter than entire galaxies. The script describes them as having a supermassive black hole surrounded by a whirlpool of superheated plasma, and sometimes even jets of particles moving near the speed of light.

💡Supermassive Black Hole

A supermassive black hole is a black hole with a mass of millions to billions of times that of the sun. These cosmic entities are central to the script's discussion of quasars, as they are the power source behind the intense luminosity of these objects. The script explains that every decent-sized galaxy has a supermassive black hole at its core, which can drive the formation of quasars when gas is driven into the galactic core.

💡Accretion Disk

An accretion disk is a rotating disk of matter that forms around a massive object, such as a black hole. In the context of the video, the accretion disk is described as a solar system-sized whirlpool of superheated plasma that orbits the supermassive black hole at the center of a quasar. The energy of motion of the gas in the accretion disk is converted into heat, which is so intense that it outshines entire galaxies.

💡Redshift

Redshift refers to the stretching of light waves as they travel through the expanding universe, causing the light to shift towards the red end of the spectrum. In the script, the redshift of 3C273's light was used to determine its immense distance from Earth, indicating that it is located two billion light years away. This concept is crucial for understanding the scale and age of the universe as well as the properties of distant objects like quasars.

💡Occultation

Occultation is an astronomical event where one object passes in front of another, obscuring it from view. The script describes the use of an occultation involving the moon passing in front of the radio source 3C273, which allowed astronomers to pinpoint the exact location of the radio emission and identify the object as a quasar.

💡Active Galactic Nucleus (AGN)

An active galactic nucleus is a compact region at the center of a galaxy that has a much higher than normal luminosity. The term is used in the script to describe the general family of phenomena that includes quasars, which are powered by accreting supermassive black holes. The video explains that the appearance of an AGN can vary greatly depending on factors such as the presence of jets and the viewing angle relative to the observer.

💡Galactic Merger

A galactic merger is an event where two or more galaxies come together to form a single, larger galaxy. In the script, it is mentioned as one way that gas can be driven into the galactic core, fueling the accretion disk and leading to the creation of a quasar. This process is part of the broader theme of the video, which explores the dynamics and evolution of galaxies and their central black holes.

💡Relativistic Beaming

Relativistic beaming is a phenomenon in which radiation from a source moving at relativistic speeds (close to the speed of light) is preferentially directed along the direction of motion. In the video, this effect is mentioned in the context of blazars, a type of AGN where the jet is pointed nearly towards the observer, resulting in a highly magnified appearance due to the relativistic motion of the jet material.

💡Radio Galaxy

A radio galaxy is a type of active galactic nucleus that emits strong radio waves. The script describes radio galaxies as having powerful jets that blast through the galaxy and fill intergalactic space with radio plumes. This term is used to illustrate the variety of phenomena that can be observed in active galactic nuclei, depending on their orientation and properties.

💡Blazar

A blazar is a special type of active galactic nucleus with a jet pointed almost directly towards the Earth. The script uses the term to describe rare cases where the relativistic beaming effect causes the light from the jet to be vastly magnified, making blazars some of the most luminous objects in the universe.

💡Starburst Galaxy

A starburst galaxy is a galaxy undergoing an exceptionally high rate of star formation. In the script, starburst galaxies are mentioned as a phase in the universe's history when galaxies coalesced and produced new stars at an intense rate. This concept is tied to the video's theme by illustrating the conditions that precede the formation of quasars and the eventual decline of extreme star formation activity.

Highlights

Quasars are among the most enigmatic and awe-inspiring astrophysical phenomena, with their study being close to the speaker's heart.

Quasars consist of supermassive black holes millions to billions of times the mass of the sun, surrounded by solar system-sized whirlpools of superheated plasma.

Quasars are incredibly luminous, sometimes outshining entire galaxies and even exhibiting jets of near light speed particles.

The study of quasars is not only for their impressive nature but also because they played a crucial role in shaping the universe.

Early radio telescopes discovered radio light sources, which were later identified as quasars through the use of the moon's occultation in 1962.

The term 'quasi stellar radio source' was coined after the discovery of 3C273, which had a unique spectrum unlike any star.

3C273's light was found to be redshifted, indicating it was located two billion light years away, emitting light equivalent to many galaxies from a tiny region.

The modern understanding of quasars involves supermassive black holes at the center of galaxies, with gas being driven into the galactic core, forming an accretion disk.

Accretion disks around quasars are so bright that they can be seen across the universe, affecting the surrounding galaxy with powerful winds of gas.

In some quasars, gas can be channeled into jets erupting from the poles, possibly due to the magnetic field of a rapidly rotating black hole.

The appearance of a quasar depends on the viewing angle, with different phenomena observed such as radio galaxies and blazars.

Quasars and active galactic nuclei are part of a family of accreting supermassive black holes, with a simplified modern understanding of their nature.

The discovery and study of quasars have been challenging due to their small size and the vast distances from which they are observed.

Quasars are believed to have influenced the universe by heating gas, which in turn reduced star formation and allowed life a chance to evolve.

The Great Courses Plus is highlighted as a sponsor, offering a wide range of educational content from various professors.

The speaker thanks Patreon supporters and mentions a special acknowledgment for Tambe Barsbay, who is supporting at the 'quasar level'.

Transcripts

[MUSIC PLAYING]

This episode is supported by the Great Courses Plus.

One of the most enigmatic of all astrophysical phenomena

is the mighty quasar.

They're also a subject of my own research,

and so are close to my heart.

Let's talk about what happens when the largest black holes

in the universe start to feed.

[MUSIC PLAYING]

Space stuff is awesome.

Take stars-- 100 billion megaton per second thermonuclear

explosions that just don't stop exploding.

Pulsars-- city-size atoms that beam

deathrays through the galaxy.

Giant molecular clouds-- beautiful and tranquil,

but also screaming vortices spitting stars into the cosmos.

Of course, everyone knows that quasars are the most awesome

of all.

They have everything.

They're like the fire-breathing bat-winged vampire rainbow

zebra unicorns of astrophysical phenomena.

They don't just have a black hole.

They have a supermassive black hole,

millions to billions of times the mass of the sun.

That's surrounded by a solar system-sized whirlpool

of superheated plasma that shines

brighter than an entire galaxy.

Sometimes they even have jets of near light speed

particles filling the surrounding universe

with giant radio plumes.

Yep, quasars are clearly the most metal

of all the space things.

This is one reason why I study them myself.

But it's not just that they're cool.

Quasars helped shape our universe.

In fact, without these most violent

of all astrophysical phenomena, we

might not be here to think about them.

Let me start with a bit of history.

When the very first radio telescopes

pointed to the heavens, they saw fat blobs

of radio light, whose sources were unknown.

Those blobs were only blobby because those early radio

antennae had some pretty bad spatial resolution,

making it difficult to pinpoint exactly where on the sky

they were located.

Then, in 1962, astronomers caught a break.

In an event known as an occultation,

the moon passed right in front of one of the brightest

of these radio blobs.

It was object number 273 in the brand new 3rd Cambridge Radio

Catalog--

3C273, for short.

The Parkes radio telescope in Australia

was trained on the occultation and

registered the exact instant that the radio signal vanished

behind the moon.

That timing allowed astronomers to identify

a tiny star-like point of bluish light

as the source of the radio emission.

Astronomers turned their optical telescopes

on this strange star, and split the light into a spectrum.

It looked nothing like the spectrum of any star ever seen.

And so the name quasi stellar radio source was born.

Later, to become quasar.

But what was so different?

For one thing, its spectrum was redshifted,

the wavelength of its light stretched out

as those photons traveled through the expanding universe.

That put 3C273 very far away.

Its light must have been traveling from two billion

light years away to acquire the observed redshift.

Yet, to be as bright as it appeared at that distance,

the weird object had to be emitting

many galaxies worth of light from a seemingly impossibly

small region of space.

A hysterical flurry of hypothesizing followed--

swarms of neutron stars, an alien civilization

harnessing their entire galaxy's power,

bright, fast-moving objects being ejected

by our own galaxy's core.

But by the 1980s, we were converging on the most awesome

explanation.

It goes a little like this.

Take a black hole of millions to billions of times the mass

of the sun.

Where from?

Well, it turns out that every decent sized

galaxy has one at its core.

Now, drive gas into the galactic core.

One way this can happen is when galaxies merge and grow.

That gas descends into the waiting

black hole's gravitational well and gains incredible speed

on the way.

It is swept up into a raging whirlpool around the black hole

that we call an accretion disk, where its energy of motion

is turned into heat.

The heat glow of the accretion disk

is so bright that we can see quasars

to the ends of the universe.

Some gas is swallowed, causing the black hole to grow.

However, a lot of it never makes it below the event horizon.

Some is converted directly into energy and radiated as light.

And this same light drives powerful winds of gas back out

into the surrounding galaxy.

In some cases, for reasons we don't fully understand,

some of that gas can also be swept up and collimated,

channeled into jets that erupt from the poles of the quasar.

This may be due to the magnetic field

of a rapidly rotating black hole,

but the jury is still out.

The exact appearance of this phenomenon

depends enormously on our viewing angle.

Looking down onto a bright accretion disk,

we see a quasar in all of its glory.

But viewed side on, that disk is obscured

by a thick ring of dusty gas.

Then, we only see hints of the central monster

because it lights up gas in the surrounding galaxy.

However, if such an edge-on quasar has powerful jets,

we see them blasting through the galaxy

and even filling intergalactic space with beautiful radio

plumes.

We call these radio galaxies.

Oh, and if one of these jets happens to be pointed directly

at us, then we see strange effects

due to the near light speed motion of the jet material.

In an effect called relativistic beaming, the light from the jet

is vastly magnified.

These rare cases are called blazars.

So when a supermassive black hole feeds and blasts energy

into the universe, what we see depends on its orientation,

whether or not it has a jet, the power of the accretion disk,

and a few other properties besides.

However, the family name for any type

of accreting supermassive black hole

is active galactic nucleus.

This is a simplified description of our modern understanding

of quasars and active galactic nuclei.

But it was a hard won understanding.

Most of the energetic craziness happens

on a size scale similar to our solar system, or even smaller.

We're talking, at most, a few light days across.

But when viewed from halfway across the observable universe,

that is impossibly tiny.

Even for 3C273, the nearest bright quasar,

the accretion disk falls into a region less than 100,000

times smaller than a single pixel on the Hubble Space

Telescope.

Over half a century after their discovery,

we're still hard at work on this puzzle,

and not just for the fun of it.

Anything as energetic as a quasar

must have had an influence on the universe.

The first quasars turned on in a very young universe

that was still thick with the raw hydrogen

gas produced in the Big Bang.

As the first galaxies coalesced from this gas,

the universe entered a long period

of violent star formation.

As galaxies coalesced, they went through starburst phases,

producing new stars at insane rates.

The birth of large numbers of new stars

is always quickly followed by the explosive deaths

of the most massive, shortest lived of those stars.

Waves of star formation, followed

by waves of supernovae.

These forming galaxies were continuously blasted

with energetic radiation and cosmic rays.

If life did manage to evolve during this earlier epoch,

it would have been quickly obliterated.

However, the same rich gas supplies

that fueled those starbursts also

gave rise to the epoch of quasars.

As some of this gas found its way

into the nuclei of galaxies, it encountered

there the supermassive black holes

that had been growing since the beginning of the universe.

Accretion disks formed, and many knew quasars were born.

Each burst of quasar activity in a given galaxy

probably only lasts 10 million years or so.

However, that's enough to heat gas throughout the galaxy.

Hot gas doesn't collapse into stars,

and so the extreme starburst activity was shut down.

A few billion years after the Big Bang,

when the universe was around a quarter of its current age,

both starbursts and quasars started to dwindle.

Galaxies had formed, but were no longer wracked by supernovae.

Life finally had a chance.

We are now well out of the quasar epoch.

Active galactic nuclei still do fire up in the modern universe,

although usually they are at full quasar power.

The much weaker, Seyfert galaxies are more common.

But good old 3C273 is a full blown quasar.

In fact, it's one of the most luminous known.

Although it's far away, its light

comes to us from a time long after the peak of the quasar

epoch.

It's a late relic from a more violent time.

But it's not the last.

Perhaps in a few billion years, when

the Andromeda galaxy and the Milky Way

inevitably collide and their supermassive black holes merge,

the violence will deliver one last wave of fuel

to the combined galactic core, and a new quasar

will shine forth, illuminating this little patch of spacetime.

Thanks to the Great Courses Plus for sponsoring this episode.

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Hey, guys, I want to give a big thank

you to all our Patreon supporters,

and to all our about to be Patreon supporters.

Links to follow.

And a very, very big thank you to Tambe Barsbay,

who's supporting us at the quasar level.

Tambe, your own personal spacetime quasar

is in the mail.

Expect it in two to four billion years.

[MUSIC PLAYING]